A Review of Air Pollution from Petroleum Refining and Petrochemical Industrial Complexes: Sources, Key Pollutants, Health Impacts, and Challenges

Abstract

Petroleum refining and petrochemical complexes are significant sources of air pollution, emitting a variety of harmful pollutants with substantial health risks for nearby populations. While much of the information regarding this issue and the potential health impacts of this pollution has been documented, it remains fragmented across studies focusing on specific regions or health outcomes. These studies are often clustered into meta-analyses or reviews or exist as undeclared knowledge held by experts in the field, making it difficult to fully grasp the scope of the issue. To address this gap, our review consolidates the existing knowledge on the sources of air pollution from petroleum refining and petrochemical industries, the main pollutants involved, and their associated health outcomes. Additionally, we conducted an umbrella review of systematic reviews and meta-analysis and also included critical reviews. With this approach, we identified 12 reviews that comprehensively evaluate the health impacts in populations living near petroleum refining and/or petrochemical complexes. These reviews included studies spanning several decades (from 1980 to 2020) and encompassing regions across North America, Europe, Asia, South America, and Africa, reflecting diverse industrial practices and regulatory frameworks. From these studies, our umbrella review demonstrates that residents living near these facilities face elevated risks related to leukemia, lung and pancreatic cancer, nonmalignant respiratory conditions (such as asthma, cough, wheezing, bronchitis, and rhinitis), chronic kidney disease, and adverse reproductive outcomes. Furthermore, we discuss the key challenges in mitigating these health impacts and outline future directions, including the integration of cleaner technologies, which can significantly reduce harmful emissions; strengthening policy frameworks, emphasizing stringent emission limits, continuous monitoring, and regulatory enforcement; and advancing research on underexplored health outcomes. This review emphasizes the need for coordinated global efforts to align the industry’s evolution with sustainable development goals and climate action strategies to protect the health of vulnerable communities.

1. Introduction

Air pollution has become one of the most pressing environmental and public health challenges of the 21st century. According to the most recent State of Global Air (SoGA) report, released in June 2024 and based on 2021 data, air pollution was responsible for approximately 8.1 million total deaths worldwide [1]. This report, a collaboration between the Health Effects Institute, the Institute for Health Metrics and Evaluation’s Global Burden of Disease project, and the United Nations Children’s Fund (UNICEF), revealed that air pollution is now the second largest risk factor for deaths worldwide, only after high blood pressure [1,2]. It is also the second leading risk factor for mortality in children under the age of five. The harmful effects of exposure to air pollutants on human health are well documented, with numerous studies linking air pollution to a wide range of negative outcomes, mainly respiratory and cardiovascular diseases [2,3,4,5]. As urbanization and industrial activities continue to expand globally, the burden of air pollution on public health has increasingly grown, sparking widespread concern among health professionals, policymakers, and the general public alike.

Among the various sources of air pollution, petroleum refining and the upstream process of the petrochemical industrial complexes have been recognized as significant contributors to localized environmental degradation, as they are closely related to soil contamination, water pollution, and air quality deterioration in nearby regions, primarily due to the release of hazardous substances during industrial operations [6,7]. It is a fact that petroleum and its refined products play a vital role in the global economy. Beyond serving as a primary energy source, refined petroleum products are essential feedstocks for a wide array of industries, underscoring their significant and multifaceted impact on modern society. However, communities living in close proximity to these industrial hubs often face disproportionately higher risks of exposure to harmful pollutants [8], positioning these areas as “hotspots” for air-quality-related health issues. The proximity to refineries and petrochemical plants elevates the concentration of hazardous substances in the air, including volatile organic compounds (VOCs) [9], sulfur dioxide (SO₂) [10], nitrogen oxides (NO_x) [11], fine and coarse particulate matter (PM_2.5 and PM₁₀) [12,13], carbon monoxide (CO) [14], and multiple other air pollutants [15]. According to the 2020 National Emissions Inventory of the United States Environmental Protection Agency (US EPA) for petroleum refining facilities [16] and considering only criteria air pollutants and precursors (CAPs), VOC emissions accounted for approximately 26%, NO_x 32%, CO 22%, particulate matter 9%, and SO₂ 13%. However, these values vary significantly depending on the refinery evaluated [17]. These pollutants, both individually and in combination, contribute to a range of adverse health outcomes, particularly affecting vulnerable populations such as children, the elderly, and individuals with pre-existing conditions.

In this context, while many of the potential health impacts of air pollution from petroleum refining and petrochemical industries have been documented, this information is often scattered across studies focused on specific regions or outcomes, clustered into meta-analyses or reviews, or held as undeclared knowledge by experts in the field. Therefore, it is important to consolidate the available information related to air pollution from these industries and its health impacts to improve access to knowledge and address potential gaps. This review and discussion article focuses on air pollution from petroleum refining and the upstream processes of the petrochemical industrial complexes, offering guidance into the primary emission sources, the key air pollutants released, and their main health impacts. It also presents a critical review of the existing research, including systematic approaches to studies that have conducted reviews or meta-analyses on specific health outcomes related to these industries. Additionally, we explore potential air quality management strategies and the current challenges these industries face as they seek to mitigate their impact on public health.

2. Sources of Air Pollution from Petroleum Refining Industries

There are multiple sources of air pollutant emissions within the petroleum refining and petrochemical industries. According to the US EPA in its AP-42: Compilation of Air Emissions Factors from Stationary Sources [15], the major categories of general refinery processes and associated operations can be divided into five: separation processes, petroleum conversion processes, petroleum treating processes, feedstock and product handling, and auxiliary facilities. Within this framework and considering these major categories, the emission sources can be further categorized into process emissions, combustion emissions, fugitive emissions, storage and product handling emissions, and auxiliary emissions [15,18]. These sources are illustrated, in a simplified manner, in Figure 1.

Each of these sources contributes to varying degrees to the overall pollutant load released into the atmosphere, with combustion emissions typically being the most significant source, followed by process emissions and fugitive emissions. Combustion sources contribute the largest share of the main criteria air pollutants, such as NOx, CO, and PM emissions, while processes and fugitive emissions dominate in terms of VOC outputs [15,18]. However, the exact contributions vary widely depending on refinery-specific factors [17]. Currently, globally and/or regionally harmonized data quantifying the emissions for these subsections are unavailable. In this sense, a deeper understanding of these sources and their nature is crucial for designing effective mitigation strategies that balance operational efficiency with environmental responsibility.

2.1. Process Emissions

In petroleum refining and petrochemical industries, the core processes include separations (such as atmospheric distillation, vacuum distillation, and light ends recovery), conversions (such as cracking, reforming, alkylation, polymerization, isomerization, coking, and visbreaking), and treatments (such as hydrodesulfurization, hydrotreating, chemical sweetening, acid gas removal, and de-asphalting). The emissions generated during these activities are classified as process emissions, often arising directly from the steps involved in separating, converting, or treating petroleum products.

Among these processes, those that stand out as significant contributors to air pollution include vacuum distillation, catalytic cracking, thermal cracking processes, utility boilers, catalytic reforming, hydrogen production (when reliant on fossil fuels), sulfur recovery, blowdown systems, heaters, compressor engines, sweetening, and asphalt blowing. The emissions from these processes typically originate from sources such as steam ejectors, vacuum pumps, and process vents, which release pollutants into the atmosphere [15]. In addition to direct emissions from the refining processes, there are also emissions associated with the combustion of fuels required to power these operations (as discussed in the next section). This overlap between process and combustion emissions is important, as the energy demands of these complex refining operations can significantly amplify their environmental and health impact.

2.2. Combustion Emissions

Combustion emissions originate from the burning of fossil fuels, which serve as the primary energy source in petroleum refining and petrochemical industries. These emissions are mainly generated by stationary fuel combustion sources, such as furnaces, heaters, and steam boilers, which are essential for providing the necessary heat for various refining processes. The type and quantity of combustion emissions depend largely on the fuel being burned, with common fuels including natural gas, refinery gas, and various liquid hydrocarbons [15].

In addition to these fixed combustion sources, flares are also a significant source of emissions [15]. Flares are safety devices used to burn off excess hydrocarbons during process upsets, equipment malfunctions, or emergency situations, converting these hydrocarbons into carbon dioxide (CO₂) and water vapor. While flaring is necessary to prevent the uncontrolled release of hazardous gases, it also contributes to air pollution by emitting not only CO₂ but a range of air pollutants linked to health issues. Although flares are used intermittently, their contribution to total emissions can be substantial, particularly during operational upsets.

The emissions from combustion sources are typically dominated by greenhouse gases (GHGs) such as CO₂ and methane (CH₄), which are not directly associated with immediate health impacts. However, a significant portion of these emissions also includes air pollutants with considerable implications for human health. In this sense, improving fuel efficiency, utilizing cleaner fuel sources, and implementing advanced combustion control technologies are the main strategies for reducing the overall emission footprint of these operations.

2.3. Fugitive Emissions

Fugitive emissions refer to the unintended and often undetected leaks of vapors, gases or liquids from equipment, pipelines, and other process components. Unlike vented emissions or those from flaring, which are typically controlled and directed, fugitive emissions can occur at numerous points across a facility, making them more challenging to identify and manage. Common sources of fugitive emissions include valves, pumps, compressors, piping flanges, and other equipment that handles pressurized gases or liquids [15]. Over time, seals, gaskets, and fittings can degrade, leading to small, continuous leaks that are difficult to detect without specialized equipment. Additionally, operational wear and tear, as well as fluctuations in temperature and pressure, can cause equipment components to fail, resulting in more significant releases. Though individual leaks are usually minor, the total volume of fugitive leaks at a refinery is a major emission source of pollution.

Addressing fugitive emissions requires a proactive approach through the implementation of Leak Detection and Repair (LDAR) programs. These programs involve regular monitoring of potential leak points using infrared cameras, gas detectors, or other technologies capable of identifying leaks. Once detected, leaks are promptly repaired to minimize the release of pollutants. In addition to robust monitoring, improving equipment design and material selection can help reduce fugitive emissions. Furthermore, process optimization, including reducing the pressure in equipment and pipelines where feasible, can also help minimize the likelihood of fugitive emissions. Through a combination of advanced detection techniques, maintenance improvements, and operational adjustments, it is possible to significantly reduce the occurrence of fugitive emissions and their impact on both the environment and human health.

2.4. Feedstock and Product Handling Emissions

Emissions related to the handling of petroleum feedstock and its derivatives are common across all petroleum refining and petrochemical industries, including distribution sites. These emissions primarily occur during loading and unloading operations, where petroleum products are transferred to customers or storage facilities. While pipelines are the main method of transportation due to their efficiency and lower risk of emissions, other methods such as marine vessels, rail cars, and trucks are also used, contributing to the overall emission profile, particularly during the transfer of materials. Each stage of transfer presents opportunities for vapor release, particularly when there are leaks or inadequate containment measures in place [15].

Storage tanks at production facilities and transportation terminals are another significant source of emissions, primarily due to evaporation losses, often referred to as “boil-off” during storage. This is particularly common when VOCs within the stored petroleum products vaporize under high temperatures. Breathing losses are another type of emission that occurs as the air inside storage tanks expands and contracts due to temperature changes, causing vapor to be expelled from the tank. These breathing cycles can lead to the continuous release of pollutants into the atmosphere. Improving tank designs can help mitigate these emissions.

2.5. Auxiliary Emissions

Auxiliary emissions are generated by support units within petroleum refining and petrochemical facilities. These emissions, while secondary to the primary refining processes, still represent a considerable source of air pollutants. Cooling towers, boilers, sulfur recovery units, and industrial wastewater treatment facilities are among the main contributors to auxiliary emissions [15]. It is important to note that boilers and sulfur recovery units, while they are listed here as auxiliary sources, also contribute to direct process emissions, as described in Section 2.1, highlighting their dual role depending on their specific function within a facility.

Cooling towers primarily release atmospheric emissions when gases are stripped as water comes into contact with air during the cooling process. Moreover, drift, the small water droplets carried by the airflow, can also contain pollutants, including chemicals used for water treatment, contributing to air pollution. Industrial wastewater treatment facilities within refineries and petrochemical plants also contribute to auxiliary emissions. As contaminated wastewater undergoes treatment processes such as aeration, air pollutants can be released. Ponds, pits, and drains where wastewater is stored or treated can also serve as sources of emissions, particularly if the wastewater contains high levels of organic material or chemicals [15]. Covering industrial wastewater treatment ponds and utilizing advanced aeration technologies can help to minimize these emissions, while regular monitoring and maintenance of treatment systems are crucial to preventing leaks and inadvertent releases.

3. Main Air Pollutants from Petroleum Refining and Their Health Impacts

As observed, there are numerous sources of air pollutants linked to the petroleum refining and petrochemical industries. When all possible emission sources are considered, certain pollutants stand out (Figure 2). The primary air pollutants emitted by these industries are volatile organic compounds (VOCs); however, significant amounts of sulfur oxides (mainly sulfur dioxide—SO₂), nitrogen oxides (mainly nitrogen dioxide—NO₂), particulate matter (fine and coarse—PM_2.5 and PM₁₀), ozone (O₃), carbon monoxide (CO), hydrogen sulfide (H₂S), hydrogen cyanide (HCN), and trace metals (mainly lead—Pb) are also released, primarily through process and combustion emissions [15,19,20]. According to the 2020 National Emissions Inventory of the US EPA, for petroleum refining facilities, the approximate annual emissions of these pollutants in tons to the environment were as follows: VOCs, 57,294; SO₂, 28,813; NOx, 70,522; PM (fine and coarse), 18,983; CO, 48,348; HCN, 2326; and Pb, 1.97 [16]. It is important to note that NOx comprises all nitrogen oxides, which is why the specific quantity of NO₂ is believed to be smaller than the total amount of VOCs. Additionally, O₃ and H₂S are not directly monitored in these emission inventories. These figures, provided by the US EPA, are recognized for their high reliability and comprehensive scope. However, it is important to highlight that these estimates are specific to the United States, as global emission data for all these pollutants from petroleum refining are currently non-existent.

Each of these pollutants warrants considerable attention due to their health impacts, as refinery operations, if not well managed, pose both chronic and acute risks from exposure to toxic air pollutants. Below, each of the primary air pollutants and its main recognized health impacts are elaborated further. However, it is important to note that the health effects of exposure to these pollutants are extensive. For more detailed information, we recommend consulting guidelines dedicated to the health effects of exposure to these pollutants, such as the Integrated Science Assessments (ISA) by the US EPA [21] and the Agency for Toxic Substances and Disease Registry (ATSDR) Toxicological Profiles [22].

3.1. Volatile Organic Compounds (VOCs)

VOCs are a significant concern in petroleum refining due to their health risks and widespread release during various stages of the refining process [15,23]. The petroleum refining industry is the largest global emitter of VOCs as air pollutants [8]. VOCs are composed primarily of hydrocarbons, including both aliphatic and aromatic compounds. Among the most concerning aromatic VOCs are Benzene, Toluene, Ethylbenzene, and Xylene, collectively referred to as “BTEX” [24,25]. Polycyclic aromatic hydrocarbons (PAHs) are also part of the VOC group and are of particular concern due to their carcinogenic properties [26]. Numerous other VOCs are associated with petroleum refining, each with their own level of toxicity and adverse effects on human health. These compounds are released from leakage points and venting operations and during the evaporation of products, with high concentrations found near refining facilities [27,28].

Studies have shown that exposure to VOCs can cause a wide range of health issues [29,30,31,32]. Short-term exposure to VOCs, especially at elevated levels, may result in irritation of the throat, nose, and eyes, as well as headaches, dizziness, fatigue, and nausea [29,31]. Prolonged or chronic exposure, especially at higher concentrations, can lead to more severe health effects, including lung irritation, damage to the central nervous system, liver and kidney impairment, and cancer [30,32]. Benzene in particular is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC), meaning there is sufficient evidence to support its role in causing cancer in humans, while Ethylbenzene is recognized as a potential carcinogen, Toluene and Xylene are classified as Group D carcinogens, or simply non-carcinogenic [33]. Long-term exposure to Benzene is strongly linked to leukemia and other blood disorders, making it one of the most dangerous VOCs emitted from refineries [29,31,32].

Toluene, another component of the BTEX group, has been associated with neurological effects, including cognitive impairments, while Ethylbenzene and Xylene are known to cause respiratory issues and skin irritation. Prolonged exposure to high levels of determined VOCs may also lead to systemic organ damage [29,31,32]. Additionally, PAHs, which are formed during the incomplete combustion of organic material, are highly toxic and pose a significant cancer risk with long-term exposure [34,35]. The health impact of VOCs depends not only on the type of compound but also on the duration and concentration of exposure. Vulnerable populations, such as children, the elderly, and individuals with pre-existing respiratory or cardiovascular conditions, are particularly susceptible to the harmful effects of VOCs.

The atmospheric lifetime of these compounds plays a critical role in their dispersion and impact on nearby populations. For instance, Benzene has an atmospheric lifetime of approximately 9.4 days, while other VOCs like Toluene and Ethylbenzene have shorter atmospheric lifetimes, ranging from a few hours to a few days [36]. These estimates are derived from model simulations based on their reactivity with hydroxyl (OH) radicals under typical atmospheric conditions [36]. However, the actual atmospheric lifetimes can vary depending on meteorological and geographical factors and OH radical concentrations, which influence the degradation rates of these compounds. VOCs with extended atmospheric lifespans can travel greater distances, potentially affecting populations beyond the immediate vicinity of refineries and posing distinct health risks, including an increased likelihood of chronic exposure-related conditions. In contrast, VOCs with shorter lifetimes are more likely to impact communities in closer proximity to the source. However, even with relatively short atmospheric lifetimes, continuous emissions from refineries ensure that VOCs remain a persistent health hazard for communities living in close proximity to these facilities [31,32].

3.2. Sulfur Dioxide (SO₂)

The effects of SO₂ inhalation on human health demonstrate that prolonged exposure to SO₂ has adverse effects on the respiratory, cardiovascular, and nervous systems [37,38]. Additionally, it has been linked to the development of type 2 diabetes and an increase in overall mortality, including deaths attributed to respiratory and cardiovascular causes [38]. Chronic exposure to SO₂, even at lower concentrations, can lead to inflammation of the respiratory airways, the exacerbation of asthma, and long-term degradation of lung function [39]. Populations living in areas with higher SO₂ concentrations, such as those near refineries, are at a greater risk of developing chronic respiratory diseases, such as bronchitis and emphysema [40].

Exposure to high concentrations of SO₂ can trigger immediate symptoms such as breathing difficulties, chest tightness, and wheezing, particularly in individuals with pre-existing respiratory conditions. Acute exposure can cause irritation of the eyes, nose, throat, and lungs, leading to coughing and shortness of breath [37,38,40]. Vulnerable populations, such as children, the elderly, and those with asthma or other respiratory conditions, are especially susceptible to the harmful effects of SO₂ exposure.

In addition to these immediate effects, numerous studies have shown that short-term exposure to elevated levels of SO₂ is associated with an increase in mortality [39]. SO₂ has been linked to premature deaths and increases in hospitalizations, particularly from respiratory and cardiovascular causes [38]. Furthermore, SO₂ is a precursor to the formation of fine particulate matter (PM_2.5) [41], which exacerbates the health risks associated with air pollution.

3.3. Nitrogen Dioxide (NO₂)

NO₂ is one of a group of highly reactive gases known as nitrogen oxides (NO_x) [42], and it is the primary air pollutant within this group associated with petrochemical activities. NO₂ is predominantly formed during combustion processes at high temperatures, many of which occur in petroleum refining and related industrial operations [42,43].

Exposure to NO₂ is strongly linked to various adverse health effects, particularly affecting the respiratory system [42,43,44]. Short-term exposure to elevated concentrations of NO₂ can irritate the airways, leading to symptoms such as coughing, wheezing, and shortness of breath, often resulting in increased hospital admissions and emergency room visits [43,44,45]. Vulnerable groups, including children, the elderly, and individuals with pre-existing respiratory conditions, are at greater risk of experiencing severe effects of NO₂ exposure [44,45].

Longer-term exposure can contribute to the development of chronic respiratory conditions, including asthma in both children and adults [43,44]. It can also increase one’s susceptibility to respiratory infections by impairing the body’s natural defense mechanisms. Additionally, there is strong evidence linking prolonged exposure to NO₂ with the worsening of bronchitis in children, as well as a deterioration in the health of individuals with pre-existing cardiovascular or respiratory diseases [44,45].

Recent reviews and meta-analyses have further confirmed the significant health impacts of NO₂ exposure. For instance, Huang et al. [46] provided robust epidemiological evidence showing that long-term exposure to NO₂ is associated with a higher risk of all-cause mortality, as well as deaths from cardiovascular and respiratory causes. Their findings suggest that NO₂’s health effects may be independent of those of other common air pollutants. Similarly, Chen et al. [47] observed that NO₂ exposure was linked to childhood asthma, preterm births, lung cancer, diabetes, and chronic obstructive pulmonary diseases, highlighting the multifaceted impact of this air pollutant on public health. In addition to its direct health effects, NO₂ is also a precursor to the formation of fine particulate matter (PM_2.5) [41], which further compounds its role in air pollution and its detrimental effects on human health.

3.4. Ground-Level Ozone (O₃)

Ozone can have either beneficial or harmful effects on health and the environment depending on its location in the atmosphere. Stratospheric ozone acts as a protective layer, shielding living organisms from harmful ultraviolet radiation. In contrast, ground-level ozone poses serious health risks [48]. Unlike pollutants that are directly emitted, ground-level ozone is formed by chemical reactions between nitrogen oxides (NO_x) and volatile organic compounds (VOCs) in the presence of sunlight [49,50]—compounds that are commonly emitted by industrial activities in the petrochemical sector. As previously mentioned, the recent 2024 SoGA report highlighted that air pollution was responsible for 8.1 million deaths worldwide in 2021, with 6% of these deaths attributed to ozone exposure [1].

Exposure to elevated levels of ground-level ozone can lead to a variety of respiratory issues. Short-term exposure can cause coughing, throat irritation, and chest pain, as well as difficulty taking deep breaths. O₃ inflames and damages the airways, making the lungs more susceptible to infections and worsening chronic lung diseases such as asthma, emphysema, and bronchitis [43,51,52]. Additionally, ozone has been linked to the development of cardiovascular problems. These effects are more pronounced in vulnerable groups, such as children, the elderly, and individuals with pre-existing respiratory and cardiovascular conditions [51,52].

Moreover, long-term exposure to O₃ has been linked to a range of other health problems. Research suggests that chronic exposure to ozone can lead to metabolic disorders, damage to the nervous system, reproductive health issues such as reduced fertility and poor birth outcomes, and even certain types of cancer [51,52]. Furthermore, studies have consistently shown that higher daily ozone concentrations are linked to increased hospital admissions and mortality from respiratory and cardiovascular conditions [51,53]. The relationship between ozone exposure and mortality is especially pronounced during warmer seasons, when ozone levels are typically higher due to increased sunlight.

3.5. Particulate Matter (PM)

PM refers to a complex mixture of solid particles and liquid droplets suspended in the air, whose size and composition determine their ability to penetrate the respiratory system and cause adverse health effects [3,54]. PM is typically classified based on the diameter of the particles, with two primary categories: PM₁₀, which includes inhalable particles with diameters of 10 μm or less, and PM_2.5, which encompasses fine particles with diameters of 2.5 μm or less. The composition of PM can include a variety of substances, such as heavy metals, organic compounds, nitrates, sulfates, and dust particles, all of which contribute to its potential toxicity [3,54].

These small particles are able to evade the body’s natural defenses, penetrate deep into the alveolar regions of the lungs, and, in some cases, enter the bloodstream, thereby exerting systemic effects [3,55]. Of particular concern, PM_2.5 poses the greatest health risk [4]. Allied with this, the 2024 SoGA report highlights that ambient PM_2.5 was responsible for 58% of the 8.1 million global deaths attributed to air pollution in 2021 [1].

Exposure to both PM₁₀ and PM_2.5 is known to affect both the respiratory and cardiovascular systems [3]. Short-term exposure to elevated levels of PM can lead to immediate symptoms such as irritation of the airways, coughing, difficulty breathing, and shortness of breath. It has also been associated with an increased number of hospital admissions, emergency room visits, and the exacerbation of chronic respiratory diseases like asthma and bronchitis [3,4,55,56]. In addition to respiratory issues, PM exposure has been linked to cardiovascular problems, including heart attacks and stroke, as well as premature mortality [2,5].

Long-term exposure to PM can have even more severe health consequences. Studies have shown that chronic exposure to PM_2.5 can lead to reduced lung function, slower lung development in children, and an overall increased risk of developing chronic respiratory and cardiovascular diseases [5,54,57]. Emerging evidence suggests that PM may also contribute to adverse reproductive outcomes, including low birth weight, preterm deliveries, and fetal and infant deaths [58]. There are also indications that PM exposure could be linked to metabolic disorders such as diabetes [59]. Furthermore, the populations most vulnerable to the harmful effects of particulate matter include older adults, children, and individuals with pre-existing heart or lung diseases [60]. In these groups, exposure to PM has been shown to accelerate the decline in lung function, increase susceptibility to respiratory infections, and exacerbate existing health conditions [3,4].

In recent years, the investigation of PM’s health impacts has expanded significantly, revealing a broad range of potential health outcomes. While many associations between PM_2.5 exposure and health effects have been firmly established, such as respiratory and cardiovascular impacts, there are still emerging areas of research that require further study to confirm the relationships. For example, the potential links between PM_2.5 and neurodegenerative diseases [61], autoimmune disorders [62], and certain cancers [63] are subjects of ongoing investigation, highlighting the need for continued research to understand the full extent of PM’s effects on human health better.

3.6. Carbon Monoxide (CO)

CO is a colorless, odorless gas produced by the incomplete combustion of carbon-containing fuels [64]. Its primary health risk stems from its ability to interfere with the oxygen-carrying capacity of the blood [64,65]. Hemoglobin, the molecule responsible for transporting oxygen throughout the body, binds preferentially to CO rather than oxygen, forming carboxyhemoglobin. This reduces the amount of oxygen that can be delivered to vital organs, such as the heart and brain. As a result, tissues are deprived of the oxygen necessary for normal function, which can have serious health consequences, particularly for individuals with pre-existing health conditions [64,65].

People with cardiovascular diseases are particularly vulnerable to the effects of CO. Since their ability to circulate oxygenated blood is already compromised, the additional reduction in oxygen delivery due to CO exposure can lead to myocardial ischemia or reduced blood flow to the heart muscle [65,66]. This condition is often accompanied by chest pain (angina), especially during physical exertion or periods of stress, when the heart’s demand for oxygen increases [64,66]. Other vulnerable populations include individuals with anemia, diabetes, chronic obstructive pulmonary disease, and the elderly, who may also experience more severe effects of CO exposure due to their diminished physiological capacity to manage hypoxia [64,65,66].

In poorly ventilated or enclosed environments, CO can accumulate to dangerously high levels, causing acute symptoms such as dizziness, confusion, headaches, and, in severe cases, loss of consciousness or death [64,66]. While outdoor concentrations of CO are generally lower and less likely to reach lethal levels, elevated CO levels in outdoor environments can still pose significant health risks, particularly for individuals with heart conditions [65,66]. The most recent World Health Organization (WHO) air quality guidelines recommend exposure limits for outdoor air pollution at 4 mg/m³ for 24 h, 10 mg/m³ for 8 h, 35 mg/m³ for 1 h, and 100 mg/m³ for 15 min [67]. Additionally, the National Institute for Occupational Safety and Health (NIOSH) defines a maximum occupational exposure limit of 35 mg/m³ for 8 h, with levels above 150 mg/m³ (approximately 130 ppm) for 8 h considered life-threatening and brief exposures at or above 1200 ppm potentially fatal within minutes [68]. Short-term exposure to elevated CO levels can further reduce oxygen delivery to the heart, resulting in chest pain and decreased exercise tolerance [64,66]. In addition, prenatal exposure to CO has been linked to developmental issues in unborn babies [69]. The reduced oxygen supply can impair fetal growth and brain development, increasing the risk of neurodevelopmental problems and long-term health complications in infants and children [65,69].

3.7. Hydrogen Sulfide (H₂S)

H₂S is a highly toxic, flammable gas commonly associated with petroleum refining. It is characterized by its distinct smell of rotten eggs, and when combined with CO₂, it forms acid gas, which is corrosive and dangerous [70,71]. H₂S is a known irritant and chemical asphyxiant, posing significant risks to human health, particularly in industrial environments [70,72]. The health effects of H₂S exposure depend on both the concentration of the gas and the duration of exposure.

At low concentrations (2–5 ppm), H₂S can cause mild symptoms such as headaches, eye irritation, fatigue, vomiting, breathing difficulties, and skin irritation [71,73,74]. However, as its concentrations increase, so does the severity of the symptoms. Moderate levels of exposure (above 10 ppm) may result in more pronounced effects, including severe eye and respiratory irritation, dizziness, nausea, vomiting, and, in some cases, unconsciousness [71,74]. At extremely high concentrations (above 100 ppm), H₂S can rapidly lead to respiratory failure, coma, and death [70,74]. The NIOSH establishes occupational exposure limits for this pollutant at 10 ppm for 10 min and a time-weighted average of 1 ppm for 8 h, and above 100 ppm it is considered Immediately Dangerous to Life or Health (IDLH) [75]. Industrial fatalities related to H₂S exposure have been well documented, often occurring in settings where the gas is not properly controlled [70,72,76].

H₂S primarily affects organs with high oxygen demand, such as the lungs and brain, as well as the mucous membranes in the eyes and nose. It acts as a chemical asphyxiant by blocking cellular respiration, preventing cells from using oxygen, and leading to cellular anoxia and subsequent tissue damage [72,74,76]. The toxicity of H₂S is a well-documented health hazard, particularly in industrial environments such as petroleum refineries. Recent research by Salih et al. [77] explored the spatial and temporal dispersion of the H₂S emissions from oil refineries. This study found that refinery workers are frequently exposed to harmful levels of H₂S, and the gas disperses up to 550 m from refineries, potentially affecting the most nearby communities [77]. This underscores the broader public health risks posed by H₂S emissions, particularly in residential areas in close proximity to refineries.

3.8. Hydrogen Cyanide (HCN)

HCN is a toxic air pollutant emitted by petroleum refineries. Once inhaled, HCN rapidly enters the systemic circulation and is distributed uniformly throughout the body [78]. Its acute toxicity via inhalation poses significant health risks, especially in industrial environments. Even at low concentrations (up to 4.7 ppm), chronic exposure to HCN can result in serious health effects [79].

The central nervous system is the primary target of cyanide toxicity. Exposure to elevated levels of HCN (above 10 ppm) can cause symptoms such as nausea, vomiting, dizziness, and confusion. Severe exposure (above 50 ppm) can lead to precordial pain, palpitations, chest pain, seizures, and fainting, with the potential for rapid death in extreme cases [78,80]. The NIOSH establishes occupational exposure limits for this pollutant at a time-weighted average of 4.7 ppm for 10 h, with levels above 50 ppm classified as IDLH [81].

Chronic exposure to lower concentrations of HCN, commonly observed in occupational settings, has been linked to a range of adverse health effects. Workers exposed to HCN over prolonged periods have reported neurological symptoms, such as headaches and tremors, as well as disruptions in thyroid function. Beyond these effects, HCN can exert toxic impacts on the respiratory, endocrine, and cardiovascular systems, contributing to long-term health complications in affected individuals [78,79,82].

3.9. Lead (Pb)

While the petroleum refining process does not typically produce lead (Pb) as a direct emission, there are specific circumstances where lead may be present. These include the use of catalysts containing lead and, more commonly, trace contamination in crude oil. Crude oil can contain small amounts of heavy metals, with lead being one of the primary contaminants, although these metals are generally present at very low concentrations [83,84]. During the refining process, advanced treatment technologies are employed to capture or treat these metals. However, in certain cases, trace amounts of lead may be released into the air as emissions [83,85].

Pb is a highly toxic metal that accumulates in the body’s soft tissues, bones, liver, and bloodstream [86,87]. Once absorbed, lead remains in the body for extended periods, which can result in long-term health effects, especially with chronic exposure [88]. The health impacts of lead are broad and affect multiple systems in the body. Lead exposure can damage the nervous system, impair kidney function, weaken the immune system, and disrupt the reproductive and developmental systems [86,87,88]. Additionally, lead has detrimental effects on the cardiovascular system, contributing to hypertension and heart disease [86,87,88]. One of the key concerns with lead exposure is its ability to interfere with the blood’s oxygen-carrying capacity, similar to carbon monoxide. The current most significant health risk posed by lead is that to infants and young children [88]. Due to their developing nervous systems, children are particularly vulnerable to the neurotoxic effects of lead. Even low levels of lead exposure in children can result in neurological deficits, including behavioral problems, learning difficulties, and a reduced IQ.

4. Health Outcomes of Petroleum Refining for Local Populations: Insights from an Umbrella Review of Systematic Reviews and Meta-Analyses

4.1. The Rationale and Framework

To elucidate the multiple health outcomes and impacts of air pollution emitted by petroleum refining industries on nearby residents, we conducted a systematic search for data from the literature and a critical discussion of the findings. Given the complexity of this topic and the fact that various studies have focused on the specific health outcomes related to this issue, our approach was designed to include only review studies—whether critical, systematic, or with or without meta-analysis—forming an umbrella review that also considered critical review studies. This methodology ensured that we incorporated only studies that had already evaluated a wide range of health outcomes in populations living in proximity to these industries, meaning that each included study had reviewed numerous others. This approach allows us to focus on and highlight the most robust and current body of knowledge on this subject.

Additionally, it became apparent from a preliminary analysis that it would be beneficial to include studies examining petrochemical industrial complexes in our findings. This is because most petrochemical industrial complexes combine multiple refineries and chemical manufacturing plants in the same area, reducing the transportation costs and streamlining production processes, which, in turn, amplifies their pollution [89]. The upstream segment of the petrochemical industry typically involves refining, whereas the downstream segment refers to chemical manufacturing and the processing of refined products. The upstream segment is the main source of air pollution in this segment.

4.2. The Search Strategy

To identify relevant studies, we derived search terms for both exposure and health outcomes. Exposure-related terms included “Air pollution”, “Petroleum refining”, “Refinery”, “Petrochemical”, and “Oil refining”, while outcome-related terms focused on “Health”. We combined these terms using Boolean operators (e.g., AND, OR) and applied them across three major databases: PubMed, SCOPUS, and Web of Science. The general search string used was “(Air pollution) AND ((Petroleum refining) OR (Petrochemical) OR (Oil refining) OR (Refinery)) AND ((Review) OR (Meta-analysis)) AND (Health)”, with minor adaptations based on the specific search rules of each database. The search was conducted on 28 September 2024 by two independent researchers, who screened the titles and abstracts and confirmed eligibility through full-text reviews.

4.3. The Study Selection and Eligibility Criteria

The inclusion criteria were as follows: (i) review articles, with or without a meta-analysis, that assessed one or multiple health outcomes in residents living near petroleum refining industries or petrochemical industrial complexes or in cities with them and (ii) systematic review articles, with or without a meta-analysis, that assessed one or multiple health outcomes in residents living near petroleum refining industries or petrochemical industrial complexes or in cities with them. Only studies published in English or Spanish were considered. The exclusion criteria were (i) studies that did not have petroleum refining or petrochemical industrial complexes as the exposure source and (ii) studies that focused exclusively on occupational exposure.

Although occupational exposure to air pollutants in the petroleum refining and petrochemical industries is a critical health issue, this review did not include studies focused solely on occupational settings. This decision was made because occupational exposures typically involve different pollutant concentrations, exposure durations, and health outcomes compared to residential exposures. Workers in these industries often experience much higher levels of pollutants over shorter periods, leading to acute health effects that differ from the chronic, lower-level exposures seen in residential populations. Including occupational studies could have obscured the specific health impacts on communities living near these facilities, which was the primary focus of this review. Therefore, only studies examining health outcomes in residents near petrochemical facilities were included to provide a clearer understanding of the risks associated with environmental, rather than occupational, exposure to air pollutants from these industries.

4.4. Quality Assessment and Data Extraction

The methodological quality of the included systematic reviews and meta-analyses was evaluated using the AMSTAR-2 (A Measurement Tool to Assess Systematic Reviews) checklist. The tool comprises 16 items, of which 7 are designated as critical domains: (1) the presence of a registered a priori protocol for the review, (2) adequacy and comprehensiveness of the literature search strategy, (3) transparency in reporting the justification for excluded articles, (4) assessment of the risk of bias in the studies included in the review, (5) appropriateness of the analytical methods used for any meta-analyses conducted, (6) evaluation of potential biases in interpreting the findings, and (7) consideration of publication bias and its potential influence on the results. Reviews were classified based on their adherence to these domains as high-quality (no critical weaknesses and at most one non-critical weakness), moderate-quality (no critical weaknesses but more than one non-critical weakness), low-quality (one critical weakness, with or without non-critical weaknesses), and critically low-quality (more than one critical weakness, with or without non-critical weaknesses). For this umbrella review, the seven critical domains were emphasized to provide a robust evaluation of methodological quality. Of the 12 studies included, all of the systematic reviews and meta-analyses underwent this quality assessment. Critical review studies, however, were not subjected to AMSTAR-2 due to their inherently subjective nature and narrative synthesis approach, and all of those identified were included in this review. The methodological quality was independently assessed by two authors (R.A.T. and R.D.P.F.), with any disagreements resolved through reaching a consensus with three additional authors.

From the full-text review stage to the final inclusion of the studies, the agreement rate between the two researchers involved was 100%. The data extracted from the included studies encompassed the type of study, the health outcomes analyzed, the number of studies included in the review, the number of participants evaluated, the key findings, and the date of the review. The number of studies included in the review, the number of participants evaluated, and the date of the review were expressed to provide a sense of the scale of the evidence synthesized in each review included. These figures contextualize the robustness of the findings presented. The study selection process and data extraction were systematically organized using Microsoft Excel. It is also important to note that the meta-analysis studies reported different measures of association, such as odds ratios (ORs), relative risk (RR), and effect size (ES). This variability did not hinder the analysis of the results, as the findings were compared within the context of their respective meta-analyses.

4.5. Results and Discussion of the Umbrella Review

A total of 211 studies were initially identified, and 55 duplicates were excluded. Of the 156 studies that were screened, 138 irrelevant studies were excluded based on the title and abstract screening. From the remaining 18 studies, 7 were excluded after full-text screening based on exclusion criteria. Of these, three were review studies focused on occupational exposure in the same setting, three were reviews that did not address health outcomes but had a more chemical focus, and one was found to be a case study rather than a review. Additionally, one study was added after being identified from the reference list of the other studies. Therefore, the total number of studies included in our systematic review was 12. A flowchart detailing the study selection process is presented in Figure 3. Furthermore, the data extracted from the studies are described in

Table 1. Summary of systematic reviews, meta-analyses, and critical reviews that investigated the health impacts of air pollution from petroleum refining and petrochemical complexes on local populations.

Health Outcomes Analyzed	Number of Studies Included	Number of Residents Investigated	Location of Studies	Key Findings	Date of Study [Reference]
Systematic reviews and meta-analyses
Lung cancer mortality	13	2,017,365	Italy, Taiwan, the United Kingdom, the United States	The pooled analysis showed a slightly elevated risk of lung cancer mortality among residents near petrochemical complexes (RR = 1.03; 95% CI = 0.98–1.09), though this association did not reach statistical significance.	2017 [90]
Lung cancer incidence	6	466,066	Ecuador, Israel, Italy, Serbia, Sweden, the United States	Residents living near petrochemical industrial complexes had a 19% higher risk of lung cancer compared to those who lived farther away (95% CI = 1.06–1.32). By sex, the risks were higher and more significant for females (RR = 1.29; 95% CI = 1.09–1.54) than males (RR = 1.12; 95% CI = 0.95–1.33).	2018 [91]
Leukemia incidence and mortality	13	125,580	Croatia, Finland, Italy, Serbia, Spain, Sweden, Taiwan, the United Kingdom, the United States	The moderate certainty of the evidence indicated an increased risk of leukemia incidence (RR = 1.18; 95% CI = 1.03–1.35) and mortality (RR = 1.26; 95% CI = 1.10–1.45) in residents near petrochemical complexes. The subgroup analysis showed a higher risk in distance-based exposure studies (RR = 1.11; 95% CI = 1.00–1.23) and in those with longer follow-up periods (RR = 1.24; 95% CI = 1.06–1.45).	2020 [92]
Nonmalignant respiratory symptoms.	16	14,532	Argentina, Brazil, Italy, Spain, Taiwan, Thailand, the United Kingdom	Significant associations between residential exposure to petrochemical industrial complexes and higher incidences of cough (OR = 1.35), wheezing (OR = 1.28), bronchitis (OR = 1.26), and rhinitis (OR = 1.17). The association with asthma (OR = 1.15) did not reach statistical significance.	2020 [93]
Hematological malignancies: leukemia, Hodgkin’s lymphoma, Non-Hodgkin’s lymphoma, and multiple myeloma	16	187,585	Israel, Finland, Italy, Serbia, Spain, Sweden, Taiwan, the United States, the United Kingdom	Residents of fenceline communities, living less than 5 km from a petrochemical facility, had a 30% higher risk of developing leukemia compared to residents from communities without petrochemical activity (pooled RR = 1.30; 95% CI = 1.09–1.55). However, the association between exposure and rarer forms of hematological malignancies remains uncertain, requiring further research. Hodgkin’s lymphoma (pooled RR = 1.03; 95% CI = 0.81 to 1.30), Non-Hodgkin’s lymphoma (RR = 1.06; 95% CI = 0.97 to 1.17), and multiple myeloma (RR = 0.97; 95% CI = 0.78 to 1.20).	2020 [94]
Leukemia risk and its subtypes	7	2322	Croatia, Finland, Sweden, Taiwan, the United States, the United Kingdom	Residential exposure within 8 km of petrochemical industrial complexes increased leukemia risk by 36% (pooled RR = 1.36; 95% CI = 1.14–1.62). For the subtypes, the risks were as follows: acute myeloid leukemia (RR = 1.61; 95% CI = 1.12–2.31), chronic lymphocytic leukemia (RR = 1.85; 95% CI = 1.11–6.42), and acute lymphoblastic leukemia (RR = 1.50; 95% CI = 0.97–1.69).	2020 [95]
Cancer—multiple types	14 *	~2,595,931	Ecuador, Italy, South Korea, Spain, Sweden, Taiwan, the United Kingdom, the United States	Residential proximity to petroleum facilities was associated with childhood leukemia (ES = 1.90; CI: 1.34–2.70).	2021 [96]
Kidney-related outcomes: chronic kidney disease (CKD), end-stage renal disease (ESRD), proteinuria/albuminuria, reduced renal function (based on estimated glomerular filtration rate—eGFR), kidney cancer, hypertension, and diabetes	14	-	Brazil, Ecuador, Estonia, Italy, Nigeria, Spain, Taiwan, the United States	Residents of exposed communities had an increased risk of chronic kidney disease (OR = 1.70; 95% CI 1.44–2.01), a lower eGFR (OR = 0.55; 95% CI 0.48–0.67), and higher serum creatinine (OR = 1.39; 95% CI 1.06–1.82) compared to less exposed or unexposed populations. The risks for hypertension and kidney cancer were not significantly different between the groups.	2022 [97]
Pancreatic cancer and mortality	7	1,605,568	Italy, Serbia, Taiwan, the United States	The pooled analysis revealed a significantly higher risk of pancreatic cancer among residents living near petrochemical complexes (RR = 1.31; 95% CI = 1.21–1.42), with a higher effect observed in female residents (RR = 1.34; 95% CI = 1.18–1.53) compared to male residents (RR = 1.26; 95% CI = 1.12–1.41).	2023 [98]
Critical reviews
Respiratory health outcomes in children	9	~10,830	Argentina, Brazil, Canada, Italy, Puerto Rico, South Africa, Taiwan, the United States	Short-term exposure to petrochemical air pollutants was associated with increased respiratory symptoms in children, reduced lung function, and higher asthma incidence, especially for those living within 5 km of the industry.	2016 [99]
Cancer or cancer mortality	23	-	Italy, Nigeria, Spain, Taiwan, the United Kingdom, the United States	Leukemia and other hematological malignancies were the most reported cancers among populations living near petrochemical industries. Other studies noted a high incidence of lung and bladder cancers, as well as excess mortality from bone, brain, liver, pleural, larynx, and pancreas cancers, in those living near petrochemical complexes in different countries.	2020 [100]
Adverse health effects, focusing on non-cancer outcomes	27	-	Argentina, Brazil, Canada, China, Italy, Spain, South Africa, Taiwan, Thailand	Increased prevalence of asthma and other respiratory problems (acute lower respiratory infections and chronic obstructive pulmonary disease) in both children and adults living near petrochemical complexes, along with reproductive outcomes like low birth weight, preterm births, and small-for-gestational-age births. Very few studies addressed other health outcomes.	2020 [101]

* This systematic review included analyses for both occupational exposure (petroleum workers) and residential exposure (residents living near petroleum facilities). Only data from studies focused on residential exposure were extracted and included.

.

It is important to highlight that all of the key findings presented in Table 1 are statistically significant, with p-values below 0.05, indicating robust associations between proximity to petroleum refining and petrochemical facilities and the reported health outcomes. Furthermore, the systematic reviews and meta-analyses included in this umbrella review incorporated studies that performed different adjustments for potential confounding variables, such as age, sex, smoking status, socioeconomic factors, and/or others, in their analyses. These adjustments enhanced the reliability of the reported associations by reducing the potential influence of these factors on the observed results.

One of the most well-documented effects is the increased risk of lung cancer and leukemia among residents living near petrochemical facilities. The pooled analysis across multiple studies indicates an elevated risk of lung cancer. Lin et al. [91] found that residents living near petrochemical industrial complexes had a 19% higher risk of lung cancer incidence compared to those living farther away, with a particularly higher risk for females. However, in terms of lung cancer mortality, this risk was only slightly elevated and did not reach statistical significance [90]. The evidence for leukemia is even more concerning, with both its incidence and mortality rates showing a significant increase. For instance, Boonhat and Lin [92] found a 1.18-fold increase in leukemia incidence and a 1.26-fold increase in mortality for residents near petrochemical complexes. Additionally, residential exposure within an 8 km radius of petrochemical complexes was associated with a 36% increased risk of leukemia, particularly for subtypes such as acute myeloid leukemia and chronic lymphocytic leukemia [95]. Moreover, Jephcote et al. [94] observed that residents of fenceline communities (those living within 5 km of facilities) had a 30% higher risk of developing leukemia compared to those living further away, underscoring the geographical impact of these emissions. It is important to note that these findings come from separate systematic reviews that analyzed studies with different methodologies, definitions of proximity, and population characteristics. Thus, the percentages reported should not be interpreted as directly comparable but rather as consistent evidence of the heightened risks associated with living closer to petrochemical facilities.

In addition to cancer outcomes, nonmalignant respiratory conditions are also a significant concern for populations living near petrochemical industries. Several studies found a strong association between residential exposure and respiratory symptoms such as cough, wheezing, bronchitis, and rhinitis. For example, Chang et al. [93] identified significantly higher odds of respiratory symptoms among residents living near petrochemical industrial complexes, though the association with asthma did not reach statistical significance (OR = 1.15). Children appear to be particularly vulnerable, with studies showing an increased prevalence of asthma, reduced lung function, and other respiratory issues in those living within a 5 km radius of these industries [99]. The adverse respiratory effects extend beyond immediate symptoms to long-term health complications, suggesting that chronic exposure to air pollutants from petrochemical operations plays a critical role in shaping the respiratory health of nearby populations [101].

Furthermore, other systemic health outcomes have been observed in relation to chronic exposure to petrochemical emissions. For example, residents of exposed communities have shown an increased risk of chronic kidney disease (CKD), with a 70% higher likelihood of developing CKD compared to that in unexposed populations. This was accompanied by lower estimated glomerular filtration rates (eGFRs) and higher serum creatinine levels, suggesting renal function impairment due to long-term exposure to air pollution from petrochemical activities [97]. Additionally, a study on pancreatic cancer revealed a significantly higher risk of developing this cancer among residents near petrochemical complexes, with females being slightly more affected than males [98].

It is important to note that while the primary exposure pathway for residents living near petroleum refineries and petrochemical industrial complexes is through air pollutants, proximity to these facilities can also lead to contamination of the soil and water. However, the primary mechanism through which these contaminants reach other environmental matrices (such as soil and water) is through air deposition processes. Thus, air pollution remains the principal concern for communities living in these areas.

Critical reviews also provide important insights into the broader health impacts on populations living near petrochemical industries. Domingo et al. [100] identified leukemia and other hematological malignancies as the most reported cancers in these populations, alongside a higher incidence of lung and bladder cancers. This study also found excess mortality from cancers affecting the bone, brain, liver, pleura, larynx, and pancreas in individuals residing near petrochemical complexes in various countries. Additionally, Marquès et al. [101] observed an increased prevalence of asthma and other respiratory problems (including acute lower respiratory infections and chronic obstructive pulmonary disease) in both children and adults living near petrochemical complexes, along with adverse reproductive outcomes such as low birth weight, preterm births, and small-for-gestational-age births. However, few studies addressed other non-cancer health outcomes.

A detailed analysis of the studies included in the reviews demonstrates important information in terms of their temporal and geographical distribution. These studies span several decades, ranging from 1980 to 2020, with some investigations originating as early as the 1960s. Geographically, these studies covered a wide array of regions, with the majority conducted in North America, Europe, and Asia, highlighting these continents as focal points for research on air pollution from petroleum refining and petrochemical industries. South America and Africa were less represented, with fewer studies contributing to these systematic reviews and meta-analyses. Oceania, notably, did not feature in any of the studies included in the reviews, underscoring a significant regional gap in the literature. This uneven geographic distribution likely reflects disparities in industrial practices, regulatory frameworks, and research funding across continents. Additionally, the varying degrees of representation emphasize the need for a more globally inclusive approach to future research, particularly in underrepresented regions, where industrial emissions may still pose significant risks to nearby populations.

A recent study by Boonhat et al. [102] provides a comprehensive global estimate of cancer-related deaths attributable to residential exposure to petrochemical industrial complexes, shedding light on the severe long-term impacts of living near such facilities. This study estimated that in 2020 alone, there were 19,083 cancer-related deaths globally due to this exposure, with this number expected to rise significantly to 27,366 deaths by 2040. These findings underscore the substantial and growing contribution of petrochemical industrial complexes to the global cancer burden. However, it is important to note that these projections are based on factors such as the inclusion of petrochemical plants and oil refineries currently under construction or planned for after 2020 (the final year included in their study), as well as assumptions about global population growth and urbanization trends that could bring residential areas closer to industrial sites. Consequently, these estimates do not account for potential reductions in emissions or operational activities that could result from global efforts to transition to renewable energy as part of climate change mitigation strategies. Therefore, while the projected increase in cancer deaths is alarming, it highlights the continued and growing contribution of petrochemical industrial complexes to the global cancer burden under the current operational trends.

What is particularly critical about the finding of Boonhat et al. [102] is that they only accounted for cancer-related deaths, meaning the actual health burden from exposure to petrochemical industrial complexes may be significantly higher when considering non-cancer outcomes, such as respiratory, cardiovascular, and metabolic diseases. These non-cancer effects, although they were not included in this global cancer burden analysis, represent a significant part of the overall health impact on exposed populations. Therefore, while the projected increase in cancer deaths is alarming, it only represents part of the broader public health challenge posed by proximity to these industrial operations.

In this context, the study by Buonocore et al. [103] further highlights the extensive health impacts of air pollution from oil and gas production, especially concerning non-cancer outcomes. Their analysis of air quality and the associated health effects in the United States revealed that emissions from the oil and gas sector in 2016 contributed to 410,000 asthma exacerbations, 2200 new cases of childhood asthma, and 7500 excess deaths, amounting to an estimated USD 77 billion in total health-related costs. Notably, NO₂ emerged as the largest contributor to health impacts (37%), followed by ozone (35%) and PM_2.5 (28%). These findings illustrate the far-reaching and severe consequences of air pollution across the entire lifecycle of oil and gas production. The substantial health burden observed in this study underscores the urgent need for targeted interventions to mitigate these impacts, particularly in communities with heightened vulnerability due to their proximity to industrial operations. Moreover, it highlights the necessity of considering not just cancer outcomes but also the broader spectrum of respiratory and cardiovascular health impacts when evaluating the overall health burden of air pollution associated with the petrochemical and refining sectors.

Furthermore, an additional, often overlooked, aspect of this issue is the disproportionate burden placed on socially vulnerable populations. Petrochemical facilities are frequently located in economically disadvantaged areas, where land is cheaper, and regulatory enforcement may be less stringent [104,105]. This results in low-income communities bearing the brunt of industrial pollution. Socially vulnerable individuals, due to economic constraints, are often forced to live in closer proximity to these facilities. In many cases, people residing near these industrial complexes may have limited access to healthcare or the financial resources needed to relocate. Compounding this issue is the fact that these populations often include a higher proportion of minority groups, exacerbating existing health inequities [104]. This confluence of social vulnerability and environmental exposure creates a vicious cycle, where individuals are more likely to work in hazardous jobs at these very facilities while simultaneously being exposed to harmful pollutants in their living environments. The concept of environmental justice becomes critical in this context, as these communities face not only the direct health impacts of air pollution but also broader systemic issues of inequality and marginalization.

The cumulative evidence from these studies underscores the profound and multifaceted health burden that petrochemical industrial complexes and petroleum refining operations impose on nearby communities. Vulnerable populations, including children, the elderly, and individuals with pre-existing conditions, are disproportionately affected by the toxic air pollutants emitted from these facilities. Their heightened susceptibility to air pollution exacerbates the severity of health outcomes, from respiratory illnesses and cancer to systemic diseases affecting multiple organs. These pollutants not only affect immediate health outcomes but also have long-term and often irreversible impacts, contributing to chronic diseases and premature mortality. Beyond the immediate health risks, the broader challenge lies in the public health implications of continued exposure to petrochemical emissions, which have the potential to perpetuate health inequities and place a sustained burden on healthcare systems. The research presented in these studies serves as a clarion call for policymakers to adopt stronger interventions that address both the environmental and health dimensions of petrochemical pollution. Targeted air quality management programs, tighter emission controls, and continuous monitoring of health outcomes are critical steps to safeguard the well-being of populations living in close proximity to these industrial operations.

4.6. Limitations of the Umbrella Review

As an umbrella review, this investigation synthesized findings from multiple systematic reviews and meta-analyses, with each encompassing numerous primary studies. While this approach provides a comprehensive overview of the current evidence, it is inherently accompanied by limitations stemming from the heterogeneity across the included reviews and their primary studies. One of the primary challenges lies in the variability in the exposure definitions. Among the primary studies included in the systematic reviews, the definitions of proximity to refineries ranged from fixed radii (e.g., 5 km, 8 km, 10 km, or larger) to broader categorizations, such as entire cities with refineries compared to those without, or other types of classification. This diversity precluded standardization in reporting specific distances in our analysis and reflected the methodological differences among the original studies. Including these highly variable measures in a single summary would risk oversimplifying or misrepresenting the findings.

Similarly, the identification and quantification of air pollutants varied widely across the primary studies—when such data were available. While some studies measured specific pollutant concentrations, others focused primarily on linking geographic proximity to health outcomes without assessing individual pollutants. Even when pollutant data were available, differences in the measurement techniques and reporting standards across the studies introduced significant variability. The exposure duration also varied extensively, with some studies assessing long-term exposure spanning decades or specific years, often based on the operational timelines of the facilities. These inconsistencies underscore the diversity inherent in the primary studies and highlight the challenges of summarizing these aspects across the reviews included.

The global scope of the included reviews presents another limitation, as the primary studies originated from various regions worldwide, each with distinct regulatory frameworks, socioeconomic contexts, and environmental conditions. While this diversity provides a broad perspective, it complicates direct comparisons of the results, particularly given differences in the regulatory standards across continents. Additionally, all of the systematic reviews and meta-analyses incorporated primary studies that adjusted for confounding variables such as age, sex, smoking history, and socioeconomic factors. While these adjustments enhance the reliability of the findings, it is important to acknowledge that the conclusions of this umbrella review remain tied to the methodologies and quality of the systematic reviews and meta-analyses included in our approach.

By addressing these limitations, this subsection aims to provide transparency regarding the inherent challenges of synthesizing findings from diverse reviews and studies. Despite these challenges, our umbrella review offers valuable information into the health impacts of petroleum refining and petrochemical industrial complexes on nearby populations while also emphasizing the need for future research to adopt more standardized methodologies. Improved consistency in the exposure definitions, pollutant measurements, and duration assessments will be crucial to enhance comparability and reliability in this field.

5. Challenges and Perspectives

Addressing the health and environmental impacts of air pollution from petroleum refining and petrochemical complexes presents significant challenges that require coordinated efforts across multiple sectors. The complexity of this issue is compounded further by diverse stakeholder interests, regulatory inconsistencies, technological barriers, and still insufficient research. Consequently, this section explores the main challenges in and outlines perspectives on mitigating the health burden posed by air pollution from these anthropogenic activities on affected populations.

5.1. Cross-Sector Collaboration: Necessity, Challenges, and Potential

One of the most crucial pathways for mitigating the health risks posed by petrochemical air pollution is effective cross-sector collaboration [106]. Addressing the multidimensional nature of this problem requires the active participation of government agencies, the petrochemical industry, technology developers, public health institutions, non-governmental organizations (NGOs), and community groups. Each sector brings unique expertise and resources that, when synergistically combined, can drive more comprehensive and sustainable solutions [107].

Despite the clear need, achieving such collaboration is not without its challenges. Regulatory bodies often operate in silos, with limited engagement with industry stakeholders. Meanwhile, the petrochemical industry may resist adopting cleaner technologies due to the perceived economic disadvantages, regulatory pressure, or a lack of incentives. Public health entities, on the other hand, might lack the technical expertise or data needed to fully understand the scope of emissions and their health impacts. NGOs and community organizations, while advocating for stricter regulations and community protection, may face resource constraints that limit their influence. Overcoming these challenges requires establishing transparent channels of communication and fostering a collaborative environment where each stakeholder is committed to a shared goal: protecting public health and the environment. Cross-sector collaboration is the key to building more resilient communities [108].

The potential benefits of such collaboration are substantial. Governments can introduce policies and incentives that encourage the adoption of cleaner technologies, while the industry can invest in innovations that reduce emissions and improve community health outcomes. Public health agencies can provide critical data on health impacts, enabling more targeted interventions, while NGOs can serve as intermediaries, facilitating dialogue between communities and decision-makers. Additionally, integrating advanced technologies, such as real-time air quality monitoring and pollution control systems, enhances these efforts by bridging the data gaps, enabling precise regulation and compliance, and supporting informed decision-making. Together, these collaborative and technological approaches can create a robust framework for addressing the health and environmental challenges posed by petrochemical emissions.

5.2. Technological and Operational Strategies for Mitigating Air Pollution

A critical challenge in reducing the health and environmental impacts of petrochemical and petroleum refining activities lies in overcoming the existing technological and operational barriers. Many refineries continue to operate with outdated infrastructure, relying on conventional processes that are highly pollutive and energy-intensive. Upgrading these facilities to incorporate cleaner technologies is not only a financial challenge but also involves complex technical modifications that may disrupt production and reduce profitability in the short term. As a result, many companies resist adopting these changes unless they are driven by regulatory mandates or substantial economic incentives.

Despite these barriers, several technological advancements, innovative methods, and improvement approaches have emerged as potential solutions to reduce air pollution from these industries while maintaining profitability. One key strategy is enhancing combustion processes by integrating technologies such as low-NO_x burners and wet or dry flue gas desulfurization systems into existing combustion units to reduce the formation of primary air pollutants, among other approaches, such as water injection, air staging, flow gas recirculation, low excess air, oxy-fuel combustion, fuel staging, and chemical looping combustion [109,110,111,112]. Additionally, advanced process control systems can be used to monitor and adjust the combustion parameters in real time, ensuring the optimal efficiency and minimizing pollutant emissions [111,112]. Another effective strategy is reducing and controlling flaring emissions, which are significant sources of VOCs and GHGs. This can be achieved through advanced flare gas recovery systems that capture and reuse gases which would otherwise be combusted, thereby reducing the overall emissions [113,114]. Moreover, improved flare monitoring technologies and the adoption of the best practices for flare operation could reduce unnecessary flaring and the associated pollution further [115].

Pollution control technologies are also essential in capturing and removing pollutants before they are released into the atmosphere. Wet scrubbers can be used to remove acidic gases, while catalytic converters facilitate chemical reactions that convert air pollutants into less harmful substances [116,117]. Particulate filters, including mechanical filters and electrostatic precipitators, capture particulate matter, thus reducing these pollutants in the nearby atmosphere [118,119]. Additionally, advanced air filtration systems—including photocatalytic oxidation, which employs a catalyst along with UV light to oxidize and break down airborne pollutants, selective catalytic reduction, plasma air purification systems, and activated carbon filters—are also effective in removing VOCs and other gaseous pollutants [111,120]. Each of these technologies has a range of subdivisions, with specific adaptations and modifications that enhance their efficiency depending on the pollutant profile and environmental conditions. Combining these technologies through multi-stage filtration systems could achieve more efficient removal of various air pollutants.

Furthermore, implementing robust Leak Detection and Repair (LDAR) programs, as previously mentioned in Section 2, is crucial for controlling fugitive emissions. Utilizing advanced technologies such as infrared cameras and gas detectors can enhance the effectiveness of these programs, allowing for the early identification and prompt repair of leaks, thereby minimizing emissions [121]. Improving the energy efficiency in refining operations is another approach to reducing overall emissions. Upgrading equipment, utilizing heat recovery systems, and optimizing energy use through process integration are effective strategies. Additionally, transitioning to cleaner fuels or integrating renewable energy sources can reduce overall emissions further [122,123]

In this sense, continuous monitoring and compliance play a fundamental role in ensuring that refineries adhere to environmental regulations and emission standards [115]. Implementing continuous emission monitoring systems provides real-time tracking of the pollutant levels, ensuring compliance and offering data for further optimization of pollution control measures. Integrating digital technologies such as machine learning and artificial intelligence can enhance these systems by enabling their predictive capabilities and preemptive maintenance, preventing excess emissions.

Governments and policymakers are pivotal in creating favorable conditions for the adoption of these technologies. Policies such as tax incentives, subsidies for retrofitting costs, and support for collaborative research and development initiatives can help industries overcome the financial hurdles associated with adopting new technologies. Collaborative efforts between the petrochemical industry, technology developers, and academic institutions can also accelerate the development and deployment of cleaner production technologies [98]. While modern refineries in developed countries are increasingly incorporating eco-friendly designs and utilizing the technologies and approaches mentioned to minimize their impact on air pollution [124], the situation is different in middle- and low-income countries. These regions face financial constraints, less stringent regulatory frameworks, and lower levels of technological development, which hinders the implementation of advanced pollution control strategies. Consequently, populations in these regions remain disproportionately affected by the adverse health impacts of air pollution from petrochemical activities.

It is important to acknowledge that even though modern refineries strive to minimize air pollution, the refining process itself inherently generates emissions. Therefore, ongoing efforts to improve and innovate environmental practices are essential for further reducing the impact of refineries on air quality. Coordinated efforts, international cooperation, and strategic investments are necessary to ensure that the industry evolves towards a cleaner, more sustainable future that safeguards both public health and the environment.

5.3. Strengthening Policy and Regulatory Frameworks

Effective policy and regulatory frameworks are essential to driving the transition towards cleaner technologies and operational practices. Currently, regulatory inconsistencies between regions, a lack of stringent emission standards, and insufficient enforcement of the existing regulations present considerable barriers to progress. This fragmentation can lead to regulatory arbitrage, where industries relocate to regions with less stringent environmental regulations, perpetuating the global health and environmental impact of air pollution. To address this, policymakers must work towards harmonizing regulations at the national and international levels, setting more ambitious emission reduction targets, and ensuring that industries are held accountable for their environmental footprint. Strengthening the enforcement mechanisms, such as regular inspections, emission reporting, and stringent penalties for non-compliance, is crucial to ensuring that industries adhere to established standards.

International cooperation is also critical, as pollution and its health impacts do not respect geopolitical boundaries. Collaborative frameworks such as global treaties and regional agreements can help align efforts, facilitate technology transfer, and provide financial support for regions with limited resources. The creation of international funds dedicated to retrofitting refineries and supporting the adoption of cleaner technologies could incentivize industries to transition away from pollutive processes. Additionally, fostering partnerships between government bodies, international organizations, and private industries can promote the best practices and enhance the regulatory coherence across different jurisdictions. Such cooperative efforts will be essential for advancing towards global climate goals, ensuring sustainable development, and protecting public health.

5.4. Addressing Socioeconomic Disparities and Environmental Justice

The health burden of air pollution from petrochemical industries is disproportionately borne by socially vulnerable populations who often reside in closer proximity to these facilities due to economic constraints. These communities face heightened exposure to harmful pollutants and consequently greater health risks. Addressing this issue requires the integration of environmental justice principles into policy and regulatory frameworks, which involves not only mitigating emissions but also ensuring the equitable distribution of health benefits and resources. Policies should prioritize the implementation of community-level air quality monitoring, health impact assessments, and targeted interventions designed to protect the most at-risk groups. Furthermore, enforcing buffer zones between industrial sites and residential areas and offering relocation or compensation programs can be effective strategies to reduce direct exposure for nearby communities.

Future efforts should focus on engaging local communities in decision-making processes related to industrial activities, providing them with the tools and resources to advocate for their health and well-being. Establishing platforms for dialogue between communities, industry stakeholders, and policymakers is essential to ensure that community concerns are adequately addressed and that local populations have a voice in shaping the environmental policies that affect them. Empowering these communities through education and access to health information is a crucial step in achieving more equitable health outcomes. By addressing the socioeconomic factors that exacerbate health disparities, we can develop more comprehensive strategies that promote environmental justice and protect public health.

5.5. Future Research Directions and Knowledge Gaps

Despite substantial progress in understanding the health impacts of the air pollution from petrochemical industries, significant knowledge gaps remain. The current research has primarily focused on acute exposure effects, cancer outcomes, and respiratory diseases, while other critical areas, such as long-term, low-level exposure, interactions between multiple pollutants, and non-cancer health outcomes, remain underexplored. There is a pressing need to expand the research to include reproductive, neurodevelopmental, and metabolic disorders, as well as the impacts of chronic exposure on vulnerable populations such as children and the elderly. Additionally, more studies should investigate the cumulative and synergistic effects of simultaneous exposure to multiple pollutants, as real-world scenarios often involve complex mixtures of chemicals that may interact in unpredictable ways.

Another emerging area of research is the feasibility and environmental performance of repurposing existing refineries into biorefineries or “stand-alone unit” facilities capable of processing renewable feedstocks [125,126]. Understanding the potential health benefits and unintended consequences of such transitions will be critical to ensuring that future industrial activities are aligned with both environmental sustainability and public health goals. Research should also focus on evaluating the lifecycle emissions of these new processes and their overall impact on air quality to ensure that any technological shift results in tangible health benefits for surrounding communities. Developing advanced methods for long-term monitoring of the health and environmental outcomes will be crucial to bridging these knowledge gaps and informing future policy decisions.

The petroleum industry holds a crucial role as a primary energy provider but remains under close scrutiny by researchers and the public due to its significant contributions to climate change. This scrutiny, alongside the growing focus on Environmental, Social, and Governance (ESG) factors, makes it imperative for this sector to take proactive steps. Meeting the ESG criteria not only helps mitigate environmental impacts but also enables the industry to maintain its position in terms of sustainable investment indices such as the Dow Jones Sustainability Index (DJSI) and the FTSE4Good Index. Approaches to achieving these goals include reducing carbon footprints through clean technologies such as carbon capture and renewable energy integration, enhancing social responsibility by minimizing air pollution’s impacts on surrounding communities, and promoting transparent ESG performance reporting. Additionally, upgrading existing refineries with advanced emission control systems and optimizing their energy efficiency represent a forward-looking strategy to reduce emissions and support a circular economy. By adopting these measures or similar ones aligned with the same commitment to environmental stewardship and social responsibility, the petroleum sector can mitigate its environmental impacts, demonstrate leadership in advancing global sustainability objectives, and ensure its long-term relevance and adaptability.

Strengthening research initiatives to cover these knowledge gaps is critical, but this must be paired with international collaboration to promote technology transfer, capacity building, and policy alignment. Aligning the industry’s evolution with global climate goals, such as the 2030 Agenda for Sustainable Development and the United Nations Sustainable Development Goals (SDGs), is essential for achieving a sustainable future. Specifically, these efforts resonate with SDG 3 (Good Health and Well-being), SDG 7 (Affordable and Clean Energy), SDG 9 (Industry, Innovation, and Infrastructure), SDG 11 (Sustainable Cities and Communities), and SDG 13 (Climate Action). Advancing these goals will require not only enhanced research and technological innovations but also a strong commitment for multiple sectors. Only through such comprehensive and inclusive strategies can we safeguard the health and well-being of populations while fostering sustainable industrial development.