Preliminary Assessment into the Prevalence and Distribution of Microplastics in North and South Pacific Island Beaches

Abstract

Microplastic pollution has become an increasing danger to marine wildlife and ecosystems worldwide. The continued increase in the production of plastic products has caused microplastic pollution to become more distributed, especially along shorelines. Therefore, to better assess the pervasiveness of microplastics around the Pacific Islands, in this work, we conducted a preliminary investigation into the pervasiveness of microplastics along eight different North and South Pacific Island beaches located in New Zealand and Hawaii. Microplastic prevalence was investigated as a function of beach location, sand type, and microplastic type. Our analysis found that all eight locations contained some level of microplastics, and sheltered fine-grained sand beaches contained the highest level of microplastics, with the largest particle size distribution. In addition, spectroscopy analysis was conducted to assess the plastic type, which showed that nylon and polypropylene were the most common types of microplastics among the tested samples. The results of this study offer a preliminary insight into the microplastic accumulation among different beaches, indicating that sheltered fine-grained beaches and ecosystems may be more susceptible to microplastic accumulation.

1. Introduction

Microplastics and nanoplastics are considered pervasive contaminants, which have been extensively found in marine life, aquatic systems, and even, human blood and lung tissue [1,2,3,4,5,6,7,8,9]. These particle plastics are considered a well-known threat to marine life, and this issue is expected to significantly worsen in the near future, due to the increasing production of plastic products. Global plastic production from over 173 countries is estimated to increase to between 19 and 23 million metric tons (MT) by 2030 [8], while plastic waste from the plastics industry is expected to surpass 53 MT/year in the next decade [8]. Meanwhile, the industrial worldwide production of plastic waste materials is expected to exceed 12,000 MT by 2050 [9], with global plastic dependency and usage expected to increase steadily over the next decade.

Current research indicates that a large influx of plastic enters the marine environment either by industrial chemical waste runoff, human plastic waste that is inadequately managed, or through the deliberate dumping of plastics into the oceans [10,11]. As global plastic usage has increased, improperly disposed plastic products have accumulated in the natural environment, making them an ecological threat to marine animals and organisms [11,12,13,14,15].

Several different types of microplastics have been found, which can be organized and categorized by type and composition of the debris (micro-beads, single-use plastic bottles, and discarded packaging) [1,5,14]. Plastic waste can be generally classified as ranging from mega-, macro-, and micro-plastics [16,17]. As large pieces of plastic break down, they become microplastics, which can be defined as plastic debris between 1 μm and 5 mm in size [18]. Further complicating the issue is the pervasiveness of plastic materials, which do not naturally and quickly break down into innocuous materials [8,18,19,20]. Microplastics can be then distributed by ocean currents, as well as through physical fragmentation. As a result, microplastic debris has become widespread, especially in marine ecosystems, and numerous studies have found microplastics to be a severe marine ecological threat, from the toxic bioaccumulation of microplastic particles to man-made polymer compounds that enter watershed runoffs and oceans [1,2,3,4,5,6,7,12,14,18,20]. Additional studies on high microplastic concentration in freshwater streams and river systems have shown a high probability of transport from landfills to open marine ocean environments [21,22].

Environmental microplastic pollution threatens the existing food web and can directly harm marine ecosystems, adversely affecting the biological functions of many marine organisms ranging from single-cellular plankton to more complex marine life such as coral reefs, invertebrates, fish, sea reptiles, sea birds, and cetacean mammal species [17,19,23]. Microplastics and plastic waste are often ingested by marine life, as they can resemble food. However, these plastic pieces/particles are non-digestible and can be life-threatening to marine life if ingested. In addition, they can be sources of toxic contaminants, specifically HCHs, BPA, PCBs, and HCHs [17,19,24].

Unfortunately, the long-term lifecycle and breakdown cycle of plastic materials is not well understood, especially in marine environments [25]. Specifically, polymer/plastic materials used in cosmetics and industrial cleaning products (liquid gel-based surfactants, oral care, and various facial/body cleansers) can be directly connected to the microplastics that enter the oceans via downstream hydrological cycling (rivers and streams) of terrestrial manufacturing to the ocean [26,27,28]. In the past decade, there has been an increase in the number of plastic products that contribute to marine system pollution [29,30]. Plastic debris in marine environments can be exposed to physical (ocean wave friction) and chemical (photochemical ultraviolet degradation) processes, which can alter the plastic debris waste structure, further breaking down the plastic particles into smaller fragments. Depending on the environmental conditions, the rate of plastic degradation into smaller micro- or nanoparticles may be contingent on exposure to mechanical or chemical forces, e.g., the salinity of ocean water, the intensity of photon radiation (UV), abrasion forces, and relative temperature [6,31]. These microplastics may then make their way back to land, washing up on shorelines and affecting local ecosystems. Therefore, the accumulation and presence of microplastics along shorelines are of particular concern. Specifically, the transport of microplastics in the Pacific Ocean region may indicate the prevalence of microplastics regionally, indicating regional pollution [30,31,32].

In this work, we conducted a preliminary investigation into the prevalence of microplastics in eight South and North Pacific Island beaches, namely in New Zealand and Hawaii, to investigate microplastic accumulation as a function of microplastic size distribution, sand type of beach, microplastic morphology, and plastic composition. This investigation was conducted to provide preliminary insight into which beach types, sand types, and locations may be more prone to microplastic accumulation.

2. Methods

To assess the presence of microplastics along various beaches, two Pacific islands were chosen for this study, namely, New Zealand and Oahu, Hawaii, as the South Pacific and North Pacific locations, respectively. To assess beaches with various sand types, locations were chosen to provide a wide sand size distribution range, from exposed rocky beaches, such as Napier Beach, NZ, to very fine-grain sheltered beaches, such as Children’s Bay, Akaroa. These eight different beach types were selected to provide a preliminary assessment of which, if any, beaches contained microplastics, and which beaches may be more susceptible to microplastic accumulation, in terms of microplastic prevalence by mass and type. Both high- and low-energy systems were selected, to provide variations in tidal systems and inflow of water, which could distribute potential microplastic pollution. The selected beaches also varied in location and proximity to population densities.

2.1. Collection of Samples

Samples were taken from four beaches and water inlets in New Zealand and Oahu, Hawaii in January 2020. In New Zealand, samples were taken at the following locations: (1) Children’s Bay, Akaroa (43°47′59.0″ S, 172°58′01.7″ E), a sheltered very fine-grain intertidal beach located on the eastern side of South Island; (2) Shelley Beach (41°17′13.2″ S, 174°00′35.6″ E), a sheltered coarse grain beach located on the northern side of South Island, (3) Napier Beach (39°31′30.0″ S, 176°55′09.6″ E), an exposed rocky coastline beach located on the eastern side of North Island, and finally (4) Papamoa Beach (37°41′52.2″ S, 176°17′27.0″ E), an exposed medium grain coastline beach located on the northern side of North Island (Figure 1a).

The Hawaii (Oahu) samples were obtained at the following locations: (1) Kawaikui Beach (21°16′43.788″ N, 157°44′40.848″ W), an exposed coastline beach located on the south-eastern edge of Oahu with medium grain sand, (2) Sandy Beach (21°17′7.8″ N, 157°40′21.774″ W), an exposed coastline beach with medium-to-fine-grain sand, (3) Makapu’u Tide Pools (21°18′15.2712″ N, 157°38′56.832″ W), sheltered tidepools with areas of exposed beachfront consisting of fine to medium-grain sand on the eastern edge of Oahu, and (4) Kapalaoa Beach (21°36′37.944″ N, 157°54′33.12″ W), an exposed coastline beach located on the northern edge of Oahu with medium-grain sand. Each of the Hawaii (Oahu) sampling locations is shown in Figure 1b.

2.2. Plastic Sampling

Sand samples were taken along each beach location, no farther than 2 m from the waterline, at 10 separate random locations along each beachfront (20 g obtained at each random location), to provide variability in sampling, with a total of 200 g of samples obtained from each location. The random location strategy was chosen to minimize bias toward any particular area. The sand samples from each sampling location were washed with deionized water to help separate the microplastics from the sand or organic particles. An optical microscope (Olympus BX51-P) was then used to help manually separate the microplastics from the sand, and images were obtained of the representative microplastics from each location. For each sample batch, the total mass of microplastics was obtained by weighing all microplastic samples using a high-precision analytical balance lab scale (IVYX Scientific, Seattle, WA, USA), to determine the microplastic content per sampling location.

For each sample batch, the microplastics were counted and labeled according to their size and shape, and categorized by particle size distribution and type, namely, as microparticles or microfibers, to assess the microplastic content at each beach location.

2.3. Plastic Composition

Fourier transform infrared (FTIR) spectroscopy was used to analyze the composition of the microplastics in this study. A Thermo Scientific Nicolet NEXUS 670 FTIR spectrometer was used to obtain the spectra of the microplastics. Prior to analysis, the spectrometer was calibrated with reference materials, and the spectra were collected over a range of 4000–400 cm⁻¹ with a resolution of 4 cm⁻¹ to characterize the compositions of the microplastics. The compositions of the microplastics were compared to the spectra of known polymer standards, utilizing the software library and by comparing to literature sources. Due to instrument limitations, only microplastic samples larger than approximately 1 mm in size could be assessed, and a total of 111 microplastic samples were ultimately analyzed due to equipment/sample limitations. These results were used as representative examples to provide an approximate indication of the plastic type at each sampling location.

3. Results

The samples from the eight coastline beaches were assessed according to the total weight of microplastic for each location, with the values listed in

Table 1. Microplastic content from the samples obtained from each island’s beach location.

Sampling Location	Microplastic Content (g)	Number of Microplastics
Children’s Bay, Akaroa (NZ)	0.92	47
Shelley Beach (NZ)	0.36	33
Napier Beach (NZ)	0.11	9
Papamoa Beach (NZ)	0.21	13
Kawaikui Beach (Hawaii)	0.28	24
Sandy Beach (Hawaii)	0.29	38
Makapu’u Tide Pools (Hawaii)	0.85	39
Kapalaoa Beach (Hawaii)	0.13	18

. Surprisingly, all beach locations assessed in this study contained some form of microplastics, with variations in size, morphology, and microplastic composition, and a total of 221 microplastic samples obtained from all eight beach locations. The results showed that Children’s Bay, Akaroa (NZ) contained the highest total mass of microplastic content per 200 g, with a microplastic content value of 0.92 g, while Napier Beach (NZ) had the lowest amount of microplastic content, with a value of 0.11 g. The samples obtained from the beaches in Hawaii had overall lower microplastic content by mass compared to the samples obtained from the beaches in New Zealand, with a total of 1.35 g of microplastic content obtained from the Hawaii beaches, and 1.51 g of microplastic obtained from the beaches in New Zealand. However, the samples obtained from Hawaii contained a greater number of individual microplastics, with a total of 119 individual microplastics obtained from Hawaii beaches, and a total of 102 individual microplastics obtained from New Zealand beaches. According to the individual locations, Children’s Bay, Akaroa (NZ) contained the highest number of microplastics (47), while Napier Beach (NZ) contained the lowest number (9) of microplastics. Notably, Kawaikui Beach (Hawaii) and Sandy Beach (Hawaii) contained similar microplastic content by mass, at 0.28 g and 0.29 g, respectively, but differed in the number of individual microplastics. A fairly high amount of plastic content was also found in the Makapu’u Tide Pools in Hawaii, with a total microplastic content value of 0.85 g.

The microplastics were also assessed according to their size (mass) distribution, and categorized into microparticles and microfibers, with their features recorded by optical microscopy. The collected microplastics showed various morphologies, ranging from fragmented particles to microfibers. As shown in Figure 2a–d, many of the obtained microplastics exhibited rough surfaces indicative of degradation, with some of the microplastics even appearing to contain smaller microplastic fragments, visible only under an optical microscope (Figure 2a). The images of the microplastics obtained from Shelley Beach (NZ) and Kawaikui Beach (Hawaii) were used as examples to show some of the representative surface morphologies that were observed in many of the microplastic samples (Figure 2a,d). Figure 2c shows a microfiber obtained from Makapu’u Tide Pools (Hawaii), which was later identified as nylon. The possible origins of these microplastics are provided in the discussion.

In addition, as presented in

Table 2. Microplastic size distribution for the samples obtained from each island’s beach location.

Sample Location	Microplastic Size Distribution
	<500 μm	500–999 μm	1–5 mm
Children’s Bay, Akaroa (NZ)	19.3%	53.1%	27.6%
Shelley Beach (NZ)	3.30%	39.2%	57.5%
Napier Beach (NZ)	0%	33.3%	66.6%
Papamoa Beach (NZ)	7.6%	23.2%	69.2%
Kawaikui Beach (Hawaii)	4.1%	12.5%	83.4%
Sandy Beach (Hawaii)	5.2%	42.2%	52.6%
Makapu’u Tide Pools (Hawaii)	5.1%	23.1%	71.8%
Kapalaoa Beach (Hawaii)	5.5%	33.4%	61.1%

, there was large variability in the microplastic size distribution, with the largest variations observed in the samples obtained from New Zealand. Notably, the microplastics obtained from Children’s Bay, Akaroa (NZ) showed a considerable range, with the highest number of microplastics <500 μm in size (length or approximate diameter). By contrast, Napier Beach (NZ) contained no microplastics <500 μm in size, and this location contained the highest number of microplastics between 1–5 mm. The samples obtained from Hawaii also showed a trend toward larger microplastic sizes, with the distribution leaning more toward microplastics 1–5 mm, compared to the samples obtained from New Zealand. The size distribution results shown in Table 2 indicated that fine-sand beaches, especially sheltered beaches (Children’s Bay, Akaroa (NZ)), contained higher levels of microplastics compared to rocky, exposed beaches (Napier Beach (NZ)).

The microplastics were also assessed according to their morphology, namely, microparticle or microfiber, to determine the microplastic type and potential origin. As shown in Figure 3, the microplastics obtained from the Makapu’u Tide Pools (Hawaii) and Kapalaoa Beach contained the highest percentage of microfibers, with nearly 40% of the total microplastic content consisting of microfiber plastics. All samples obtained from Hawaii contained a larger portion of microfibers compared to the samples obtained from New Zealand, indicating that the microplastics found in Hawaii were of a different origin than those found in New Zealand, with their origins being more likely to come from netting or fiber sources. This was partially confirmed by the FTIR results, as discussed below. In contrast, the microplastic samples obtained from New Zealand had a distinctly lower percentage of microfibers, with more microparticles observed. In addition, the microplastics obtained from the beaches of New Zealand were more degraded, with an overall rougher morphology compared to the samples obtained from Hawaii, though the reason for this was unclear. This phenomenon should be investigated in future work.

To further determine the microplastic origin, FTIR spectroscopy analysis was only conducted on microplastic samples larger than approximately 1 mm in size (Figure 4) and the data were extrapolated according to composition (Figure 5). Figure 4a–c shows the FTIR spectra of the three most common microplastics among the tested samples, with the assessed microplastic spectra shown in red, and the reference spectra shown in black. The main types of plastics present among the assessed samples were polyethylene, polypropylene, and nylon, with different ratios at each Pacific Island location. Among the samples tested, polypropylene was the most common in all beaches, with Napier Beach containing the highest percentage, followed by Shelley Beach (NZ) and Sandy Beach (Hawaii). Polyethylene was the second most common polymer type with the highest percentage found in Kawaikui Beach. Nylon, polystyrene, and polyethylene were also found in most of the samples, but their percentages varied between the locations (Figure 5). In addition, styrene butadiene rubber was found in two of the beaches, along with poly(methyl methacrylate) and polybutylene terephthalate. Notably, Makapu’u Tide Pools (Hawaii) and Kapalaoa Beach contained the highest levels of nylon, while Napier Beach (NZ) contained the highest amount of polypropylene. An example of this is the microfiber shown in Figure 2c, which was obtained from Makapu’u Tide Pools (Hawaii), and was later identified as nylon. In addition, the microplastics experienced various levels of degradation, as most prominently indicated by the FTIR spectrum of nylon (Figure 4a).

4. Discussion

Overall, we made a few observations considering the above results. Notably, a significant amount of microplastics was found at certain locations, with certain beaches containing higher levels of certain types of microplastics, both in terms of morphology and composition. Specifically, Children’s Bay, Akaroa (NZ) and the Makapu’u Tide Pools (Hawaii) contained the highest amount of microplastics, at 0.92 g and 0.85 g, respectively, though their microplastic size distributions differed considerably. The microplastics found in the sand samples from Children’s Bay, Akaroa (NZ) leaned heavily toward a smaller microplastic size distribution, with a higher number of microplastics that were <500 μm and 500–999 μm in size, compared to 1–5 mm in size. In contrast, the microplastics obtained from the Makapu’u Tide Pools (Hawaii) leaned heavily toward larger microplastics, with 71.8% of the microplastics 1–5 mm in size and 23.1% that were 500–999 μm, and only 5.1% that were <500 μm in size. Similarly, according to the samples obtained in this study, no microplastics were found in Napier Beach (NZ) that were <500 μm in size. Notably, the total microplastic mass between Children’s Bay, Akaroa (NZ) and Makapu’u Tide Pools (Hawaii) was minimal, but significant variations in microplastic type were observed.

The high number of microplastics found in Children’s Bay, Akaroa (NZ) (0.92 g) was potentially related to the location and sand quality and size of this particular location, which consisted of a sheltered intertidal beach with very fine-grain sand and silt on the eastern side of South Island. Similarly, the Makapu’u Tide Pools (Hawaii), which are sheltered shallow-tide pools with fine-to-medium-grain sand, contained the second-highest amount of microplastics at 0.85 g. Thus, sheltered areas with fine-grain and medium-grain sand appeared to contain the highest load of microplastics, with the smallest particle size, likely because the fine sand acted as a filter, trapping even the smallest microplastics.

According to FTIR analysis, polypropylene was the most common type of microplastic found in all beaches, with Napier Beach containing the highest percentage. This was consistent with previous studies that identified polypropylene as a major source of microplastic pollution in the ocean [21,31], likely due to its widespread use in consumer products such as packaging materials and textiles. Polyethylene was also found in all tested samples, with the highest percentage found in Kawaikui Beach (Hawaii). These results correlated with previous studies that showed polyethylene as one of the most common microplastics, due to its wide use in single-use plastic products such as bags and food packaging, with its presence in the samples beaches corresponding to its ubiquity as a commodity plastic.

Interestingly, the study also found varying levels of other types of microplastics, such as nylon, polystyrene, polyethylene, and polycarbonate, with nylon being the most prevalent in the Makapu’u Tide Pools. This also correlated with the microplastic morphology results, as the Makapu’u Tide Pools contained the greatest percentage of microfibers among the tested locations. The different plastic compositions at each Pacific Island location suggested that the sources of plastic pollution varied by region and could be influenced by factors such as waste management and ocean currents.

Furthermore, the variability in the size distribution of microplastics observed across different beach locations could reflect differences in the sources of microplastics, with larger microplastics potentially originating from less-degraded macroplastic debris, and smaller microplastics potentially originating from more degraded debris, or products such as personal care products or textiles. The presence of microfibers in samples obtained from certain locations suggested that woven plastic products could be a significant contributor to microplastic pollution in those areas. Nylon, commonly used in fishing nets and textiles, was found at the highest levels in the Hawaii samples, as highlighted by the microfiber sample shown in Figure 2c, which was identified as nylon. Considering its size and composition, we speculated that this microfiber possibly originated from fishing nets or nylon produce netting, which have similar coloring and composition. This could potentially indicate that this region is especially susceptible to microplastic pollution from discarded fishing nets. Possible sources of polyethylene microplastics could also include the breakdown of larger macroplastics, as well as microbeads from consumer products. However, further research investigations will be required in the future to better determine the exact origins of the obtained microparticles and microfibers. For example, we were unable to elucidate how many of the microplastics experienced mechanical breakdown from larger pieces, or were the result of hydrolytic damage, which would give us a better determination of age and possibly origin. Furthermore, according to FTIR spectra, the nylon samples showed degradation of the amide bonds, as well as hydrolytic damage, suggesting that the microplastics were present in the environment for some time and were subjected to weathering and degradation processes, potentially impacting their persistence in the environment and potential harm to marine organisms.

It should be noted, however, that there were limitations to this study, in particular the sample size. The FTIR spectra were obtained from larger obtained microplastics in this study (1–5 mm), due to the limitations of the equipment. As a result, the characterization results of this study, as shown in Figure 5, were indicative of the larger samples, and not of all samples that were obtained. This was a limitation of this preliminary study and will be expanded upon in future work.

The presence of microplastics in all beach locations assessed in the study highlights the widespread distribution of microplastics in marine environments. The smaller size distribution of microplastics found in Children’s Bay, Akaroa (NZ) could make them more easily available to smaller organisms, such as zooplankton, which form the base of the marine food web [1,23]. The higher microplastic content observed in fine-sand, sheltered beaches compared to rocky, exposed beaches suggested that the physical characteristics of the beach environment could influence the accumulation of microplastics, with fine-sand beaches more susceptible to microplastic accumulation. The presence of microplastics in these coastal environments may have significant implications for the local ecosystems, as they can be ingested by marine organisms and potentially enter the food chain. In addition, the degradation of nylon observed in the FTIR results is also cause for concern, as it may potentially indicate continued degradation of the material itself, and a larger distribution of nylon pollution in this area.

Further studies are needed to investigate the potential effects of microplastic pollution on the health and survival of marine life in these areas. This study highlights the need for further research to assess the extent of microplastic contamination in different marine environments and the potential impact on the marine food web. Furthermore, additional work will need to be conducted to determine the sources of the smaller microplastics, whether they were residues or fragments, or remnants of cosmetics products. The findings of this study could be used as a baseline to evaluate plastic pollution in coastal areas and the effects of microplastics on marine biodiversity in the future.

5. Conclusions

In this work, we conducted a preliminary investigation into the prevalence and distribution of microplastics in South and North Pacific Island beaches and found that microplastic content was highest in secluded areas with fine to medium coarse grain sand, namely, Children’s Bay, Akaroa (NZ) and Makapu’u Tide Pools (Hawaii), with a microplastic content of 0.92 and 0.85 g, respectively. In addition, Hawaii, contained the highest percentage of microfiber content, while New Zealand contained more microparticles, and the size distribution also varied between the different sampling locations. Notably, Children’s Bay, Akaroa (NZ), contained the largest size distribution of microplastics, with the highest amount of microplastics that were <500 μm in size. This was attributed to the secluded location and fine sand system of the beach. Polyethylene, polypropylene, and nylon were found at different ratios at each Pacific Island location, with polypropylene the most common plastic type among all samples. Though several locations were assessed in this work, additional investigations and more sampling will need to be conducted to determine why certain beach locations appear to be more prone to the accumulation of microplastics and even nanoplastics, and why the microplastics obtained in New Zealand appeared to have a rougher morphology than those obtained in Hawaii. Overall, this study underscores the need for continued efforts to reduce the production and release of plastics into the environment, as well as to develop effective strategies for the removal and disposal of plastic waste. The findings of this study also suggest that efforts to reduce microplastic pollution may benefit from targeted interventions that take into account the physical characteristics of the beach environment and potential sources of microplastics in different locations.