Monitoring of the Surfactants in Surface Waters in Slovakia and the Possible Impact of COVID-19 Pandemic on Their Presence

Abstract

In order to keep the home and occupational environment clean and non-infectious, the consumption of cleaners and disinfectants, including cosmetics, is increasing. Excessive use of these products results in their accumulation in the aquatic environment. Conventional wastewater treatment plants are unable to effectively remove the emergent pollutants, including personal care products. This article is focused on the monitoring of the presence of personal care products in surface waters in two river basins in the Slovak Republic, in terms of the surfactant content. Ecotoxicological evaluation of the selected samples from the monitored river basins was performed by an acute toxicity test using the test organism Daphnia magna. The monitoring results indicate the presence of personal care products in the aquatic environment which poses an ecological and environmental risk. Monitoring in the Hron and Nitra river basins confirmed contamination with the surfactants, to which the measures related to the COVID-19 pandemic contributed. The content of the surfactants in personal care products is significant, and their impact on the aquatic environment is not sufficiently monitored.

1. Introduction

The impact of the wastewater discharged into recipients represents a serious global problem for the aquatic environment. The wastewater is a high-risk mixture of pollutants, which may endanger human health. In most cases, wastewater treatment plants only partially reduce the content of the specific pollutants, which mainly include new, unexplored, anthropogenic contaminants [1]. These are emerging pollutants whose properties are unknown in comparison with known conventional substances. They have a potential and confirmed impact on human health and the environment [2,3]. These are mainly substances that reach the recipients for a long time, but their importance and impact on the quality of the aquatic environment have not been investigated. Emergent pollutants can include persistent organic pollutants, pesticides and other biocidal preparations, flame retardants, e.g., based on polybrominated compounds, preservatives and other products used not only in the food industry, pharmaceutical products and personal care products, etc. [4,5]. Emergent pollutants have attracted worldwide attention due to their highly toxic effect, very low degradation, long-term exposure and extensive distribution in the environment [6]. Currently, the detection of their presence poses new challenges in the field of pollution control in all components of the environment. In order to improve the level and increase the quality of environmental analysis, they are beginning to be determined in waste, surface and drinking water in the whole world [2,7].

A special group of emergent pollutants consists of pharmaceuticals and personal care products (PPCPs). These include, e.g., medications, nutritional supplements, cleaners and disinfectants, cosmetics and other products that companies normally use to remove dust particles, impurities and organic substances (such as blood, secretions, etc.). They ensure the cleanliness and reduce the infectivity of the home and work environment [1,8,9,10,11,12]. Their presence in water can cause a change in sensory, physical and chemical properties and affect biological processes in water [13]. Emergent pollutants are usually hardly biodegradable compounds, which limit the passage of airborne O₂ into the water and negatively affect the biocenosis of the environment [14,15]. Their presence can cause increased solubility of organic substances in water, which would not normally dissolve [16,17,18].

According to Zhang et al. [19], the increased consumption and intensity of the use of PPCPs (cleaners, disinfectants and cosmetics) was caused by the global pandemic caused by the COVID-19 virus. Consumption of contact surface cleaning products (door and window handles, floors, food preparation and serving areas, worktops, public toilets, touch screens, keyboards and other work equipment) and personal care products (soaps, creams, shampoos and others) has increased significantly. Previous studies pointed out their release into the environment, in which serious biological damage occurs, such as persistence in the form of bioaccumulation in the environment, thus damaging the fauna and flora [20,21,22].

Each cleaner and disinfectant has a specific composition and characteristics, which are indicated on the label or in the Material Safety Data Sheet (MSDS), which is freely available to consumers. Based on the compositions, which are listed in the MSDS of the individual products, these components can be classified into the following groups: surfactants, alcohols, acids and bases, sodium salts, peroxides and hydrogen peroxides, oxides and additives. Surfactants have the highest percentage of representation.

Surfactants are pollutants whose primary function is to reduce surface tension at the phase interface, which will facilitate the wetting and dispersion of impurities in the liquid that do not mix with it. The main advantages of surfactants are washing, wetting, emulsifying, dispersing, stabilizing and foaming effects [23]. Of the total amount of the existing surfactants, up to 55% are commonly used in households; in the cosmetics and pharmaceutical industries, it is about 10%. Surfactants are also used in the agriculture, textile, food and paper industries, etc. Wastewater concentrates all cleaning, disinfecting and cosmetic products, which cause problems at the wastewater treatment plant (WWTP) [11,19,24].

In Slovakia, the wastewater treatment process is standardly aimed at achieving the quality of the discharged treated water in terms of selected physico-chemical indicators resulting from Slovak legislation (Regulation of the Government of the Slovak Republic No. 269/2010 Coll., which sets requirements for achieving good water status—BOD₅, COD_Cr, insoluble matter, nitrogen and phosphorus). The content of PPCPs in the aquatic environment is not one of the monitored indicators. Their presence poses an ecological and environmental risk to the aquatic environment [25]. PPCPs can affect enzymatic, metabolic and other mechanisms in aquatic animals and plants, leading to negative effects on their physiological functions, endocrine system, metabolism and reproduction. Their action can cause chronic toxicity (mutagenicity, carcinogenicity) [22]. Surfactants are difficult to degrade; they cannot be effectively removed. PPCPs have the highest content of surfactants in their composition.

The presence of PPCPs can also be determined by the content of surfactants in the water environment. The maximum permissible concentrations of anionic surfactants in water are as follows: surface water = 1.0 mg/L and water intended for irrigation = 2.0 mg/L [26].

This article deals with the monitoring of the surfactant content as an indicator of the presence of PPCPs in surface water before (2019) and during the COVID-19 pandemic (2020) in Slovakia in two river basins. The ecotoxicity of the monitored waters was assessed using a bioassay with Daphnia magna. The essence of the study is to point out the fact that the COVID-19 pandemic has caused an increase in surfactants in the water environment, which poses a risk to the environment.

2. Materials and Methods

2.1. Field Mapping and Study Area

For sampling, monitoring sites were chosen within two river basins in Slovakia—the river basin Hron and the river basin Nitra. Samples from surface streams were not only taken directly from these two rivers (Hron and Nitra) but also from smaller streams that flow into them and thus contribute to their characteristic properties.

Globally, it is a locality of central Slovakia (Trenčín, Nitra and Banská Bystrica Self-Governing Region). From the point of view of the global climate classification, the territory of Slovakia belongs to the northern temperate climate zone with a regular alternation of four seasons and changeable weather with a relatively even distribution of precipitation throughout the year.

Water abstraction from surface water was carried out on days that were meteorologically constant (no precipitation activity was recorded; temperatures were without fluctuations). The collection was carried out in the period of spring 2019 and 2020, between March and April, and it was carried out at two points. The results presented in the tables and figures are represented as averages of these measurements. Selected monitoring sites are recorded in Figure 1A,B—Nitra river basin and Hron river basin, respectively.

2.2. Determination of Anionic Surfactant Content

Cationic surfactants make up only an insignificant share of total surfactants. For that reason, we focused on the content of anionic surfactants. The determination of anionic surfactant content is based on the reaction of a water sample with methylene blue. Anionic surfactants in alkaline media form colored ionic associates with methylene blue, which are extracted with chloroform. The absorbance of the samples at 650 nm was evaluated. The WTW CINTRA 20 spectrophotometer was used [27].

In Slovakia, the method STN EN 903: 1999 is standardized. In this method, chloroform is given as the solvent. For that reason, chloroform was also used in this study. Its use was in accordance with all safety measures, including its disposal after use.

To calculate the concentration of surfactants in samples, more calibration curves were used. We present one of them as an example. The calibration curve for the calculation of surfactant content was prepared at regular intervals. The calibration curve was prepared for the standard: sodium n-dodecane sulfonate (C₁₂H₂₅NaO₃S) (Figure 2). The detection limit resulting from the standard STN EN 903:1999 is 0.05 mg/L.

2.3. Ecotoxicological Tests

Acute toxicity test on Daphnia magna: principle of the test is an assessment of percentage of immobilized individuals after 48 h from the beginning of exposure of a tested sample to test organisms of Daphnia magna [28,29]. Conditions of the preliminary test, including control of meeting test conditions with a reference substance, are shown in Table 1.

Daphnia magna was used as the test organism. Its age must be less than 24 h. During the test, the following must be ensured: suitable temperature and suitable pH of the aquatic environment. The control sample is prepared from the solutions listed in Table 1. The test lasts 48 h. At the end of the test, the percentage of immobilized organisms is evaluated. The control of the accuracy of the work is evaluated on the basis of a reference substance, the result of which is shown in Table 1, line “reference substance”. This condition has been met.

Figure 1. (A) Monitoring sites—river basin Hron (QGIS Desktop 3.12.2). (B) Monitoring sites—river basin Nitra (QGIS Desktop 3.12.2) [30]. Explanations: Sites of river basin Hron: 1—Pohorelá; 2—Polomka; 3—Brezno; 4—Valaská; 5—Podbrezová; 6—Lopej; 7—Predajná; 8—Nemecká; 9—Brusno; 10—Slovenská Lupča; 11—Šalková; 12—Poníky; 13—Čerín; 14—Dolná Mičiná; 15—Harmanec; 16—Banská Bystrica; 17—Tajov; 18—Králiky; 19—Kordíky; 20—Malachov; 21—Badín; 22—Kremnička; 23—Vlkanová; 24—Hronsek; 25—Sliač; 26—Kováčová; 27—Zvolen; 28—Vígľaš; 29—Budča; 30—Banská Štiavnica; 31—Kozelník; 32—Hronská Dúbrava; 33—Ladomerská Vieska; 34—Sklené Teplice; 35—Hliník nad Hronom; 36—Dolná Ždaňa; 37—Vyhne; 38—Bzenica; 39—Žarnovica; 40—Hodruša-Hámre; 41—Voznica; 42—Rudno nad Hronom; 43—Nová Baňa; 44—Tekovská Breznica; 45—Hronský Beňadik. Sites river basin Nitra: 1—Kľačno-Horný koniec; 2—Kľačno-Dolný koniec; 3—Nitrianske Pravno; 4—Poluvsie; 5—Nedožery-Brezany; 6—Kanianka; 7—Bojnice; 8—Prievidza; 9—Handlová; 10—Ráztočno; 11—Jalovec; 12—Chrenovec-Brusno; 13—Veľká Čausa; 14—Opatovce nad Nitrou; 15—Nováky; 16—Nitrianske Rudno; 17—Diviacka Nová Ves; 18—Nitrica; 19—Chalmová; 20—Skačany; 21—Veľké Uherce; 22—Partizánske; 23—Bošany; 24—Uhrovec; 25—Biskupice; 26—Horné Naštice; 27—Rybany; 28—Krušovce; 29—Prázdnovce; 30—Topoľčany; 31—Solčany; 32—Nitrianska Streda; 33—Chrabrany; 34—Čeladince; 35—Oponice; 36—Hrušovany; 37—Koniarovce; 38—Jelšovce; 39—Čakajovce-Zbehy; 40—Lužianky 1; 41—Lužianky 2; 42—Nitra; 43—Čechynce; 44—Veľký Cetín; 45—Vinodol.

Figure 1. (A) Monitoring sites—river basin Hron (QGIS Desktop 3.12.2). (B) Monitoring sites—river basin Nitra (QGIS Desktop 3.12.2) [30]. Explanations: Sites of river basin Hron: 1—Pohorelá; 2—Polomka; 3—Brezno; 4—Valaská; 5—Podbrezová; 6—Lopej; 7—Predajná; 8—Nemecká; 9—Brusno; 10—Slovenská Lupča; 11—Šalková; 12—Poníky; 13—Čerín; 14—Dolná Mičiná; 15—Harmanec; 16—Banská Bystrica; 17—Tajov; 18—Králiky; 19—Kordíky; 20—Malachov; 21—Badín; 22—Kremnička; 23—Vlkanová; 24—Hronsek; 25—Sliač; 26—Kováčová; 27—Zvolen; 28—Vígľaš; 29—Budča; 30—Banská Štiavnica; 31—Kozelník; 32—Hronská Dúbrava; 33—Ladomerská Vieska; 34—Sklené Teplice; 35—Hliník nad Hronom; 36—Dolná Ždaňa; 37—Vyhne; 38—Bzenica; 39—Žarnovica; 40—Hodruša-Hámre; 41—Voznica; 42—Rudno nad Hronom; 43—Nová Baňa; 44—Tekovská Breznica; 45—Hronský Beňadik. Sites river basin Nitra: 1—Kľačno-Horný koniec; 2—Kľačno-Dolný koniec; 3—Nitrianske Pravno; 4—Poluvsie; 5—Nedožery-Brezany; 6—Kanianka; 7—Bojnice; 8—Prievidza; 9—Handlová; 10—Ráztočno; 11—Jalovec; 12—Chrenovec-Brusno; 13—Veľká Čausa; 14—Opatovce nad Nitrou; 15—Nováky; 16—Nitrianske Rudno; 17—Diviacka Nová Ves; 18—Nitrica; 19—Chalmová; 20—Skačany; 21—Veľké Uherce; 22—Partizánske; 23—Bošany; 24—Uhrovec; 25—Biskupice; 26—Horné Naštice; 27—Rybany; 28—Krušovce; 29—Prázdnovce; 30—Topoľčany; 31—Solčany; 32—Nitrianska Streda; 33—Chrabrany; 34—Čeladince; 35—Oponice; 36—Hrušovany; 37—Koniarovce; 38—Jelšovce; 39—Čakajovce-Zbehy; 40—Lužianky 1; 41—Lužianky 2; 42—Nitra; 43—Čechynce; 44—Veľký Cetín; 45—Vinodol.

Figure 2. Calibration curve for determining the content of surfactants.

Figure 2. Calibration curve for determining the content of surfactants.

Table 1. The test conditions for Daphnia magna [28,29,31].

Test Organism	Daphnia magna Straus, individuals younger than 24 h since birth (no feeding)
Biotest Conditions	21 ± 2 °C; 7.80 ± 0.20; laboratory conditions
Test Sample	freshly collected surface water, without additions and modifications
Control Sample	diluting water prepared from the solutions of CaCl2·2H2O (1), p.a., MgSO4·7H2O (2), p.a., NaHCO3 (3), p.a., KCl (4), p.a.; by the addition of solutions (1)–(4) per 10 mL and adding demineralized water to a volume of 1 L
Reference Substance	K2Cr2O7, EC50 = 0.82 mg/L (confidence interval 0.3–1.5 mg/L)
Test Duration	48 h
Preliminary Test	20 daphnia/undiluted sample (10 mL), same conditions for control
Validity of the Test	immobilization ≤ 10%, change in concentration of dissolved oxygen O2 ≤ 2.0 mg/L
Monitored Response	% of immobilized individuals

Table 1. The test conditions for Daphnia magna [28,29,31].

Test Organism	Daphnia magna Straus, individuals younger than 24 h since birth (no feeding)
Biotest Conditions	21 ± 2 °C; 7.80 ± 0.20; laboratory conditions
Test Sample	freshly collected surface water, without additions and modifications
Control Sample	diluting water prepared from the solutions of CaCl2·2H2O (1), p.a., MgSO4·7H2O (2), p.a., NaHCO3 (3), p.a., KCl (4), p.a.; by the addition of solutions (1)–(4) per 10 mL and adding demineralized water to a volume of 1 L
Reference Substance	K2Cr2O7, EC50 = 0.82 mg/L (confidence interval 0.3–1.5 mg/L)
Test Duration	48 h
Preliminary Test	20 daphnia/undiluted sample (10 mL), same conditions for control
Validity of the Test	immobilization ≤ 10%, change in concentration of dissolved oxygen O2 ≤ 2.0 mg/L
Monitored Response	% of immobilized individuals

3. Results and Discussion

The determined contents of surfactants in the surface water samples from the monitoring sites were evaluated according to the Regulation of the Government of the Slovak Republic No. 269/2010 Coll. The limit value for surface water is 1 mg/L of the surfactants. Microsoft Office Excel and MATLAB^® (R-2021) were used for processing and evaluating the results.

3.1. River Basin Nitra

The determined surfactant concentration values are shown in Figure 3 and

Table 2. Statistical data of the samples from surface waters in the Nitra river basin.

	Spring 2019				Spring 2020
Sites	Sample		Average	SD	Sample		Average	SD
	1	2			1	2
1	0.3	0.2	0.2	0.0636	0.1	0.1	0.1	0.0283
2	2.7	2.6	2.7	0.1273	3.1	3.2	3.1	0.0919
3	1.6	1.3	1.5	0.2333	2.2	2.3	2.2	0.0778
4	1.4	1.7	1.5	0.2121	2.4	2.5	2.4	0.0778
5	0.4	0.3	0.4	0.0212	1.0	0.9	1.0	0.0566
6	1.2	1.2	1.2	0.0141	2.7	2.6	2.6	0.0566
7	0.9	0.8	0.9	0.1061	2.6	2.5	2.6	0.0424
8	1.2	1.3	1.3	0.0990	3.7	3.6	3.6	0.0566
9	3.8	3.6	3.7	0.1697	4.1	4.2	4.1	0.0707
10	1.3	1.9	1.6	0.4243	0.7	0.8	0.7	0.0636
11	1.0	0.9	0.9	0.0849	0.6	0.6	0.6	0.0141
12	0.7	0.8	0.7	0.0919	0.3	0.3	0.3	0.0424
13	1.0	0.9	0.9	0.0566	0.7	0.7	0.7	0.0141
14	1.5	1.4	1.4	0.0919	1.7	1.7	1.7	0.0141
15	0.8	0.6	0.7	0.1061	1.4	1.4	1.4	0.0071
16	3.9	3.6	3.8	0.1626	4.4	4.2	4.3	0.1131
17	0.4	0.2	0.3	0.1202	0.6	0.6	0.6	0.0071
18	3.9	3.5	3.7	0.3041	5.0	5.1	5.0	0.0354
19	0.1	0.3	0.2	0.1414	3.1	3.3	3.2	0.1202
20	0.9	0.4	0.7	0.3606	0.6	0.7	0.7	0.0283
21	0.6	0.4	0.5	0.0990	0.8	0.8	0.8	0.0636
22	1.0	0.9	1.0	0.0636	1.8	2.0	1.9	0.0849
23	1.0	1.2	1.1	0.1344	2.3	2.3	2.3	0.0141
24	3.4	3.0	3.2	0.2758	3.7	4.0	3.8	0.2192
25	2.1	1.9	2.0	0.1485	2.3	2.3	2.3	0.0636
26	0.3	0.1	0.2	0.1485	0.8	0.8	0.8	0.0424
27	2.7	2.5	2.6	0.1485	4.7	4.6	4.6	0.0636
28	0.3	0.2	0.3	0.0283	1.3	1.3	1.3	0.0566
29	0.8	0.5	0.7	0.1768	0.6	0.7	0.7	0.0495
30	1.6	1.4	1.5	0.1768	4.0	3.8	3.9	0.1414
31	0.7	0.5	0.6	0.1697	1.1	1.0	1.0	0.0566
32	1.0	0.9	0.9	0.0636	0.5	0.4	0.5	0.0778
33	1.3	1.1	1.2	0.1768	1.6	1.7	1.6	0.0636
34	0.7	0.6	0.6	0.0778	1.2	1.3	1.3	0.0566
35	2.6	2.3	2.4	0.1768	3.6	3.7	3.6	0.0636
36	0.5	0.8	0.6	0.2475	1.1	1.0	1.1	0.0354
37	1.1	1.1	1.1	0.0354	2.3	2.2	2.3	0.0636
38	1.1	0.9	1.0	0.1980	1.1	1.1	1.1	0.0212
39	3.9	3.6	3.8	0.1768	4.9	4.9	4.9	0.0283
40	4.0	3.6	3.8	0.2758	5.3	5.2	5.3	0.0141
41	0.7	0.5	0.6	0.1556	3.7	3.5	3.6	0.1344
42	0.9	0.6	0.8	0.1768	2.5	2.6	2.5	0.0778
43	1.1	1.0	1.0	0.0566	1.2	1.3	1.3	0.0424
44	1.5	1.3	1.4	0.1697	1.6	1.7	1.6	0.0636
45	1.0	0.9	1.0	0.0636	1.1	1.2	1.2	0.1061

. The graph shows that the concentration of the surfactants was exceeded in several places even in the period before the COVID-19 pandemic. It is interesting that the Nitra river has increased concentrations of the surfactants in samples from Kľačno (1), above which it springs.

We state that the increased concentration of the surfactants in this area indicates an increased presence of the septic tanks (the households without a connection to the public sewerage). The concentration of the surfactants is also above the limit at other sampling points (2–4). The reason may be the remnants of industrial activity (mining) in Horná Nitra, which is mentioned as a possible source of environmental contamination in the State of the Environment Report (2022). In the State of the Environment Report, it is stated that the Nitra river has long been considered a polluted river, which is mainly affected by mining activities in the town of Prievidza (brown coal mining). In addition to mining activities, the food and chemical industries (plastic production) are characteristic. There is a thermal power plant with the associated production of building materials too [32].

The increased concentration of the surfactants is also due to the fact that they are larger cities, with an extended infrastructure and population, but not all households are drained into the sewerage. Excessive surfactant concentrations are also recorded in the area around the city of Nitra (37–40), again, especially in municipalities that do not have a sufficiently built sewerage network.

During the COVID-19 pandemic (spring 2020), the number of monitoring sites with above-limit surfactant concentrations increased by 20%. The highest concentrations of the surfactants were in the range of 1.0–5.3 mg/L (the limit value for surfactants in surface waters is 1 mg/L; the highest value was at sampling point no. 40). The Nitra river showed an above-limit concentration of the surfactants from monitored site (33) to the end of the monitoring section (45), which represents 13 consecutive monitoring points on the approximate length of the Nitra river 55.2 km (river km 94.3–river km 39.1).

3.2. River Basin Hron

The surfactant concentrations determined in the samples from the monitored sites in the Hron river basin are shown in Figure 4 and

Table 3. Statistical data of the samples from surface waters in the Hron river basin.

	Spring 2019				Spring 2020
Sites	Sample		Average	SD	Sample		Average	SD
	1	2			1	2
1	0.0	0.2	0.1	0.0000	0.1	0.1	0.1	0.0000
2	0.1	0.2	0.1	0.0424	0.1	0.1	0.1	0.0141
3	1.0	1.1	1.0	0.0566	3.1	3.3	3.2	0.1556
4	0.6	0.5	0.6	0.0707	1.0	1.0	1.0	0.0283
5	0.3	0.2	0.3	0.1202	1.9	1.9	1.9	0.0354
6	0.2	0.2	0.2	0.0354	1.0	1.1	1.1	0.0636
7	2.8	2.7	2.8	0.0919	5.0	5.0	5.0	0.0636
8	3.1	2.8	3.0	0.2051	4.1	4.3	4.2	0.1273
9	0.7	0.6	0.7	0.0354	2.1	2.1	2.1	0.0424
10	1.4	1.0	1.2	0.2404	0.6	0.6	0.6	0.0424
11	0.8	0.4	0.6	0.3111	0.6	0.6	0.6	0.0212
12	0.2	0.5	0.4	0.1768	1.1	1.1	1.1	0.0354
13	0.4	0.8	0.6	0.2899	1.0	1.0	1.0	0.0283
14	0.1	0.3	0.2	0.1131	0.7	0.8	0.7	0.0354
15	1.1	0.7	0.9	0.3041	1.4	1.5	1.5	0.0778
16	2.3	2.0	2.2	0.2121	5.2	5.4	5.3	0.1273
17	1.1	1.0	1.0	0.0566	1.1	1.2	1.2	0.0283
18	0.7	1.0	0.8	0.2051	1.5	1.5	1.5	0.0283
19	0.4	0.3	0.4	0.0778	0.6	0.7	0.6	0.0354
20	0.6	0.4	0.5	0.1131	0.6	0.6	0.6	0.0283
21	1.9	2.0	1.9	0.1131	3.4	3.2	3.3	0.1626
22	0.8	0.5	0.6	0.1838	1.6	1.8	1.7	0.0990
23	2.9	2.7	2.8	0.1202	3.2	3.3	3.2	0.0778
24	1.0	0.3	0.7	0.4667	0.9	0.9	0.9	0.0424
25	1.5	1.3	1.4	0.1556	4.0	4.2	4.1	0.1485
26	2.6	1.9	2.3	0.5303	2.5	2.7	2.6	0.1131
27	1.0	0.8	0.9	0.1061	0.9	0.9	0.9	0.0071
28	1.2	0.9	1.1	0.2121	1.2	1.2	1.2	0.0566
29	3.0	3.0	3.0	0.0212	4.7	5.0	4.8	0.1980
30	1.9	1.6	1.7	0.2404	1.9	2.0	1.9	0.0636
31	1.6	1.2	1.4	0.2333	1.9	2.0	1.9	0.0778
32	0.5	0.9	0.7	0.2616	1.3	1.2	1.3	0.0424
33	0.3	0.2	0.2	0.1131	0.7	0.7	0.7	0.0212
34	2.8	2.3	2.5	0.3536	5.0	4.7	4.8	0.2192
35	1.6	1.0	1.3	0.4313	2.2	2.1	2.1	0.1131
36	1.1	1.0	1.0	0.0283	1.4	1.5	1.4	0.0778
37	1.9	1.7	1.8	0.1414	3.7	3.6	3.6	0.0778
38	0.3	0.1	0.2	0.1626	0.6	0.6	0.6	0.0424
39	1.4	1.4	1.4	0.0141	1.7	2.0	1.8	0.2192
40	1.0	0.7	0.9	0.1768	0.1	0.1	0.1	0.0141
41	1.0	1.1	1.1	0.0354	1.3	1.3	1.3	0.0354
42	0.7	0.6	0.6	0.0566	1.0	1.0	1.0	0.0212
43	0.9	0.5	0.7	0.2546	1.1	1.0	1.1	0.0495
44	1.80	2.0	1.9	0.1556	3.1	3.2	3.1	0.0636
45	0.90	1.1	1.0	0.1556	1.9	1.9	1.9	0.0636

.

From the period before the COVID-19 pandemic (spring 2019), the samples at the monitoring sites (1–6) were negative, which is also in line with the information provided in the State of the Environment Report [32], where it is stated that Hron has very pure water in this part. The assessment of water quality in the Report on the State of the Environment is based on the mandatory monitored parameters from the applicable legislation (Regulation of the Government of the Slovak Republic No. 269/2010 Coll., which sets requirements for achieving good water status). The character changes in the cities of Brezno and Podbrezová, where the engineering, metallurgical and petrochemical industries are concentrated. The lower part of the monitoring section concentrates the pharmaceutical industry (Slovenská Ľupča), wood processing and paper production, the food industry (Banská Bystrica and Zvolen) and aluminum production (Žiar nad Hronom) [32]. Information from the Report is consistent with our results: the composition of the water varies in the localities of the cities (7–10), where the quality of the flow is affected by the presence of industrial activities. Elevated surfactant concentrations occur in samples from larger sites along the river, such as, e.g., monitoring sites (16, 27, 30 and 33). We expect that it is not only the industrial activities and population that have an impact but also the several smaller inflows from areas where the sewerage system is not sufficiently built.

The second monitoring period (spring 2020) shows an increase in the number of the monitored samples with above-limit surfactant concentrations, from 22 to 33 monitoring sites with an increased surfactant concentration, which represents an increase of 22.22% (from 48.88% before the pandemic to 73.33% during the COVID-19 pandemic).

In the section from the monitored site (3) to site (45) (river km 225.10–river km 82.10 of the Hron river), the permitted concentration of the surfactants was exceeded in each monitored site. Streams as tributaries to the Hron river basin in this part (monitored sites 10, 14, 20, 24, 33, 38 and 40) in terms of the surfactant content did not exceed the permitted limit. The highest surfactant concentrations in this period were at the monitored sites (16), where the permitted surfactant concentration was exceeded by 4.3 mg/L, (7), where it was exceeded by 4.0 mg/L, and (29 and 34), where it was exceeded by 3.8 mg/L.

From the quality monitoring of the surface waters, in terms of the surfactant concentration, follows that before the COVID-19 pandemic in the Nitra river basin, 55.55% of the samples exceeded the maximum limit value resulting from the Regulation of the Government of the Slovak Republic no. 269/2010 Coll (<1.0 mg/L). During the pandemic, the number of positive samples in the Nitra river basin increased by 20% in terms of the surfactant content. The number of positive samples from monitoring sites in the Hron river basin increased from 48.88% to 73.33%. Contaminated waters pose a potential ecological and environmental risk.

We state that the increase in the surfactant concentration is related to the overuse and consumption of PPCPs due to more intensive disinfection and cleaning of public spaces, the working environment and households in order to prevent the spread of the infectious disease. The pollution caused by the presence of PPCPs has also been addressed in several studies, which confirm that the use and release of PPCPs into the environment currently have an intensive impact on the quality of the biotic environment, on which these products have a negative impact and pose an ecological and environmental risk [20,21,33,34,35].

In order to indicate the effect of the water in the monitored surface waters on aquatic organisms, a preliminary ecotoxicological test was performed using aquatic crustaceans Daphnia magna.

Available literature [36,37,38,39], and many studies within the world [40,41,42,43,44], states that test organisms that are trophic-level consumers, namely test organisms Daphnia magna, are the most sensitive to the presence of a toxicant in the sample. With the ecotoxicity test, we wanted to point out the dependence of the immobilization of the test organism on the concentration of surfactants in the selected samples. The results of the performed preliminary test are shown in

Table 4. Ecotoxicological evaluation of selected surface water samples.

Locality	Spring 2019		Spring 2020
	Concentration of the Surfactants (mg/L)	Test with Daphnia magna	Concentration of the Surfactants (mg/L)	Test with Daphnia magna
River basin Nitra
(1)	0.2	-	0.1	-
(5)	0.4	-	1.0	+
(7)	0.9	+	2.6	+
(18)	3.5	+	5.1	+
(28)	0.3	-	1.3	+
(42)	0.9	+	2.5	+
(45)	1.0	+	1.2	+
River basin Hron
(6)	0.2	-	1.1	+
(19)	0.4	-	0.7	+
(25)	1.3	+	4.0	+
(34)	2.5	+	4.7	+
(37)	1.7	+	3.6	+
(41)	1.1	+	1.3	+
(44)	1.8	+	3.1	+

Explanations: (-) negative preliminary test (immobilization percentage <50%); (+) positive preliminary test (immobilization percentage >50%) [28,29].

.

The results of the preliminary tests of the selected samples from both river basins confirmed that the presence of the surfactants causes immobilization of the test organism Daphnia magna from a concentration of 0.7 mg/L. However, the permitted limit for the presence of surfactants in surface waters is 1 mg/L. The results of the preliminary test provide a quick overview of the ecotoxicity of the water and also of the need for further testing of the surface waters in terms of their quality.

The use of a bioassay is a good indicator of pollution, and its use is becoming more frequent. The test organisms Daphnia magna have also been confirmed in other studies to be sufficiently sensitive to the presence of substances in water. We chose the Daphnia magna test organisms on the basis of knowledge and experience from other authors [31,45,46,47,48]. The proof is their use in quality biomonitoring, for example, drinking water [49]. In the rivers where biomonitoring was carried out (with Daphnia magna) and the content of surfactants was monitored, no extraordinary event related to pollution was recorded, and therefore we predict that this pollution is caused by the increased use of surfactants based on recommendations in the fight against the spread of COVID-19. The presence of chemical substances, including surfactants, affected the quality of both sewage and surface water. The measures taken due to the pandemic have limited the conduct of research in many studies. For this reason, there are few such relevant studies with which the results could be compared [50].

According to Slovak legislation, surfactants are not among the basic indicators of surface water quality. The monitoring of the presence of surfactants is usually carried out at the time of an emergency, in order to determine the extent of the contamination of the river. In other cases, the determination of the surfactant content is for information only and is performed one to two times a year in the minimum range of the monitoring points on river basin sections. The exceeded limit concentrations of the surfactants in surface waters, which are also confirmed by the positivity of the results of the immobilization tests of Daphnia magna, indicate the need to include the surfactant indicator among the more frequently monitored surface water quality indicators.

4. Conclusions

The monitoring, in terms of the surfactant content, shows that the monitoring points in the Hron river basin in 2019 did not meet the criterion resulting from the Regulation of the Government of the Slovak Republic no. 269/2010 Coll. up to 48.88%, and in 2020 (during the COVID-19 pandemic), there was an increase of 24.45%. The number of unsatisfactory water samples in water samples from the Nitra river basin increased from 55.55% (2019) to 75.55% (2020) in terms of the surfactant content. Selected surface water samples tested by the acute toxicity test with the test organism Daphnia magna indicate that the increased consumption of PPCPs during the COVID-19 pandemic caused up to 92.86% of the positive samples tested. The monitored samples are an ecological and environmental risk for the aquatic environment. In the analyzed surface water samples, in addition to surfactants, other indicators resulting from the Regulation of the Government of the Slovak Republic No. 269/2010 Coll., which sets requirements for achieving good water status, were simultaneously monitored. Limit values were not exceeded during this period. Surfactants are not among the basic monitored indicators, and therefore we conclude that it is surfactants that are pollutants primarily contributing to the ecotoxicity of water. Based on these facts, we recommend including surfactants among the basic indicators monitored in surface waters.

Khordagui et al. [51] also reported the negative impact of surfactants on the aquatic environment also described. In order to reduce the negative impacts of human activity on the environment, innovative methods of wastewater treatment are coming to the fore. An example is root wastewater treatment plants, which can also remove the present emergent pollutants, including surfactants. Lobotková et al. [31] concluded the positive impact of the built wastewater treatment plants. In addition, it is necessary for the human population to use less harmful personal care and hygiene products and replace them with ecological ones.