Dynamics of changes in the concentration of polycyclic aromatic hydrocarbons in selected Polish surface water

Water is one of the most important elements of the natural environment and is the only resource without which life on Earth would not be possible. Any water contamination causes miscellaneous diseases and death of living organisms. Increasing amounts of industrial and municipal wastewater threaten life in rivers, lakes, seas and oceans (Kowalski et al. 2007; Michalski 2005; Nawała et al. 2016; Siudek et al. 2016a,b). At present, water purity is a worldwide problem, as even the most advanced technologies cannot eliminate all pollutants. In addition, wastewater generated by industry, agriculture and households is increasingly contributing to the deterioration of water status. Most surface waters are already polluted, and the discharge of toxic waste and sewage should be stopped (Jabłońska, Kluska 2019; Jabłońska et al. 2020; Kluska et al. 2018; Michalski, Ficek 2016; Popiel, Nawała 2013; Popiel et al. 2014).

Polycyclic aromatic hydrocarbons (PAHs) are found in different compartments of the natural environment: soil, water, air. PAHs have been identified as priority substances responsible for ecosystem pollution (Directive 2013/39/EU). Water quality is an extremely important criterion for environmental sustainability. Water is used in industry, agriculture and, above all, in households for human consumption. PAHs may enter water through i.a. surface runoff, precipitation or industrial and municipal waste (Kończyk et al. 2018). They pose a serious threat, both to humans and aquatic organisms.

Lipophilic properties of PAHs facilitate active dissolution in non-polar solvents. PAHs undergo bioaccumulation at a lower trophic level; fish, mammals and birds have a well-developed detoxification system (Mogashane et al. 2020). Therefore, PAHs negatively affect human health, causing mutagenic, genotoxic, immunotoxic, carcinogenic and hormonal disorders (Zhang et al. 2019). Determination of concentrations and identification of PAH sources in surface water and environmental samples are crucial for assessing a potential risk to humans and organisms living in ecosystems (Kiełbasa, Buszewski 2015; Kiełbasa, Buszewski 2017a,b; Levkina et al. 2018).

Analysis of PAHs in different matrices is usually performed by applying chromatographic techniques, of which gas chromatography combined with mass spectrometry, mass spectrometry with electron ionisation, supercritical fluid chromatography with flame ionisation detection, two-dimensional gas chromatography and high-performance liquid chromatography (HPLC) are frequently used (Adamczewska et al. 2000; Buszewski et al. 2012; Kluska 2008; Levkina et al. 2017; Słomińska et al. 2014; Tolmacheva et al. 2017; Qian et al. 2020). HPLC is the most commonly used method of PAH determination (Levkina et al. 2017).

For the determination of compounds containing aromatic rings, it is recommended to use chemically bonded aryl stationary phases, where π–π type interactions between an analyte and a stationary phase dominate (Kluska et al. 2007; Kluska et al. 2008a,b; Kluska, Pypowski 2007; Małkiewicz et al. 2015; Prukała et al. 2008; Pypowski et al. 2006).

Analysis of PAHs in environmental samples is relatively difficult due to the complexity of the analysed matrix and the low level of their contamination with aromatic hydrocarbons. Preparation of samples is a very important stage in the analysis of trace environmental pollution. At this stage, PAHs are extracted from the sample's matrix and pre-concentrated before quantitative analysis. The most preferred technique of PAH extraction is the solid phase extraction (SPE) (Kiełbasa, Buszewski 2017a; Słomińska et al. 2014), which is very often used for pre-treatment in environmental, biomedical and pharmaceutical studies. This extraction method plays a very important role due to its low cost, simplicity, high recovery, good enrichment ratios and low consumption of organic solvents. In addition, it can be combined with a range of on-line or off-line detection techniques.

The SPE method is most often used to analyse PAHs in surface water and sewage sludge. Significant amounts of wastewater from industrial processes, plant production and municipal wastewater, including many PAH compounds, are discharged into surface water. Compared to the previous decade, the number of scientific studies on the presence of PAHs in surface water has slightly decreased. This is due to a variety of reasons, including the fact that increasing financial resources are being allocated to environmental protection and, at the same time, many societies have been increasingly taking care of specific elements of the natural environment. Unfortunately, this is not always the case due to various types of failures or intentional sewage disposal. Such situations particularly affect long rivers with many tributaries and those that form borders between countries.

The objective of the present study was to determine the dynamics of changes in the concentration of 16 PAHs (according to the World Health Organization [WHO] list) in surface waters of the Bug River, the Liwiec River and the Muchawka River.

Water samples were collected from the Muchawka River (in the town of Siedlce), Liwiec River (in the town of Węgrów) and Bug River (in the town of Wyszków). The Muchawka River is a left-bank tributary of the Liwiec River and its length is 32.1 km. The Liwiec River is 126.3 km long and it is the longest tributary of the Bug River. Chemical status of surface water in the Muchawka and Liwiec rivers is described as moderate. The study area is presented in Fig. 1.

Figure 1

Along its large section, the Bug River is located in the border regions of Ukraine and at the same time receives large amounts of wastewater. Large loads of pollutants are discharged from the Toczna and Cetynia rivers. The latter receives effluents from the Sokołów Podlaski WWTP. In the Mazovia province, the main source of pollution in the Bug River is the town of Wyszków. It discharges on average 3000 m³ of effluent per day from a treatment plant with increased removal nutrients. All water samples collected for the analysis had a slightly alkaline reaction in all sampling periods. Their average pH values were as follows: 7.58 for the Liwiec River, 7.23 for the Muchawka River and 8.31 for the Bug River.

In order to determine the dynamics of concentration changes for 16 PAHs, five samples of surface water (1 litre each) were collected from the three rivers. The research was conducted in four time frames, i.e. in January, April, June and September 2019. The research involved qualitative and quantitative analysis as well as the temporal dynamics of concentration changes of the following PAHs: naphthalene (Na), acenaphthylene (Ace), acenaphthene (Acn), fluorene (Flu), phenanthrene (fen), anthracene (An), fluoranthene (Fl), pyrene (Pir), benzo(a)anthracene (B(a)A), chrysene (Ch), benzo(b)fluoranthene (B(b)F), benzo(k)fluoranthene (B(k)F), benzo(a)pyrene (B(a)P), dibenzo(a,h)anthracene (D(ah)A), benzo(g,h,i)perylene (B(ghi)P), indeno(1,2,3-c,d) pyrene (IP).

During the sampling process, 1.2 cm³ of hyamine was added to each litre of water as a fixing agent. Samples of surface water were analysed the next day after their collection. For this purpose, each water sample was mixed and passed through the pre-prepared RP Si-C18 PAH (Merck) extraction column at a rate of 3–4 drops/sec. Then the column was purged with nitrogen and the adsorbed hydrocarbons were eluted with 8 cm³ of dichloromethane.

The resulting eluate was mixed with 2 cm³ of acetonitrile and the obtained solution was concentrated under a nitrogen stream at room temperature up to a volume of 0.5 cm³. After the process of concentration, distilled water was added up to a volume of 1 cm³ and the mixture was analysed using HPLC at a wavelength of 254 nm and a methanol flow rate of 0.8 cm³ min⁻¹. In order to carry out the analyses in accordance with the recommendations, an aryl chromatographic column with a naphthylpropyl chemically bonded stationary phase was used (Fig. 2).

Figure 2

The mobile phase was methanol (for HPLC, Merck). The reference material for qualitative and quantitative analysis by HPLC was a mixture of 16 PAHs at a precisely known concentration (Merck). Uncertainty of reference material (16 PAH) was 27 ng dm⁻³. Analyses of the prepared samples were carried out using HPLC. An HPLC apparatus (Shimadzu, Japan) consisted of a UV/Vis SPD–6A detector, LC–6A pump, CR 6A Chromatopac recorder, Rheodyne 7125 dispenser with a loop of 20 μL and RP Si-NAF column, with an internal diameter of 4.6 mm and length of 125 mm (Department of Bioanalytics and Environmental Chemistry, Toruń, Poland) (Gadzała et al. 2005).

According to the Regulation of the Minister of Maritime Economy and Inland Navigation of 29 August 2019 on the quality criteria for surface waters used as a source of drinking water, the permissible PAH content for quality classes A1 and A2 is 200 ng dm⁻³ and for class A3 is 1000 ng dm⁻³.

Protection of surface water against pollution is not a one-off measure; it is an important aspect of the economic life in each country. It consists primarily in avoiding, reducing and eliminating pollution of these waters. Irresponsible human activities have led to a situation where environmental protection is necessary. As a result of this negative activity, the state of equilibrium between the amount of pollution generated and the capacity of nature for self-cleaning has in many cases been disturbed.

The obtained results of the surface water analysis are presented in Tables 1–3 and are still below the permissible content under the 2019 regulation. The highest mean total PAH concentration was found in samples collected from the Bug River in the first three time frames (Table 1). The average concentration was 184.4 ± 58.3 ng dm⁻³ in the samples collected in January, 126.2 ± 37.8 ng dm⁻³ in the samples collected in April and 130.7 ± 40.2 ng dm⁻³ in the samples collected in June. A typical contaminant of the Bug River is total suspended solids.

On the other hand, the lowest mean total PAH concentration was recorded in the Muchawka River in June and September (Table 2). The average total concentration was 97.2 ± 32.2 ng dm⁻³ in samples collected in January, 74.3 ± 25.4 ng dm⁻³ in samples collected in April, 54.7 ± 24.2 ng dm⁻³ in samples collected in June and 46.5 ± 18.1 ng dm⁻³ in samples collected in September.

Surface water samples were collected in different seasons of the year to determine the dynamics of changes in the concentration of the analysed PAHs. The highest temporal dynamics of PAH concentration changes was recorded in the Bug River, where the value was 184.4 ± 58.3 ng dm⁻³ in January and 81.7 ± 26.6 ng dm⁻³ in September. A slightly smaller difference in the concentrations was found in samples of surface water collected from the Muchawka River: 97.2 ± 32.2 ng dm⁻³ in January and 46.5 ± 18.1 ng dm⁻³ in September.

The data presented in Tables 1–3 show that the mean total PAH concentrations decreased with the passing months in almost all surface water samples collected (Fig. 3), except for the samples collected in April and June from the Bug River. The dynamics of PAH concentration changes can also be observed along the surveyed surface water section, i.e. starting from the Muchawka River, then the Liwiec and Bug rivers. The highest mean total concentrations of PAHs were recorded in January in samples collected from all three rivers and the lowest was recorded in September (Tables 1–3, Fig. 3). Similar mean total PAH concentrations were recorded in water collected from the Liwiec River. The values ranged from 94.9 ± 33.3 ng dm⁻³ in January to 51.6 ± 20.5 ng dm⁻³ in September. Similar concentration values were obtained by other authors conducting research in their respective countries in Europe and other parts of the world (Feng et al. 2016; Froger et al. 2019; Milyukin, Goncharuk 2019; Szabó et al. 2013).

Figure 3

Prevention of water degradation should be comprehensive and cover all domains of human activity. The process of preventing water degradation is supported by various water law regulations and directives of the Ministry of Maritime Economy and Inland Navigation. For humans and other living organisms, water is the most important chemical compound; it is not enough to prevent it from being contaminated, but its protection must also be ensured. Such measures can often help to avoid irreversible losses such as the disappearance of flora and fauna species, permanent degradation of landscapes and deterioration of human health.

Of the 16 aromatic hydrocarbons analysed in the Bug River, the largest number of them – 11 PAHs – was determined in June, and nine hydrocarbons were determined in each of the remaining months. Nine hydrocarbons were determined in samples collected from the Muchawka River in January and June, and only seven hydrocarbons in April. Ten of the analysed PAHs were determined in samples collected from the Liwiec River in each of the sampling months. Despite the presence of many of the 16 PAHs analysed in the surface water samples, the limits permissible in Poland were not exceeded.

PAHs were found in all samples of surface water collected for the analysis. These values ranged from 184.4 ± 58.3 ng dm⁻³ in the Bug River in January to 46.5 ± 18.1 ng dm⁻³ in the Muchawka River in September. The temporal dynamics of PAH concentration changes was visible in the surface water of each river and usually showed a decreasing trend. On the other hand, it was slightly increasing along the examined section of the surface waters, starting from the Muchawka River, through the Liwiec River to the Bug River sampling sites. The low content of PAHs in surface water samples determined in the study indicates that a negative impact of human activity is becoming apparent. At present, no such correlation was found along the surveyed section of the surface waters due to the fact that environmental pollution is still low.