Presence of PFAS in a Variety of Fish Species from the Baltic Sea and Freshwater Areas of Finland – August 19, 2022 – Eva Kumar, Jani Koponen, Panu Rantakokko, Riikka Airaksinen, Päivi Ruokojärvi, Hannu Kiviranta – Life Science News Items

Per- and polyfluoroalkyl substances (PFAS) are a large group of fluorinated chemicals that have been widely used in industrial and consumer applications since the 1950s, due to their water, oil and dirt repellent properties. Over 4,000 PFAS have been identified as likely to be available on the global market (OECD, 2018). The distribution of perfluoroalkyl acids (PFAAs), one of the subcategories of PFAS, is ubiquitous globally in the environment and biota. PFAAs are even found in the fauna of Antarctica which is the most pristine continent (Garcia et al., 2022). PFAAs are chemicals of health concern due to their persistent nature, potential for bioaccumulation, toxicity of some PFAAs, and association with adverse health effects, including developmental effects, harmful to the liver, serum cholesterol and the immune system (EFSA, 2020).
Due to related concerns, the production and use of specific PFAS have been restricted or severely limited globally. Perfluorooctane sulfonic acid (PFOS) and its derivatives were listed in Annex B of the Stockholm Convention in 2009 to eliminate their use globally. In addition, perfluorooctanoic acid (PFOA), its salts and PFOA-related compounds were listed in Annex A of the Stockholm Convention in 2020. Two groups of PFAS (perfluorobutane sulfonic acid and its salts; 2 ,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionic acid, its salts and its acyl halides) have also been identified as substances of very high concern and are on the REACH candidate list.
The main source of exposure to PFAS for the general population is food, however, other sources such as drinking water, ingestion of dust, inhalation of indoor air can also contribute significantly. substantial. Fish flesh, which is a vital source of protein for the global population, is one of the major food categories contributing to PFAA exposure for all population groups (Figure 1). A new safety threshold – group tolerable weekly intake (TDI) of 4.4 ng kg-1 body weight (bw) per week, which would protect against adverse effects observed in humans – has been derived by the European Authority of 2020 for the four PFAS (PFOA, perfluorononanoic acid (PFNA), perfluorohexane sulfonate (PFHxS) and PFOS) that contribute the most to the levels observed in human serum (EFSA, 2020). PFAS monitoring in commercially important fish species and exposure assessment is therefore relevant with respect to dietary exposure pathways.

Figure 1. Human exposure to PFAS via consumption of contaminated fish.
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In this regard, the Chemical Hazards Team of the Finnish Institute for Health and Welfare (THL), together with the Finnish Institute of Natural Resources, the Finnish Environment Institute and the Authority Finnish Food Service, conducted extensive monitoring fish health assessments from 2001 and assessed the concentrations of several persistent organic pollutants, including PFAS, in freshwater and Baltic Sea fish and assessed the risk that these pollutants present for human health. The last sampling for this monitoring program was carried out in 2016-2017. The analysis of PFAAs in fish was carried out in the laboratory of the Chemicals Risk team of THL, which is accredited by the Finnish Accreditation Services according to SFS-EN ISO/IEC 17025:2017. THL’s Chemical Hazards team has the ability to analyze a wide variety of industrial chemicals and their by-products from various human and environmental matrices, including dioxins, polychlorinated biphenyls, flame retardants, PFAS, phthalates, bisphenols.

PFAS analyzes of fish from Finnish sub-basins and lakes of the Baltic Sea

Fish sampling for this monitoring and assessment program was carried out in the four sub-basins of the Baltic Sea (Bothnian Bay, Bothnian Sea, Archipelago Sea and Gulf of Finland) bounded by the Finland and freshwater lakes (Lake Päijänne, Lake Saimaa, Lake Oulujärvi) in 2016-2017. Commercial and dietary importance were the main criteria for selecting fish species. 13 fish species were sampled and a total of 1134 individual fish specimens were collected. Fish species specific data including length, weight, age and fat content were recorded. PFAS analysis was performed using part of the homogenates. 13 PFAA (perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), PFOA, PFNA, perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), perfluorotridecanoic acid (PFTrDA), perfluorotetradecanoic acid (PFTeDA), PFHxS , perfluoroheptane sulfonate (PFHpS), PFOS and perfluorodecane sulfonate (PFDS)) were studied in the study samples. The PFAS analyzes were carried out by liquid chromatography (Dionex Ultimate 3000 RS) coupled to triple quadrupole mass spectrometry (Finnigan TSQ Quantum Discovery Max) in electrospray negative ionization mode (LC-ESI-MS/MS). Limits of quantification for individual PFAAs ranged from 0.25 to 0.37 ng g-1 wet weight (ww).

PFAA concentrations in fish from the Baltic Sea

Several PFAAs have been detected in fish species caught in the Baltic sub-basins. PFOS was present in at least 97% of fish samples from the Baltic Sea and dominated the PFAA profile in fish, followed by PFNA and PFUnDA (Figure 2). The contribution of PFOA and PFTrDA to overall PFAA concentrations in Baltic Sea fish species was minor. PFOA has been found in Baltic herring and smelt, which could be explained by dietary, behavioral factors and/or species-specific toxicokinetic behavior. The results of this study have been published in detail elsewhere (Kumar et al., 2021).
Figure. 2: Contribution (%) of individual homologs to ∑PFAA in Baltic Sea fish species. Reprinted from (Kumar et al., 2021).
The highest median concentrations of ∑PFAA were observed in smelt (33.1 ng g-1 wet weight), lamprey (5.86 ng g-1 wet weight) and vendace (5.75 ng g -1 wet weight), mainly due to high concentrations of PFOS (Figure 3). Junttila et al. (2019) previously reported the prevalence of PFOS in fish caught in marine and coastal areas in southern Finland. The lowest median concentrations of ∑PFAA were found in roach (1.45 ng g-1 ww) and burbot (1.43 ng g-1 ww). These observations are different from those found in the previous PFAS surveillance study conducted by THL and collaborators in 2009-2010 (Koponen et al., 2015).
Figure. 3. Median concentration of ΣPFAA (ng g-1 ww) grouped by species and location of capture in the Baltic Sea. Reprinted from (Kumar et al., 2021).

PFAS concentrations in freshwater fish

The PFAA profile of fish from freshwater lakes was different from that of fish from the Baltic Sea. Major homologues found in lake fish samples included PFOS, PFTrDA, PFDoDA, PFUnDA and PFDA. The PFAA profile in lake fish was dominated by PFUnDA, PFTrDA and PFOS (Figure 4). The highest concentrations of ∑PFAA were observed in zander (4.78 ng g-1 ww) and vendace (3.04 ng g-1 ww).
The concentration ratios of PFOS to other PFAAs in lake fish were different from those observed in fish from the Baltic Sea. This can be attributed to the difference in pollution pattern in freshwater and marine fish species. PFOS contributes more to PFAA contamination in the Baltic Sea than C9-C14 perfluoroalkylcarboxylic acids. Overall, fish from Finnish lakes had lower ∑PFAA concentrations than fish from the Baltic Sea.
Figure 4. Median ΣPFAA concentration (ng g-1 ww) and corresponding homologous PFAA profiles in Finnish lake fish species. Reprinted from (Kumar et al., 2021).

Exposure to PFAS in Finnish consumers via fish diet

We compared results based on PFAA concentration in fish and calculated PFAA intake with the TWI group proposed by EFSA for the sum of PFOA, PFNA, PFHxS and PFOS (∑PFAS-4 = 4.4 ng kg-1 pc week-1). Mean ΣPFAS-4 concentrations ranged from 1.12 ng g-1 ww in roach to 23.27 ng g-1 ww in smelt. The average consumption of wild caught fish in Finland was 46 g week-1 in 2018 and that of smelt was marginal (Luke, 2019). Therefore, assuming a weekly fish consumption of 46 g and a body weight of 70 kg, the DHT would be exceeded for smelt only. Nevertheless, these results highlight the need for environmental and human biomonitoring and demonstrate the importance of fish diet for total dietary PFAS intake.


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