Toxicokinetics of perfluorooctane sulfonate in birds under environmentally realistic exposure conditions and development of a kinetic predictive model

Blood Kinetics of Lipophilic and Proteinophilic Pollutants during Two Types of Long-Term Fast in King Penguins

In vertebrates, fasting is an intricate physiological process associated with strong metabolic changes, yet its effect on pollutant residue variation is poorly understood. Here, we quantified long-term changes in plasma concentrations of 20 organochlorine and 16 perfluoroalkyl pollutants in king penguins Aptenodytes patagonicus during the breeding and molting fasts, which are marked by low and high levels of protein catabolism, respectively, and by strong lipid use. The profile of measured pollutants in plasma was dominated by perfluorooctanesulfonic acid (PFOS, initial relative contribution of 60%). Initial total pollutant concentrations were similar in molting (3.3-5.7 ng g-1 ww) and breeding penguins (range of 4.2-7.3 ng g-1 wet weight, ww). Long-term fasting (25 days) for molting and breeding led, respectively, to a 1.8- and 2.2-fold increase in total plasma pollutant concentrations, although the rate and direction of change were compound-specific. Hexachlorbenzene (HCB) and PFOS concentrations increased in plasma (net mobilization) during both types of fasting, likely due to lipid use. Plasma perfluoroundecanoate (PFUnDA) and perfluorotridecanoate (PFTrDA) concentrations increased in breeders (net mobilization) but decreased in molting individuals (net excretion), suggesting a significant incorporation of these pollutants into feathers. This study is a key contribution to our understanding of pollutant variation in blood during long-term fasting in wildlife.

Understanding the dynamics of physiological changes, protein expression, and PFAS in wildlife

Per- and polyfluoroalkyl substances (PFAS) accumulation and elimination in both wildlife and humans is largely attributed to PFAS interactions with proteins, including but not limited to organic anion transporters (OATs), fatty acid binding proteins (FABPs), and serum proteins such as albumin. In wildlife, changes in the biotic and abiotic environment (e.g. salinity, temperature, reproductive stage, and health status) often lead to dynamic and responsive physiological changes that alter the prevalence and location of many proteins, including PFAS-related proteins. Therefore, we hypothesize that if key PFAS-related proteins are impacted as a result of environmentally induced as well as biologically programmed physiological changes (e.g. reproduction), then PFAS that associate with those proteins will also be impacted. Changes in tissue distribution across tissues of PFAS due to these dynamics may have implications for wildlife studies where these chemicals are measured in biological matrices (e.g., serum, feathers, eggs). For example, failure to account for factors contributing to PFAS variability in a tissue may result in exposure misclassification as measured concentrations may not reflect average exposure levels. The goal of this review is to share general information with the PFAS research community on what biotic and abiotic changes might be important to consider when designing and interpreting a biomonitoring or an ecotoxicity based wildlife study. This review will also draw on parallels from the epidemiological discipline to improve study design in wildlife research. Overall, understanding these connections between biotic and abiotic environments, dynamic protein levels, PFAS levels measured in wildlife, and epidemiology serves to strengthen study design and study interpretation and thus strengthen conclusions derived from wildlife studies for years to come.

Quantitative Chemical Proteomics Reveals Interspecies Variations on Binding Schemes of L-FABP with Perfluorooctanesulfonate

Evaluating interspecies toxicity variation is a long-standing challenge for chemical hazard assessment. This study developed a quantitative interspecies thermal shift assay (QITSA) for in situ, quantitative, and modest-throughput investigation of chemical-protein interactions in cell and tissue samples across species. By using liver fatty acid binding protein (L-FABP) as a case study, the QITSA method was benchmarked with six per- and polyfluoroalkyl substances, and thermal shifts (ΔT_m) were inversely related to their dissociation constants (R² = 0.98). The QITSA can also distinguish binding modes of chemicals exemplified by palmitic acid. The QITSA was applied to determine the interactions between perfluorooctanesulfonate (PFOS) and L-FABP in liver cells or tissues from humans, mice, rats, and zebrafish. The largest thermal stability enhancement by PFOS was observed for human L-FABP followed by the mouse, rat, and zebrafish. While endogenous ligands were revealed to partially contribute to the large interspecies variation, recombinant proteins were employed to confirm the high binding affinity of PFOS to human L-FABP, compared to the rat and mouse. This study implemented an experimental strategy to characterize chemical-protein interactions across species, and future application of QITSA to other chemical contaminants is of great interest.

Exposure assessment of PFAS-contaminated sites using avian eggs as a biomonitoring tool: A frame of reference and a case study in the Po River valley (Northern Italy)

For many years, eggs of diverse bird species have been used as monitoring tools in studies investigating perfluoroalkyl substances (PFAS) contamination, especially in marine and remote areas. Avian eggs are a suitable monitoring matrix because they are relatively easy to collect and their yolks store diverse maternally transferred PFAS. Moreover, the concentrations of PFAS detected in the eggs are a good proxy for maternal exposure and allow the assessment of the potential risk for birds. These features support the use of avian eggs as a key monitoring tool in exposure assessment of PFAS-contaminated sites. We first review the recent application of avian eggs in PFAS monitoring in environmental risk assessment schemes, highlighting strengths and limitations and suggesting which criteria should be considered when selecting a proper study species and structuring the sampling and analytical protocol. Eventually, we report findings from a field study realized in 2020 near a perfluoropolymer factory site in the upper Po plain (Northern Italy), revealing an unprecedented contamination level of PFOA and C6O4 in three species of wild passerines. In future, long-term monitoring of PFAS contamination using avian eggs should be maintained, to provide crucial information on the temporal trend of fluorochemical production and waste disposal, while facilitating early identification of emerging PFAS as well as the quantification of their biomagnification across the trophic web. Integr Environ Assess Manag 2021;17:733-745. © 2021 SETAC.

Per- and polyfluoroalkyl substances (PFAS) in livestock and game species: A review

Per- and polyfluoroalkyl substances (PFAS) are synthetic, organic chemicals that resist environmental breakdown. The properties that made PFAS into an industrial success also led to their persistence and bioaccumulation. As PFAS were widely used for many decades their presence is evident globally, and their persistence and potential for toxicity create concern for human, animal and environmental health. Following the precautionary principle, a reduction in human exposure is generally recommended. The most significant source of human exposure to PFAS is dietary intake (food and water) with additional exposure via dust. As PFAS concentrations have been more frequently studied in aquatic food sources, there is less understanding of exposure via terrestrial animals. To further define human exposure via animal products, it is necessary to determine PFAS concentrations and persistence in terrestrial livestock and game species. Studies assessing ambient concentrations of PFAS have noted that, aside from point sources of contamination, there is generally low input of PFAS into terrestrial agricultural food chains. However, livestock and game species may be exposed to PFAS via contaminated water, soil, substrate, air or food, and the contribution of these exposures to PFAS concentrations in food products is less well studied. This review focuses on perfluoroalkyl substances (PFAAs) and compiles information from terrestrial livestock and game species as a source of dietary exposure in humans, and discusses toxicokinetics and health effects in animals, while identifying future focus areas. Publications describing the transfer of PFAAs to farmed and hunted animals are scarce, and demonstrate large variability in distribution and elimination. We outline several relatively small, short-term studies in cattle, sheep, pigs and poultry. While negative effects have not been noted, the poultry investigations were the only studies to explicitly assess health effects. Comparative information is presented on PFAA concentrations in livestock products and edible tissues of game animals.

Assessing the Ecological Risks of Per- and Polyfluoroalkyl Substances: Current State-of-the Science and a Proposed Path Forward

Per- and poly-fluoroalkyl substances (PFAS) encompass a large, heterogenous group of chemicals of potential concern to human health and the environment. Based on information for a few relatively well-understood PFAS such as perfluorooctane sulfonate and perfluorooctanoate, there is ample basis to suspect that at least a subset can be considered persistent, bioaccumulative, and/or toxic. However, data suitable for determining risks in either prospective or retrospective assessments are lacking for the majority of PFAS. In August 2019, the Society of Environmental Toxicology and Chemistry sponsored a workshop that focused on the state-of-the-science supporting risk assessment of PFAS. The present review summarizes discussions concerning the ecotoxicology and ecological risks of PFAS. First, we summarize currently available information relevant to problem formulation/prioritization, exposure, and hazard/effects of PFAS in the context of regulatory and ecological risk assessment activities from around the world. We then describe critical gaps and uncertainties relative to ecological risk assessments for PFAS and propose approaches to address these needs. Recommendations include the development of more comprehensive monitoring programs to support exposure assessment, an emphasis on research to support the formulation of predictive models for bioaccumulation, and the development of in silico, in vitro, and in vivo methods to efficiently assess biological effects for potentially sensitive species/endpoints. Addressing needs associated with assessing the ecological risk of PFAS will require cross-disciplinary approaches that employ both conventional and new methods in an integrated, resource-effective manner. Environ Toxicol Chem 2021;40:564-605. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Correlations between Per- and Polyfluoroalkyl Substances and Body Morphometrics in Fledgling Shearwaters Impacted by Plastic Consumption from a Remote Pacific Island

We investigated the concentrations of 45 per- and polyfluoroalkyl substances (PFASs) in fledgling flesh-footed shearwater (Ardenna carneipes; n = 33) and wedge-tailed shearwater (A. pacifica; n = 9) livers via liquid chromatography-tandem mass spectrometry and their relationship to body morphometrics and ingested plastic mass recorded in 2019 on Lord Howe Island (NSW, Australia). Sixteen PFASs were detected, of which perfluorooctanesulfonate (PFOS) was the dominant compound, detected in 100% of birds (1.34-13.4 ng/g wet wt). Long-chain perfluorocarboxylic acids, including perfluorodecanoic acid (PFDA; <0.04-0.79 ng/g wet wt) and perfluorotridecanoic acid (PFTrDA; <0.05-1.6 ng/g wet wt) were detected in >50% of birds. There was a positive correlation between PFDA and PFTrDA concentrations and wing chord length (R_s  = 0.36, p = 0.0204; R_s  = 0.44, p = 0.0037, respectively), and between PFDA concentrations and total body mass (R_s  = 0.33, p = 0.032), suggesting that these compounds may impact shearwater fledgling morphometrics. Plastic was present in the intestinal tract of 79% of individuals (<7.6 g), although there was no correlation between PFAS concentrations and plastic mass, indicating that ingested plastic is not the likely primary exposure source. The widespread occurrence of PFASs in fledgling marine birds from a relatively pristine location in the Southern Hemisphere suggests that further studies in adult shearwaters and other marine birds are warranted to investigate whether there are any long-term physiological effects on bird species. Environ Toxicol Chem 2021;40:799-810. © 2020 SETAC.

Species- and Tissue-Specific Avian Chronic Toxicity Values for Perfluorooctane Sulfonate (PFOS) and a Binary Mixture of PFOS and Perfluorohexane Sulfonate

To further characterize avian toxicity to environmental levels of select per- and poly-fluoroalkyl substances (PFAS), we established species- and tissue-specific PFAS chronic toxicity values (CTVs) associated with a lowest-observable-adverse effect level (LOAEL) threshold previously established for northern bobwhite quail (Colinus virginianus) chronically orally exposed via drinking water to either perfluorooctane sulfonate (PFOS) or a simple PFAS mixture. Aided by advances in analytical techniques, the novel avian oral PFAS CTVs reported in the present study are lower than the previously reported toxicity reference values (TRVs) estimated for birds chronically exposed via feed. Thus, current avian PFOS TRVs may not be fully protective of wild avian populations at PFAS-impacted sites. Also, likely due to differences in bioavailability, bioaccessibility, and toxicokinetics among individual PFAS between oral exposure types, we found higher bioaccumulation factors in all assessed tissues from birds exposed via water versus feed. Thus, we propose that future characterization of chemical toxicity due to ingestion exposure initially include a full examination of all probable sources of oral exposure for the most accurate derivation of TRVs and a more complete picture of ecological risk. The avian PFAS LOAEL CTVs established in the present study can be modified with the use of uncertainty factors to derive site-specific avian TRVs for ecological risk assessment at PFAS-impacted sites. From differences observed in the behavior of PFOS when administered as either a single chemical or part of a binary mixture with perfluorohexane sulfonate (PFHxS), we verified that PFOS was absorbed and distributed differently when coadministered with PFHxS and that PFOS likely interacted with PFHxS differently among tissues, helping to explain the differences observed in avian toxicity between exposures. Environ Toxicol Chem 2021;40:899-909. © 2020 SETAC.

Understanding PFAAs exposure in a generalist seabird species breeding in the vicinity of a fluorochemical plant: Influence of maternal transfer and diet

Perfluoroalkyl acids (PFAAs) are a focus of scientific and regulatory attention nowadays. However, PFAAs dynamics in the environment and the factors that determine wildlife exposure are still not well understood. In this study we examined PFAAs exposure in chicks of a generalist seabird species, the lesser black-backed gull (Larus fuscus), breeding 49 km away of a PFAAs hotspot (a fluorochemical plant in Antwerp, Belgium). In order to study the pathways of PFAAs exposure, we measured how chicks' PFAAs burden varied with age, sex, and body condition. In addition, we related PFAA concentrations to chicks' diet using stable isotope signatures. For this purpose, we studied plasma PFAA concentrations in 1-week and 4-week-old gull chicks. Only 4 (PFOS, PFOA, PFDA and PFNA) out of the 13 target PFAA compounds were detected. Measured concentrations of PFOS and PFOA were generally high compared to other seabird species but were highly variable between individuals. Furthermore, our results suggest that maternal transfer plays a significant role in determining chicks' PFAAs burden, and that there are variable sources of exposure for PFOS and PFOA during post-hatching development. The association between PFOS and specific stable isotopes (i.e. δ¹⁵N and δ¹³C) suggests a higher exposure to PFOS in birds with a predominantly marine diet. We also found that males' condition was positively associated with PFOS plasmatic concentration, probably due to the indirect effect of being fed a high quality (marine) diet which appears PFOS rich. Yet, exact exposure source(s) for PFOA remain(s) unclear. Given that PFOS concentrations measured in some chicks surpassed the toxicity reference value calculated for top avian predators, continued monitoring of exposure and health of this gull population, and other wildlife populations inhabiting the area, is highly recommended.

Legacy and Novel Per- and Polyfluoroalkyl Substances in Juvenile Seabirds from the U.S. Atlantic Coast

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic, globally distributed chemicals. Legacy PFAS, including perfluorooctane sulfonate (PFOS), have been regularly detected in marine fauna but little is known about their current levels or the presence of novel PFAS in seabirds. We measured 36 emerging and legacy PFAS in livers from 31 juvenile seabirds from Massachusetts Bay, Narragansett Bay, and the Cape Fear River Estuary (CFRE), United States. PFOS was the major legacy perfluoroalkyl acid present, making up 58% of concentrations observed across all habitats (range: 11-280 ng/g). Novel PFAS were confirmed in chicks hatched downstream of a fluoropolymer production site in the CFRE: a perfluorinated ether sulfonic acid (Nafion byproduct 2; range: 1-110 ng/g) and two perfluorinated ether carboxylic acids (PFO4DA and PFO5DoDA; PFO5DoDA range: 5-30 ng/g). PFOS was inversely associated with phospholipid content in livers from CFRE and Massachusetts Bay individuals, while δ 13C, an indicator of marine versus terrestrial foraging, was positively correlated with some long-chain PFAS in CFRE chick livers. There is also an indication that seabird phospholipid dynamics are negatively impacted by PFAS, which should be further explored given the importance of lipids for seabirds.

Interactions between Environmental Contaminants and Gastrointestinal Parasites: Novel Insights from an Integrative Approach in a Marine Predator

Environmental contaminants and parasites are ubiquitous stressors that can affect animal physiology and derive from similar dietary sources (co-exposure). To unravel their interactions in wildlife, it is thus essential to quantify their concurring drivers. Here, the relationship between blood contaminant residues (11 trace elements and 17 perfluoroalkyl substances) and nonlethally quantified gastrointestinal parasite loads was tested while accounting for intrinsic (sex, age, and mass) and extrinsic factors (trophic ecology inferred from stable isotope analyses and biologging) in European shags Phalacrocorax aristotelis. Shags had high mercury (range 0.65-3.21 μg g^-1 wet weight, ww) and extremely high perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA) residues (3.46-53 and 4.48-44 ng g^-1 ww, respectively). Males had higher concentrations of arsenic, mercury, PFOA, and PFNA than females, while the opposite was true for selenium, perfluorododecanoic acid (PFDoA), and perfluooctane sulfonic acid (PFOS). Individual parasite loads (Contracaecum rudolphii) were higher in males than in females. Females targeted pelagic-feeding prey, while males relied on both pelagic- and benthic-feeding organisms. Parasite loads were not related to trophic ecology in either sex, suggesting no substantial dietary co-exposure with contaminants. In females, parasite loads increased strongly with decreasing selenium:mercury molar ratios. Females may be more susceptible to the interactive effects of contaminants and parasites on physiology, with potential fitness consequences.

Spatial and Interspecies Heterogeneity in Concentrations of Perfluoroalkyl Substances (PFASs) in Seabirds of the Southern Ocean

In this study, we evaluate the main factors driving the exposure of Southern Ocean seabirds to perfluoroalkyl substances (PFASs) across a wide geographic range. Five perfluoroalkane sulfonates (PFSAs, C_4-12), 10 perfluoroalkyl carboxylic acids (PFCAs, C_4-13), and perfluorooctane sulfonamide (FOSA) were analyzed in plasma (n = 128) from eight species, including penguins, giant petrels, skuas, albatrosses, and shearwaters, breeding at four sites in the Antarctic, sub-Antarctic, and adjacent cool-temperate regions. Mean ∑PFAS concentrations ranged from 0.53 to 53 ng/g wet weight from black-browed albatross to giant petrels, respectively. As expected due to biomagnification, greater concentrations of most PFASs were found in species near the top of marine food webs such as giant petrels. However, our results suggest that other factors, i.e., metabolic capabilities and spatial movements, can mask interspecies differences in PFASs, especially PFCAs, expected from trophic structure. For instance, trans-equatorial migratory seabirds exhibited PFAS levels and profiles that are consistent with northern hemisphere exposure, reflecting their potential biovector role in the global transport of these pollutants. Among resident species, greater concentrations of PFASs, especially long-chain PFCAs, were found in seabirds breeding or foraging north of the Antarctic Circumpolar Current (ACC) than in those restricted to Antarctic/sub-Antarctic distributions. Moreover, composition profiles of PFAS in Antarctic seabirds agree well with those expected from long-range transport. Our results confirm the importance of the ACC in protecting Antarctic food webs from water-phase-transported PFASs.

Perfluoroalkyl substances (PFASs) and polychlorinated naphthalenes (PCNs) add to the chemical cocktail in peregrine falcon eggs

A suite of perfluoroalkyl substances (PFASs) and polychlorinated naphthalenes (PCNs) were determined in 41 peregrine falcon eggs collected in South Greenland between 1986 and 2014. Median concentrations of perfluorinated sulfonic acids (ΣPFSA) and perfluorinated carboxylic acids (ΣPFCA) were 303 ng/g dry weight (dw) (58 ng/g wet weight, ww) and 100 ng/g dw (19 ng/g ww), respectively, which was comparable to other studies. Perfluorooctane sulfonate (PFOS) accounted for 94% on average of all PFSAs, but did not show a significant time trend. Perfluorohexane sulfonate (PFHxS), perfluoroheptane sulfonate (PFHpS) and perfluorodecane sulfonate (PFDS) showed non-linear decreases over the study period, while some long-chain PFCAs increased significantly. The PCN profile was dominated by the penta-, hexa- and tetrachlorinated congeners CN-52/60, CN-66/67 and CN-42. CN-54, an indicator of combustion, accounted for 2.4% of ΣPCN on average. All PCN congeners showed a decreasing tendency, which was significant for lipid-normalized concentrations of CN-53, CN-54 and CN-63. The ΣPCN median concentration was 21 ng/g lipid weight, which is in the high end of concentrations reported for bird eggs. The PCN and PFAS concentrations add to an already high contaminant burden and a complex chemical cocktail in the peregrine falcon population in Greenland, mainly reflecting contaminant exposure during migration and winter stays in Central and South America.

Current EU research activities on combined exposure to multiple chemicals

Humans and wildlife are exposed to an intractably large number of different combinations of chemicals via food, water, air, consumer products, and other media and sources. This raises concerns about their impact on public and environmental health. The risk assessment of chemicals for regulatory purposes mainly relies on the assessment of individual chemicals. If exposure to multiple chemicals is considered in a legislative framework, it is usually limited to chemicals falling within this framework and co-exposure to chemicals that are covered by a different regulatory framework is often neglected. Methodologies and guidance for assessing risks from combined exposure to multiple chemicals have been developed for different regulatory sectors, however, a harmonised, consistent approach for performing mixture risk assessments and management across different regulatory sectors is lacking. At the time of this publication, several EU research projects are running, funded by the current European Research and Innovation Programme Horizon 2020 or the Seventh Framework Programme. They aim at addressing knowledge gaps and developing methodologies to better assess chemical mixtures, by generating and making available internal and external exposure data, developing models for exposure assessment, developing tools for in silico and in vitro effect assessment to be applied in a tiered framework and for grouping of chemicals, as well as developing joint epidemiological-toxicological approaches for mixture risk assessment and for prioritising mixtures of concern. The projects EDC-MixRisk, EuroMix, EUToxRisk, HBM4EU and SOLUTIONS have started an exchange between the consortia, European Commission Services and EU Agencies, in order to identify where new methodologies have become available and where remaining gaps need to be further addressed. This paper maps how the different projects contribute to the data needs and assessment methodologies and identifies remaining challenges to be further addressed for the assessment of chemical mixtures.

High levels of PFOS in eggs of three bird species in the neighbourhood of a fluoro-chemical plant

We studied perfluorooctane sulfonate (PFOS) levels in the eggs of three primarily invertivorous bird species sampled in 2006 near a fluoro-chemical plant: the great tit (Parus major), the northern lapwing (Vanellus vanellus) and the Mediterranean gull (Larus melanocephalus). Our study reported some of the highest PFOS levels ever measured in wildlife to date (i.e. up to 46182ng/g ww in lapwing eggs). A pronounced decrease in PFOS concentration in the Northern lapwing eggs with distance from the fluoro-chemical plant was found. A similar relationship was found for the great tit, with eggs being collected close to the fluoro-chemical plant having significantly higher PFOS levels than eggs collected 1700m further away. When comparing the PFOS levels in eggs for the three species, collected between 1700 and 5500m no significant differences were observed. In addition, when comparing PFOS levels in eggs between Northern lapwing and great tits closer to the plant (900-1700m) no significant differences were found neither. Despite the high levels found in great tit eggs, plasmatic biochemical biomarker responses did not appear to be affected.

The origin and evolution of assessment criteria for persistent, bioaccumulative and toxic (PBT) chemicals and persistent organic pollutants (POPs)

General public concern over the effects of persistent chemicals began in the early 1960s. Since then, significant scientific advances have increased our understanding of persistent, bioaccumulative, and toxic (PBT) chemicals and the properties and processes that influence their fates in, and adverse effects on, human health and the environment. In addition to the scientific advances, a number of legislations and agreements for national, international, and global identification and control of PBT chemicals have been adopted. However, some of the rationales and thoughts that were relied upon when the first criteria were developed to identify and categorize PBT chemicals and then POPs (persistent organic pollutants) have not been carried forward. Criteria have been based upon available data of neutral hydrophobic substances as reference chemicals, derived under laboratory conditions. They evolved over the last decades due to the diversification of the protection aims under various national regulatory frameworks and international agreements, advances in methods for estimation of physical/chemical properties, and the identification of chemicals which are non-traditional POPs. Criteria are not defined purely by science; they also are subject to the aims of policy. This paper offers a historical perspective on the development of criteria for PBT chemicals and POPs. It also offers suggestions for rationalization of protection goals, describes some emerging procedures for identification of compounds of concern, and proposes information that needs to be considered when applying criteria to screening and/or evaluation of new chemicals.

Toxicokinetics of short-chain chlorinated paraffins in Sprague-Dawley rats following single oral administration

Short-chain chlorinated paraffins (SCCPs) have attracted considerable attention for their characteristic of persistent organic pollutants. However, very limited information is available for their toxicokinetic characteristics, limiting the evaluation of their health risks. In this study, we performed a toxicokinetics study to explore the absorption and excretion processes of SCCPs (a mixture of C10-, C11-, C12- and C13-CPs) after a single oral administration to the Sprague-Dawley rats. The toxicokinetic results showed that peak blood concentration of total SCCPs was attained at 2.8 day with Cmax value of 2.3 mg L(-1). The half-lives of total SCCPs in blood for the absorption t1/2 (ka), distribution t1/2 (α) and elimination phases t1/2 (β) were calculated to be 1.0, 1.7 and 6.6 days, respectively. During the 28 days post-dosing, about 27.9% and 3.5% of orally administrated SCCPs were excreted through feces and urine without metabolism, respectively. Congener group abundance profiles indicate a relative increase of Cl5-SCCPs in blood and urine in the elimination stage, and a higher accumulation of Cl8-10-SCCPs in feces. The distribution discrepancies of SCCPs congener groups in blood and excreta were more dependent on chlorine contents than on carbon chain lengths.