Developing Methods for Assessing Trophic Magnification of Perfluoroalkyl Substances within an Urban Terrestrial Avian Food Web

We investigated the trophic magnification potential of perfluoroalkyl substances (PFAS) in a terrestrial food web by using a chemical activity-based approach, which involved normalizing concentrations of PFAS in biota to their relative biochemical composition in order to provide a thermodynamically accurate basis for comparing concentrations of PFAS in biota. Samples of hawk eggs, songbird tissues, and invertebrates were collected and analyzed for concentrations of 18 perfluoroalkyl acids (PFAAs) and for polar lipid, neutral lipid, total protein, albumin, and water content. Estimated mass fractions of PFCA C8-C11 and PFSA C4-C8 predominantly occurred in albumin within biota samples from the food web with smaller estimated fractions in polar lipids > structural proteins > neutral lipids and insignificant amounts in water. Estimated mass fractions of longer-chained PFAS (i.e., C12-C16) mainly occurred in polar lipids with smaller estimated fractions in albumin > structural proteins > neutral lipids > and water. Chemical activity-based TMFs indicated that PFNA, PFDA, PFUdA, PFDoA, PFTrDA, PFTeDA, PFOS, and PFDS biomagnified in the food web; PFOA, PFHxDA, and PFHxS did not appear to biomagnify; and PFBS biodiluted. Chemical activity-based TMFs for PFCA C8-C11 and PFSA C4-C8 were in good agreement with corresponding TMFs derived with concentrations normalized to only total protein in biota, suggesting that concentrations normalized to total protein may be appropriate proxies of chemical activity-based TMFs for PFAS, which predominantly partition to albumin. Similarly, TMFs derived with concentrations normalized to albumin may be suitable proxies of chemical activity-based TMFs for longer-chained PFAS, which predominantly partition to polar lipids.

Dietary Bioaccumulation and Biotransformation of Hydrophobic Organic Sunscreen Agents in Rainbow Trout

The present study investigated the dietary bioaccumulation and biotransformation of hydrophobic organic sunscreen agents, 2-ethylhexyl-4-methoxycinnamate (EHMC) and octocrylene (OCT), in rainbow trout using a modified Organisation for Economic Co-operation and Development 305 dietary bioaccumulation test that incorporated nonbiotransformed reference chemicals. Trout were exposed to 3 dietary concentrations of each chemical to investigate the relationship between dietary exposure concentration and observed accumulation and depuration. Both EHMC and OCT were significantly biotransformed, resulting in mean in vivo whole-body biotransformation rate constants (k_MET ) of 0.54 ± 0.06 and 0.09 ± 0.01 d^-1 , respectively. The k_MET values generated for both chemicals did not differ between dietary exposure concentrations, indicating that chemical concentrations in the fish were not high enough to saturate biotransformation enzymes. Both somatic and luminal biotransformation substantially reduce EHMC and OCT bioaccumulation potential in trout. Biomagnification factors (BMFs) and bioconcentration factors (BCFs) of EHMC averaged 0.0035 kg lipid kg lipid^-1 and 396 L kg^-1 , respectively, whereas those of OCT averaged 0.0084 kg lipid kg lipid^-1 and 1267 L kg^-1 . These values are 1 to 2 orders of magnitude lower than the BMFs and BCFs generated for reference chemicals of similar log K_OW . In addition, for both chemicals, derived BMFs and BCFs fell below established bioaccumulation criteria (1.0 kg lipid kg lipid^-1 and 2000 L kg^-1 , respectively), suggesting that EHMC ad OCT are unlikely to bioaccumulate to a high degree in aquatic biota. Environ Toxicol Chem 2020;39:574-586. © 2019 SETAC.

Growth-Correcting the Bioconcentration Factor and Biomagnification Factor in Bioaccumulation Assessments

We illustrate that the Organisation for Economic Co-operation and Development guideline 305 (OECD-305) for growth-correcting bioconcentration factors (BCFs) and biomagnification factors (BMFs) violates the mass-balance assumption underlying the definition of BCFs and BMFs and provides unrealistic estimates of BCFs and BMFs of chemicals in nongrowing fish. We present and test alternative methods for growth-correcting BCFs and BMFs that maintain mass balance. We conclude that the OECD-305-recommended growth correction of BCFs and BMFs causes error, is unnecessary, and should be revisited. Environ Toxicol Chem 2019;38:2065-2072. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Concentration dependence of in vitro biotransformation rates of hydrophobic organic sunscreen agents in rainbow trout S9 fractions: Implications for bioaccumulation assessment

In vitro biotransformation studies were performed to support the bioaccumulation assessment of 3 hydrophobic organic ultraviolet filters (UVFs), 4-methylbenzylidene camphor (4-MBC), 2-ethylhexyl-4-methoxycinnamate (EHMC), and octocrylene. In vitro depletion rate constants (kdep ) were determined for each UVF using rainbow trout liver S9 fractions. Incubations performed with and without added cofactors showed complete (4-MBC) or partial (EHMC and octocrylene) dependence of kdep on addition of the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH), suggesting that hydrolysis of EHMC and octocrylene by NADPH-independent enzymes (e.g., carboxylesterases) is an important metabolic route. The concentration dependence of kdep was then evaluated to estimate Michaelis-Menten parameters (KM and Vmax ) for each UVF. Measured kdep values were then extrapolated to apparent whole-body biotransformation rate constants using an in vitro-in vivo extrapolation (IVIVE) model. Bioconcentration factors (BCFs) calculated from kdep values measured at concentrations well below KM were closer to empirical BCFs than those calculated from kdep measured at higher test concentrations. Modeled BCFs were sensitive to in vitro binding assumptions employed in the IVIVE model, highlighting the need for further characterization of chemical binding effects on hepatic clearance. The results suggest that the tested UVFs are unlikely to accumulate to levels exceeding the European Union Registration, Evaluation, Authorisation, and Restriction regulation criterion for bioaccumulative substances (BCF > 2000 L kg-1 ). However, consideration of appropriate in vitro test concentrations and binding correction factors are important when IVIVE methods are used to refine modeled BCFs. Environ Toxicol Chem 2019;38:548-560. © 2018 SETAC.

A chemical activity approach to exposure and risk assessment of chemicals: Focus articles are part of a regular series intended to sharpen understanding of current and emerging topics of interest to the scientific community

To support the goals articulated in the vision for exposure and risk assessment in the twenty-first century, we highlight the application of a thermodynamic chemical activity approach for the exposure and risk assessment of chemicals in the environment. The present article describes the chemical activity approach, its strengths and limitations, and provides examples of how this concept may be applied to the management of single chemicals and chemical mixtures. The examples demonstrate that the chemical activity approach provides a useful framework for 1) compiling and evaluating exposure and toxicity information obtained from many different sources, 2) expressing the toxicity of single and multiple chemicals, 3) conducting hazard and risk assessments of single and multiple chemicals, 4) identifying environmental exposure pathways, and 5) reducing error and characterizing uncertainty in risk assessment. The article further illustrates that the chemical activity approach can support an adaptive management strategy for environmental stewardship of chemicals where "safe" chemical activities are established based on toxicological studies and presented as guidelines for environmental quality in various environmental media that can be monitored by passive sampling and other techniques. Environ Toxicol Chem 2018;37:1235-1251. © 2018 The Authors. Published by Wiley Periodicals, Inc. on behalf of SETAC.

Thin-film solid-phase extraction to measure fugacities of organic chemicals with low volatility in biological samples

To investigate the environmental fate, food chain bioaccumulation, and toxicity of organic chemicals, it is often preferable to measure the chemical's fugacity rather than its concentration. However, simple methods to do this are rare. This paper presents a novel yet simple method to measure fugacities of a range of poorly volatile hydrophobic organic chemicals ranging in octanol-air partition coefficients from 10(5.6) to 10(9.2). Thin films of ethylene vinyl acetate coated on glass surfaces are used as solid-phase samplers of contaminated biological tissues. The technique is applied to fish tissue samples and spiked fish diets to determine method feasibility, equilibration times, reproducibility, and property characteristics of the thin films. It is concluded that the method provides an attractive technique to measure chemical fugacities in biological tissues without requiring solvent extractions and cleanup. The method is further expected to be applicable to investigate the fugacity of semivolatile and poorly volatile organic chemicals in air, water, sediments, and soil.

Bioaccumulation of persistent organic pollutants in lichen-caribou-wolf food chains of Canada's Central and Western Arctic

While biomagnification of persistent organic pollutants (POPs) in aquatic food chains is well documented, there have been few investigations of the trophodynamics of POPs in Arctic terrestrial food chains. This study presents field-collected concentration data and corresponding fugacities of various hydrophobic organic chemicals (ranging in octanol-water partition coefficients or K(OW) from approximately 10(3.8) to 10(9)) in two lichen species (Cladina rangiferina and Cetraria nivalis), willow leaves (Salix glauca), barren-ground caribou (Rangifer tarandus), and wolves (Canis lupus) from Canada's Central and Western Arctic region. The results show that, in contrast to aquatic food chains, persistent substances including beta-hexachlorocyclohexane and 1,2,4,5-tetrachlorobenzene with a K(OW) <10(5) can substantially biomagnify in lichen-caribou-wolf food chains in Canada's Central and Western Arctic. Strong positive correlations between the biomagnification factor and the octanol-air partition coefficients (K(OA)) of nonmetabolizable compounds were observed in wolves. In caribou, the biomagnification factors dropped slightly with increasing K(OA). K(OA) proved to be a better indicator of biomagnification than K(OW). Current management policies that consider only chemicals with K(OW) values >10(5) as bioaccumulative substances fail to identify substances that have the potential to biomagnify in Arctic terrestrial food chains despite a low K(OW) because of a high K(OA).

Relative contributions of aqueous and dietary uptake of hydrophobic chemicals to the body burden in juvenile rainbow trout

This study assessed the relative contributions of aqueous versus dietary uptake of three hydrophobic chemicals, 1,2, 4-trichlorobenzene (1,2,4-TCB), 1,2,3,4,5-pentachlorobenzene (PeCB), and 2,2',4,4',6,6'-hexachlorobiphenyl (HCBP). Juvenile rainbow trout (Oncorhynchus mykiss) were exposed separately to chemically spiked water and food for 4 days and 12 days, respectively. Chemical concentrations were measured in the food, water, and tissues, and this allowed calculation of uptake rate constants (k(1) from water exposure, k(d) from food exposure). The k(1) values for the three test chemicals were approximately five orders of magnitude greater than the k(d) values. Using these measured uptake rate constants, a simulation model was used to predict the relative aqueous versus dietary uptake when fish were exposed simultaneously to water and food contaminated with these hydrophobic chemicals. The model predicted for all three test chemicals that the two uptake routes would contribute equally to the chemical body burden in fish whenever the food:water chemical concentration ratio was near 10(5). However, using food:water chemical concentration ratios that might be expected in nature, the model predicted that gill uptake could account for over 98% of fish body burden for both 1,2,4-TCB and PeCB uptake (log K(ow) values of 3.98 and 5.03, respectively). For HCBP (log K(ow) of 7.55), the model predicted that the dietary uptake could contribute over 85% of the body burden. Thus, depending on the actual food:water chemical concentration ratio, aqueous uptake via the gills can predominate even when the chemicals have a log K(ow) value greater than 5.0. In addition, we confirmed that dietary uptake of hydrophobic xenobiotics increases with increasing log K(ow).

A pharmacokinetic analysis of interspecies extrapolation in dioxin risk assessment

This study entails a pharmacokinetic analysis of the relationship between the external dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin, TCDD) and resulting concentrations of TCDD in internal tissues and organs of humans and rodent species. The methodology is based on the development and testing of physiologically based pharmacokinetic models for several rodent species and humans. The results indicate that the relationship between the external dose of TCDD and resulting TCDD concentrations in liver and adipose tissue of humans and various species of rats and mice can vary by as much as 725 fold, illustrating that humans and experimental animals differ considerably in their ability to convert external dosages of dioxin to tissue concentrations. Interspecies scaling factors are reported to express the differences in tissue concentrations of dioxin between mice, rats and humans in response to an equivalent external dose. The significance of these findings for conducting human cancer and ecological risk assessments is discussed. It is recommended that pharmacokinetic differences be considered explicity in risk estimation, while separately recognizing interspecies differences in pharmacodynamics (sensitivity).

Bioavailability of organochlorines in fish

1. An overview is presented of the process of chemical sorption and membrane permeation that control the bioavailability of organochlorines in natural waters. 2. The mechanisms of membrane permeation and chemical sorption to various types of dissolved and particulate matter is discussed and simple models are presented that can be used to estimate the bioavailability of organic chemicals in natural waters.

A novel method for measuring membrane-water partition coefficients of hydrophobic organic chemicals: comparison with 1-octanol-water partitioning

A novel method of measuring membrane-water partitioning characteristics of very hydrophobic organic chemicals is described. Partition coefficients are reported for a series of halogenated aromatic hydrocarbons of varying molar volume between water and L-a-phosphatidylcholine dimyristoyl (DMPC) membrane vesicles and two solvents, n-hexane and 1-octanol. The results indicate that n-hexane and 1-octanol are satisfactory surrogates for DMPC membranes for chemicals with 1-octanol-water partition coefficients (log KOW) less than 5.5 or molar volumes less than 230 cm3/mol. Chemicals with higher log KOW or molar volume values display marked differences in membrane-water, 1-octanol-water, and n-hexane-water partitioning. Implications for lipid- and organism-water partitioning of hydrophobic chemicals are discussed.