The Value of Using Multiple Metrics to Evaluate PCB Exposure

Evaluating the trophic transfer of PCBs from fish to humans: Insights from a synergism of environmental monitoring and physiologically-based pharmacokinetic modeling

Accumulation of polychlorinated biphenyls (PCBs) within fish tissues has prompted many states to issue consumption advisories. In Pennsylvania such advisories suggest one meal per month for most game species harvested from Lake Erie; however, these advisories do not account for the emergent properties of regional PCB mixtures, and the downstream accumulation of PCB congeners into human tissues is poorly documented. This study aimed to demonstrate the utility of pairing environmental monitoring with pharmacokinetic modeling for the purpose of estimating dietary PCB exposure in humans. We qualified and quantified the PCB congeners present in the filets of five Lake Erie fish species and used these data to estimate exposure under consumption scenarios that matched or exceeded the advisories. Physiologically-based pharmacokinetic (PBPK) modeling was then employed to predict PCB accumulation within seven tissue compartments of a hypothetical man and woman over 10 years. Twenty-one congeners were detected between the five fish species at concentrations ranging from 56.0 to 411.7 ng/g. Predicted accumulation in human tissues varied based on tissue type, the species consumed, biological sex, and fish-consumption rate. Notably, steady-state concentrations were higher in fatty tissue compartments ("Fat" and "Liver") and across all tissues in women compared to men. This study serves as a preliminary blueprint for generating predictions of site-specific and tissue-specific exposure through the integration of environmental monitoring and pharmacokinetic modeling. Although the details may vary across applications, this simple approach could complement traditional exposure assessments for vulnerable communities in the Great Lakes region that continue to suffer from legacy contamination.

PCB exposure is associated with reduction of endosymbionts in riparian spider microbiomes

Microbial communities, including endosymbionts, play diverse and critical roles in host biology and reproduction, but contaminant exposure may cause an imbalance in the microbiome composition with subsequent impacts on host health. Here, we examined whether there was a significant alteration of the microbiome community within two taxa of riparian spiders (Tetragnathidae and Araneidae) from a site with historical polychlorinated biphenyl (PCB) contamination in southern Ontario, Canada. Riparian spiders specialize in the predation of adult aquatic insects and, as such, their contaminant levels closely track those of nearby aquatic ecosystems. DNA from whole spiders from sites with either low or high PCB contamination was extracted, and spider microbiota profiled by partial 16S rRNA gene amplicon sequencing. The most prevalent shift in microbial communities we observed was a large reduction in endosymbionts in spiders at the high PCB site. The abundance of endosymbionts at the high PCB site was 63 % and 98 % lower for tetragnathids and araneids, respectively, than at the low PCB site. Overall, this has potential implications for spider reproductive success and food webs, as riparian spiders are critical gatekeepers of energy and material fluxes at the land-water interface.

Determining the reusability of Tenax beads (60-80 mesh) in estimates of bioaccessibility using single-point extractions

Single-point Tenax extractions are a viable means of estimating bioaccessibility of hydrophobic organic contaminants in sediment, soil, and intestinal fluids. One advantage of this extraction technique is that after thorough cleaning and drying, Tenax beads can be reused in subsequent extractions with the assumption that no changes in bioaccessibility estimates will occur. This assumption of reusability, however, has not been tested. Therefore, the objective of the current study was to evaluate the reusability of Tenax beads by comparing bioaccessible polychlorinated biphenyl (PCB) concentrations measured by differently aged Tenax beads. New Tenax beads (60-80 mesh) were aged through 24 h single-point Tenax extractions of clean sand 0, 1, 5, 10, 15, 20, and 25 times. The aged Tenax was then used to extract 27 PCB congeners from laboratory spiked sediment and the bioaccessible PCB concentrations were compared. Despite significant effects of PCB congener (F_{26, 567} = 97.291, p = 2.00 × 10^-16), Tenax age (F_{6, 567} = 14.735, p = 1.12 × 10^-15), and the interaction of these two terms (F_{156, 567} = 1.711, p = 4.79 × 10^-6) on bioaccessible concentrations measured by Tenax, the significance was due to two PCB congeners that showed large variation during analytical quantification. For the remaining 25 congeners, no differences in bioaccessible PCB concentrations were found between differently aged Tenax, suggesting repeated use did not impact bioaccessible estimates provided by Tenax. Scanning electron microscope imaging revealed no significant changes in the visible surface area of the Tenax beads after aging (F_{6, 203} = 1.434, p = 0.203), suggesting no significant changes in the Tenax phase volume resulting in consistent estimates of bioaccessibility through repeated use. Given the strong correlations between single-point Tenax extractable and tissue concentrations, providing data to detail the reusability of Tenax in repeated extractions further demonstrates the applicability of this extraction technique in risk assessment.

Pesticide residues in juvenile Chinook salmon and prey items of the Sacramento River watershed, California - A comparison of riverine and floodplain habitats

Juvenile Chinook salmon (Oncorhynchus tshawytscha) of the Sacramento River system encounter many anthropogenically-induced stressors while rearing and migrating to the Pacific Ocean. Located in a prominent agricultural region, the watershed serves as a source of notable contaminants including pesticides. Salmon rearing in riverine and floodplain areas are potentially exposed to these compounds via dietary exposure, which can vary based on selected food webs. Previous studies have suggested that juvenile Chinook salmon rearing in riverine and floodplain environments of the Sacramento River watershed are characterized by different dietary preferences, with potential for contrasting pesticide exposure between habitats. To examine the potential for pesticide exposure, juvenile Chinook salmon and known dietary items were collected in the mainstem Sacramento River and an adjacent floodplain, the Yolo Bypass, in 2019 and 2020, and analyzed for 33 pesticides, including degradates and isomers. Organochlorine pesticides including the DDX group (p,p'-DDT, p,p'-DDD and p,p'-DDE) were prevalent in all examined biota. There was a significantly greater number of total pesticide detections across all classes in zooplankton compared to macroinvertebrates, coupled with higher bifenthrin concentrations in zooplankton across regions and years, which may indicate different exposure potential depending on fish dietary preferences. Detection frequencies and concentrations of organochlorines were higher in prey items during flooding than in drought conditions, suggesting resuspension of legacy compounds. Significantly higher concentrations of organochlorines were recorded in floodplain rearing fish compared to the Sacramento River. These findings suggest that within these habitats, juvenile Chinook salmon feeding primarily on zooplankton within the water column may be exposed to a greater range of pesticides than those feeding on benthic macroinvertebrates, and that the benefits of floodplain rearing may come at a cost of increased organochlorine exposure.

Use of Riparian Spiders as Sentinels of Persistent and Bioavailable Chemical Contaminants in Aquatic Ecosystems: A Review

Aquatic ecosystems around the world are contaminated with a wide range of anthropogenic chemicals, including metals and organic pollutants, that originate from point and nonpoint sources. Many of these chemical contaminants have complex environmental cycles, are persistent and bioavailable, can be incorporated into aquatic food webs, and pose a threat to the health of wildlife and humans. Identifying appropriate sentinels that reflect bioavailability is critical to assessing and managing aquatic ecosystems impacted by contaminants. The objective of the present study is to review research on riparian spiders as sentinels of persistent and bioavailable chemical contaminants in aquatic ecosystems. Our review of the literature on riparian spiders as sentinels suggests that significant progress has been made during the last two decades of research. We identified 55 published studies conducted around the world in which riparian spiders (primarily of the families Tetragnathidae, Araneidae, Lycosidae, and Pisauridae) were used as sentinels of chemical contamination of lotic, lentic, and estuarine systems. For several contaminants, such as polychlorinated biphenyls (PCBs), Hg, and Se, it is now clear that riparian spiders are appropriate sentinels. However, many contaminants and factors that could impact chemical concentrations in riparian spiders have not been well characterized. Further study of riparian spiders and their potential role as sentinels is critical because it would allow for development of national-scale programs that utilize riparian spiders as sentinels to monitor chemical contaminants in aquatic ecosystems. A riparian spider sentinel program in the United States would be complementary to existing national sentinel programs, including those for fish and immature dragonflies. Environ Toxicol Chem 2022;41:499-514. © 2021 SETAC.

Utility of normalizing Tenax extractable concentrations for phase volume in application as an environmental screening tool

Bioaccessibility-based extraction tools, such as single-point Tenax extractions (SPTEs), provide cost-effective and accurate estimates of bioaccumulation and toxicity of hydrophobic organic contaminants during environmental sampling. Use of SPTEs as a screening tool in risk assessment is hindered by the requirement for normalization of extractable concentrations for organic carbon (OC). Normalizing SPTE concentrations for the volume of Tenax used during the extraction could improve the applicability of this methodology by removing the system dependence when applying SPTE concentrations to estimates of bioaccumulation. The objective of this study was to examine the utility of Tenax phase volume normalization in place of OC normalization when using SPTEs to estimate bioaccumulation. No significant differences were observed between the slope of regression lines generated between SPTE concentrations normalized for either Tenax phase volume or OC (p = 0.410), but slight improvement of the regression was noted when using phase volume normalization (R² = 0.829) compared to OC normalization (R² = 0.740). Replacing OC normalization with phase volume normalization in use of SPTEs more accurately represents the partition of the chemical to the Tenax during the SPTE, improves estimates of bioaccumulation, and expands the use of SPTEs as a rapid assessment tool for determining bioaccumulation during screening of contaminated environments.

Lifelong Exposure to Dioxin-Like PCBs Alters Paternal Offspring Care Behavior and Reduces Male Fish Reproductive Success

Offspring survival, cohort performance, and ultimately population dynamics are strongly influenced by maternal characteristics (e.g., fecundity), whereas paternal contribution is often considered limited to genetic-driven fitness of males through sexual selection. However, male contribution to reproductive success can be particularly influential in species exhibiting paternal offspring care. Polychlorinated biphenyls (PCBs) are widespread, persistent contaminants that can disrupt maternal reproductive processes and negatively affect offspring. In contrast, how PCBs affect paternal reproductive success is largely unknown, but could ultimately affect population dynamics. We examined the effects of lifelong PCB exposure on the reproductive processes of male fathead minnows (Pimephales promelas), a species exhibiting sole paternal offspring care, by examining endocrine-associated gene expression, testes histology, secondary sexual characteristics, courtship ability, offspring care, and offspring survival. PCBs minimized male secondary sexual characteristics, but did not affect gonadal end points or inhibit ability to court females. Fathers exposed to high concentrations of dioxin-like PCBs had changes in gene expression, reduced offspring care behavior, and higher embryo mortality, possibly due to fathers spending less time within nests and less frequently tending to embryos. Through complex interactions among gene expression, physical characteristics, and behavior, PCBs inhibit paternal reproductive success and have the potential to suppress population size.