Formatted Title:

Bioaccumulation and Maternal Transfer of PFOS in a Multi-Generational Zebrafish Exposure

Background/Objectives:

The presence of per- and polyfluoroalkyl substances (PFAS) in the environment poses exposure risks to diverse ecological systems and to humans. A recent review evaluating the state of the science for ecological risk characterization of PFAS identified the need for measuring and predicting PFAS bioaccumulation as a significant challenge and a critical need for understanding effects on ecological and human health (Ankley et al., Environ. Toxicol. Chem. 40, 564, 2021). One such PFAS, perfluorooctane sulfonic acid (PFOS), represents a broadly distributed environmental contaminant in surface waters and is toxic to a variety of aquatic organisms including fish. An evaluation of PFAS bioaccumulation and bioconcentration data summarized for aquatic species indicated the potential for substantial bioconcentration of PFOS where median concentrations in fish tissues were three orders of magnitude higher than concentrations in exposure water (Burkhard, 2021). Though PFOS bioconcentration has been broadly documented in fish, bioconcentration factors (BCF) may vary greatly even within individual species as illustrated by Tal and Vogs (Env. Hlth. Persp., 129 (7), 2021) where BCF values summarized for zebrafish whole-body tissues ranged from 82 to 5,400, varying with exposure concentrations, exposure durations, and developmental life stages. To understand how variables such as these influence uptake of PFOS an extended chronic and multi-generational exposure of PFOS was conducted with the zebrafish (Danio rerio).

Approach/Activities:

Zebrafish were exposed continuously for two generations (from post-fertilization developing embryos to breeding adults) to environmentally relevant PFOS concentrations (0, 0.1, 0.6, 3.2, 20, 100 µg/L PFOS) through 180 days post fertilization (dpf) in parental generation (P) and first filial generation (F1) fish. Whole-body PFOS concentrations were measured at 14 and 29 dpf in the P generation analyzing 20 to 35 fish collected from each of five replicate tanks and at 180 dpf for the P and F1 generations analyzing one fish of each sex from each of five replicate tanks. As maternal transfer of PFOS to eggs has been demonstrated in other fish species, we evaluated whether maternal transfer of PFOS from P generation females to the F1 generation eggs could serve as a mechanism for PFOS depuration and explain the observed decreased female body burdens relative to males.

Results/Lessons Learned:

PFOS bioaccumulation reached an apparent steady state at ≤ 14 dpf where whole body wet-weight concentrations remained constant through 180 dpf in the P and F1 generations. The median bioconcentration factor (BCF) of 934 L/kg was observed for all PFOS exposures with a range from 255 to 2,136 L/kg, which varied with PFOS exposure concentration and sex of adult fish. Significantly lower BCFs were observed for the 20 and 100 µg/L PFOS exposures versus 0.1 and 0.6 µg/L, indicating exposure concentration dependance. Additionally, males had significantly increased (̴̴ 2x) PFOS bioaccumulation and BCFs versus females in both P and F1 generations. Maternal transfer of PFOS was observed from P females to F1 eggs where maternal whole body and egg PFOS burdens were equivalent, suggesting PFOS transfer to eggs was not a depuration mechanism.

Mitch Wilbanks

Affiliation

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Bioaccumulation and Maternal Transfer of PFOS in a Multi-Generational Zebrafish Exposure