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Cross-taxa distinctions in aquatic toxicity between representative species for risk assessment
Citation:
Awkerman, J., R. Hemmer, C. Lilavois, C. Lavelle, P. Harris, N. Zielinski, A. Almario, J. Ford, D. MacMillan, AND Sandy Raimondo. Cross-taxa distinctions in aquatic toxicity between representative species for risk assessment. SETAC North America 38th Annual Meeting, Minneapolis, MN, November 12 - 16, 2017.
Impact/Purpose:
Growth endpoints of fish and larval amphibians exposed to the herbicide trifluralin are compared to evaluate the efficacy of using larval fish data as representative of aquatic phase amphibians. While fish acute sensitivity is protective of larval amphibians, nonmontonic growth effects and measured thyroid hormones in tadpoles at sublethal exposures suggest a complex endocrine response with compensatory molecular mechanisms.
Description:
Standard ecological risk assessment practices often rely on larval and juvenile fish toxicity data as representative of the amphibian aquatic stage. Although empirical evidence suggests fish early life stage tests frequently are sufficiently sensitive to protect larval amphibians, the process of metamorphosis relies on endocrine cues that affect development and morphological restructuring. Altered developmental effects can lead to detrimental impacts at the population level that are not captured in standard early life stage fish tests. This study compares developmental endpoints for zebrafish (Danio rerio) and the African clawed frog (Xenopus laevis), two standard test species, exposed to the herbicide trifluralin for 30 and 70 days, respectively. Zebrafish were more sensitive in acute toxicity and demonstrated a reduction in growth measurements with increasing trifluralin exposure. Growth measurements in X. laevis at metamorphosis were not correlated with exposure; however, time to metamorphosis was delayed relative to trifluralin concentration. Nonmonotonic growth effects and elevated T4 levels suggest compensatory molecular mechanisms are responsible for complex endocrine responses to trifluralin in amphibians. Such responses are not completely represented by early life stage fish tests. Additional comparison of gene expression will contribute to identification of key molecular initiating events representative of complex alterations in biochemical pathways. Interpretation of developmental effects in the context of altered vital rates will improve assessment of sublethal impacts on amphibian species.