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Comparative Trifloxystrobin Toxicity of Early Life Stage Zebrafish, Fathead Minnow and African Clawed Frog
Citation:
Lavelle, C., P. Harris, C. Lilavois, J. Awkerman, N. Zielinski, M. Hamilton, H. Skowronski, AND S. Raimondo. Comparative Trifloxystrobin Toxicity of Early Life Stage Zebrafish, Fathead Minnow and African Clawed Frog. Southeast SETAC Meeting, Pensacola, FL, September 13 - 14, 2019.
Impact/Purpose:
An early life stage study of the comparative toxicity of the fungicide trifloxystrobin was conducted with a model frog and two model fish species. This is part of a larger project to evaluate the use of fish as surrogate species for amphibians in risk assessments and develop tools to translate laboratory effects into population models for native species. This research will be of interest to the ecotoxicology scientific community as well as to environmental risk assessors and managers.
Description:
Changes in size at and time to metamorphosis indicate developmental effects in amphibians that could result in population-level impacts. Current risk assessment practice uses early life stage fish data when data for larval amphibians are not available. While fish are sufficiently sensitive to a range of chemicals, developmental delays could have relatively greater impacts on subsequent amphibian life stages. As pesticide exposure has been suggested to contribute to amphibian declines, it is important to understand the uncertainties around using this form of surrogacy in risk assessments aimed at protecting amphibian populations. Strobilurin fungicides are an economically important class of pesticides designed to inhibit the mitochondrial respiratory chain ultimately interfering with ATP production. Trifloxystrobin (TX), a heavily used strobilurin, is frequently detected in aquatic systems, often at levels known to cause sub-lethal toxicity in a range of species. In this study we conducted 10-day early life stage exposures of zebrafish, Danio rerio, fathead minnow, Pimephales promelas, and African clawed-frog, Xenopus laevis, to TX to determine if growth, development, and gene expression changes were similarly altered. Survival curves for D. rerio, P. promelas, and X. laevis determined the 96h LC50s to be 132.1 (95% CI of 122.2 - 142.6) μg/L, 53.2 (95% CI of 33.9 - 83.6) μg/L, and 44.3 (95% CI of 36.3 – 54.1) μg/L, respectively. LC50 values at test termination remained unchanged from the 96h LC50 for X. laevis but decreased to 78.4 μg/L for D. rerio and 28.0 μg/L P. promelas suggesting that the early life stage sensitive window is longer in these fish than in X. laevis. While a delay in hatching was observed in both fish species, weight and length were only decreased in P. promelas. A dose-dependent decrease in weight and a developmental delay were observed in X. laevis. Tissues collected from exposed individuals were used to compare differential gene expression on targets related to endocrine signaling, oxidative stress, mitochondrial function, growth, and apoptosis. Gene expression patterns suggest that biological pathways are perturbed by TX exposure in a species-specific manner. Future studies will examine the potential of the observed changes in gene expression to be predictive of more population-relevant endpoints, such as time to metamorphosis.