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Effects of volume on acute toxicity and the transcriptome in fathead minnow exposures.
Citation:
Le, M., D. Bencic, A. Biales, R. Flick, J. Martinson, Dan Villeneuve, AND K. Flynn. Effects of volume on acute toxicity and the transcriptome in fathead minnow exposures. SETAC North America, Fort Worth, TX, November 15 - 19, 2020. https://doi.org/10.23645/epacomptox.13182593
Impact/Purpose:
Purpose To present ongoing development of a high throughput transcriptomic-based assay with fathead minnow focused on the effects that exposure volume may have on the transcriptome. Audience Those interested in the development and use of transcriptomic data in ecological risk assessments. Impact There is interest by regulatory agencies (ex, USEPA and Environment and Climate Change Canada), international organizations (ex., OECD), and the regulated community in leveraging high throughput assays to increase the efficiency of chemical risk assessments. The current battery of assays is focused on mammalian toxicological pathways. This presentation will summarize recent efforts to a develop a high throughput assay with fathead minnows. An important research question is whether exposure in small volumes, as required for a high throughput assay, has an impact on both apical endpoints and the fathead minnow transcriptome.
Description:
A core mission of the US Environmental Protection Agency (USEPA) is to assess the effects of anthropogenic chemicals on freshwater ecosystems. One species commonly used is the fathead minnow (Pimephales promelas). Traditional fathead minnow tests last days to weeks and involve relatively large exposure volumes. However, the USEPA’s Office of Research and Development is conducting research into the use of high throughput methods and technologies to improve the efficiency and cost-effectiveness of testing strategies including those with the fathead minnow. A test design that involves 24-hour exposure of 24-hour post-hatch fathead minnows exposed in individual wells of multi-well plates is being evaluated. In addition to traditional apical endpoints like survival, whole transcriptome dose-response modeling is a desired endpoint. The purpose of the present study was to evaluate the effect that differences in solution volume and associated loading density could have on both survival and the transcriptome-level response in the type of assay system being considered. A series of 24-hour static exposures to fathead minnow larvae were conducted with CuSO4, NiSO4, and ZnSO4 using three different exposure systems: 96-well plates, 24-well plates, and single 15 ml vessels. Survival was assessed with exposures in full dose-response with 12 concentrations of half-log dilutions of each chemical starting at high concentrations of CuSO4, NiSO4, and ZnSO4 of 2 mg/L, 15.8 mg/L, and 4 mg/L, respectively. RNA-seq data was collected from a subset of two of these concentrations for each chemical. First, transcriptomic data (RNA-seq) from the control fish from these different exposures was compared to determine the impact exposure volume alone may have on the transcriptome. Second, to further explore potential impacts of exposure volume on the transcriptomic response, lists of differentially expressed genes for specific chemicals were compared across formats. Survival across the different exposure formats was similar in all three chemicals, and LC50 values calculated from the these were similar to published 24-hour LC50’s. For instance, the LC50 for CuSO4 from exposure in a 96-well plate was 0.57 mg/L, close to 0.74 mg/L, the median value from several published tests documented in the EPA’s ECOTOX knowledgebase. Comparable results were also observed for NiSO4 and ZnSO4. Implications for design of a standardized, high throughput test with a transcriptomic-based POD endpoint are considered. The contents of this abstract neither constitute nor necessarily reflect US EPA policy.
URLs/Downloads:
DOI: Effects of volume on acute toxicity and the transcriptome in fathead minnow exposures.