A combination of high-throughput in vitro and in silico new approach methods for ecotoxicology hazard assessment for fish.

Fish acute toxicity testing is used to inform environmental hazard assessment of chemicals. In silico and in vitro approaches have the potential to reduce the number of fish used in testing and increase the efficiency of generating data for assessing ecological hazards. Here, two in vitro bioactivity assays were adapted for use in high-throughput chemical screening. First, a miniaturized version of the Organisation for Economic Co-operation and Development (OECD) test guideline 249 plate reader-based acute toxicity assay in RTgill-W1 cells was developed. Second, the Cell Painting (CP) assay was adapted for use in RTgill-W1 cells along with an imaging-based cell viability assay. Then, 225 chemicals were tested in each assay. Potencies and bioactivity calls from the plate reader and imaging-based cell viability assays were comparable. The CP assay was more sensitive than either cell viability assay in that it detected a larger number of chemicals as bioactive, and phenotype altering concentrations (PACs) were lower than concentrations that decreased cell viability. An in vitro disposition (IVD) model that accounted for sorption of chemicals to plastic and cells over time was applied to predict freely dissolved PACs and compared with in vivo fish toxicity data. Adjustment of PACs using IVD modeling improved concordance of in vitro bioactivity and in vivo toxicity data. For the 65 chemicals where comparison of in vitro and in vivo values was possible, 59% of adjusted in vitro PACs were within one order of magnitude of in vivo toxicity lethal concentrations for 50% of test organisms. In vitro PACs were protective for 73% of chemicals. This combination of in vitro and in silico approaches has the potential to reduce or replace the use of fish for in vivo toxicity testing.