Model validation in aquatic toxicity testing: Implications for regulatory practice

► Conducted a preliminary quality control (QC) evaluation of the 96 h LC50 testing protocol. ► Eight percent of data failed key assumption validation, no steady-state LC50s could be estimated. ► Remaining data contained unquantified variance from toxicity modifying factors. ► A formal QC evaluation is warranted as results are not comparable measures of relative toxicity. ► Interim improvements in design, execution, and interpretation of LC50 tests are needed.