Research Product

Variability in acute to chronic ratios (ACRs; LC5O/chronic value) has been a continuing interest in aquatic toxicology because of the reliance on ACRs to estimate chronic toxicity for chemicals and species with known acute toxicity but limited or no information on sublethal toxicity. To investigate variability and significant differences in ACRs, an extensive dataset was compiled of 503 same-species pairs of acute and maximum accepted toxicant concentration values for metals, narcotics, pesticides, and other organic chemicals. The overall median value of the aquatic invertebrate and fish ACRs analyzed in this study was 8, with a 140,000-fold range (0.13 to 18550) in values, and a 38-fold range (2.1 to 79.5) in 10th and 90th percentile values. Median ACRs for taxa, ambient habitat media, test type, endpoint, and chemical MOA/class categories were generally similar, but in some cases extremely variable (ranges of <1 to >10,000). There were no significant differences in median ACRs between taxa, although invertebrates were more variable than fish. Freshwater organisms had median ACRs significantly greater than saltwater species and were more variable. There were no significant differences in median ACRs among chemical MOA/class datasets, however ACR variance differed significantly among MOAs. Although few significant differences occurred among median ACRs for different groups, those categories that were highly variable are at an increased risk of underestimated chronic toxicity when mean or median ACRs are used.