Prediction of population-level response from mysid toxicity test data using population modeling techniques

Acute and chronic bioassay statistics are used to evaluate the toxicity and risks of chemical stressors to the mysid shrimp Americamysis bahia (formerly Mysidopsis bahia). These include LC50 values from acute tests, chronic values (the geometric mean of the no-observed-effect concentration and the lowest-observed-effect concentration from 7-d and life-cycle tests), and U.S. Environmental Protection Agency water quality criterion continuous concentration (CCC). Because these statistics are generated from responses of individual organisms, the relationships of these statistics to significant effects at higher levels of ecological organization are unknown. This study was conducted to evaluate the quantitative relationships between toxicity test statistics and a concentration-based statistic derived from exposure–response models relating projected population growth rate to stressor concentration. This statistic, C*, describes the concentration above which mysid populations are projected to decline in abundance as determined using population modeling techniques. An analysis of responses of A. bahia to 10 metals, nine organic compounds, and ammonia surprisingly indicated the acute LC50 to be the best predictor of C*, followed by the chronic value from life-cycle tests, which predicted population-level response almost equally as well. The chronic value for the 7-d test was less predictive of population-level effects. The CCC was lower than C* for 94% of the compounds evaluated, indicating the criterion value to be protective of population-level effects for A. bahia, as intended.