An evaluation of the seven‐day toxicity test withAmericamysis bahia(formerlyMysidopsis bahia)

Abstract

The7‐d test measuring survival, growth, and fecundity of Americamysis bahia (formerly Mysidopsis bahia) was developed for estimating the chronic toxicity of effluents and associated receiving waters for National Pollutant Discharge Elimination System permits. Currently, this test and its derivatives are also used in toxicity identification evaluation (TIE), risk assessment, and other applications. To evaluate the relative sensitivity of three measurement endpoints (survival, growth, and fecundity), we analyzed results from 115 tests with effluents, organic or inorganic chemicals, and receiving waters suspected of being toxic. Controls for 78 of these (68%) achieved acceptable survival and growth. Fifty of these 78 tests (64%, i.e., 43% of the total tests) also achieved acceptable control fecundity. In the 47 tests with significant effects, survival was the most sensitive response in 57%, fecundity in 30%, and growth in 30%. There was little duplication in responses. Improving pretest holding conditions by decreasing the maximum density from ∼20 to 10 animals/L and increasing the temperature from ∼26°C to a range of 26 to 27°C improved the growth and fecundity in controls. Although the percentage of tests achieving acceptable control survival (>80%) and growth (>0.20 mg) decreased from 93 to 86%, the percentage achieving acceptable fecundity in controls (>50%) increased from 60 to 97%. Seasonal differences in fecundity were detected among control groups. Although variable, fecundity is often the most sensitive measure of response. The 7‐d mysid test estimates the chronic toxicity of effluents most effectively when all three endpoints are used.