A reformulated, reconstituted water for testing the freshwater amphipod, Hyalella azteca

Toxicity testing with the freshwater amphipod, Hyalella azteca, has routinely been conducted using nonstandard waters. Four waters were tested for acceptability for aqueous reference toxicant testing with H. azteca. These included three formulated (standardized) waters: moderately hard reconstituted water (MHRW), reformulated moderately hard reconstituted water (RMHRW), and 25% dilute mineral water (DMW). The water used for comparison was a nonstandard, in‐house culture water mixture of well water and dechlorinated tap water, diluted with Super‐Q® deionized water to a hardness of 100 mg/L, as CaCO3 (LL/SQ). Control survival was less than the 90% minimum control survival criteria in all tests with MHRW. Two of five tests with DMW also failed to pass the minimum control survival criteria. All five tests with the RMHRW passed the control survival criteria. The mean 50% lethal concentration (LC50) for the tests in RMHRW was 320 mg/L KCl, with a coefficient of variation of 8.5%. Concurrent tests with the in‐house water yielded control survival greater than 90% and a mean LC50 of 216 mg/L KCl with a coefficient of variation of 13.4%. Tests in an interlaboratory study yielded similar results. Whole‐sediment toxicity tests conducted using RMHRW as the overlying water routinely exceed the 80% minimum survival criteria in the control and reference sediments. The failure of MHRW and DMW to produce acceptable results, as well as the inability of other laboratories to produce LL/SQ, makes RMHRW the best candidate for a standard water for H. azteca testing.