Using an inter-lab study to revise methods for conduction 10- to 42-d water or sediment toxicity tests with Hyalella azteca

Studies have been conducted to refine USEPA, ASTM, and Environment Canada standard methods for conducting 42-d reproduction tests with H. azteca in water or in sediment. Modifications to the H. azteca method include better defined ionic composition requirements for exposure water (i.e., >15 mg/L of chloride and >0.02 mg/L of bromide) and improved survival, growth and reproduction with alternate diets provided as increased rations over time in water-only or whole-sediment toxicity tests. A total of 24 laboratories volunteered to participate in an inter-laboratory study evaluating the performance of H. azteca in 42-d studies in control sand or control sediment using the refined methods. Improved growth and reproduction of H. azteca was observed with 2 alternate diets of (1) ramped diatoms (Thalassiosira weissflogii) + ramped Tetramin or (2) Yeast-cerophyl-trout chow (YCT) + ramped Tetramin, especially when compared to results from the traditional diet of 1.8 mg YCT/day. Laboratories were able to meet proposed test acceptability criteria (TAC) and in most cases had lower variation in growth or reproduction compared to previous inter-laboratory studies using the traditional YCT diet. Laboratory success in conducting 42-d H. azteca exposures benefitted from adherence to several key requirements of the detailed testing, culturing, and handling method. Results from this inter-laboratory study are being used to help revise standard methods for conducting 10- to 42-d water or sediment toxicity exposures with H. azteca.