USE OF SUBLETHAL END-POINTS IN SEDIMENT TOXICITY TESTS WITH THE AMPHIPOD HYALELLA-AZTECA

Short-term sediment toxicity tests that only measure effects on surviv al can be used to identify high levels of contamination but may not be able to identify marginally contaminated sediments. The objective of the present study was to develop a method for determining the potentia l sublethal effects of contaminants associated with sediment on the am phipod Hyalella azteca (e.g., reproduction). Exposures to sediment wer e started with 7- to 8-d-old amphipods. On day 28, amphipods were isol ated from the sediment and placed in water-only chambers where reprodu ction was measured on day 35 and 42. Typically, amphipods were first i n amplexus at about day 21 to 28 with release of the first brood betwe en day 28 to 42. Endpoints measured included survival (day 28, 35, and 42), growth (as length and weight on day 28 and 42), and reproduction (number of young/female produced from day 28 to 42). This method was used to evaluate a formulated sediment and field-collected sediments w ith low to moderate concentrations of contaminants. Survival of amphip ods in these sediments was typically >85% after the 28-d sediment expo sures and the 14-d holding period in water to measure reproduction. Re production was more variable than growth; hence, more replicates might be needed to establish statistical differences among treatments. Prev ious studies have demonstrated that growth of H. azteca in sediment te sts often provides unique information that can be used to discriminate toxic effects of exposure to contaminants. Either length or weight ca n be measured in sediment tests with H. azteca. However, additional st atistical options are available if length is measured on individual am phipods, such as nested analysis of variance that can account for vari ance in length within replicates. Ongoing water-only studies testing s elect contaminants will provide additional data on the relative sensit ivity and variability of sublethal endpoints in toxicity tests with H. azteca.