INFLUENCE OF AGE ON THE RELATIVE SENSITIVITY OF HYALELLA-AZTECA TO DIAZINON, ALKYLPHENOL ETHOXYLATES, COPPER, CADMIUM, AND ZINC

Laboratories testing Hyalella azteca use a wide range of ages (or sizes) of the amphipod in their studies. The objective of this study was to investigate age-specific differences in sensitivity of the amphipod to contaminants with varying toxic modes of action. Hyalella azteca, ranging in age from <1 to 26 d, were tested in 96-h water-only exposures with the organophosphate pesticide diazinon, a mixture of alkylphenol ethoxylates (nonionic surfactants), copper sulfate, cadmium chloride, and zinc sulfate. Overall age-specific differences in sensitivity to the five test chemicals were relatively small; 96-h LC50 values typically varied by 50% or less among the various age classes of H. azteca. When differences in sensitivity were observed, trends were apparently related to the contaminant tested rather than to the age of the amphipods, i.e., no particular age class consistently was the most sensitive to the toxicants.