Waterborne toxicity of several dichlorodiphenyltrichloroethane congeners to Hyalella azteca and its implications for contaminated sediment assessment

Although banned long ago in many countries and jurisdictions, the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT) and compounds related to it remain in the aquatic environment, particularly in sediments, and can pose risks to aquatic life. To inform ecological risk assessment of these compounds, we tested the toxicity of six DDT congeners, specifically the p, p' (4,4') forms of DDT, dichlorodiphenyldichloroethylene (DDE), dichlorodiphenyldichloroethane (DDD), and dichlorodiphenylchloroethylene (DDMU), as well as the o, p' (2,4') isomers of DDT and DDD. The epibenthic amphipod, Hyalella azteca, was exposed for 7 days to waterborne chemical and assessed for changes in survival and growth. Median effect concentrations for biomass gain (aggregating effects on growth and survival) ranged from 0.14 µg/L (p, p'DDT) to 5.8 µg/L (o, p'DDD). Among p, p' congeners, relative toxicity was DDT ≫ DDD > DDE ≈ DDMU. Ortho-para' isomers were approximately five-fold less toxic than their p, p' analogs. Much of the observed effect was expressed as lethality, as half maximal effect concentrations based on biomass were on average only 25% lower than the corresponding median lethal concentration. Effects in parallel 7-day and 10-day exposures indicated close comparability between the two durations for o, p'-DDT. Application of these waterborne exposure endpoints in ecological risk assessment of contaminated sediments is discussed.