Short-term lethality and sediment avoidance assays with endrin-contaminated sediment and two oligochaetes from Lake Michigan

In single species tests with Stylodrilus heringianus (4 assays) and Limnodrilus hoffmeisteri (2 assays) exposed to endrin-contaminated sediment, mean 96 h LC50 (and standard deviations) were 2588 (1974) and 2725 (955) ug endrin per g dry sediment, respectively. In one mixed species assay, the 96 h LC50 for L. hoffmeisteri (5600 ug per g) was higher than the single species value, whereas the 96 h LC50 for S. heringianus was approximately the same. In a repeat mixed species assay, no dose response relationship was observed, so further clarification was necessary. Both species initially burrowed into the contaminated sediment, then returned to the surface in numbers roughly proportional to the sedimentary endrin concentration and the length of exposure. The 0.5, 2 and 96 h EC50 values were 1000, 180 and 15-19 ug endrin per g dry sediment for S. heringianus, and 300, 255 and 59 ug per g, respectively, for L. hoffmeisteri. An approximate equilibrium in response was reached after 8 h (S. heringianus) or 32-48 h (L. hoffmeisteri). Monitoring oligochaete behavioural responses to sublethal sediment contamination might be a useful method of assessing pollution impact on benthic communities.