Preliminary studies on the effect of feeding during whole sediment bioassays using Chironomus riparius larvae

Abstract

Current protocols for freshwater sediment bioassays require feeding, which will likely alter the exposure to sediment-associated contaminants. To determine the potential change in exposure brought about by adding uncontaminated food, whole sediment contaminant bioaccumulation by the midge, Chironomus riparius, was determined in the presence and absence of added food. Lake Michigan sediment was dosed with radiolabeled polycyclic aromatic hydrocarbons (PAHs) and/or DDT and trans-chlordane. Three groups of organisms (Feeding Levels I and II plus a control) were exposed in static assays. After two-, four-, seven-, and ten-day exposures, individual larvae were analyzed for contaminant concentration, mass, and total lipid content. After 7 to 10 days, accumulation of pyrene and benzo( a)pyrene was significantly greater with feeding, while larvae exposed to chrysene accumulated significantly less contaminant when fed, compared to controls. No feeding-related differences in accumulation of the two insecticides were observed. Significant differences in larval mass between test animals and controls were observed only with pyrene-dosed sediment. Larval lipid content tended to remain constant throughout the exposures and did not differ between fed and unfed organisms. Thus, it appears that contaminant bioavailability can be altered by the addition of uncontaminated food. However, this phenomenon appears to be compound-specific and not broadly predictable.