Sediment microbes and biofilms increase the bioavailability of chlorpyrifos in Chironomus riparius (Chironomidae, Diptera)

In a microcosm study, the importance of different sources of organic matter (humic acids, sterile sediment, sediment. and a microbial extract) for the bioavailability of the hydrophobic pesticide chlorpyrifos to Chironomus riparius larvae was quantified. In the last two treatments biofilms were allowed to grow before 14 C-chlorpyrifos, addition. Chlorpyrifos accumulation was quantified after 25h of exposure and after 21 h of depuration. Larval accumulation was twice as high in the microbial extract treatment (447 +/- 79 mu g/kg ww larvae) and 1.7 times higher in the sediment treatment (371 +/- 33 mu g/kg). After depuration, chlorpyrifos accumulation in larval tissue showed even higher differences; 3.1 times higher tissue concentrations in the microbial extract treatment (218 +/- 21 mu g/kg) and 2.2 times higher in the sediment treatment (156 +/- 35 mu g/kg). In contrast, chlorpyrifos accumulation in the humic acid and sterile sediment did not differ from that in controls. These results show that living microbes and biofilms, by creating a microenvironment and providing food for larvae, markedly increase the bioavailability of chlorpyrifos to Chironomus riparius. (c) 2007 Elsevier Inc. All rights reserved.