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 14C-chlorpyrifos addition. Chlorpyrifos accumulation was quantified after 25 h of exposure and after 21 h of depuration. Larval accumulation was twice as high in the microbial extract treatment (447±79 μg/kg ww larvae) and 1.7 times higher in the sediment treatment (371±33 μg/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 μg/kg) and 2.2 times higher in the sediment treatment (156±35 μg/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.