Life-cycle effects of sediment-associated 2,4,5-trichlorophenol on two groups of the midge Chironomus riparius with different exposure histories.

Effects of 2,4,5-trichlorophenol (TCP) on life-cycle traits of the midge Chironomus riparius and the ability of the midge to evolve tolerance to TCP were assessed using a reference group and a group preexposed to TCP during three generations, both originating from the same laboratory culture. F1 larvae of these groups were then exposed to nominal TCP concentrations of 51, 177, 355, and 532 micromol TCP/kg dry sediment and a control sediment in a life-cycle experiment. Most studied life-cycle traits (mortality, egg production, life span, male dry wt) were fairly insensitive to TCP, and significant effects were observed only at high (> or = 355 micromol/kg) concentrations. Larval development rate was variable, and in some cases it responded more readily to low TCP concentrations than other life-cycle parameters. Some of the observed responses were attributed to changes in food availability. No clear evidence of tolerance to 2,4,5-trichlorophenol was found, but the preexposed midges produced more eggs than the reference group. They also emerged earlier and at a smaller size than the reference midges. These differences between the midge groups suggest that some changes toward tolerance induction had occurred during the preexposure.