Body Residues and Responses of the Midge Chironomus riparius to Sediment-Associated 2,4,5-Trichlorophenol in Subchronic and Chronic Exposures

Abstract.

Subchronic and chronic toxicity of sediment-associated 2,4,5-trichlorophenol to the midge Chironomus riparius was determined by conducting a 10-day growth and a 50-day emergence tests with spiked lake sediment (nominal initial TCP concentrations were 25, 51, 101, 203, 304 and 405 μmol kg⁻¹ dry weight in the growth test and 25, 76, 152 and 304 μmol kg⁻¹ dry weight the emergence test). In addition, we measured the residue of chlorophenol in larval tissue and made an attempt to relate it with the observed adverse biological responses. The larvae were exposed individually to avoid density-dependent effects of mortality on food ration and growth of the surviving larvae. In the growth test, mortality was low at sediment concentrations ≤193 μmol TCP kg⁻¹, but it increased sharply at the higher concentrations being 37 and 94% at 334 and 441 μmol kg⁻¹ DW, respectively. The effect of sediment TCP concentration on larval mortality was highly significant (10-day LC50 337 μmol TCP kg⁻¹ dry sediment) in the growth test. In the emergence test, however, mortality was low (3–13%) at all concentrations. TCP did not affect larval growth at the concentrations used. The concentration of TCP in the whole larvae after the 10-day exposure was proportional to sediment concentration, being at highest 160 μmol kg⁻¹ fresh weight. When the average body residues of TCP were below 80 μmol kg⁻¹, mortality was low, but it increased when the body residue approached 100 μmol kg⁻¹. After the 10-day exposure, the body residue, at which 50% of the larvae survived (CBR50) was 113 μmol g⁻¹. TCP exposure accelerated larval development and the midges exposed to 171 and 324 μmol TCP kg⁻¹ emerged earlier than those in the other concentrations or in the control sediment. In natural environments, sediment-associated chlorophenolics are probably not a major environmental problem to benthic fauna because concentrations similar to that which we observed to cause adverse effects to C. riparius (>60 mg kg⁻¹ dry sediment) are rare.