Effect of 3,4,3',4'-tetrachlorobiphenyl on the reworking behavior of Lumbriculus variegatus exposed to contaminated sediment.

The reworking response (bioturbation) of the oligochaete Lumbriculus variegatus was measured by following the burial rate and spread of a 137Cs marker layer translating worm activity into a biological burial rate (Wb) and a biological diffusion rate constant (Db) for surficial sediment mixing. Reworking was measured at 10 and 22 degrees C in two sediments: a reference site sediment dosed with 3,4,3',4'-tetrachlorobiphenyl (TCBP) and a field-collected sediment from a polychlorinated biphenyl (PCB)-contaminated site in Dicks Creek (DCC, Middletown, OH, USA). The body residue associated with response to TCBP also was determined. Reduction in the temperature from 22 to 10 degrees C reduced both Wb and Db by a factor of approximately two. The internal TCBP concentration to reduce the Wb by 50% was 96 nmol/g (95% CI 45-225 nmol/g) and 124 nmol/g (40-547 nmol/g) (28 and 36 microg/g) wet weight at 22 and 10 degrees C, respectively, and was independent of temperature. The Wb for the DCC sediment was lower than observed for the highest TCBP treatment. The internal body residue for total PCB for worms exposed to DCC sediment was 20-fold lower than TCBP in worms exposed to the lowest TCBP treatment on a molar basis. Comparing body residues of total PCB to TCBP assumes that the PCB congeners act additively on a molar basis. The DCC site contained a higher proportion of coarse material and a lower organic carbon concentration. The difference in sediment characteristics was assumed to be responsible for differences in the Wb.

Comparing behavioral and chronic endpoints to evaluate the response of Lumbriculus variegatus to 3,4,3',4'-tetrachlorobiphenyl sediment exposures.

The response of Lumbriculus variegatus to 3,4,3',4'-tetrachlorobiphenyl (TCBP) was examined with feeding behavior and changes in carbon assimilation by using stable carbon isotopes at 22 and 10 degrees C. The classical measure of feeding behavior determined on a subset of sediment for which the biological burial rate was determined in a companion study allowed direct method comparison. This comparison helped address relationships between biological burial rate, feeding rate, and bioaccumulation. The change in stable isotope composition reflects the total metabolic activity by measuring carbon assimilation rate and was compared to feeding rate, biological burial rate (as determined in the companion study), and reproduction. Decreasing the temperature from 22 to 10 degrees C resulted in a twofold reduction in feeding rate and carbon assimilation. The fractional decline in feeding rate relative to the control mimicked the decline in the biological burial rate with increasing TCBP concentration that was found in the companion study. The bioaccumulation factor declined with increasing TCBP sediment concentration, tracking the feeding rate decline. Stable isotope measures showed differences in metabolic rates between the exposure temperatures but did not distinguish a metabolic rate change at 22 degrees C among TCBP treatments. Likewise, reproduction declined from 22 to 10 degrees C, with no reproduction at 10 degrees C. Like the stable isotope measure, no dose response was found among TCBP treatments at 22 degrees C. The reduction in carbon assimilation rate tracked the reduction in reproduction with lower temperature.