BIOACCUMULATION OF POLYCHLORINATED DIBENZO-P-DIOXINS IN SEDIMENT BY OLIGOCHAETES - INFLUENCE OF EXPOSURE PATHWAY AND CONTACT TIME

Oligochaetes (Lumbriculus variegatus) were exposed simultaneously to r adiolabeled [H-3]2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and [C-14] octachlorodibenzo-p-dioxin (OCDD) in sediment for 28 d, in order to st udy accumulation processes of hydrophobic substances. Elimination was studied for a further 20 d. The uptake and elimination rate constants and the bioaccumulation factors (BAFs) were determined for TCDD and OC DD in the presence and absence of sediment (overlying water). Steady-s tate concentrations in oligochaetes were achieved for TCDD but not for OCDD over the 28-d exposure. Biota-sediment accumulation factors (BSA Fs) after a 28-d exposure were 1.6 +/- 0.27 for TCDD and 0.07 +/- 0.02 for OCDD. Steady-state log BAF values (lipid based) for TCDD and OCDD in oligochaetes in the overlying water were 5.9 and 5.5 L/kg, respect ively. The effect of incubation time between sediment and contaminants was investigated by repeating the accumulation study after a contact period of 21 months. BSAFs of sediment-sorbed TCDD and OCDD were 1.5 t o 2-fold lower for the long contact time sediment. Based on comparison of predicted accumulation from pore water and observed accumulation b y sediment-exposed oligochaetes, it was concluded that 1.4-fold greate r accumulation occurred due to assimilation of TCDD and OCDD from inge sted sediment. This additional accumulation in the presence of sedimen t, not accounted for by uptake only from pore waters, was consistent w ith literature data for other hydrophobic organochlorines.