DEPURATION AND UPTAKE KINETICS OF I, CS, MN, ZN AND CD BY THE EARTHWORM (LUMBRICUS-TERRESTRIS) IN RADIOTRACER-SPIKED LITTER

The relative depuration and uptake kinetics of contaminants should be known to interpret appropriately the use of organisms such as earthwor ms in environmental bioassays and monitoring. For example, 14-d earthw orm bioassays should be interpreted with the knowledge that some conta minants will continue to accumulate in tissues for months. The radiotr acers I-125, Cs-134, Mn-54, Zn-65, and Cd-109 were applied to deciduou s litter and specimens of Lumbricus terrestris were exposed, either to litter alone or to litter on the top of soil columns. Depuration was monitored for 120 d and uptake, in a separate experiment, for 20 d. Bo th depuration and uptake were described using two-phase, first-order s tatistical models. Gut clearance had a mean half-time of 1.4 d. The me an half-time for physiological depuration decreased from I (210 d) > C d (150 d) > Zn (69 d) > Mn (40 d) > Cs (24 d). Both the depuration and the uptake experiments were necessary to resolve even partially the m ultiphase processes. Earthworm/soil dry weight concentration ratios de creased from Cd > Zn > I greater than or equal to Cs greater than or e qual to Mn. The very slow kinetics indicate that tissue concentrations will increase continuously for a long time, with important implicatio ns for subsequent food-chain transfers.