The purpose of this study was to clarify the kinetic bioaccumulation potential of herbicides in the earthworm, Pheretima spp., the most common earthworms throughout Asia, and Eisenia spp., litter-feeding earthworms included in the test species recommended by the Organization for Economic Co-operation and Development. The kinetic bioaccumulation factors of trifluralin and pendimethalin were estimated from an uptake test for 10 or 12 days and from an elimination test for 10 days. The time required to reach a steady state following herbicide exposure was 7 days for both herbicides in Eisenia spp. and 1 day in Pheretima spp. The uptake rate constant (g-soil/g-worm/day) and elimination rate constant (per day) for trifluralin were 2.1 and 0.23 in Eisenia spp. and 0.42 and 0.45 in Pheretima spp., respectively, and those for pendimethalin were 1.5 and 0.26 in Eisenia spp. and 0.27 and 1.0 in Pheretima spp., respectively. Kinetic bioaccumulation factors of both herbicides were relatively close to bioaccumulation factors in steady state and were higher in Eisenia spp. (8.9 for trifluralin and 5.7 for pendimethalin) than in Pheretima spp. (0.95 and 0.26). These results demonstrated that the herbicide bioaccumulation risk is lower for Pheretima spp. than for Eisenia spp. because of the lower uptake rate and higher elimination rate in Pheretima spp.
Keywords: Elimination rate constant; Kinetic bioaccumulation factor; Pendimethalin; Pheretima spp.; Soil uptake rate constant; Trifluralin.