Accelerated Metolachlor Degradation in Soil by Zerovalent Iron and Compost Amendments.

Intensive use of chlorinated herbicides in Korea has become a potential threat to soil and water quality. Soil incubation and germination tests were conducted to assess zerovalent iron (ZVI), organic compost, moisture and their combinations on metolachlor degradation in soil. The ZVI alone degraded 91% of metolachlor in soil within 40 days following bi-phasic kinetics. Organic amendment alone facilitated metolachlor degradation in soil up to 60% after 40 days depending on the amendment rate. Two soil moisture levels by themselves showed no differences in metolachlor degradation and no additional benefits were found when combined with ZVI for metolachlor degradation. However, the combination of ZVI with compost amendment at 30 ton ha^–1 and 30% moisture content accelerated metolachlor degradation to 90% degradation after 3 days and 98% after 40 days. The half life (t_1/2) of metolachlor degradation with ZVI, compost at 30 ton ha^–1, and 30% moisture was about 1 days, which was faster than ZVI treatment alone and 98% faster than controls. Germination and growth of lettuce (Lactuca sativa) and crabgrass (Digitaria sanguinalis L. Scop.) with ZVI treatment were comparable with those of the water only treatments, whereas germination and growth were severely inhibited in unamended metolachlor-contaminated soils. The enhanced efficiency of ZVI in metolachlor degradation was accompanied by both increases in pH and Fe concentration in soil. Metolachlor degradation was greatest when ZVI, compost and moisture were used together, suggesting that these treatments will maximize in-situ remediation of metolachlor-contaminated soils in the field.