MP5 Agrochemicals and Pesticides
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(CHA-1117-597088) Anaerobic soil metabolism of ¹⁴C-Metamifop under chemically reduced condition with sodium sulfide.

Chang, H.-R.¹, Yang, K.-W.², Chung, B.-J.², Kim, K.¹, Kim, Y.-H.¹, ¹ Korea Institute of Toxicology, Daejeon, Republic of Korea² Dongbu Hannong Chemical Co., Ltd.

ABSTRACT- A laboratory study was conducted to develop a method requiring shorter incubation time in anaerobic soil metabolism by introducing a chemically reduced condition with sodium sulfide and to determine the transformation rate and identify major metabolites of ¹⁴C-metamifop, a new herbicide developed in Korea, in non-sterile and sterile anaerobic soils. ¹⁴C-metamifop was applied to chemically reduced anaerobic soil at a rate of 0.1 ppm, equivalent to approximately field application rate of 100 g of active ingredient per hectare. The soil treated with ¹⁴C-metamifop was incubated in the flow-through systems in the dark at 20±2°C for 90 days. Under chemically reduced anaerobic condition with sodium sulfide, the redox potential declined below -200 mV without pre-incubation and the range of pH, dissolved oxygen(DO), and microbial activities were comparable to the incubation method of OECD guideline(TG307) and conventional anaerobic metabolism studies. The half-life of ¹⁴C-metamifop in non-sterile and sterile anaerobic soil were 53 and 78 days, respectively. Two metabolites were identified: HPFMPA and MFA. A major metabolite with levels of more than 10% of the applied radioactivity was HPFMPA. This study confirmed that use of a chemical reducing agent could shorten the pre-incubation time of the anaerobic soil metabolism study, while the incubation method of the OECD guideline could not generate the anaerobic condition within 30 days after flooding. Further study is needed to confirm the wide applicability of the chemically reduced anaerobic soil metabolism to the other pesticides.

Key words: metamifop, anaerobic soil metabolism, chemically reduced condition, anaerobic soil degradation