Degradation kinetics of anilofos in soil and residues in rice crop at harvest.

BACKGROUND

Pesticides used on rice, which is widely grown in India in the rainy season, must be investigated for the persistence and magnitude of their residues in the crop and soil to ensure human and environmental safety. Anilofos is widely used in rice, and its persistence and dissipation behaviour in soil and rice was investigated in field trials under subhumid and subtropical conditions.

RESULTS

The persistence of anilofos in soil, husk, grain and rice straw was evaluated at two application rates (0.4 and 0.8 kg AI ha(-1) ) by RP-HPLC. In soil, residues were detected up to 45 and 75 days after application at 0.4 and 0.8 kg AI ha(-1) respectively. No residue was observed in soil, husk, grain or rice straw at the time of harvest at either application rate. Detector response was linear within the concentration range 0.1-5.0 µg mL(-1) at 2.22% standard deviation. The limit of detection was 0.003 µg mL(-1) , and the limit of quantification of the method for soil, straw, grain and husk was 0.007, 0.01, 0.008 and 0.01 µg g(-1) respectively.

CONCLUSION

The dissipation of herbicide from soil appeared to occur in a single phase and conformed to pseudo-first-order kinetics. The calculated half-life values of anilofos residue in soil were 13 days for the lower rate of application (0.4 kg AI ha(-1) ) and 15.5 days for the higher rate (0.8 kg AI ha(-1) ). Anilofos residues were below the maximum residue level in soil, husk, rice grain and rice straw at harvest.