Degradation dynamics of an oxime carbamate insecticide (methomyl) in aqueous medium of varying pH under laboratory simulated condition

Laboratory degradation studies were performed in water at pH 4.0, 7.0 and 9.2 using methomyl (Lannate 12.5 L) formulation at the rates of 1.0 (T1) and 2.0 (Tz) HgmL". Water samples collected on 0 (2 h), 3, 7, 15, 30, 45, 60 and 90 days after treatments were processed for residue analysis of methomyl by HPLC equipped with Photo Diode Array Detector. In 60 days, dissipation was 84-87% at pH 4.0, 71-77% at pH 7.0, and 91-93% at pH 9.2 in both treatments showing very little effect of pH on dissipation. The half-life periods observed were 20.76 and 22.13 days at pH 4.0, 27.87 and 28.67 days at pH 7.0 and 15.84 and 16.54 days at pH 9.2 at Ti and Tz doses respectively.