| Abstract: | In order to determine the effect of pH and temperature on post-harvest dip solutions of dimethoate (500 mg litre?1), the half-lives and pseudo first-order rate constants were calculated from measurements at pH 4, 6, 8, 10, 11.5, and at two temperatures 25 and 52°C. The half-lives ranged from 206 days to 39.3 min at 25°C, and from 5.6 days to 205s at 52°C; the rate constants ranged from 3.9 × 10?8 s?1 to 2.9 × 10?4 s?1 at 25°C, and from 1.4 × 10?6 s?1 to 3.4 × 10?3 s?1 at 52°C. The results show that the water used in dips should have a pH≤7. The addition of benomyl to the dip solutions at two concentrations (0.5 and 1.0 g litre?1) had no effect on the half-lives and rate constants. The use of hard and salted waters in dips also showed no major effect. A formula was developed that gives the half-life of the dimethoate as a function of the pH and temperature. |
