Environmental behavior of the fungicide metalaxyl in experimental tobacco field
The loss of metalaxyl, a systemic fungicide, was determined in runoff water from loamy soil plots of various surface slopes cultivated with tobacco, over a period of 170 days. Conditions were selected to simulate agricultural practices employed in the Mediterranean region. The surface slopes of plots were 0, 2.5, 5, 7.5, 10% and both cultivated and uncultivated (control) areas were simultaneously monitored. The cumulative losses of metalaxyl in surface runoff from tilled and untilled plots with a slope of 10% were estimated at 0.469% and 0.740% of the initial applied active ingredient respectively, while for the plots with a slope 0% they were 0.033% and 0.044%. The dissipation in topsoil was studied for a period of 110 days. The half-lives that were calculated using first-order kinetics ranged from 13.7 to 16.6 days in tobacco soil and from 13.8 to 17 days in non-cropped soil. The dissipation of metalaxyl from the topsoil in cultivation of tobacco was higher in comparison with the untilled plots (46–62% and 52–69% respectively, of the applied dose in 23 days after the second application). The slope of soil surface, the compound solubility and sorption capacities are the main parameters that influenced the transport of metalaxyl residues via surface water in soil-water systems.