Degradation of the fungicide pyrimethanil in water and soil

Pyrimethanil (PYR) is widely used to control Botrytis cinerea, Venturia inaequalis, and V. pirina. When used on crops a great quantity of this fungicide is introduced into the soil where it can accumulate if it is adsorbed in great quantities and there is little degradation. Previous works showed that PYR is strongly adsorbed on soil which consequently limits its bioavailability. Although some degradation tests on soil reported in literature produced half-life times values for this compound, no information is available regarding its degradability when a commercial product is used. G iven the current lack of information regarding the persistence of PYR in the soil, this work highlights its behaviour in two soils and concentrates on how the commercial product behaved rather than the pure active ingredient. Degradation tests were also carried out in sterile water with different pH (4, 7 and 9) and in two water samples taken from the Simeto R iver (Sicily, I taly). The half-life times found were lower than those reported in the literature. Degradation time was lower in the soil containing the largest amount of organic matter, thus confirming the important role played by the micro-organisms it contains in the degradation of the molecule. T he commercial product behaved differently both as regards adsorption and degradation. I n fact, a weak adsorption was accompanied by faster degradation. PYR did not degrade in sterile water at any of the pHs tested. T he same result was obtained from natural water even when the samples were added with glucose to encourage the development of micro-organisms, demonstrating the incapacity of the microflora present in water to degrade the molecule.”