Behaviour of metamitron and hydroxy-chlorothalonil in low-humic sandy soils

The behaviour of the herbicide metamitron and of the main transformation pr oduct, hydroxy-chlorothalonil (HTI), of the fungicide chlorothalonil was st udied to assess the risk of leaching from low-humic sandy soil. The adsorpt ion of metamitron corresponded to a K-om value of about 60 dm(3) kg(-1) (mo derate adsorption). The half-life of metamitron in soil at 15 degrees C was only three days, presumably due to adaptation of the micro-organisms. In t he autumn, the residue of metamitron in the soil profiles corresponded to l ess than 1% of the cumulative dosage. The half-life of chlorothalonil at 15 degrees C was about 12 days and about 45% of it was transformed to HTI. Th e adsorption of HTI to the soils corresponded to a K-om value of 260 dm(3)k g(-1). The incubation study (15 OC) showed the transformation of HTI in the soils to be very slow. The amounts of HTI remaining in the soil profiles i n the autumn corresponded to 4 and 16% of the cumulative dosage of chloroth alonil. In winter, the HTI residue decreased by 40% relative to the autumn level. Occasionally, HTI could be detected in the upper ground-water level (at a depth of about Im), at an average concentration of 0.1 to 0.2 mu gdm( -3) (C) 1999 Society of Chemical Industry.