TRANSFORMATION OF ALDICARB SULFOXIDE AND ALDICARB SULFONE IN 4 WATER-SATURATED SANDY SUBSOILS

The transformation of aldicarb sulfoxide and aldicarb sulfone was stud ied in incubations with water-saturated subsoils under simulated field conditions at 10 degrees C. The subsoils were collected at four locat ions from beneath the water table at a depth of 2.5 to 3.5 m. In three of the subsoils, the half-life of sulfoxide, incubated at concentrati ons of 0.14-0.17 mg litre(-1), ranged from 0.7 to 2.8 years. At higher concentrations (8-13 mg litre(-1)), its half-life ranged from 3.4 to 6.4 years. At the lower concentration, a large fraction of sulfoxide w as transformed into sulfone. The rates of transformation of the sulfon e at the lower concentration in the three subsoils corresponded to hal f-lives of 3.3 to 8.1 years, but in only one subsoil was a significant transformation rate (half-life 6.7 years) measured at the higher conc entration during the 2.3-year incubation period. The half-lives at the lower concentrations were more like those in field studies, and perha ps would still underestimate transformation rates under field conditio ns. After a year, 2.5-15% of the higher sulfoxide and sulfone doses ha d been trapped as [C-14] carbon dioxide. In the fourth subsoil, with m ore anaerobic conditions, the half-life of sulfoxide at both concentra tions was less than 0.02 year and that of sulfone was about 0.04 year. Four or five radio-labelled transformation products could be traced i n this subsoil and about half of the dose of both compounds was trappe d as [C-14] carbon dioxide.