PERSISTENCE AND METABOLIC-FATE OF FENITROTHION IN NORTHERN ONTARIO FOREST SOILS AND LEAF LITTER UNDER LABORATORY CONDITIONS

Sandy and clay loam forest soils and leaf litter were fortified with C-14-fenitrothion (10-mu-g/g) and incubated in an evironmental chamber (20-degrees-C, 80% RH, 16 h light and 8 h dark) for a period of 75 d. Fenitrothion loss, metabolites and bound residues formed and (CO2)-C-14 produced, were measured at intervals of time by TLC, and radiochemical methods. The radioactivity decreased exponentially in sandy and clay loam soils, and in litter. Dissipation was slower in forest litter than in soils, and the corresponding DT50 values (d) were: 6.34, 7.98 and 16.42. The residual amounts (%) of fenitrothion on the 75th day were respectively 1.5, 1.1 and 10.2. The peak concentrations of the major metabolite (4-nitrocresol) and the corresponding periods (d) found in sandy and clay loam soils and leaf litter were respectively 25.1%, 10; 16.6%, 15 and 6.9%, 15. The metabolite dissipated more rapidly in the soils than in litter. Aminofenitrothion was detected sporadically in sandy loam soil at low concentrations compared to its frequent occurrence at slightly higher levels in clay loam soil and litter. Maximum concentrations of unidentified metabolites in sandy loam (10.9%) and clay loam (9.9%) soils and litter (9.1%) were found on day 20. The amount of (CO2)-C-14 formed increased with time to maximum values on day 75 of 46.4%, 42.4% and 38.1% respectively for sandy and clay loam soils and litter. Very little (CO2)-C-14 (CO2)-C-14 was evolved from the sterilized soils and litter indicating that microbes played a significant role in fenitrothion degradation. The highest concentrations of bound residues in the three matrices were: sandy loam 41.7% on day 50, clay loam 44.3% on day 40 and litter 38.6% on day 40. The principal degradative pathway for the chemical in forest soils and litter appears to be the hydrolysis of P-O-Ar bond, ring cleavage, oxidation and eventual conjugation of the fragments to soil litter matrices.