Effects of Organic Fertilizers on the Fate of 14C Carbofuran in an Agro-microcosm Under Soil Run-off Conditions

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Abstract
The effects of cow manure and sewage sluge on the fate of 14C carbofuran applied to soil were investigated in a run-off microcosm. Both manure and sludge reduced the uptake of 14C carbofuran and its metabolites from soils into oat plant tissue. Movement of 14C carbofuran-derived 14C also occurred in the soil, because 22 to 25% of radiocarbon recovered from the soil was associated with the lower, originally untreated soil layer. After two applications of “rain”, 6.4 to 7.0% of soil-applied 14C had been carried off with the runoff soil and water, but only 3.3 to 3.7% of soil-applied 14C were associated with the aquatic component at the end of the experiment. Of these 14C residues, more than half were recovered from the bottom soil-mud sediments. Run-off water and aquaria water were not toxic to Aedes aegypti L. mosquito larvae. Carbofuran was the major compound detected in terrestrial soils, whereas 3-hydroxycarbofuran was the major compound detected in oat leaves. In all experiments with manure-amended soil, an increased degradation of 14C carbofuran was noticed as evidenced by recoveries of reduced amounts of organic-soluble 14C, by an increased evolution of 14CO2 (144% of control) and by an increased production of bound 14C residues. Apparently, manure microorganisms were responsible for the enhanced 14C carbofuran degradation in soil, based on increased carbofuran recoveries and formation of reduced amounts of bound 14C residues and 14CO2 in soils previously mixed with sterilized manure.