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Influence of Soil Temperature and Soil Moisture on Degradation and Metabolism of Carbofuran in Soils¹

ABSTRACT

This study was conducted to determine the effects of soil moisture and soil temperature on mineralization rate and the solvent-extractable ¹⁴C-activity disappearance rate of ¹⁴C-carbofuran (2,3-dihydro-2, 2-dimethyl-7-benzofuranyl-N-methylcarbamate) and the formation of nonextractable ¹⁴C-activity in six U.S. soils, to evaluate the difference between the two rates, and to statistically correlate these rates with key soil factors.

Both mineralization rate and solvent-extractable ¹⁴C-activity disappearance rate approximated to first-order kinetics. The solvent-extractable ¹⁴C-activity disappearance rates were much higher than the mineralization rates. The difference was reflected in the formation of nonextractable ¹⁴C-activity in soils. As high as 94.5% of ¹⁴C-activity became nonextractable at the end of 28 days of incubation. Four metabolites, 3-hydroxycarbofuran, 3-ketocarbofuran, carbofuran phenol, and 3-ketocarbofuran phenol were detected in the solvent extracts. ¹⁴C-activity associated with these metabolites in the extracts were generally <5% of the ¹⁴C-carbofuran applied, so that the difference between the solvent-extractable parent-chemical disappearance rate and the solvent-extractable ¹⁴C-activity disappearance rate was insignificant. In general an increase in temperatures from 15 to 27°C had a greater influence on solvent-extractable ¹⁴C-activity disappearance rate than did an increase from 27 to 35°C, and the temperature for maximum rate was between 27 to 35°C. Logarithmic k₁ values of solvent-extractable ¹⁴C-activity appeared to be inversely correlated with logarithmic soil-water tension (). No statistical correlation with key soil factors was observed for either the solvent-extractable ¹⁴C-activity disappearance rate or minralization rate.

Key Words: pesticides • insecticides • pesticide persistence • mineralization • degradation rates • half lives • metabolites • bound residues

¹ Joint contribution of the Soil Science Dep. and Food Science and Human Nutrition Dep., Univ. of Florida, Gainesville. Supported by USEPA Grant no. R805529. Florida Agric. Exp. Stn. J. Ser. no. 3165.

² Assistant Research Scientist, Laboratory Technologist, Assistant Professor, and Professor, respectively, Soil Science Dep., Univ. of Florida, Gainesville, FL 32611.

³ Professor, Food Science and Human Nutrition Dep., Univ. of Florida, Gainesville.

Received for publication July 6, 1981.