| Autor: |
Bromilow, Richard H., Briggs, Geoffrey G., Williams, Mark R., Smelt, Johan H., Tuinstra, Louis G. M. Th., Traag, Wim A. |
| Předmět: |
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| Zdroj: |
Pesticide Science; 1986, Vol. 17 Issue 5, p535-547, 13p |
| Abstrakt: |
The carbamoyloxime pesticides methomyl, oxamyl and aldicarb, together with the oxidation products of aldicarb, are known to break down much more rapidly in certain anaerobic subsoils than in the aerobic topsoils from the same site. Ferrous ions have now been shown to be involved in this reaction. Oxamyl was degraded in aqueous solutions at 30°C containing 250 μg ml−1 Fe2+ with a half-life of about 10 h, independent of pH in the range of 5.65-7.66; the observed products of this reaction were N,N-dimethyl-l-cyanoformamide and methanethiol. These same products, rather than the oximino hydrolysis product observed from degradation in aerobic soils, were rapidly and quantitatively formed from oxamyl in suspensions of anaerobic reduced subsoils (Fe2+ concentration 27-41 μg ml−1 soil water), but oxamyl was rather stable in water-saturated Vredepeel subsoil (Fe2+ concentration 0.65 μg ml−1) in which the redox potential was much higher. Methomyl behaved similarly. The rates of reaction in the suspensions of anaerobic subsoils were greater than expected from the concentrations of Fe2+ in the soil water, but most of the Fe2+ present in soil was bound to the soil particles by cation exchange and this bound Fe2+ may have participated. Breakdown of aldicarb was accelerated both in solutions of Fe2+ and in the suspensions of anaerobic reduced subsoils, though the rate enhancement was less than observed with methomyl and oxamyl; 2-methyl-2-methylthiopropionitrile and 2-methyl-2-methylthiopropionaldehyde were the observed products from aldicarb in anaerobic soil but only the former was produced in Fe2+ solutions; the corresponding nitriles and aldehydes were also yielded by aldicarb sulphoxide and aldicarb sulphone in the anaerobic, reduced subsoils. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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