?DEGRADATION OF 14C-LABELLED CYFLUTHRIN IN SOIL AND INCORPORATION OF 14CINTO HUMUS FRACTIONS AS AFFECTED BY WHEAT STRAW AMENDMENT AND MOISTURE CONDITIONS

Abstract

Anincubationexperimentwasconductedinthelaboratoryto studytheeffectofmoistureandwheatstrawamend-
ment on the mineralization and transformationof phenyl-t'C cyfluthrin (activeingredientof Baythroid, aninsecticide
manufactured by Bayer AG, Leverkusen, Germany) into differentsoil fractions.The treated soil was incubated at40,
60 or 100%water holding capacity (WHC) moisture and with or without wheat straw amendment. After 18weeks of
incubation, 44-58% of the cyfluthrin-r'Cwas lost fromthesoil asCOr Mineralizationof cyfluthrin was more rapid in
unamended soilandatlowermoistureregimes;themaximumbeingat40%WHC.Inunamendedsoil,ahigherpropor-.
tion of the applied 14Cwas found in forms extractable with methanol (anefficient solvent of cyfluthrin). In amended
soil, on theother hand,a greaterproportionoftheadded14Cwasfoundinbound formsi.e.,fulvic acid,humic acid and
humins. Transformation of cyfluthrin-v'Cinto stable humic compounds was more intense at lower moisture regimes.
However, in all treatments, a higher proportion of bound residues extractable with alkali was present in fulvic acid
fraction.