Quantification of the Fate of Aminocyclopyrachlor in Soil Amended with Organic Residues from a Sugarcane System

Abstract

Aminocyclopyrachlor is a persistent herbicide in soil; in the presence of organic matter, this persistence can be increased and can contribute to environmental contamination. The objective of this study was to verify the effects of organic materials derived from the sugarcane cultivation system on the mineralization and degradation of aminocyclopyrachlor in the soil. 14C-aminocyclopyrachlor was applied to soil with organic residues (sugarcane straw, filter cake and vinasse) and evaluated for 112 days of incubation. Mineralization was quantified by the weekly evolution of 14CO2, and the extracted, bound residues and the formation of metabolites of aminocyclopyrachlor were quantified. The mineralization was lower than 45% in all treatments. The degradation half-life (DT50) is being 187 days for unamended soil and > 240 days for soils amended with organic materials. For 90% of the herbicide to be degraded (DT90), between 622 and 921 days was required in all soils. Bound residues were formed in the soil (30% of the total applied in all treatments). No metabolites were formed during the whole incubation period, regardless of the treatment. The presence of organic materials in the soil increased the persistence of aminocyclopyrachlor in the soil, so that persistence of the herbicide may promote a residual effect on weeds and carryover in subsequent crops.