Dissipation of Atrazine and Two N‐Dealkylated Metabolites in Soils of Sugarcane Plantations Under Field Conditions in Barbados

Abstract

The widespread use of atrazine (AT) as a preemergent herbicide has raised concerns about its persistence in soils of sugarcane plantations in Barbados. Reported are results of field studies to measure the dissipation of AT and two primary metabolites at two sites in sugarcane plantations in Barbados. The investigation was intended to provide values of the half‐lives for dissipation of the herbicide at various depths in the soil profile. Field studies indicated that there is significant potential for AT to leach from Barbados soils to vulnerable groundwater. Residues of the parent and the two metabolites persisted and leached to all profiles of the soil throughout the study period. AT dissipation occurred at all soil depths, was described by first‐order kinetics, and proceeded with half‐life values of 15–28 days. In Profile 1 at the Henley study site, AT concentration decreased exponentially by 72% from 1.16 µg/g on the application day of the herbicide to 0.084 µg/g at the end of day 84 of the study period. A similar decrease occurred in soils from a second site, Edgecumbe; from 2.84 g/g to 0.077 g/g. At deeper depths, the concentration of AT appeared to decrease at a slower rate than near‐surface soils. Dissipation of AT concentration in both fields was generally accompanied by increases in the concentration of the dealkylated metabolites: deethylatrazine (DEAT) and deisopropylatrazine (DIAT). For example, 14% and 7% conversion of AT to DEAT and DIAT occurred by day 14 of the application, respectively. Generally, the deethylated metabolite was present at a higher concentration than the deisopropylated metabolite. By day 274, the day before the second application of AT, the concentration was 0.01 µg/g, typically only 0.3–0.9% of the AT applied. In general, dissipation of AT appeared to be independent of localized factors, such as soil type (silt, clay, and sand), organic matter content, pH, cation exchange capacity, total pore size, bulk density, particle density, and saturated hydraulic conductivity.