Degradation of Atrazine in Four Hawaiian Soils

Abstract

The degradation of14C ring-labeled 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) was studied in the laboratory with four Hawaiian soils selected for their wide range of organic matter contents (4 to 29%), pH values (4.4 to 6.3), and different mineralogies. Atrazine concentrations of 1, 5, 10, 50 and 100 ppmw in soils incubated at 30 C gave similar14C-recovery curves. Degradation was rapid in all four soils; atrazine recovery at 34 days (30 C) ranged from 15 to 30% of the quantity applied. Degradation was accelerated by a temperature increase from 30 to 50 C, suggesting a chemical rather than a biological process. The loss of atrazine from soils approached a first order reaction rate at 30 C, and deviated from this at 50 C. Hydroxyatrazine was the main degradation product with only a slight amount of an unidentified “Product B”. It was concluded that chemical degradation (hydrolysis) was the major pathway of atrazine loss in these soils. This process was more closely related to pH, i.e. faster on low pH soils, than with organic matter content or adsorption. The fraction of atrazine adsorbed on soil increased with the decrease in total atrazine caused by degradation. Extraction of soils with both water and methanol and subsequent analysis of extracts by thin-layer chromatography showed that some of the methanol-extractable atrazine was not readily desorbed by water. These results indicate that some of the residual atrazine extracted chemically may not be available for uptake by plants and would be relatively immobile in soil water.