Anaerobic Degradation of Atrazine and Metolachlor and Metabolite Formation in Wetland Soil and Water Microcosms

Abstract

The half-lives, degradation rates, and metabolite formation patterns of atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] were determined in an anaerobic wetland soil incubated at 24 degrees C for 112 d. At 0, 7, 14, 28, 42, 56, and 112 d, the soil and water were analyzed for atrazine and metolachlor, and their major metabolites. The soil oxidation-reduction potential reached -200 mV after 14 d. Degradation reaction rates were first-order for atrazine in anaerobic soil and for metolachlor in the aqueous phase. Zero-order reaction rates were best fit for atrazine in the aqueous phase and metolachlor in anaerobic soil. In anaerobic soil, the half-life was 38 d for atrazine and 62 d for metolachlor. In the aqueous phase above the soil, the half-life was 86 d for atrazine and 40 d for metolachlor. Metabolites detected in the anaerobic soil were hydroxyatrazine and deethylatrazine for atrazine, and relatively small amounts of ethanesulfonic acid and oxanilic acid for metolachlor. Metabolites detected in the aqueous phase above the soil were hydroxyatrazine, deethylatrazine, and deisopropylatrazine for atrazine, and ethanesulfonic acid and oxanilic acid for metolachlor. Concentrations of metabolites in the aqueous phase generally peaked within the first 25 d and then declined. Results indicate that atrazine and metolachlor can degrade under strongly reducing conditions found in wetland soils. Metolachlor metabolites, ethanesulfonic acid, and oxanilic acid are not significantly formed under anaerobic conditions.

Influence of a Riparian Wetland on Nitrate and Herbicides Exported from an Agricultural Field

“…Although the DAR concept is typically used to distinguish groundwater sources from runoff water sources in stream water, processing of ground water through an anaerobic, high-organic matter (OM) wetland soil (and subsequent removal of CIAT) will alter the signal. Kruger et al (15) reported that anaerobic processes were more active at removing atrazine and atrazine metabolites than were aerobic processes; Seybold et al (16) also noted high atrazine degradation in anaerobic soil. High DAR values in oxic ground water, then, can diminish as ground water moves up through anoxic soil (Figure 6), as the degradate (CIAT) is consumed or adsorbed in that environment.…”

Kinetics of aerobic and anaerobic biomineralization of atrazine in surface and subsurface agricultural soils in Ohio

“…Anaerobic biodegradation of atrazine has been shown to occur in soil, wetland, and wastewater samples. [8][9][10][11][12] However, in aquifers atrazine and metabolites can persist for decades or even longer. [13][14][15] The known biochemical steps of atrazine biodegradation are hydrolytic and do not require molecular O 2 .…”

Redox effects on resin extraction of herbicides from soil1

“…Glucose is a much more soluble compound than the three herbicides and a poor competitor for adsorption sites. Also, it appears unlikely that microbial degradation of any of the herbicides was greatly affected by the incubation with glucose; Seybold et al [23] have shown losses of less than 5% of freshly added atrazine or metolachlor during 7 days incubation at 24°C. Here anaerobiosis was achieved in 5 2 days and then microbial activity was inhibited by the addition of methanol (20%).…”