Transformation of the Herbicides MCPP and Atrazine under Natural Aquifer Conditions

Abstract

The potential for aerobic biotransformation of the herbicides MCPP [(+/ ‐)‐2‐(4‐chloro‐2‐methylphenoxy)propionic acid] and Atrazine [2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine] under natural aquifer conditions was investigated. A natural gradient experiment was carried out in an aerobic ground‐water zone at the Canadian Forces Base Borden, Borden, Ontario, Canada. Over 90 days, a continuous plume was created by weekly injections of the herbicides (average concentrations of 400 jug/1 each), together with a conservative tracer, chloride. The fate of the herbicides was monitored at multilevel piezometers located downgradient from the injection well. In parallel, experiments with in situ testers (Gillham et al., 1990) were set up in the aquifer and microcosms were set up in the laboratory. For MCPP, the natural gradient experiment showed an adaptation period of 42‐56 days followed by transformation from 400 to 30 μg/1. As predicted, MCPP was not retarded compared to the conservative tracer. No transformation was observed in the in situ testers over 47 days. In the laboratory experiments no transformation was observed over 74 days. Atrazine was recalcitrant within the experimental period of 96 days in the natural gradient experiment. A retardation factor R = 1.2, within the predicted range, was found for Atrazine in the Borden aquifer. No transformation was observed either in the in situ testers or in the laboratory experiments after a period of 96 and 74 days, respectively. These results suggest that both MCPP and Atrazine are mobile in sand aquifers. Atrazine appears persistent, at least for 96 days, while MCPP undergoes considerable transformation.

Atrazine, Deethylatrazine, and Deisopropylatrazine Persistence Measured in Groundwater in Situ under Low-Oxygen Conditions

“…Vanderheyden et al (1997) observed rapid degradation of atrazine in sediment samples collected from the saturated zone, and the metabolites were unidentified; mineralization of [ 14 C]atrazine began after a lag phase of ∼25 days and ∼25% of the applied [ 14 C]atrazine was mineralized in 75 days. Agertved et al (1992) observed no decrease in atrazine concentrations during 74 days in laboratory microcosms of groundwater and aquifer material.…”

“…The persistence of contaminants in situ can be determined by monitoring groundwater concentrations in field transport studies. Agertved et al (1992) observed no degradation of high concentrations of atrazine (∼400 µg/L) in 96 days in an aerobic aquifer [dissolved oxygen (DO) ranging from 2.1 to 8.0 mg/L]. Widmer and Spalding (1995) observed no degradation at concentrations more typical of nonpoint source contamination [atrazine, DEA [2-amino-4-chloro-6-(isopropylamino)-1,3,5-triazine], and DIA, each at ∼3 µg/L] in 3 months in an aerobic aquifer (DO ≈6.9 mg/L).…”

“…Much of the research on the rate of triazine herbicide degradation in groundwater has been conducted in the laboratory. Field studies have largely been conducted under aerobic conditions (Agertved et al, 1992;Widmer and Spalding, 1995). The objective of this study was to use ISMs to determine the persistence of atrazine and two of its dealkylated metabolites, DEA and DIA, under oxygen-limited conditions induced in a shallow sand and gravel aquifer contaminated by both atrazine and nitrate.…”

“…They also minimize disturbance of the aquifer and allow for measurement of reaction rates under aquifer conditions, since parameters such as pH, Eh, DO, the composition of the groundwater and solid matrix, and the microbial population remain essentially unchanged (Gillham et al, 1990). Agertved et al (1992) used microcosms of this design to determine the persistence of 400 µg/L atrazine and MCPP [potassium salt of 2-(2-methyl-4-chlorophenoxy)propionic acid] in an aerobic aquifer; they observed minimal degradation of both compounds in 47 days.…”

Atrazine degradation in a small stream in Iowa

“…For small particles of -l-pm diameter it varies between a few days and 4-6 weeks, but is only a few days or less than 1 day for particles with l-10-pm diameter (5). Most studies show that atmospheric input is the primary source of PAHs to sediments and soils, especially for remote sites (6)(7)(8)(9)(10)(11)(12)(13)(14).…”