Ecology of Atrazine Natural Attenuation in Soil From a Major Spill

Authors: Sims, Gerald; SHAFFER, ELIZABETH - UNIVERSITY OF ILLINOIS

Submitted to: Society of Environmental Toxicology and Chemistry (SETAC)
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2007
Publication Date: 11/1/2007
Citation: Sims, G.K., Shaffer, E.A. 2007. Ecology of Atrazine Natural Attenuation in Soil From a Major Spill [abstract]. Society of Environmental Toxicology and Chemistry Abstracts. Paper No. ECO2-4.

Interpretive Summary:

Technical Abstract: Biodegradation of atrazine was examined in soil from a recent major atrazine spill site in Illinois. The site had been excavated to a depth of 2 meters and the soil stored under cover for future land application (land farming), a form of remediation by natural attenuation. We examined some of the physical and biological factors controlling atrazine degradation in this soil, using a combination of conventional process and microbial ecology measurements that were facilitated by use of 14C-ring-, 15N-ring-, and 15N-ethylamino-labeled atrazine. The soil exhibited a very high rate of atrazine mineralization (1.8 × 10-5 mmoles day-1), that was accompanied by an accumulation of degradation products, including hydroxyatrazine and cyanuric acid, the latter of which, though a known intermediate in microbial degradation of atrazine, does not commonly accumulate in soils. Ambient high concentrations of nitrate (> 160 mg/kg) appeared to be the result of atrazine degradation combined with nitrification. Nitrate appeared not to inhibit atrazine degradation at the site. Biodegradation was limited primarily by bioavailability constraints. An isolate, ES-1, obtained from the soil by direct plating (without enrichment) quantitatively converted atrazine to cyanuric acid (via hydroxyatrazine) at an unusually rapid rate, and the termination of the degradative pathway at cyanuric acid was precedented by the atrazine degradative genes detected in the organism by PCR amplification. Genes detected included a 400bp amplicon for trzN (chlorohydrolase), a 500bp amplicon for atzB, and a 600bp amplicon for atzC (aminohydrolases). No PCR products were detected using primers specific to atzA (another chlorohydrolase) or trzD (ring-cleavage enzyme). The organism, like other atrazine degraders, was unable to assimilate atrazine ring carbon and released excess N from the atrazine side chains as ammonium. Analysis of 16S rRNA gene sequences confirmed that ES-1 is closely related (99%) to Arthrobacter sp. T-RFLP analysis of soil-extracted DNA revealed fragments consistent with the Arthrobacter sp., though no enrichment of these fragments was observed when stable isotope probing was performed using atrazine labeled with ethylamino-15N, thus the role of ES-1 in atrazine fate at the site remains circumstantial.