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Microbial Versus Chemical Degradation of Atrazine in Soils¹

ABSTRACT

Significance of microbial vs. chemical degradation of atrazine was determined using ¹⁴C-labeled atrazine and greenhouse incubation studies. Bacterial isolates evolved 0.4–0.7% of the input ethylamino chain-labeled atrazine as ¹⁴CO₂ in 2 weeks, whereas, Aspergillus fumigatus respired 4.0% in sterile soil. No detectable ¹⁴CO₂ was evolved from ring-labeled atrazine by any of the cultures tested. In nonsterile soils degradation of the hydroxyatrazine ring was 3-fold greater than for chloroatrazine in 2 weeks (1.5% vs. 0.5%). The native soil population respired 2.2–2.6% of chain-labeled atrazine in 4 weeks. Hydroxyatrazine accounted for approximately 20% of the extracted ¹⁴C-activity after 2–4 weeks incubation of ¹⁴C-atrazine in nonsterile or sterile soils. Greenhouse bioassay data showed a 73% loss of atrazine toxicity after 3–4 weeks incubation at 30C in nonsterile soil. These results support chemical hydrolysis of chloroatrazine to hydroxyatrazine as the major pathway of degradation in soils with microbial attack being of minor importance.

Key Words: pesticides in soils

¹ Contribution from the Departments of Farm Crops and Microbiology, Oregon State University, Corvallis. Published with approval of the Director, Oregon Agr. Exp. Sta., Corvallis, Oregon, as Technical Paper no. 2200 under Public Health Service Grant ES-00040-02. Presented before Div. S-3, Soil Science Society of America, Aug. 25, 1966, at Stillwater, Okla. Taken in part from the Master's thesis of the Senior Author, Oregon State Univ., 1966.

² Research Fellow in Farm Crops, Professor of Microbiology, and Professor of Farm Crops, respectively. Present address of senior author: Department of Soils.

Received for publication October 12, 1966. Accepted for publication May 10, 1967.