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Microbial Decomposition of Ring-¹⁴C Atrazine, Cyanuric Acid, and 2-Chloro-4,6-diamino-s-triazine¹

ABSTRACT

The relative degradation rates of 2.5 ppm 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 2,4,6-trihydroxy-s-triazine (cyanuric acid), and 2-chloro-4,6diamino-2-triazine were studied in Greenfield sandy loam soil and in pure culture. Only 18% of the activity from added ring-¹⁴C labeled atrazine was recovered as ¹⁴CO₂ after 550 days of incubation at 60% water-holding capacity. Ring-¹⁴C 2-chloro-4,6-diamino-s-triazine yielded 40% of the added activity as ¹⁴CO₂ during 192 days. After 16 days, 87% of the labeled cyanuric acid had evolved as ¹⁴CO₂ and after 32 days, the percentage had increased to 96% indicating that after ring cleavage the cyanuric acid C is not used for cell synthesis by the soil organisms. Evolution of ¹⁴CO₂ from the three compounds was greatly retarded under saturated soil conditions. Losses were less than 0.6% for ring-¹⁴C atrazine during 375 days, 83% for cyanuric acid in 66 days and 22% for 2-chloro-4,6-diamino-s-triazine in 192 days. If cyanuric acid and 2-chloro-4,6-diamino-s-triazine are intermediates in atrazine degradation, their detection in soils would be difficult because they are more rapidly oxidized than atrazine.

Atrazine did not affect the activity of the soil microbes as measured by total CO₂ evolution, numbers of microorganisms, or ability of soil microbes to decompose lima bean straw (Phaseolus limensis).

Pure culture studies with two soil fungi, Stachybotrys chartarum and Hendersonula toruloidea, showed that neither was able to cleave the s-triazine ring of atrazine or 2-chloro-4,6-diamino-s-triazine, but both could degrade cyanuric acid to CO₂.

Key Words: herbicide degradation • s-triazine herbicides • Hendersonula toruloidea • Stachybotrys chartarum • microbial activity • microbial numbers

¹ Contribution from the Department of Soil Science and Agricultural Engineering, University of California, Riverside 92502. The work reported here is part of the Ph.D. dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree.

² Former Graduate Student, and now Assistant Professor of Agronomy, Department of Agronomy, University of MaiTland, and Professor of Soil Science, Dept. of Soil Science & Agricultural Engineering, Univ. of California, respectively.

Received for publication April 26, 1974.

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