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

Abstract

AbstractThe 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.