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TECHNICAL REPORTS

Organic Compounds in the Environment

Atrazine Dissipation in s-Triazine–Adapted and Nonadapted Soil from Colorado and Mississippi: Implications of Enhanced Degradation on Atrazine Fate and Transport Parameters

^a USDA-ARS, Southern Weed Science Research Unit, P.O. Box 350, Stoneville, MS 38776
^b USDA-ARS, Water Management Research Unit, 2150 Centre Ave., Fort Collins, CO 80526
^c Dep. of Agro-Environmental Science and Technology, Univ. of Bologna, V. le Fanin 44, Bologna, Italy 40127
^d USDA-ARS, Corn Plant Host Resistance Unit, Dorman 117 Box 9555, Mississippi State, MS 39762

^* Corresponding author (jason.krutz{at}ars.usda.gov).

Received for publication August 22, 2007. Soil bacteria have developed novel metabolic abilities resulting in enhanced atrazine degradation. Consequently, there is a need to evaluate the effects of enhanced degradation on parameters used to model atrazine fate and transport. The objectives of this study were (i) to screen Colorado (CO) and Mississippi (MS) atrazine-adapted and non-adapted soil for genes that code for enzymes able to rapidly catabolize atrazine and (ii) to compare atrazine persistence, Q₁₀, β, and metabolite profiles between adapted and non-adapted soils. The atzABC and/or trzN genes were detected only in adapted soil. Atrazine's average half-life in adapted soil was 10-fold lower than that of the non-adapted soil and 18-fold lower than the USEPA estimate of 3 to 4 mo. Q₁₀ was greater in adapted soil. No difference in β was observed between soils. The accumulation and persistence of mono-N-dealkylated metabolites was lower in adapted soil; conversely, under suboptimal moisture levels in CO adapted soil, hydroxyatrazine concentrations exceeded 30% of the parent compounds' initial mass. Results indicate that (i) enhanced atrazine degradation and atzABC and/or trzN genes are likely widespread across the Western and Southern corn-growing regions of the USA; (ii) persistence of atrazine and its mono-N-dealkylated metabolites is significantly reduced in adapted soil; (iii) hydroxyatrazine can be a major degradation product in adapted soil; and (iv) fate, transport, and risk assessment models that assume historic atrazine degradation pathways and persistence estimates will likely overpredict the compounds' transport potential in adapted soil.

Abbreviations: DEA, desethylatrazine • DIA, deisopropylatrazine • FC, field capacity • HA, hydroxyatrazine • HPLC, high-performance liquid chromatography • LOQ, limit of quantitation, PCR, polymerase chain reaction

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