Abundance of atrazine degrading genes <i>trzN versus atzA</i> in soil cultures and <i>in situ</i> degradation rates

BACKGROUND: Atrazine is a widely used herbicide whose persistence and mobility have led to frequent contamination of soils and water bodies. Atrazine can be degraded in soils through two primary biotic pathways: an oxidative route that produces the relatively persistent metabolites desethylatrazine and deisopropylatrazine, and a hydrolytic route mediated by chlorohydrolases encoded by atzA or trzN, leading to the less recalcitrant intermediate hydroxyatrazine. This study quantified atrazine degradation rates in 17 agricultural soils overlying a regional aquifer and evaluated degradation potential through complementary laboratory experiments. RESULTS: The soils contained hydroxyatrazine and desethyl-2-hydroxyatrazine, indicating active hydrolytic transformation in the fields, while varying proportions of dealkylated metabolites suggested concurrent oxidative degradation. Field-derived half-lives ranged from 36 to 225 days, with evidence of biphasic kinetics, as younger atrazine residues degraded more rapidly than aged residues. Finally, laboratory enrichment cultures of all soils confirmed the capability of indigenous bacteria to hydrolyze atrazine, with a clear predominance of trzN over atzA across cultures. CONCLUSION: The findings of the current study indicate that while the predominance of the hydrolytic pathway suggests reduced risk of rapid atrazine migration to groundwater, the observed biphasic degradation behavior indicates that residual atrazine may continue leaching over extended timescales with prolonged risk for groundwater quality. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.