Persistence and degradation of [14C]atrazine and [14C]deisopropylatrazine as affected by soil depth and moisture conditions

Abstract

The fate of atrazine and one of its degradation products deisopropylatrazine has been investigated using radiotracers under laboratory conditions. The metabolic route and rate were investigated under saturated and unsaturated conditions, with samples of soil taken from four depths down to 120 cm. The major degradation products identified from [¹⁴C]atrazine and [¹⁴C]deisopro‐pylatrazine treatments were deethylatrazine and didealkylatrazine, respectively. The detected minor degradation products were hydroxyatrazine, deethylhydroxyatrazine, and deisopropylhydroxyatra‐zine. Under unsaturated conditions atrazine and deisopropylatrazine were least persistent in the top 30 cm, and their persistence increased with increase in depth. The half‐life of atrazine under unsaturated conditions increased with depth and ranged from 41 to 231 d for the studied depths, whereas the half‐life of deisopropylatrazine ranged from 32 to 173 d. Deisopropylatrazine was more susceptible to mineralization than atrazine, and the amount of mineralization decreased with increase in depth. Bound residues were formed to a greater extent in surface soils. Under saturated conditions at the 90‐ to 120‐cm depth, the half‐life of atrazine was 87 d. Deisopropylatrazine was less persistent in saturated soil than in unsaturated soil at the 90‐ to 120‐cm depth, with a half‐life of 58 and 173 d, respectively. The increased degradability of deisopropylatrazine as compared with atrazine and the decreased persistence of deisopropylatrazine under saturated soil conditions provides a logical explanation for its relatively low concentrations in ground water as compared with atrazine.