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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.

Atrazine is a commonly used herbicide in corn (Zea mays L.) growing areas of the USA. Because of its heavy usage, moderate persistence, and mobility in soil, monitoring of atrazine movement under field conditions is essential to assess its potential to contaminate groundwater. Concentrations of atrazine, deisopropylatrazine (DIA), and deethylatrazine (DEA) were measured in subsurface drainage and shallow groundwater beneath continuous, no-till corn. Water samples were collected from the subsurface drain (tile) outlets and suction lysimeters in the growing seasons of 1990 and 1991, and analyzed for atrazine and two principle degradates using solid-phase extraction and HPLC. In 1990, atrazine concentration ranged from 1.3 to 5.1 µg L −1 in tiledrain water and from 0.5 to 20.5 µg L −1 in lysimeter water. In general, concentrations of parent and degradates in solution were atrazine > DEA > DIA. Lesser levels of atrazine were measured in 1991 from Plots 2 and 4; however, greater concentrations of atrazine (6.0-8.4 µg L −1) were measured from Plot 5. Throughout the two growing seasons, atrazine concentration in Plot 5 tile-drain water was greater than that of Plots 2 and 4, suggesting a preferential movement of atrazine. Concentrations of DIA and DEA ranged from 0.1 to 2.2 and 0.9 to 3.2 µg L −1 , respectively, indicating that the degradation products by themselves or in combination with parent atrazine can exceed the maximum contaminant level (mcl) of 3 µg L −1 even though atrazine by itself may be <3 >µg L −1. The deethylatrazineto-atrazine ratio (DAR) is an indicator of residence time in soil during transport of atrazine to groundwater. In Plots 2 and 4, DAR values for tile-drain water ranged from 0.43 to 2.70 and 0.50 to 2.66, respectively. By comparison, a DAR of 0.38 to 0.60 was observed in Plot 5, suggesting less residence time in the soil.

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The soil thin layer chromatography technique was employed to assess the mobility of 21 chemicals (6 insecticides, 4 herbicides, and 11 of their hydrolysis metabolites) in 6 different soils. The hydrolysis products of the four studied organophosphorus insecticides were significantly more mobile than their parent compounds, but the metabolites of carbamates, s triazines and phenoxy alkanoic acids were less mobile than their parent compounds. For the chemicals for which significant effects of soil variables were observed, greater levels of organic matter, clay, cation exchange capacity and water holding capacity (at one‐third bar) lowered the mobility Soil pH significantly affected mobility of many of the chemicals studied, with increased mobility in soils with higher pH values. Both water solubility and octanol/water partition coefficient (Kow) significantly correlated with the mobility of the chemicals studied, however, Kow was found to be the better predictor of mobility No direct relationship existed between the pKa of the chemicals and their mobility