Solvent extraction characterization of bioavailability of atrazine residues in soils

Characterization of pesticide bioavailability, particularly in aged soils, is of continued interest because this information is necessary for environmental risk assessment. The objective of this study was to correlate atrazine residue bioavailability in aged soils, as determined by solvent extraction methods, to atrazine mineralization by an atrazine-degrading bacterium. Webster clay loam and Zimmerman fine sand soils were treated with UL-ring-labeled [ ¹⁴C]atrazine and incubated for up to 8 weeks. At the end of each incubation period, soils were either not extracted, extracted with 0.01 M CaCl₂, or extracted with 0.01 M CaCl₂/aqueous methanol. Soils were then inoculated with the bacterium Pseudomonas sp. strain ADP, which is capable of rapidly mineralizing the atrazine ring. This allowed for the evaluation of the bioavailability of aged atrazine residues without the contribution of atrazine desorption from soil. Results of these studies indicated that the amounts of atrazine residues in aged soils extracted by 0.01 M CaCl₂ and aqueous methanol were correlated to amounts of atrazine mineralized by Pseudomonas sp. strain ADP. Consequently, 0.01 M CaCl ₂/methanol extractable atrazine in aged soils may be used to estimate bioavailable residues, and this technique may be useful to determine the bioavailability of other compounds in soils, especially other triazine herbicides.