ARS | Publication request: Characterization of Triazine Residue Bioavailability in Soil by Sequential Solvent Extraction

Submitted to: International Symposium On Environmental Aspects Of Pesticide Microbiology
Publication Acceptance Date: June 1, 2004
Publication Date: September 4, 2004
Citation: Barriuso, E., Koskinen, W.C., Sadowsky, M.J. 2004. Characterization Of Triazine Residue Bioavailability In Soil By Sequential Solvent Extraction. International Symposium On Environmental Aspects Of Pesticide Microbiology. P. 32.

Technical Abstract: Characterization of pesticide bioavailability, particularly in aged soils, is of continued interest because this information is necessary for environmental risk assessment. Pesticide bioavailability in aged soils has been characterized by a variety of indirect and direct methods with limited success. The most common indirect method to characterize bioavailability of pesticides is by using a simplistic sorption coefficient. Direct methods to characterize bioavailability include measurement of pesticide residues taken-up from soil by plants, earthworms, and microorganisms. Because characterization of bioavailability can be expensive and time-consuming and can also depend on the organism used, attempts have been made to characterize bioavailability using solvent extraction techniques. 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 incubated further, 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 amounts of atrazine 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 CaCl2/methanol extractable atrazine in aged soils can be used to estimate bioavailable residues in aged soils. We have shown that this technique can be used for other triazine herbicides, such as simazine. This technique may also be useful to determine bioavailability of other classes of pesticides in soils.