Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/24/2006
Publication Date: 3/27/2006
Citation: Koskinen, W.C., Barriuso, E., Regitano, J.B., Sadowsky, M.J. 2006. Bioavailability of triazine residues in aged soil [abstract]. In: Abstracts of conference "Pesticide Behaviour in Soils, Water and Air", Mar. 27-29, 2006, Warwick, UK. Interpretive Summary:
Technical Abstract: Characterization of pesticide bioavailability, particularly in aged soils, is of continued interest since this information is necessary for environmental risk assessment. However, pesticide bioavailability in aged soils has been characterized by a variety of methods with limited success, due in part to methodological limitations. The objective of this study was to determine the effect on aging or sorption-desorption and bioavailability on triazine residues in soils, and to develop a solvent extraction procedure, which would allow prediction of triazine bioavailability in aged temperate and tropical soils. Soils from Midwestern US, Hawaii, and Brazil were treated with 14C-atrazine or 14C-simazine 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. After extraction, soils were inoculated with the bacterium Pseudomonas sp. strain ADP, which is capable of rapidly mineralizing atrazine and simazine. This allowed for evaluation of bioavailability of aged triazine residues, without the contribution from soil desorption. These microorganisms were capable of mineralizing all the readily-available (water-extractable) and a great portion of the less-readily-available (methanol-extractable) 14C-triazines. The 14C-bound, nonextractable fraction, if it contains 14C-triazine, may be considered very recalcitrant and consequently unavailable in soils. The establishment of such a solvent extraction-bioavailability correlation is very useful since it allows the prediction of triazine bioavailability and helps regulatory decisions by improving exposure assessments, which are often overestimated when using more harsh procedures. The increase in calculated triazine sorption with aging was likely due to faster degradation rates in solution and on labile sites as compared to rates of desorption from soil, and simultaneous diffusion into less accessible or stronger binding sites. These results suggest that Kd values calculated for freshly added triazine may overestimate the real leaching potential and availability.