TEST OF HPLC MICRO-COLUMN METHOD FOR DIRECT MEASUREMENT OF PESTICIDE RETARDATION IN SOILS

T. YAMAGUCHI, T.G.E.POULSEN, P.MOLDRUP and D.E.ROLSTON

ABSTRACT: Rapid and accurate measurement methods for pesticide sorption onto different soil types are needed to evaluate pesticide transport and fate in soil and for risk assessment of new pesticides. Sorption of two commonly used pesticides (asulam [N-acetyl-P-amino-sulphone amide] and simazine [2-chloro-4,6 bis(ethylamino)-1 ,3,5 triazine]) in two different Japanese soils (sand and sandy loam) was measured using (i) a traditional batch experiment method and (ii) a high performance liquid chromatography (HPLC) micro-column method that measures the retardation of an adsorbing solute (e.g. pesticide) relative to a non-adsorbing solute (e.g. deuterium labeled water, D20) during different water transport conditions. The HPLC micro-column system requires only small amounts of soil and chemicals, and experiments are rapid and easy to perform compared to traditional batch or larger-scale column experiments. Retardation factors (R) for the two pesticides were estimated from both (i) batch experiments (adsorption isotherms) and (ii) microcolumn pesticide breakthrough curves using the public domain CXTFIT [U.S. Salinity Laboratory, USDA, USA] solute transport model for curve-fitting. Batch and micro-column experiments yielded similar R values ranging from 1.1 for asulam sorption onto Hiroshima sand to about 30 for simazine sorption onto Hiroshima loam. Similar values of R were obtained at two different water flow rates in the HPLC micro-column, confirming the reproducibility of the HPLC micro-column method.

Key words: adsorption, CXTFIT, HPLC micro-column method, pesticides, retardation factor (IGC: B12/D2)