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TECHNICAL REPORTS

Organic Compounds in the Environment

Size Distribution of Organic Matter and Associated Propiconazole in Agricultural Runoff Material

^a Dep. of Soil and Water Sciences, Agricultural Univ. of Norway, P.O. Box 5028, 1432-Ås, Norway
^b Inst. of Terrestrial Ecology, ETH Zurich, Grabenstrasse 3, CH-8952 Schlieren, Switzerland

^* Corresponding author (wu_qinglan{at}yahoo.com).

Received for publication October 11, 2002. Sorption and desorption characteristics of propiconazole (1-[[2-(2,4-dichlorophenyl)-4-propyl-1, 3-dioxolan-2-yl] methyl]-1H-1,2,4-triazole) to different particle/aggregate-size fractions of agricultural runoff material were investigated. Emphasis was put on clay and colloidal size fractions to evaluate their role as potential sorbents and carriers for this pesticide. The runoff material was separated into size fractions ranging from 2 mm to ca. 15 nm by wet sieving, sedimentation, centrifugation, and membrane ultrafiltration. Each fraction was characterized by its organic C content and C/N ratio. Distinctive sorption properties of clay-sized particles and colloids were investigated. The obtained size fractions differed significantly in their organic C concentration, C/N ratio, and sorption properties to propiconazole. Organic matter was mainly associated in aggregates >2 µm. Binding of propiconazole to this coarse fraction made up 80% of the sorbed propiconazole. The distribution coefficient between solid and aqueous phases increased with decreasing particle size. The colloidal fraction (<0.16 µm) exhibited the highest sorbtivity, with a distribution coefficient of 113 L kg^-1, which was more than four times higher than that in the bulk sample (27 L kg^-1). The fraction <2 µm represented 8% of the total sample weight, but contributed to 20% of the sorbed propiconazole. Strong hysteresis was observed for the sorption–desorption of propiconazole on the runoff material. Under dilution very little sorbed propiconazole will be released into the water phase. Due to its high sorbtivity and mobility and the strong sorption–desorption hysteresis, particles in the fraction <2 µm can be important carriers of propiconazole in runoff suspensions with high sediment load.

Abbreviations: K_d, distribution coefficient of a compound between aqueous and soil solid phases • K_oc, K_d–value normalized to the weight fraction of soil organic carbon • NOM, natural organic matter

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JEQ 2003 32: 1931-1938. [Full Text]