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

Abstract

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 microm. 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 microm) 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 microm 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 microm can be important carriers of propiconazole in runoff suspensions with high sediment load.

Investigating Potential Water Quality Impacts of Fungicides Used to Combat Soybean Rust in Indiana

“…Jamet and Eudeline (1992) compared the mobility of 17 triazole fungicides in a silt loam soil and concluded that their mobility was inversely related to their octanol/water partition coefficient. Wu et al (2003) investigated the sorption and desorption characteristics of propiconazole to different particle/aggregate-size fractions of agricultural runoff material and showed that sorption increased with decreasing particle size.…”

Concentration and loading of several pesticides in water, suspended solids and sediment during ordinary water discharge in Sugao marsh, Ibaraki Prefecture, Japan

“…This might be due to the difference in surface area between the two fractions of suspended solids and strong hysteresis. 14,20) As shown in Figs. 3b, c, g and h, the concentrations of esprocarb in suspended solids were higher than those of other pesticides, and thiobencarb was detected in relatively higher concentrations in SS 0.5 at the Iinuma river site, and dimethametryn in SS 1.0 at Fureaibashi.…”

Combined effects of the fungicide propiconazole and agricultural runoff sediments on the aquatic bryophyte Vesicularia dubyana

“…In the depositional runoff sediment, the fraction S1 (0.16–2.0 μm) and S2 (0.03–0.16 μm) accounted for only 7.5 and 0.8% of the total sample mass, and the coarser fractions (>2 μm) made up more than 90%. In runoff water collected at the edge of agricultural fields, however, these two size fractions (S1 + S2) have been found to make up 80% of the total sediment mass and, thereby, represent a major part of solid material suspended in water [18].…”

“…When entering the watercourse, the concentration of suspended sediment generally is diluted, and a large fraction of propiconazole originally sorbed to sediment surfaces might desorb. For some soils, propiconazole showed strong hysteresis [18]. In that case, the desorption kinetic is rather slow and, consequently, the proportion of particle‐bound propiconazole will be higher under desorption than the one calculated from the sorption coefficient.…”