azoxystrobin and chlortoluron

In intensive agriculture areas the use of pesticides can alter soil properties and microbial community structure with the risk of reducing soil quality.. In this study the fatty acid methyl esters (FAMEs) evolution has been studied in a factorial lab experiment combining five substrates (a soil, two aged composts and their mixtures) treated with a co-application of three pesticides (azoxystrobin, chlorotoluron and epoxiconazole), with two extraction methods, and two incubation times (0 and 58 days). FAMEs extraction followed the microbial identification system (MIDI) and ester-linked method (EL).. The pesticides showed high persistence, as revealed by half-life (t1/2) values ranging from 168 to 298 days, which confirms their recalcitrance to degradation. However, t1/2 values were affected by substrate and compost age down to 8 days for chlorotoluron in S and up to 453 days for epoxiconazole in 12M. Fifty-six FAMEs were detected. Analysis of variance (ANOVA) showed that the EL method detected a higher number of FAMEs and unique FAMEs than the MIDI one, whereas principal component analysis (PCA) highlighted that the monosaturated 18:1ω9c and cyclopropane 19:0ω10c/19ω6 were the most significant FAMEs grouping by extraction method. The cyclopropyl to monoenoic acids ratio evidenced higher stress conditions when pesticides were applied to compost and compost+soil than solely soil, as well as with final time.. Overall, FAMEs profiles showed the importance of the extraction method for both substrate and incubation time, the t1/2 values highlighted the effectiveness of solely soil and the less mature compost in reducing the persistence of pesticides.

Topics: Environmental Monitoring; Epoxy Compounds; Fatty Acids; Half-Life; Methacrylates; Pesticides; Phenylurea Compounds; Pyrimidines; Soil; Soil Microbiology; Strobilurins; Time Factors; Triazoles

This study investigates time-dependent sorption of pesticides in soil aggregates. We tested if the sorption kinetics of pesticides in soil aggregates can be described by modeling diffusion into aggregates for a range of soils and pesticides. Our hypothesis is that the rate of sorption is negatively related to sorption strength due to retardated diffusion. Natural aggregates of 3-5 mm diameter were separated from three soils: a clay, a silty clay loam, and a clay loam. The aggregates were stabilized with alginate gel, and adsorption of azoxystrobin, chlorotoluron, and atrazine was measured in batch experiments with eight equilibration times up to 28 days. Equilibrium sorption appeared to be reached within the 28-day period for each pesticide. An intra-aggregate diffusion model was employed to describe the increase of sorption with time. The model describes diffusion of the dissolved pesticides through the pore space inside the aggregates and sorption on internal surfaces. Sorption could be described by pore diffusion into the aggregates with diffusion coefficients between 0.5 x 10(-10) and 1.5 x 10(-10) m(2) s(-1). The model fits support the theory that pore diffusion is the rate-limiting process for sorption of pesticides in aggregates, although the diffusion coefficients were a factor 3-10 smaller than the theoretical diffusion coefficient for diffusion in water. Comparing the results from the different pesticide-soil combinations showed that the extent of nonequilibrium increased with increasing sorption strength. This confirmed that sorption takes longer to reach equilibrium for pesticides and soils with stronger sorption. The differences between the different pesticides and soils were fully accounted for in the model by stronger retardation of the more strongly sorbed pesticides. The results imply that diffusion into aggregates may be the major time-limiting process for sorption of pesticides in structured soils. Commonly performed sorption experiments with sieved soil fail to account for this process.

Topics: Adsorption; Atrazine; Diffusion; Kinetics; Methacrylates; Models, Chemical; Pesticides; Phenylurea Compounds; Porosity; Pyrimidines; Soil; Strobilurins; Time Factors

Pesticide leaching from soil has been shown to decrease with increasing time from application to irrigation. It is hypothesized that the availability of compounds for leaching decreases due to diffusion and sorption inside soil aggregates. Previous work showed that pesticide sorption inside soil aggregates increases significantly during the first days after application. The study presented here tested if diffusion into aggregates could explain the leaching of four aged pesticides from manually irrigated soil cores. Azoxystrobin, chlorotoluron, cyanazine, and bentazone were applied to 30 undisturbed cores (25 cm long, 23.7 cm diameter) from a clay loam soil. The soil cores were irrigated 1, 3, 7, 14, and 28 days after application. Leachate was collected and analyzed. The amount of pesticide found in leachate decreased rapidly with time from application. Pesticide losses in leachate declined 2.5-27 times faster than total residues in soil. The decline was 4-5 times faster for the more strongly sorbed pesticides (azoxystrobin, chlorotoluron, and cyanazine) than for bentazone. In previous work, we derived a model to describe sorption and diffusion of the pesticides in small aggregates from the same soil. The diffusion model was used here to describe sorption inside the large aggregates in the soil cores and extended to describe pesticide leaching by interaggregate flow. The model showed a significant decline in leaching with time from application, which supports the theory that diffusion-limited sorption in aggregates influences the availability for pesticide leaching, although it does not exclude alternative explanations for this decline. The model well described the decline in leaching for three out of four pesticides. The interaggregate transport model could, however, not account for the amount of preferential flow in the cores and underestimated the leaching of bentazone.

Topics: Benzothiadiazines; Environmental Monitoring; Humans; Methacrylates; Pesticides; Phenylurea Compounds; Pyrimidines; Soil Pollutants; Strobilurins; Triazines