Pesticide adsorption on a calcareous soil modified with sewage sludge and quaternary alkyl-ammonium cationic surfactants

BACKGROUND, AIM AND SCOPE: Pesticides are often found in soil as a result of their application to control pests. They can be transported on soil particles to surface waters or they can lixiviate and reach other environmental compartments. Soil modification with amendments, such as sewage sludge, and with surfactants, h been proposed to reduce pesticide environmental fate. METHODS: The sorption of atrazine, methidathion and diazinon using the batch technique has been studied on non-modified soil and soil modified with sewage sludge and cationic surfactants, as well as the effect of their addition on soil properties such as organic carbon (OC) content and exchange cations. RESULTS AND DISCUSSION: The OC content of the surfactant modified soils was the highest with the surfactant with the longest hydrocarbon chain (hexadecyltrimethyl ammonium bromide, HDTMA). The results of the OC content run in parallel with the increase in pesticide retention. When the sorption was n malized to soil OC content, the retention induced by addition of HDTMA was still the highest, which is an indication that the organic matter derived from the organic cations is a more effective medium to retain dissolved contaminants, than organic matter from native soil. The addition of sewage sludge to the soil did only result in a slight increase of the soil CEC and, hence, moderately affected the ability of the cationic surfactant to retain the pesticides. CONCLUSIONS: The addition of cationic surfactants to soil would possibly reduce the movement to groundwater of atrazine, methidathion and diazinon. In the case of HDTMA, the decrease in sorption at high surfactant loadings was very slow, being that the surfactant was able to retain the pesticides at concentration values which clearly exceeded the monolayer coverage. RECOMMENDATIONS AND PERSPECTIVES: Contamination by pesticides, which are present in the soil due to their direct input in this medium or to spills or illegal tipping, may be hindered from migration to groundwater by application of a cationic surfactant.     

Effects of biochar on the emissions,soil distribution,and nematode control of 1,3-dichloropropene

Emissions of volatile soil fumigant 1,3-dichloropropene (1,3-D) from soil to air are a significant concern in relation to air quality, and cost-effective strategies to reduce such emissions are urgently required by growers to help them comply with increasingly stringent regulations. In this work, application of a rice husk-derived biochar to the surface of a sandy loam soil chamber reduced soil–air emissions of 1,3-D from 42% in a control (no biochar) to 8% due to adsorption onto the biochar. This adsorbed 1,3-D showed a potential for re-volatilization into air and solubilization into the soil–liquid phase. Biochar at the soil surface also reduced soil–gas concentrations in the upper soil; based on the determination of concentration–time values, this may limit 1,3-D-induced nematode control in the upper soil. In batch studies, the mixing of biochar into the soil severely limited nematode control; 1,3-D application rates around four times greater than the maximum permissible limit would be required to give nematode control under such conditions. Therefore, the use of biochar as a surface amendment, while showing an emission reduction benefit, may limit pest control during subsequent fumigations if, as seems probable, it is plowed into the soil.     

Chitosan/glyphosate formulation as a potential,environmental friendly herbicide with prolonged activity

Although there are many reports on the dangers posed by glyphosate, this herbicide is still one of the most popular and widely used total weed killers. Therefore, great effort should be made to minimize exposure to this herbicide and limit its losses into the environment. The aim of this study was to prepare a new formulation consisted of various molecular weight chitosans with glyphosate and their evaluation toward active substance release, phytotoxicity, and preliminary herbicidal efficiency. The phytotoxicity study of the obtained chitosan/glyphosate formulations was determined based on the Organisation for Economic Co-operation and Development 208 guideline. Among all tested formulations evaluated for phytotoxicity, that containing the highest molecular weight of chitosan was found to be the least toxic, showing simultaneously the most effective herbicidal activity against selected weeds. The release rate of glyphosate from the obtained formulations was dependent on the molecular weight and viscosity of chitosan.     

Controlled release formulations of metribuzin: Release kinetics in water and soil

Controlled release (CR) formulations of metribuzin in Polyvinyl chloride [(PVC) (emulsion)], carboxy methyl cellulose (CMC), and carboxy methyl cellulose-kaolinite composite (CMC-KAO), are reported. Kinetics of its release in water and soil was studied in comparison with the commercial formulation (75 DF). Metribuzin from the commercial formulation became non-detectable after 35 days whereas it attained maxima between 35–49 days and became non-detectable after 63 days in the developed products. Amongst the CR formulations, the release in both water and soil was the fastest in CMC and slowest in PVC. The CMC-KAO composite reduced the rate of release as compared to CMC alone. The diffusion exponent (n value) of metribuzin in water and soil ranged from 0.515 to 0.745 and 0.662 to 1.296, respectively in the various formulations. The release was diffusion controlled with half release time (t_1/2) from different controlled release matrices of 12.98 to 47.63 days in water and 16.90 to 51.79 days in soil. It was 3.25 and 4.66 days, respectively in the commercial formulation. The period of optimum availability of metribuzin in water and soil from controlled released formulations ranged from 15.09 to 31.68 and 17.99 to 34.72 days as against 5.03 and 8.80 days in the commercial formulation.     

Metabolic fate of the 14C-labeled herbicide clodinafop-propargyl in a sediment–water system

The metabolic fate of ¹⁴C-phenyl-labeled herbicide clodinafop-propargyl (¹⁴C-CfP) was studied for 28 days in lab assays using a sediment–water system derived from a German location. Mineralization was 5.21% of applied ¹⁴C after 28 days exhibiting a distinct lag phase until day 14 of incubation. Portions of radioactivity remaining in water phases decreased at moderate rate to 18.48% after 28 days; 62.46% were still detected in water after 14 days. Soxhlet extraction of the sediment using acetonitrile released 35.56% of applied ¹⁴C with day 28, while 33.99% remained as non-extractable residues. A remarkable increase of bound ¹⁴C was observed between 14 and 28 days correlating with the distinct increase of mineralization. No correlation was found throughout incubation with microbial activity of the sediment as determined by dimethyl sulfoxide reduction. Dissolved oxygen and pH value of water phases remained almost constant for 28 days. Analyses of Soxhlet extracts of the sediment and ethyl acetate extracts of water phases by radio-TLC and radio-HPLC revealed that CfP was rapidly cleaved to free acid clodinafop (Cf), which was further (bio-) transformed. DT₅₀ values (based on radio-HPLC) were below 1 day (CfP) and slightly above 28 days (Cf). Further metabolites were not detected. Fractionation of humic and non-humic components of the sediment demonstrated that CfP's non-extractable residues were predominantly associated with fulvic acids up to 14 days of incubation (3.36%), whereas after 28 days, the majority of radioactivity was found in the humin/mineral fraction (13.30% of applied ¹⁴C). Due to high-performance size-exclusion chromatography of the fulvic acids fraction derived from assays incubated for 28 days, this portion of ¹⁴C was firmly, possibly covalently bound to fulvic acids and did not consist of CfP or Cf. Using an isolation strategy comprising preincubation of sediment with CfP and mineralization of ¹⁴C-CfP as criterion, a microorganism was isolated from the sediment examined. It grew on ¹⁴C-CfP as sole carbon source with evolution of ¹⁴CO₂. The bacterium was characterized by growth on commonly used carbon sources and 16S rDNA sequence analysis. Its sequence exhibited high similarity with that of Nocardioides aromaticivorans strain H-1 (98.85%; DSM 15131, JCM 11674).     

Aerobic degradation of diuron by aquatic microorganisms

Abstract

Degradation of diuron [3‐(3,4‐dichlorophenyl)‐l,1‐dimethyl‐urea] by microorganisms obtained from pond water and sediment was determined under aerobic conditions. Enrichment procedures were used to isolate cultures capable of degrading the herbicide. Several mixed fungal/bacterial and mixed bacterial cultures were isolated that could degrade diuron. The mixed cultures degraded 67–99% of the added diuron forming from six to seven products which were separated via TLC. The major degradation product detected in most culture extracts was 3,4‐dichloroaniline. Other identified products formed were 3‐(3,4‐dichlorophenyl)‐1‐methylurea and 3‐(3,4‐dichlorophenyl)urea.     

Field calibration of surface: A model of agricultural chemicals in surface waters

Abstract

Agricultural chemicals sporadically occur at detectable levels in the surface waters of intensively farmed watersheds. HSPF, a previously released model of agricultural chemicals in surface water, had been used to predict concentrations which were much higher (10 X) than those actually observed during monitoring studies. A new model, SURFACE, is described here which is much simpler than HSPF and gives better predictions of surface water concentrations. SURFACE uses PRZM, an EPA model, to calculate edge‐of‐field runoff losses and simple hydraulic routing algorithms to determine concentrations at the bottom of large river basins. In water systems sampled during 1985 and 1986, SURFACE predictions of annualized mean concentrations for alachlor, atrazine, cyanazine and metolachlor were within 0.09 ppb half of the time.     

Effects of glyphosate on the non-target leaf beetle Cerotoma arcuata (Coleoptera: Chrysomelidae) in field and laboratory conditions

This study aimed to assess the glyphosate application effects on the Cerotoma arcuata Oliver (Coleoptera: Chrysomelidae) population in glyphosate-resistant soybean crops. Field studies were conducted with glyphosate and the insecticide endosulfan to observe the effects of these pesticides on C. arcuata, on its damages in the crop and on the populations of natural enemies in glyphosate-resistant soybean crops. Moreover, the lethal and behavioral sublethal response of C. arcuata to glyphosate and endosulfan was conducted in the laboratory. The results of the field and laboratory experiments showed that glyphosate caused moderate toxicity and high irritability in C. arcuata and that endosulfan caused high toxicity and irritability. Therefore, the direct effect of glyphosate on C. arcuata was negative and does not explain the population increases of this pest in glyphosate-resistant soybean. However, the glyphosate also decreased the density of predators. Thus, the negative effect of glyphosate on the predators may be related to population increases of C. arcuata in glyphosate-resistant soybean crops, however, more studies are needed to better evidence this relationship. This study suggests that glyphosate can impact other non-target organisms, such as herbivorous insects and natural enemies and that the use of this herbicide will need to be carefully stewarded to prevent potential disturbances in beneficial insect communities in agricultural systems.     

Effect on herbicide adsorption of organic forestry waste products used for soil remediation

Organic soil amendments can be useful for improving degraded soil, but this increase in organic matter (OM) may influence adsorption of herbicides subsequently applied to the treated soil, even though the particle size of amendments and their nature differ from typical soil OM. In this study, a batch equilibrium method was used to measure adsorption of five herbicides following application to two organic media, wood pulp and sawdust, comparing these with two cropping soils. Herbicide adsorption, quantified by distribution coefficients (k_d), was much higher in the two organic media than in the cropping soils. The increases in adsorption were strongly correlated to the percentage of organic carbon. When the k_d was normalized to adsorption coefficients corrected for OM content (k_oc), variation in results between the media was greatly reduced, indicating that OM is an important factor influencing adsorption in these media. The results of this study suggest that herbicides will be less effective when applied to soils in which sawdust and wood pulp have been added. Using organic amendments to remediate soil will increase adsorption of pesticides, reducing their bio-availability and efficacy, but also reducing their tendency to leach into root zones of deep-rooted crops and into groundwater.