Dissipation of mecoprop-P, isoproturon, bentazon and S-metolachlor in heavy metal contaminated acidic and calcareous soil before and after EDTA-based remediation.

The ability of contaminated farmland soils reclaimed by remediation to dissipate pesticides and thus to mitigate their unwanted environmental effects, i.e., leaching and run-off, was studied. Novel EDTA-based soil washing technology (EDTA and process waters recycling; no toxic emissions) removed 79 and 73% of Pb from acidic and calcareous soil with 740 and 2179 mg kg-1 Pb, respectively. The dissipation kinetics of four herbicides: mecoprop-P, isoproturon, bentazon and S-metolachlor was investigated under field conditions in beds with maize (Zea mays) and barley (Hordeum vulgare). The biphasic First-Order Multi-Compartment (FOMC) model was used to fit experimental data and calculate the herbicides' half-life (DT50) in soil. Remediation significantly (up to 64%) decreased dehydrogenase activity assessed as a marker of soil microbial activity and prolonged the DT50 of herbicides in acidic soils from 16% (isoproturon) to 111% (S-metachlor). Remediation had a less significant effect on herbicide dissipation in calcareous soils; i.e., mecoprop-P DT50 increased by 3%, while isoproturon and S-metachlor DT50 decreased by 29%. Overall, the dissipation from remediated soils was faster than the average DT50 of tested herbicides published in the Pesticides Properties DataBase. Results demonstrate that EDTA-based remediation of the studied soils does not pose any threat of extended herbicide persistence.

Retention and transport of mecoprop on acid sandy-loam soils.

Interaction with soil components is one of the key processes governing the fate of agrochemicals in the environment. In this work, we studied the adsorption / desorption and transport of mecoprop (methylchlorophenoxypropionic acid or MCPP) in four acid sandy-loam soils with different organic matter contents. Kinetics of adsorption and adsorption/desorption at equilibrium were studied in batch experiments, whereas transport was studied in laboratory columns. Adsorption and desorption were found to be linear or nearly-linear. The kinetics of mecoprop adsorption were relatively fast in all cases (less than 24h). Adsorption and desorption were adequately described by the linear and Freundlich models, with KF values that ranged from 0.7 to 8.8Ln µmol1-nkg-1 and KD values from 0.3 to 3.6Lkg-1. The results of the transport experiments showed that the retention of mecoprop by soil was very low (less than 6.2%). The retention of mecoprop by the soils in all experiments increased with organic matter content. Overall, it was observed that mecoprop was weakly adsorbed by the soils, what would result in a high risk of leaching of this compound in the environment.

Methods comparison, transport and distribution of polar herbicides in the Baltic Sea.

Two LC-MS/MS methods including different sample preparation and quantitative processes showed a good agreement for analysis of the herbicides MCPA, mecoprop, isoproturon, bentazon and chloridazon, and the metabolite chloridazon-methyl-desphenyl (CMD) in estuarine waters. Due to different sensitivity of the methods only one could be used to analyze marine samples. The transport of these compounds to the Baltic Sea via ten German estuaries and their distribution between coastal water and sediments was studied. The results showed that all selected compounds can be transported to the Baltic Sea (0.9-747ng/L). Chloridazon, bentazon, isoproturon and CMD were detected (0.9-8.9ng/L) in the coastal waters and chloridazon and isorproturon in the sediments (5-136pg/g d.w.). Levels of contaminants in the sediments could be influenced by the total organic carbon content. Concentrations observed in the Baltic Sea are most likely not high enough to cause acute effects, but long term effect studies are strongly recommended.

Photocatalytic ozonation of pesticides in a fixed bed flow through UVA-LED photoreactor.

In this study, a fixed bed flow through UVA-LED photoreactor was used to compare the efficiency of ozone, photocatalysis and photocatalysis-ozone degradation, and mineralization of two pure pesticides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), and a commercial one, Killex®. For the degradation of the parent compounds, ozone-based processes were more effective. While for mineralization, photocatalytic processes were more effective. Photocatalytic ozonation was the most efficient process for both the degradation and mineralization of the parent compounds. The degradation rates and mineralization by photocatalytic ozonation were higher than the summation of the corresponding rates by ozonation and photocatalysis, indicating a symbiotic relationship.Overall, the photocatalytic ozonation process with the fixed bed TiO2 reduces the time needed for the degradation and mineralization of the pesticides, reduces the costs of powder catalyst separation and overcomes the reduced efficiency of immobilized catalysts, which makes the process quite attractive for practical applications.

Agro-industrial waste: a low cost adsorbent for effective removal of 4-chloro-2-methylphenoxyacetic acid herbicide in batch and packed bed modes.

The present work describes the aqueous phase removal of 4-chloro-2-methylphenoxyacetic acid herbicide by rice husk ash (RHA) using batch and packed bed adsorption techniques. The effects of dosage, initial concentration, time, pH, temperature, and particle size of adsorbent in batch compared with effects of influent concentration, flow rate, and bed height in packed bed were studied. The particle size effect reveals that the removal is dependent on chemical composition (silica and carbon content) together with BET surface area of RHA. The aptness of Langmuir isotherm to batch data indicates the favorable adsorption whereas that of Temkin isotherm informs the heterogeneous nature of RHA. The kinetics of adsorption follows the pseudo-second order and Elovich models while thermodynamics of process indicates the exothermic adsorption. Among the models applied in packed bed study, the deactivation kinetic, Yoon-Nelson and bed depth service time (BDST) models are suitable to explain the packed bed adsorption. The adsorption capacity of RHA in packed bed study is found greater than that in batch. The adsorption capacity of RHA determined by the BDST model is 3019 mg/L for 90 % saturation of bed. The adsorption capacity of RHA based on weight is ∼2.3 times and that based on surface area is ∼55.55 times greater than that of granular activated carbon.

Selective and Sensitive Chemiluminescence Determination of MCPB: Flow Injection and Liquid Chromatography.

Two new chemiluminescence (CL) methods are described for the determination of the herbicide 4-(4-chloro-o-tolyloxy) butyric acid (MCPB). First, a flow injection chemiluminescence (FI-CL) method is proposed. In this method, MCPB is photodegraded with an ultraviolet (UV) lamp and the photoproducts formed provide a great CL signal when they react with ferricyanide in basic medium. Second, a high-performance liquid chromatography chemiluminescence (HPLC-CL) method is proposed. In this method, before the photodegradation and CL reaction, the MCPB and other phenoxyacid herbicides are separated in a C18 column. The experimental conditions for the FI-CL and HPLC-CL methods are optimized. Both methods present good sensitivity, the detection limits being 0.12 µg L(-1) and 0.1 µg L(-1) (for FI-CL and HPLC-CL, respectively) when solid phase extraction (SPE) is applied. Intra- and interday relative standard deviations are below 9.9%. The methods have been satisfactorily applied to the analysis of natural water samples. FI-CL method can be employed for the determination of MCPB in simple water samples and for the screening of complex water samples in a fast, economic, and simple way. The HPLC-CL method is more selective, and allows samples that have not been resolved with the FI-CL method to be solved.

Urea Fertilizer and pH Influence on Sorption Process of Flumetsulam and MCPA Acidic Herbicides in a Volcanic Soil.

The aim of this study was to evaluate the influence of urea fertilizer and pH on the sorption process of two acidic herbicides, flumetsulam (2',6'-difluoro-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonanilide) and MCPA (4-chloro--tolyloxyacetic acid), on an Andisol. Urea reduced the adsorption of MCPA but not that of flumetsulam. The Freundlich parameter of MCPA decreased from 8.5 to 5.1 mg L kg. This finding could be attributed to an increase in dissolved organic C due to an initial increase in soil pH for urea application. The higher acidic character of MCPA compared with that of flumetsulam produced a greater hydrolysis of urea, leading to a further pH increase. A marked effect of pH on the adsorption of both herbicides was observed. The organic C distribution coefficient () values for flumetsulam were in the range of 74 to 10 L kg, while those of MCPA were in the range of 208 to 45 L kg. In the kinetic studies, the pseudo-second-order model appeared to fit the data best ( > 0.994). The initial adsorption rates () ranged from 20.00 to 4.59 mg kg h for flumetsulam and from 125.00 to 25.60 mg kg hfor MCPA. Both herbicides were adsorbed rapidly during the first stage of the sorption process, and the rates of sorption were dependent on pH. The application of the Elovich and Weber-Morris models led us to conclude that mass transfer through the boundary layer and, to a lesser degree, intraparticle diffusion were influenced by the chemical character of the herbicide. These results suggest that urea application could increase leaching of acid herbicides in soils.

Imprinting of molecular recognition sites combined with π-donor-acceptor interactions using bis-aniline-crosslinked Au-CdSe/ZnS nanoparticles array on electrodes: Development of electrochemiluminescence sensor for the ultrasensitive and selective detection of 2-methyl-4-chlorophenoxyacetic acid.

A novel strategy is reported for the fabrication of bis-aniline-crosslinked Au nanoparticles (NPs)-CdSe/ZnS quantum dots (QDs) array composite by facil one-step co-electropolymerization of thioaniline-functionalized AuNPs and thioaniline-functionalized CdSe/ZnS QDs onto thioaniline-functionalized Au elctrodes (AuE). Stable and enhanced cathodic electrochemiluminescence (ECL) of CdSe/ZnS QDs is observed on the modified electrode in neutral solution, suggesting promising applications in ECL sensing. An advanced ECL sensor is explored for detection of 2-methyl-4-chlorophenoxyacetic acid (MCPA) which quenches the ECL signal through electron-transfer pathway. The sensitive determination of MCPA with limit of detection (LOD) of 2.2 nmolL(-1) (S/N=3) is achieved by π-donor-acceptor interactions between MCPA and the bis-aniline bridging units. Impressively, the imprinting of molecular recognition sites into the bis-aniline-crosslinked AuNPs-CdSe/ZnS QDs array yields a functionalized electrode with an extremely sensitive response to MCPA in a linear range of 10 pmolL(-1)-50 µmolL(-1) with a LOD of 4.3 pmolL(-1 ()S/N=3). The proposed ECL sensor with high sensitivity, good selectivity, reproducibility and stability has been successfully applied for the determination of MCPA in real samples with satisfactory recoveries. In this study, ECL sensor combined the merits of QDs-ECL and molecularly imprinting technology is reported for the first time. The developed ECL sensor holds great promise for the fabrication of QDs-based ECL sensors with improved sensitivity and furthermore opens the door to wide applications of QDs-based ECL in food safety and environmental monitoring.

Contamination of rice field water with sulfonylurea and phenoxy herbicides in the Muda Irrigation Scheme, Kedah, Malaysia.

The purpose of the present study was to investigate the potential risk of herbicide contamination (2,4-dichlorophenoxy (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA), metsulfuron, bensulfuron, and pyrazosulfuron) in the rice fields of the Muda Irrigation Scheme, Kedah, Malaysia. The study included two areas with different irrigation water sources namely non-recycled (N-RCL) and recycled (RCL) water. Periodic water sampling was carried out from the drainage canals during the planting period of the wet season 2006/2007 and dry season 2007. The HPLC-UV was used to detect herbicide residues in the water samples collected from the rice fields. The results showed that the concentration of sulfonylurea herbicides such as bensulfuron and metsulfuron in the rice field was 0.55 and 0.51 µg/L, respectively. The potential risk of contamination depended on the actual dosage of each herbicide applied by farmers to their rice fields. The potential risk of water pollution by the five herbicides studied in the area with RCL water tended to be more widespread compared to the area with N-RCL water due to surface water runoff with higher levels of weedicides to the surrounding areas. During the two seasons, 50-73% of the water samples collected from the area receiving RCL water contained the five herbicides studied at concentrations of more than 0.05 µg/L, and this percentage was higher than that from the areas receiving N-RCL water (45-69%). During the wet season, the overall total mean concentration of the eight herbicides found in the samples collected from the area with RCL water (6.27 µg/L) was significantly higher (P < 0.01) than that from the area receiving N-RCL water (2.39 µg/L). Meanwhile, during the dry season, there was no significant difference (P > 0.05) in the herbicide concentrations between the areas receiving RCL (6.16 µg/L) and N-RCL water (7.43 µg/L) water.

Environmental fate of the herbicide MCPA in agricultural soils amended with fresh and aged de-oiled two-phase olive mill waste.

Olive oil agrifood industry generates large amounts of waste whose recycling as organic amendment represents an alternative to their disposal. The impact of de-oiled two-phase olive mill waste (DW) on the fate of 4-chloro-2-methylphenoxyacetic acid (MCPA) in Mediterranean agricultural soils was evaluated. Furthermore, the effect of the transformation of organic matter from this waste under field conditions was assessed. Four Mediterranean agricultural soils were selected and amended in laboratory with fresh DW and field-aged DW (DW and ADW treatments, respectively). Adsorption capacity increased by factors between 1.18 and 3.59, for the DW-amended soils, and by factor of 4.93, for ADW-amended soil, with respect to unamended soils, when 5% amendment was applied. The DW amendment had inhibitory effect on dehydrogenase activity and slowed herbicide dissipation, whereas the opposite effect was observed in ADW treatments. In the field-amended soil, the amount of MCPA leached was significantly reduced from 56.9% for unamended soil to 15.9% at the 5% rate. However, leaching losses of MCPA increased in the laboratory-amended soils, because of their high water-soluble organic carbon values which could enhance MCPA mobility, especially in the acidic soils. Therefore, the application of DW as organic amendment in Mediterranean agricultural soils could be an important management strategy to reduce MCPA leaching, especially if the organic matter had been previously transformed by ageing processes.

Electrochemical sensor for simultaneous determination of herbicide MCPA and its metabolite 4-chloro-2-methylphenol. Application to photodegradation environmental monitoring.

The development and application of a polyaniline/carbon nanotube (CNT) cyclodextrin matrix (PANI-ß-CD/MWCNT)-based electrochemical sensor for the quantitative determination of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) and its main transformation product 4-chloro-2-methylphenol in natural waters are described. A simple cyclic voltammetry-based electrochemical methodology, in phosphate buffer solution at pH 6.0, was used to develop a method to determine both MCPA and 4-chloro-2-methylphenol, without any previous extraction or derivatization steps. A linear concentration range (10 to 50 µmol L(-1)) and detection limits of 1.1 and 1.9 µmol L(-1), respectively, were achieved using optimized cyclic voltammetric parameters. The proposed method was successfully applied to the determination of MCPA and 4-chloro-2-methylphenol in natural water samples with satisfactory recoveries (94 to 107%) and in good agreement with the results obtained by an established high-performance liquid chromatography technique, no significant differences being found between the methods. Interferences from ionic species and other herbicides used for broad-leaf weed control were shown to be small. The newly developed methodology was also successfully applied to MCPA photodegradation environmental studies.

The effects of woodchip- and straw-derived biochars on the persistence of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in soils.

Sorption and degradation are the primary processes controlling the efficacy and runoff contamination risk of agrochemicals. This study assessed the influence of two biochars, made from woodchips and straw at a pyrolysis temperature of 725°C and applied to a loamy sand and a sandy soil in the concentration of 5.3 g 100 g(-1) sandy soil and 4.1 g 100 g(-1) loamy sand soil, or 53 t ha(-1) for both soil types, on degradation of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA). Soils were spiked with 50 mg MCPA kg(-1) soil. In the sandy soil, significantly more MCPA remained after 100 days if amended with straw-derived biochar in comparison to wood-derived biochar. Both biochars types significantly increased urease activity (p<0.05) after 37 days in the loamy sand soil, but these differences disappeared after 100 days. A root and shoot elongation test demonstrated that the soils containing straw-derived biochar and spiked with MCPA, showed the highest phytotoxicity. Both biochars were found to retard MCPA degradation in loamy sand and sandy soils. This effect could not be explained only by sorption processes due to comparatively low developed micro/mesoporous structure of both biochars shown by BET surface analysis. However, an enhanced MCPA persistence and soil toxicity in sandy soil amended with straw biochar was observed and further studies are needed to reveal the responsible mechanisms.

Mecoprop (MCPP) removal in full-scale rapid sand filters at a groundwater-based waterworks.

Contamination by the herbicide mecoprop (MCPP) was detected in groundwater abstraction wells at Kerteminde Waterworks in concentrations up to 0.08µg/L. MCPP was removed to below detection limit in a simple treatment line where anaerobic groundwater was aerated and subsequently filtered by primary and secondary rapid sand filters. Water quality parameters were measured throughout the waterworks, and they behaved as designed for. MCPP was removed in secondary rapid sand filters--removal was the greatest in the sand filters in the filter line with the highest contact time (63 min). In these secondary sand filters, MCPP concentration decreased from 0.037 µg/L to below the detection limit of 0.01 µg/L. MCPP was removed continuously at different filter depths (0.80 m). Additionally, biodegradation, mineralisation and adsorption were investigated in the laboratory in order to elucidate removal mechanisms in the full-scale system. Therefore, microcosms were set up with filter sand, water and (14)C-labelled MCPP at an initial concentration of 0.2 µg/L. After 24 h, 79-86% of the initial concentration of MCPP was removed. Sorption removed 11-15%, while the remaining part was removed by microbial processes, leading to a complete mineralisation of 13-18%. Microbial removal in the filter sand was similar at different depths of the rapid sand filter, while the amount of MCPP which adsorbed to the filter sand after 48 h decreased with depth from 21% of the initial MCPP in the top layer to 7% in the bottom layer. It was concluded that MCPP was removed in secondary rapid sand filters at Kerteminde Waterworks, to which both adsorption and microbial degradation contributed.

Modeling of pH-dependent adsorption and leaching of MCPA in profiles of Polish mineral soils.

This study aimed to determine the leaching potential of MCPA and the contribution of major soil components to its retention in 27 profiles of common Polish arable soils. Results of experiments and modeling of the pH-dependent adsorption indicated that the adsorption of the neutral and anionic forms of MCPA on soil organic matter are the predominant adsorption mechanisms, even in soil horizons with very low organic matter contents. The third most important mechanism was the adsorption of MCPA anions, most likely through the water bridging mechanism on sorption sites created by exchangeable Fe cations adsorbed in soil. It was found that in acidic soils with very low organic matter contents, the neutral form of MCPA was also adsorbed on the quartz and silica sorption sites of silt and sand. The value of r(2) was 78% when it was assumed that MCPA was adsorbed only on organic matter and 93% when all indicated mechanisms of adsorption on mineral soil components were included in the model fitted to data from all soil profiles. Simulations using FOCUS PELMO indicated that in two profiles, the 80th percentiles of the average yearly concentrations of MCPA in the leachate exceeded the European Union (EU) contamination limit of 0.1 µgL(-1). It was shown that when an assumption was made in the model of pH-dependent adsorption that MCPA was adsorbed only on organic matter, the leaching potential of MCPA was overestimated in the examined soils. Much better predictions were obtained when adsorption on mineral soil components was also included in the model.

Possible source term of high concentrations of mecoprop-p in leachate and water quality: impact of climate change, public use and disposal.

Mecoprop-p herbicide is often found in wells and water abstractions in many areas around Europe, the UK inclusive. There is a growing environmental and public health concern about mecoprop-p herbicide pollution in ground and surface water in England. Reviews suggest that extensive work has been carried out on the contribution of mecoprop-p herbicides from agricultural use whilst more work needs to be carried out on the contribution of mecoprop-p herbicide from non-agricultural use. The study covers two landfill sites in Weaver/Gowy Catchment. Mecoprop-p herbicide concentrations in the leachate quality range between 0.06 and 290 microg l1 in cells. High concentration ofmecoprop-p herbicide in the leachate quality suggests that there is a possible source term in the waste stream. This paper addresses the gap by exploring possible source terms of mecoprop-p herbicide contamination on landfill sites and evaluates the impact of public purchase, use and disposal alongside climate change on seasonal variations in mecoprop-p concentrations. Mecoprop-p herbicide was found to exceed the EU drinking water quality standards at the unsaturated zone/aquifer with observed average concentrations ranging between 0.005 and 7.96 microg l1. A route map for mecoprop-p herbicide source term contamination is essential for mitigation and pollution management with emphasis on both consumer and producer responsibility towards use of mecoprop-p product. In addition, improvement in data collection on mecoprop-p concentrations and detailed seasonal herbicide sales for non-agricultural purposes are needed to inform the analysis and decision process.

An unusual case of non-fatal poisoning due to herbicide 4-chloro-2-methyl phenoxyacetic acid (MCPA).

MCPA (4-chloro-2-methyl phenoxyacetic acid) is a systemic hormone-type selective herbicide readily absorbed by leaves and roots. Use of MCPA for murder or attempted murder is very rare in Sri Lanka. However, a reported case of attempted murder by adding MCPA to water will be discussed in this paper. Three extraction methods were carried out with urine samples spiked with MCPA, namely liquid-liquid extraction with chloroform, solid phase extraction using C18 cartridges and vortex mixing with methanolic hydrochloric acid. Based on the recovery results, solid phase extraction was selected as the most suitable method and applied in the analysis of urine and water samples. Identification of MCPA in urine, water and the suspected poison bottle was carried out by HPLC and was confirmed by GC-MS. 4-chloro -2- methyl phenol metabolite was also identified and confirmed in the urine sample of the patient by GC-MS. Quantitative analysis of MCPA was carried out by HPLC using a validated method where Zorbax XDB-C18 column was used with photo diode array detector. In this case, presence of MCPA in one patient's urine sample collected four days after the incident was confirmed by GC-MS and found at a concentration of 0.83µg/ml. MCPA was not identified in the urine samples collected after 13 days in other three patients. The water sample taken from the suspected water storage tank found to contain 101µg/ml of MCPA. The results showed that HPLC combined with GC-MS is suitable for forensic analysis of MCPA in urine.

Estimation of the validation parameters for a fast analysis of herbicide residues by LC-MS/MS.

Due to strict regulatory requirements for pesticide residue analysis, only the results of residue analysis with acceptable quality should be reported. As a consequence proper validation of the measurement method is required. In this context, accuracy, precision, specificity, limit of determination (LOQ), matrix effect, linearity, uncertainty calculation and ruggedness become increasingly important. This paper reports a description of the validation parameters of a fast method for the determination of five phenoxy acid herbicides (2,4-D, MCPA, MCPP, haloxyfop and fluazifop) in food crops. The recoveries were performed in the concentration range from 0.05 to 0.5 mg kg⁻¹ for apples, pears, carrots and celeriac with five replicates at each level. The mean recoveries ranged from 70% to 95% for all crops. The precision of the method expressed as a relative standard deviation (RSD%) was found to be in the range 3-14%. For all herbicides, the linearity response of the detector was tested by correlation coefficients (r² > 0.99) in the concentration range from 0.05 to 0.5 mg kg⁻¹. The LOQ was determined as the lowest spiked level meeting the requirement of accuracy (70-120%) and precision (RSD% < 20% according to European Union guidelines. The uncertainty and robustness were calculated. On the basis of the results, the method can be considered fast, simple and robust and is suitable to be applied to the analysis of studied herbicides in routine testing laboratories.

Chiral and isotope analyses for assessing the degradation of organic contaminants in the environment: Rayleigh dependence.

The Rayleigh equation is frequently used to describe isotope fractionation as a function of conversion. In this article we propose to draw a parallel between isotope and enantiomeric enrichments and derive a set of conditions that allow the use of the Rayleigh approach to describe the enantiomeric enrichment-conversion dependencies. We demonstrate an implementation of the Rayleigh equation for the enantioselective enzymatic hydrolysis of Mecoprop-methyl, Dichlorprop-methyl, and dimethyl-methylsuccinate by lipases from Pseudomonas fluorescens, Pseudomonas cepacia, and Candida rugosa. The data obtained for all the studied reactions gave good fits to the Rayleigh equation, with a linear regression R(2) > 0.96. In addition to that, our analysis of four microcosm studies on the hydrolysis of the individual enantiomers of Dichloroprop methyl, Lactofen, Fenoxaprop-ethyl, and Metalaxyl reported in the literature by other research groups revealed a suitability of the Rayleigh dependence. Two dimensional plots describing the isotope fractionation versus enantiomeric enrichment are demonstrated for all studied cases. Processes not accompanied by enantiomeric enrichment (acid and base hydrolysis) and by isotope enrichment (transesterification) are demonstrated, their 2-D plots are either horizontal or vertical which can illuminate concealed degradation pathways.

Fast, simple and efficient supramolecular solvent-based microextraction of mecoprop and dichlorprop in soils prior to their enantioselective determination by liquid chromatography-tandem mass spectrometry.

A simple, sensitive, rapid and economic method was developed for the quantification of enantiomers of chiral pesticides as mecoprop (MCPP) and dichlorprop (DCPP) in soil samples using supramolecular solvent-based microextraction (SUSME) combined with liquid chromatography coupled to mass spectrometry (LC-MS/MS). SUSME has been described for the extraction of chiral pesticides in water, but this is firstly applied to soil samples. MCPP and DCPP are herbicides widely used in agriculture that have two enantiomeric forms (R- and S-) differing in environmental fate and toxicity. Therefore, it is essential to have analytical methods for monitoring individual DCPP and MCPP enantiomers in environmental samples. MCPP and DCPP were extracted in a supramolecular solvent (SUPRAS) made up of dodecanoic acid aggregates, the extract was dried under a nitrogen stream, the two herbicides dissolved in acetate buffer and the aqueous extract directly injected in the LC-MS/MS system. The recoveries obtained were independent of soil composition and age of herbicide residues. The detection and quantitation limits of the developed method for the determination of R- and S-MCPP and R- and S-DCPP in soils were 0.03 and 0.1 ng g(-1), respectively, and the precision, expressed as relative standard deviation (n=6), for enantiomer concentrations of 5 and 100 ng g(-1) were in the ranges 4.1-6.1% and 2.9-4.1%. Recoveries for soil samples spiked with enantiomer concentrations within the interval 5-180 ng g(-1) and enantiomeric ratios (ERs) of 1, 3 and 9, ranged between 93 and 104% with standard deviations of the percent recovery varying between 0.3% and 6.0%. Because the SUPRAS can solubilize analytes through different type of interactions (dispersion, dipole-dipole and hydrogen bonds), it could be used to extract a great variety of pesticides (including both polar and non-polar) in soils.

Does microbial centimeter-scale heterogeneity impact MCPA degradation in and leaching from a loamy agricultural soil?

The potential for pesticide degradation varies greatly at the centimeter-scale in agricultural soil. Three dimensional numerical simulations were conducted to evaluate how such small-scale spatial heterogeneity may affect the leaching of the biodegradable pesticide 2-methyl-4-chlorophenoxyacetic acid (MCPA) in the upper meter of a variably-saturated, loamy soil profile. To incorporate realistic spatial variation in degradation potential, we used data from a site where 420 mineralization curves over 5 depths have been measured. Monod kinetics was fitted to the individual curves to derive initial degrader biomass values, which were incorporated in a reactive transport model to simulate heterogeneous biodegradation. Six scenarios were set up using COMSOL Multiphysics to evaluate the difference between models having different degrader biomass distributions (homogeneous, heterogeneous, or no biomass) and either matrix flow or preferential flow through a soil matrix with a wormhole. MCPA leached, within 250 days, below 1m only when degrader biomass was absent and preferential flow occurred. Both biodegradation in the plow layer and the microbially active lining of the wormhole contributed to reducing MCPA-leaching below 1m. The spatial distribution of initial degrader biomass within each soil matrix layer, however, had little effect on the overall MCPA-leaching.