Concentrations Of Metalaxyl Research Articles

Assessment of Metalaxyl migration through vadose zone of alluvial sandy soil using column experiment and HYDRUS numerical modeling

Contemporary research on pesticides/fungicides as potential sources of groundwater contamination, including their migration pathways, especially in the Western Bengal basin (WBB), is scarce. The present research intends to study the vulnerability of groundwater towards pollution from metalaxyl. Metalaxyl is a fungicide added anthropogenically to the sandy soil of WBB for the cultivation of crops like tomatoes, potatoes and mustard. The study explores the mechanics of metalaxyl adsorption in soil and its migration to the associated groundwater system. Chemical analyses show high concentrations of metalaxyl within groundwater (472.9 μg/L, maximum amount) from the study area (Nadia district of WBB). The groundwater ubiquity score of metalaxyl (4.6) depicts that it is very much prone to leach through the sandy soils of WBB to the underlying groundwater system. The results of column leaching experiments and their congruence to the findings of numerical modelling study using HYDRUS software confirm the fact. The adsorptive resilience of the studied soils towards metalaxyl is insignificant (soils of North Chandmari (S1) =0.1087 mg/g, Ghoragacha (S2) =0.21 mg/g, and Khaldarpara (S3) =1.771 mg/g). However, the presence of excess iron concentration may enhance the adsorptive capacity of the soil toward Metalaxyl, thereby limiting its migration toward the zone of saturation.

Pharmacokinetics and residue elimination of metalaxyl enantiomers in snakehead (Channa argus)

Metalaxyl is widely used as a racemic mixture to control various plant and aquatic animal diseases caused by fungal infection. It has been proved that the two enantiomers of metalaxyl have significant differences in activity and toxicity, while little is known about the pharmacokinetics and residual elimination of the individual enantiomers of metalaxyl in aquatic animals. In this study, a simple, sensitive and reliable chiral liquid chromatography-tandem mass spectrometry method was established for the determination of metalaxyl and its metabolite metalaxyl acid enantiomers, which was applied to study the stereoselective pharmacokinetics and residue elimination of individual enantiomers in snakehead (Channa argus). The snakehead was bath administered with the racemic metalaxyl and the highly active enantiomeric R-metalaxyl, respectively. The results showed that the elimination of metalaxyl in the plasma and tissues of snakehead was enantioselective. The concentration of metalaxyl in tissues was kidney > liver > muscle, and preferential degradation of the R-metalaxyl enantiomer was observed in three tissues. However, no transformation between metalaxyl enantiomers was observed in snakehead plasma and tissues when R-metalaxyl enantiomer was administered. In addition, the distribution of metalaxyl acid enantiomers in tissues is closely related to the parent compound metalaxyl, and S-metalaxyl acid was only observed in the kidney and slowly eliminated. The highest concentrations of both metalaxyl and metalaxyl acid were observed in the kidney, suggesting that kidney is the major site of metalaxyl metabolism in snakehead. Given that the highly active R-metalaxyl has a shorter half-life and does not undergo transformation between enantiomers in snakehead, it may be a better choice to use R-metalaxyl instead of racemic metalaxyl in clinical practice. The results are helpful to understand the detailed fate of metalaxyl enantiomers and should be considered in future aquaculture, environmental pollution risk and food safety evaluations.

The Study of the Kinetics of Metalaxyl Accumulation and Dissipation in Durian (Durio zibethinus L.) Leaf Using High-Performance Liquid Chromatography (HPLC) Technique.

Metalaxyl is an effective approach to control Phytophthora palmivora infection in durian plantation. However, inappropriate metalaxyl usage may increase production cost, pathogen with fungicide resistance, and environmental toxicity. This study established and validated a simple and reproducible procedure to measure metalaxyl concentration in the durian leaf using HPLC. Linearity of the detection ranged from 1–100 µg/mL. The limits of detection (LOD) and quantification (LOQ) were 0.27 and 0.91 µg/mL, respectively. The extraction method gave recovery rates ranging from 88% to 103%. Durian seedlings were treated with 4 g/L metalaxyl either by foliar spray or soil drench. The highest metalaxyl accumulation in durian leaf was found between 6–24 h after treatment and persisted above its effective concentration at least 60 days after foliar application. The dissipation pattern fit to a first-order kinetics equation showed a half-life of 16.50 days. Soil drenching led to eight times higher metalaxyl concentrations in plants than foliar spraying and caused plant death within 15 days after application. These results suggest that foliar spraying of 4 g/L metalaxyl or soil drenching at a lower concentration every two months is sufficient in controlling P. palmivora infection in durian seedlings.

The different toxic effects of metalaxyl and metalaxyl-M on Tubifex tubifex

Metalaxyl and Metalaxyl-M are the fungicides that widely used in many countries. In this study, the environmental behaviors between metalaxyl and metalaxyl-M in Tubifex tubifex (T. tubifex) were quantitative analyzed by using a high performance liquid chromatography with photo-diode-array-detector (HPLC-DAD). Results demonstrated that there was no significant difference (p > 0.05) in the concentration of metalaxyl and metalaxyl-M in T. tubifex during the exposure process. However, the dissipation behaviors of metalaxyl and metalaxyl-M in T. tubifex were different (p < 0.05) during the non-exposure culture process. Meanwhile, the toxic effects were also evaluated by comparing the different influences of these two compounds on related physiological indicators, and functional enzyme activities. The survival rates of T. tubifex were 63.33 ± 15.28% (20 mg L−1), 63.33 ± 5.77% (200 mg L−1) treated with metalaxyl and were 50.00 ± 10.00% (20 mg L−1), 46.67 ± 11.55 (200 mg L−1) treated with metalaxyl-M at the non-exposure culture process. The autotomy rates were increased significantly compared with the initial in all treatments. Besides, the activities of CAT, SOD, and GST in T. tubifex were also inhibited by metalaxyl and metalaxyl-M treatments. Finally, the high-throughput transcriptome sequencing technology was applied to investigate the metabolic pathways of target analytes in T. tubifex, and results proved that the metabolic pathways associated with human diseases (such as viral myocarditis) were up-regulated expression for metalaxyl and metalaxyl-M treatments, and metalaxyl-M up-regulated more significantly. All the results demonstrated that metalaxyl-M had a higher toxicity than metalaxyl on T. tubifex.

Preparation and photocatalytic performance of reduced graphene oxide/ ZnO nanocatalyst for degradation of metalaxyl from aqueous solution: effect of operational parameters, mineralisation and toxicity bioassay

ABSTRACT A heterogeneous photocatalyst, ZnO/reduced graphene oxide (ZnO/rGO or ZG), was synthesised for the photocatalytic degradation of metalaxyl (MX) in aqueous solutions under UV irradiation. The characteristics of the prepared catalyst were determined by FTIR, XRD, FE-SEM, EDS, and BET analyses. The effect of various parameters such as solution pH, catalyst concentration, rGO loading in the catalyst structure, MX concentration and UV light intensity on the photodegradation of MX was investigated. The concentration of MX and the toxicity of the intermediates were determined by HPLC and the Daphnia Magna toxicity test, respectively. The effect of the water anions and radical scavenger compounds on the MX removal process was studied as well. The rate of mineralisation was determined by measuring the total organic carbon (TOC) value using the TOC analyser. The efficiency of the degradation process was compared with the real sample of agricultural drainage and deionised water. At optimum conditions (pH = 7, catalyst loading = 10%, catalyst concentration = 0.75 g/l, MX concentration = 10 mg/l, and UV intensity = 220 MW/cm2), the removal and mineralisation rates were 90.25% and 51.17% after 120 min, respectively. Reactive species scavenging experiments showed that the hole was the most effective factor for MX degradation in the ZG/UV process. The MX degradation rate in real agricultural run-off samples showed that the degradation efficiency was 50.42%, which was significantly lower than that of the synthetic samples. The toxicity bioassay by D. Magna indicated that the toxicity of MX was reduced from 51.22 to 15.17 after 96 h during the ZnO/rGO process. The photocatalytic efficiency decreased in the presence of phosphate and nitrate ions but did not change much in the presence of other water anions. Thus, the ZG/UV process can be effectively used for the degradation of organic pollutants, especially pesticides in wastewater.

Efficiency of Candida tropicalis for Potential Degradation of Metalaxyl in the Aqueous Media

Biodegradation of pesticides by bacteria, fungi, algae, and other organisms is an eco-friendly, efficient, and economical method of detoxification. This study was conducted to evaluate the efficiency of Candida tropicalis for potential degradation of metalaxyl in the aqueous media. The yeast fungus from soil with a historical application of metalaxyl has been isolated. The identification of isolated fungus was carried out using 28S rRNA. The effect of pH, temperature, and metalaxyl concentration on the growth of C. tropicalis and its ability for metalaxyl degradation was also investigated. The isolated fungus was identified as C. tropicalis based on the sequencing of D1D2 region of the 28S rRNA and BLAST search of the nucleotide sequences. The growth of C. tropicalis in the presence of metalaxyl was significantly higher than in the absence of it. A temperature of 30°C, a pH value of 7, and metalaxyl concentration of 5mg/L were the optimal conditions for C. tropicalis to grow and to obtain the highest degradation rate of metalaxyl. At the optimum conditions, the degradation rate and the half-life value of metalaxyl were 0.065 d-1 and 10.7days, respectively. Under the optimum conditions, a 98% degradation of metalaxyl initial concentration obtained within 36days. This report is novel in showing the biodegradation of metalaxyl in water by the yeast C. tropicalis, which can be a promising method in this regard.

Photocatalytic degradation of a typical agricultural chemical: metalaxyl in water using TiO2 under solar irradiation

The photodegradation and mineralization of the metalaxyl [methyl N-(2,6-dimethyl-phenyl)-N-(methoxyacetyl)-alaninate], which is a popular benzenoid fungicide, was conducted in the presence of TiO2 photocatalyst under solar irradiation. An initial metalaxyl concentration of 50 ppm was completely degraded in presence of TiO2 after 30 min irradiation, while no degradation was observed in absence of TiO2 under solar irradiation. The effect of different parameters, such as amount of TiO2, initial pH, light intensity, reaction temperature and irradiation time, on the photocatalytic degradation of metalaxyl was evaluated. The drop of total organic carbon as a consequence of mineralization of metalaxyl was detected during the photocatalytic process. The kinetics of photocatalytic degradation followed a pseudo-first order law according to Langmuir–Hinshelwood model, and the rate constant was 0.105 min−1. Ammonium ion and CO2 were speculated as the end-products after completing degradation of metalaxyl. The five types of intermediate products were identified by GC–MS during the decomposition of metalaxyl. In order to investigate the degradation pathway of metalaxyl, the point charge and frontier electron density at each atom on the molecule were determined by using MOPAC stimulation. The degradation mechanism was proposed from the identified intermediates. The solar photocatalytic degradation method can become an effective technique for the treatment of metalaxyl-polluted water.

Visible-light-driven photocatalytic degradation of Metalaxyl by reduced graphene oxide/Fe3O4/ZnO ternary nanohybrid: Influential factors, mechanism and toxicity bioassay

A heterogeneous photocatalyst, reduced graphene oxide (rGO)/Fe3O4/ZnO (GFZ) nanocatalyst, was synthesized for the oxidative degradation of Metalaxyl (MX) in aqueous solution under Vis-light irradiation. For the characterization of the synthesized catalyst FTIR, XRD, FE-SEM, EDS, BET, VSM, PL spectra and UV–Vis DRS techniques were applied. The influence of operating parameters, including solution pH, catalyst concentration, ZnO percentage in the catalyst structure, MX concentration and Vis-light intensity on the oxidative degradation of MX was studied. A probable mechanism for the degradation of MX was also proposed. Reusability, stability, intermediate products identification and quenching studies were done too. Under optimized conditions, the degradation and mineralization rates of MX were obtained 92.11 and 51.38% within 120 min, respectively. The ROS scavenging experiments confirmed the participation of •OH and O2•− radicals as reactive species in the oxidation process. Degradation rate in the presence of scavenger agents was decreased in order of t-BuOH > BQ > EDTA-2Na > AgNO3. Therefore, •OH radicals were the main species in the oxidation process. MX degradation rate in real agricultural runoff sample was 58.3%, which has been lower than that of deionized water. The kinetic experiments were in good agreement with pseudo-first-order kinetic model. The GFZ catalyst showed a good reusability after five successive runs. The toxicity bioassay by D. Magna showed that the toxicity of MX significantly decreased in the GFZ/Vis process. Finally, the application of GFZ catalyst under Vis-light for the degradation of organic materials, such as pesticides in wastewater seems to be a practical and effective process because the GFZ catalyst exhibits excellent catalytic activity and can be easily recovered from aqueous solutions.

Simultaneous determination and risk assessment of metalaxyl and azoxystrobin in potato by liquid chromatography with tandem mass spectrometry.

A liquid chromatography with tandem mass spectrometry method was developed and validated to simultaneously determine metalaxyl and azoxystrobin in soil, potato, and potato foliage samples. The samples were extracted by 20mL of acetonitrile and purified with dispersive solid-phase extraction using octadecyl silane as sorbent. The method showed good linearity (determination coefficients ≥ 0.9926) for metalaxyl (2.5-500ng/mL) and azoxystrobin (5-1000ng/mL). The limits of detection and quantification for both fungicides were 1.5-20μg/kg. The average recoveries in soil, potato, and potato foliage were 83.07-92.87% for metalaxyl and 82.71-98.53% for azoxystrobin. The intra- and inter-day relative standard deviations were all less than 9%. The method was successfully applied on the residual analysis of metalaxyl and azoxystrobin in field trial samples. The results showed that the concentrations of metalaxyl and azoxystrobin in potato samples collected from Guizhou and Hunan were below 50 and 100μg/kg (maximum residue limit set by China), respectively, at 5days after the last application. When following the recommended application manual, metalaxyl and azoxystrobin do not present health concerns to the population because the risk quotients are far below 100%. All the above data could help and promote the safe and proper use of metalaxyl and azoxystrobin in potato.

Occurrence and Distribution of Carbamate Pesticides and Metalaxyl in Southern Ontario Surface Waters 2007–2010

Surface water sampling in 2007–2010 measured the occurrence of carbamates and metalaxyl during base flow conditions and wet weather events in southern Ontario surface waters. Carbaryl, metalaxyl and pirimicarb were the most frequently detected compounds. In 2008 these three compounds were detected in over 50 % of the samples. Overall mean concentrations of carbaryl and metalaxyl over the course of the study (2007–2010) were 15 and 18 ng/L, respectively. Elevated concentrations of carbaryl (~100 to ~950 ng/L) appeared associated with wet weather (high flow) events, while highest concentrations of metalaxyl (~20–1330 ng/L) were correlated with base flow conditions. We attributed these observations as the result of runoff of carbaryl from the watershed during rain events, while metalaxyl contamination may have resulted primarily from spray drift.

Metalaxyl Induced Changes in Protein Metabolism During Germination of Maize

The present work was carried out to investigate the effect of a systemic fungicide metalaxyl as a seed treatment on the protein metabolism of maize during early germination. The study was carried out for 7 days after soaking the seeds in different concentrations of metalaxyl and a control was maintained. Biochemical analyses of whole seedlings were done up to 7 days. Changes in the amount of total soluble protein, total free amino acids, and the activity of protease were performed using standard methods. The results indicate that protein content was maximum on 4 th and 6 th day of germination in both control and treated seeds. Metalaxyl treatment resulted in decreased protein content (20-50% inhibition) over the untreated in a dose dependent manner till the 4 th day of germination. But as the growth proceeded a proportionate increase in the protein content was observed on the 6 th day of germination in fungicide treated seeds compared to the control. The specific activity of protease was decreased by 46%, 81%, 88%, 97% and 100% with 1.5mg, 3mg, 4.5mg, 6mg and 7mg concentration of metalaxyl on 3 rd day of germination when compared to the control. An increase in the total free amino acids occurred during the germination and maximum

Evaluating the enantioselective degradation and novel metabolites following a single oral dose of metalaxyl in mice

Metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-D,L-alaninemethylester] is a systemic fungicide widely used in agriculture. In this study, the enantioselective distribution, degradation and excretion of metalaxyl were investigated after oral gavage administration of rac-metalaxyl to mice. Concentration of metalaxyl and its enantiomers was determined by HPLC–MS/MS. The results showed that R-metalaxyl was much higher than S-metalaxyl in heart, liver, lung, urine and feces. As for the strong first pass effect, concentrations of metalaxyl in liver were much higher than those in other tissues. The total body clearance (CL) of metalaxyl in mice was 1.77 L h−1 kg−1 and degradation half-lives of (t1/2) of S-metalaxyl and R-metalaxyl in liver were 2.2 h and 3.0 h, respectively. Such results indicated the enantioselectivity of metalaxyl lies in distribution, degradation and excretion processes in mice. Main metabolites were also determined and biotransformation reactions were hydroxylation, demethylation and didemethylation. Furthermore, metabolite concentrations in urine and feces were much higher than those in tissues. These results may have potential implications to predict toxicity and provide additional information associated with adverse health effects for risk assessment of metalaxyl.

Enantioselective Bioaccumulation and Dissipation of Soil‐Associated Metalaxyl Enantiomers in Tubifex

Many pesticides are chiral compounds and stereochemistry is an important factor for any reaction of chiral structures in biological systems. In this study, experiment about bioaccumulation of the two metalaxyl enantiomers in Tubifex (Oligochaeta, Tubificida) was conducted in laboratory aquatic ecosystems. Terrestrial soil spiked with two dose levels of metalaxyl was employed as the artificial bottom substrate. A method of determination of metalaxyl enantiomers in tubifex tissue, soil and overlying water were developed by HPLC. During a 14-day exposure, concentrations of metalaxyl in tubifex increased with the of soil concentration, however, the enantioselective bioaccumulation was only detected at high-dose exposure group, with the preferential accumulation of (-)-(R)-metalaxyl. The bioturbation activity of tubifex decreased water clarity and released soil-associated metalaxyl to overlying water. In those experiments where tubifex was exposed to metalaxyl from soil, pore water and overlying water, each route contributed to the total body burden, and our results indicated the pore water and soil are the primary exposure routes for high-dose exposure concentration treatment.

Metalaxyl-induced changes in the antioxidant metabolism of Solanum nigrum L. suspension cells

The antioxidant responses of Solanum nigrum L. cell suspension cultures to metalaxyl exposure were investigated. An increase in lipid peroxidation and hydrogen peroxide content, for both concentrations tested (20mgL−1; 40mgL−1) revealed the response of oxidative metabolism of cell suspensions to metalaxyl. Superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6) and ascorbate peroxidase (APX; EC 1.11.1.11) activities increased, particularly in the highest concentration of metalaxyl used. An analysis by non-denaturing polyacrylamide gel (PAGE) followed by staining for enzyme activity, revealed seven SOD isoenzymes, two CAT isoenzymes, and nine APX isoenzymes. Metalaxyl levels were quantified in the culture medium and results suggest that suspension cells were able to accumulate and/or degrade the fungicide five hours after exposure. SOD, CAT and APX isoenzymes were differently affected by the metalaxyl treatment. Results suggest that the higher concentration of metalaxyl induced oxidative stress to cell suspension cultures of S. nigrum.

Pollution of surface waters by metalaxyl and nitrate from non-point sources

The mobility of contaminants in soil is highly dependent upon the characteristics of the contaminant chemical and the properties of the soil. In order to explore these relationships, the district of A Limia (Galicia, NW Spain) was selected as the study area—a cropland devoted to growing potatoes, where the soil had been managed intensively over the last 50years. The soil was characterised by low slopes with the water table located very close to the soil surface. Our aim was to study the influence of high and intensive crop production on the water bodies and non-point source contamination, with a particular focus on metalaxyl and nitrate. The highest concentrations of metalaxyl occurred when rainfalls were low and in zones of the study area where natural hydrology was significantly altered by numerous drainage canals. The spatial and temporal distributions of the nitrate also showed a high variability, with the interaction between seasons and sampling area being the most significant factor in explaining the levels found.

Enantioselective Bioaccumulation and Degradation of Sediment-Associated Metalaxyl Enantiomers in Tubifex tubifex

Knowledge about the enantioselective bioavailability of chiral pesticides in aquatic organisms facilitates more accurate interpretation of their environmental behaviors. In this study, the enantioselective bioaccumulation of metalaxyl enantiomers in Tubifex tubifex was detected in two uptake pathways. For the spike water treatment, a 16 day exposure experiment was employed and the enantiomer fractions (EFs) in tubifex tissue were maintained approximately at 0.47 during the experiment. For the spike sediment treatment, a 14 day bioaccumulation period indicated the concentrations of (-)-(R)-metalaxyl were higher than those of (+)-(S)-metalaxyl. Therefore, the bioaccumulation of metalaxyl in worms was enantioselective for these treatments. With the presence of tubifex, higher concentrations of metalaxyl in overlying water and lower concentrations in sediment were detected than in worm-free treatments. This means that tubifex has positive functions in metalaxyl's diffusion from the sediment to overlying water and in the degradation of the sediment-associated metalaxyl.

Photo-Fenton plus Solanum nigrum L. weed plants integrated process for the abatement of highly concentrated metalaxyl on waste waters

The treatment of a highly concentrated pesticide and systemic fungicide solution, containing metalaxyl as active compound (150mgL−1), was investigated by using the photo-Fenton process in combination with Solanum nigrum L. weed plants. High concentration of metalaxyl has a destructive effect on S. nigrum plants although this pesticide can be successfully degraded by the photo-Fenton process. S. nigrum seed germination and seedling development were not affected by iron species at concentrations lower than 11mgL−1, which is well above the optimal dosage for the photo-Fenton process (4mgL−1). In addition, at the referred optimal dosage, S. nigrum growth was not affected and those plants were able to extract large amounts of iron species from the solution (between 1.5–2.0 and 0.2–0.5mg of Fe per gram of dry weight of plant in their roots and shoots, respectively). Negative effects on biomass production and chlorophyll and carotenoids contents, used as stress biomarkers, were not detected. When S. nigrum plants were directly exposed to the solution pre-treated by the photo-Fenton process, an increase in glutathione-S-transferase activity in shoots, some toxicity towards the plant physiology and a decrease in the total soluble protein content, in both shoots and roots, were observed; nevertheless, the plant growth was still remarkable. These results suggest that the photo-Fenton process can be used as a chemical primary treatment, followed by S. nigrum plants biological remediation (as post-treatment) for waste waters that are contaminated with concentrations of metalaxyl as high as 150mgL−1.

Impacts of zerovalent iron application on the adsorption behavior of alachlor and metalaxyl in water and soil systems

Alachlor and metalaxyl contaminations of environmental and agricultural water and soil systems cause potential threats to human health. However, information on the pesticide adsorption quantity–intensity (Q/I) relationships in water and soil systems is limited. Therefore, adsorption behavior and the fate of alachlor and metalaxyl in the systems as influenced by the application of zerovalent iron (ZVI, Fe0) were investigated using the pesticide adsorption Q/I relationships. After treating ZVI in the systems, the concentration of alachlor rapidly decreased within a few days and then it disappeared at approximately 5–7 experiment days; whereas metalaxyl concentration was reduced by approximately 40–45% during the 28 day experimental period. In particular, ZVI adsorbed more metalaxyl in the aqueous system than in the soil-solution system. The alachlor concentration in the water and soil solution drastically decreased with increasing ZVI treatment, while metalaxyl concentration was relatively slow in its decrease. Adsorption mechanism of the pesticides in the soil-solution system was shown as multiple-site adsorption Q/I fitting. Buffering capacity (BC) of the pesticides increased with ZVI treatment in all sorption sites. The BC values in sandy soil were escalated with increasing ZVI application rates, so that the values were rather higher in sandy soil than in clayey soil. In addition, changes in alachlor concentration with applying ZVI were due to both dechlorination and adsorption; whereas metalaxyl concentration was dependent upon adsorption reaction. Thus, the pesticide adsorption Q/I relationships in different soil-solution systems were critically affected by the ZVI treatment.

The influence of small- and large-scale composting on the dissipation of pesticide residues in a biopurification matrix

Pesticides are efficiently retained and degraded in the organic matrix of a biopurification system. However, as this matrix mineralizes slowly over time, nutrients will start to become depleted and thus a decay in biomass will probably occur. At that moment, the efficiency of the system decreases and the matrix should be replaced. The spent matrix might still contain residues of pesticides. Hence treatment of this matrix is essential. In this study we opted to use composting or incubation as an effective and environmentally friendly treatment strategy. Small- and large-scale composting/incubation trials were set up to treat the presence of linuron, bentazone, metalaxyl and bifenthrin in a contaminated matrix. Large-scale composting, performed in an industrial composting facility, resulted in decreased concentrations of metalaxyl, linuron and bentazone. Degradation of bifenthrin was very limited. In the small-scale incubation process, a decrease in concentration was noted for bifenthrin, metalaxyl and bentazone. A reduction in extractable pesticide concentration does not, however, always indicate degradation but could be attributed to the formation of non-extractable residues. Industrial and small-scale composting/incubation reduced the concentration of some pesticides during the timeframe studied, although little reduction was obtained for the persistent pesticide bifenthrin in the industrial composting process and for linuron in barrel incubation.

Behaviour of metalaxyl as copper oxychloride–metalaxyl commercial formulation vs. technical grade-metalaxyl in vineyards-devoted soils

The objective of this work is to asses the sorption of metalaxyl applied as a copper oxychloride (CO)-metalaxyl formulation, for a set of selected soils devoted to vineyards. The method involved batch incubation of soils suspended with a commercial copper oxychloride–metalaxyl-based fungicide in 0.01 M CaCl 2. Afterwards, the metalaxyl concentration remaining in solution was determined by high-performance liquid chromatography (HPLC). The amount of dissolved metalaxyl in the fungicide suspension depends mainly on the soil pH, its potential acidity, and the cation exchange capacity. Of the approx. 20% metalaxyl retained by the solid colloids, the effect of organic matter colloids in soils (15–20 mg kg −1) had a poor contribution (six times lower) than the copper oxychloride colloids (40%, w/w) in the commercial fungicide formulation (100–130 mg kg −1). When comparing these retention data with the behaviour of metalaxyl used as a technical grade fungicide of about 100% purity (10–15 mg kg −1 in solids), it is clear that the commercial formulation increases a 30% retention of metalaxyl by soil (15–20 mg kg −1 in solids). The overall effect of the metalaxyl formulation plus soil show values of 10 times higher retention than technical grade-metalaxyl plus soil. Commercial formulation can decrease the mobility of soluble metalaxyl in agricultural soils with regard to the expected values obtained from batch studies using analytical grade-metalaxyl. Therefore, the effect of surfactants should be considered in the assessment of water contamination by the pesticides used in agriculture.