Sorption, desorption, and degradation of (4-chloro-2-methylphenoxy)acetic acid in representative soils of the Danubian Lowland, Slovakia

Degradation of four pesticides in five urban landscape soils: human and environmental health risk assessment

Pesticides are the most cost-effective means of pest control; however, the serious concern is about the non-target effects due to their extensive and intensive use in both agricultural and non-agricultural settings. The degradation rate constant (k) and half-life (DT₅₀) of four commonly used pesticides, glyphosate, 2,4-D, chlorothalonil and dimethoate were determined in five Australian urban landscape soils, with varying physicochemical characteristics, to assess their environmental and human health risks. The k values (day^-1) for the selected pesticides were inversely proportional to those of organic carbon (OC), silt, clay and Fe and Al oxides, and directly proportional to pH and sand content in soils. In contrast, the calculated values of DT₅₀ (days) of all the four pesticides in five soils positively correlated with OC, clay, silt and oxides of Fe and Al, whereas soil pH and sand content exhibited a negative correlation. The calculated values of environmental indices, GUS and LIX, for the selected pesticides indicate their potential portability into water bodies, affecting non-target organisms as well as food safety. The evaluation for human non-cancer risk of these pesticides, based on the calculated values of hazard quotient (HQ) and hazard index (HI), suggested that exposure of adults and children to soils, contaminated with 50% of initially applied concentrations, through ingestion, dermal and inhalation pathways might cause negligible to zero non-carcinogenic risks. The present data might help the stakeholders in applying recommended doses of pesticides in urban landscapes and regulatory bodies concerned in monitoring the overall environmental quality and implementing safeguard policies. Our study also clearly demonstrates the need for developing improved formulations and spraying technologies for pesticides to minimize human and environmental health risks.

The efficient persistence and migration of Cupriavidus gilardii T1 contribute to the removal of MCPA in laboratory and field soils

The application of exogenous biodegradation strains in pesticide-polluted soils encounters the challenges of migration and persistence of inoculants. In this study, the degradation characteristics, vertical migration capacity, and microbial ecological risk assessment of an enhanced green fluorescent protein (EGFP)-tagged 2-Methyl-4-chlorophenoxyacetic acid (MCPA)-degrading strain Cupriavidus gilardii T1 (EGFP) were investigated in the laboratory and field soils. The optimum remediation conditions for T1 (EGFP) was characterized in soils. Meanwhile, leaching experiments showed that T1 (EGFP) migrated vertically downwards in soil and contribute to the degradation of MCPA at different depths. After inoculation with T1 (EGFP), a high expression levels of EGFP gene was observed at 28 d in the laboratory soil and at 45 d in the field soil. The degradation rates of MCPA were ≥ 60% in the laboratory soil and ≥ 48% in the field soil, indicating that T1 (EGFP) can efficiently and continuously remove MCPA in both laboratory and field conditions. In addition, the inoculation of T1 (EGFP) not only showed no significant impact on the soil microbial community structure but also can alleviate the negative effects induced by MCPA to some extent. Overall, our findings suggested that T1 (EGFP) strain is an ecologically safe resource for the in situ bioremediation of MCPA-contaminated soils.

An assessment of potential pesticide transmission, considering the combined impact of soil texture and pesticide properties: A meta-analysis

Pesticides are widely employed as a cost-effective means of reducing the impacts of undesirable plants and animals. The aim of this paper is to develop a risk ranking of transmission of key pesticides through soil to waterways, taking into account physico-chemical properties of the pesticides (soil half-life and water solubility), soil permeability, and the relationship between adsorption of pesticides and soil texture. This may be used as a screening tool for land managers, as it allows assessment of the potential transmission risks associated with the use of specified pesticides across a spectrum of soil textures. The twenty-eight pesticides examined were differentiated into three groups: herbicides, fungicides and insecticides. The highest risk of pesticide transmission through soils to waterways is associated with soils containing <20% clay or >45% sand. In a small number of cases, the resulting transmission risk is not influenced by soil texture alone. For example, for Phenmedipham, the transmission risk is higher for clay soils than for silt loam. The data generated in this paper may also be used in the identification of critical area sources, which have a high likelihood of pesticide transmission to waterways. Furthermore, they have the potential to be applied to GIS mapping, where the potential transmission risk values of the pesticides can be layered directly onto various soil textures.

The Adsorption and Degradation of 2, 4-D Affected by Soil Organic Carbon and Clay

More has yet to be indicated on the adsorption and degradation processes, determining herbicides recycling in the environment. The sorption and degradation of 2, 4-D, affected by organic carbon (1.92-2.81%), soil clay (20-30%) and pH of the citrus orchards of Mazandaran province, Iran was investigated using HPLC equipped with UV detector for the identification and quantification of soil 2, 4-D. The adsorption (k_d) and degradation (K_deg) coefficients were determined using Freundlich and the first-degree kinetic equations. Gardens C (2.45 mL g^-1), and B (0.3 mL g^-1), with the highest (8.2 g day^-1) and least (2.7 g day^-1) degradation coefficients, had the highest and lowest K_d values. K_d variations with pH indicated higher adsorption of 2, 4-D in acidic pH. Due to the high presence of functional groups and soil biological activities, organic carbon affected the adsorption and degradation rates more effectively, which is of economic and environmental significance.

Effect of 4-chloro-2-methylphenoxy acetic acid on tomato gene expression and rhizosphere bacterial communities under inoculation with phosphate-solubilizing bacteria

The herbicide 4-chloro-2-methylphenoxy acetic acid (MCPA) is widely used to control the spread of broad-leaved weeds in agricultural soils, though it remains unclear how tomato plants cope with the phytotoxic effects of MCPA at the molecular level. In this study, RNA-seq and Illumina MiSeq were used to sequence bacterial communities in tomato rhizosphere soils treated with MCPA and the phosphate-solubilizing bacterial strain N3. The results showed that MCPA induced abnormal growth of lateral roots in tomato seedlings and reduced uptake of the nutrients N, P, and K as well as the hormone (ABA and GA3) levels. Inoculation with strain N3 increased nutrient uptake by roots and increased levels of the hormones ABA, ZEA, and JA in tomato seedlings and also increased the abundance of the phyla Proteobacteria and Gemmatimonadetes in soil under MCPA treatment. GO functional groups in which differentially expressed genes (DEGs) are involved included DNA binding transcription factor activity, transcriptional regulator activity, enzyme inhibitor activity, and cell wall biogenesis. The highest numbers of DEGs are annotated to ribosome, photosynthesis, and carbon metabolism categories. Our findings provide valuable information for the application of strain N3, which is beneficial for reducing the toxic effect of MCPA on vegetable plants.

Mechanisms by which different polar fractions of dissolved organic matter affect sorption of the herbicide MCPA in ferralsol

Exogenous dissolved organic matter (DOM) modifies the sorption of 4-chloro-2-methylphenoxyacetic acid (MCPA, a polar herbicide) in soil. However, how the chemodiversity and diverse fractions of DOM affect MCPA sorption is still unknown. Here, DOM was extracted from compost and rice straw; the structure-activity correlations between DOM chemodiversity and their effects on MCPA sorption were investigated by redundancy analysis. Moreover, the mechanism involved was explored by spectroscopic techniques, microbeam and modeling. DOM mainly affected MCPA sorption by altering soil surface properties and MCPA complexed form. Hydrophobic neutral (HON) and acid insoluble matter (AIM) were the fractions of DOM that most inhibited MCPA sorption through soil pore blockage, and were related to the humic-like substances with high aromaticity and large molecular weight. The hydrophobic acid fraction (HOA) only showed an intermediate inhibition on the sorption, although the largest competitive sorption occurred. This was because HOA contained abundant aromatic acid and polar groups with moderate polarity. Thus, the reduced effect caused by competitive sorption was partly compensated by the greatest co-sorption by HOA. The hydrophilic matter (HIM) had the weakest inhibition on MCPA sorption, because this fraction was rich in simple sugars, poly- and oligosaccharides, but lacked aryl groups. The results will aid in the risk assessments and prevention of MCPA in DOM-introduced soil.

Characterization of the fate and distribution of methoxyfenozide in a water-plant-fish-sediment microcosm using a multimedia fugacity model

Methoxyfenozide is widely employed in paddy land and can flow out into the aquatic environment. The present study combines two approaches, namely, an aquatic microcosm simulation experiment and a multimedia fugacity model, to study the fate and distribution of methoxyfenozide in an aquatic microcosm containing water, sediment, aquatic plants, and zebrafish. The model results indicated that the simulated concentrations agreed with the observed values within one order of magnitude. The degradation rate was less than 7.0% in the three types of aquatic microcosms at 740 h in the model. Methoxyfenozide exhibited very high persistence in the aquatic microcosm. Water played a key role in the fate of methoxyfenozide, acting as a sink in the simulated aquatic environment, followed by sediment. Only approximately 2% of methoxyfenozide entered the organisms (zebrafish and Egeria densa Planch). Methoxyfenozide underwent a significant transport process between the water and sediment. The applications of multimedia fugacity models are useful for understanding the behaviors, fate, and transport of pesticides after their release into the environment and to facilitate risk assessment and management activities.

Approaches to herbicide (MCPA) pollution mitigation in drinking water source catchments using enhanced space and time monitoring

Freshwater occurrences of the selective acid herbicide 2-methyl-4-chloro-phenoxyacetic acid (MCPA) are an ongoing regulatory and financial issue for water utility industries as the number and magnitude of detections increase, particularly in surface water catchments. Assessments for mitigating pesticide pollution in catchments used as drinking water sources require a combination of catchment-based and water treatment solutions, but approaches are limited by a lack of empirical data. In this study, an enhanced spatial (11 locations) and temporal (7-hourly to daily sampling) monitoring approach was employed to address these issues in an exemplar surface water source catchment (384 km²). The spatial sampling revealed that MCPA was widespread, with occurrences above the 0.1 μg L^-1 threshold for a single pesticide being highly positively correlated to sub-catchments with higher proportions of 'Improved Grassland' land use (r = 0.84). These data provide a strong foundation for targeting catchment-based mitigation solutions and also add to the debate on the ecosystems services provided by such catchments. Additionally, of the 999 temporal samples taken over 12 months from the catchment outlet, 25% were above the drinking water threshold of 0.1 μg L^-1. This prevalence of high concentrations presents costly problems for source water treatment. Using these data, abstraction shutdowns were simulated for five scenarios using hydrometeorological data to explore the potential to avoid intake of high MCPA concentrations. The scenarios stopped abstraction for 4.2-9.3% of the April-October period and reduced intake of water containing over 0.1 μg L^-1 of MCPA by 16-31%. This represents an important development for real-time proxy assessments for water abstraction in the absence of more direct pesticide monitoring data.

Batch and packed bed techniques for adsorptive aqueous phase removal of selected phenoxyacetic acid herbicide using sugar industry waste ash

Batch and packed bed adsorption of 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was performed using bagasse fly ash (BFA) as an adsorbent. In batch process, characteristics of adsorbent, and the influence of adsorbent dosage, initial herbicide concentration, time, pH, particle size of adsorbent and temperature on adsorption were studied. Results disclose higher removal of MCPA on bigger particles of BFA owing to higher specific surface area because of greater carbon and lesser silica percentage in bigger particles. Application of isotherm models in present study indicates the best fitting of Langmuir and Temkin isotherms whereas the kinetic models suggest the suitability of pseudo second order and Elovich models. Thermodynamic study specifies the temperature preferred adsorption process. In packed bed technique, the effect of influent concentration, flow rate and bed height were investigated. The deactivation kinetic model which was previously considered only for studies in gas-solid adsorption is applied in this study to solid-liquid adsorption along with conventional packed bed models. In packed bed study, Bohart-Adams and Wolborska models are appropriate to explain the experimental data upto 60% saturation of the column. The deactivation kinetic model is found the best to elucidate the nature of breakthrough curves till the complete saturation of column. Batch capacity and packed bed capacity per m2 specific surface area of BFA is found about two and three times greater than the previously used adsorbents for MCPA respectively.

Plant litter enhances degradation of the herbicide MCPA and increases formation of biogenic non-extractable residues in soil

Amendment of soils with plant residues is common practice for improving soil quality. In addition to stimulated microbial activity, the supply of fresh soluble organic (C) from litter may accelerate the microbial degradation of chemicals in soils. Therefore, the aim of this study was to test whether the maize litter enhances degradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) and increases formation of non-toxic biogenic non-extractable residues (bioNERs). Soil was amended with ¹³C₆-MCPA and incubated with or without litter addition on the top. Three soil layers were sampled with increasing distance from the top: 0-2 mm, 2-5 mm and 5-20 mm; and the mass balance of ¹³C₆-MCPA transformation determined. Maize litter promoted microbial activity, mineralization of ¹³C₆-MCPA and bioNER formation in the upper two layers (0-2 and 2-5 mm). The mineralization of ¹³C₆-MCPA in soil with litter increased to 27% compared to only 6% in the control. Accordingly, maize addition reduced the amount of extractable residual MCPA in soil from 77% (control) to 35% of initially applied ¹³C₆-MCPA. While non-extractable residues (NERs) were <6% in control soil, litter addition raised NERs to 21%. Thereby, bioNERs comprised 14% of ¹³C₆-MCPA equivalents. We found characteristic differences of bioNER formation with distance to litter. While total NERs in soil at a distance of 2-5 mm were mostly identified as ¹³C-bioNERs (97%), only 45-46% of total NERs were assigned to bioNERs in the 0-2 and 5-20 mm layers. Phospholipid fatty acid analysis indicated that fungi and Gram-negative bacteria were mainly involved in MCPA degradation. Maize-C particularly stimulated fungal activity in the adjacent soil, which presumably facilitated non-biogenic NER formation. The plant litter accelerated formation of both non-toxic bioNERs and non-biogenic NERs. More studies on the structural composition of non-biogenic NERs with toxicity potential are needed for future recommendations on litter addition in agriculture.

Method Validation and Investigation of the Levels of Pharmaceuticals and Personal Care Products in Sludge of Wastewater Treatment Plants and Soils of Irrigated Golf Course

The validation of a sensitive and reliable analytical procedure for the determination of pharmaceutical and personal care products (PPCPs) in solid environmental samples is reported in this study. Initially, two types of derivatization were used for the identification of the 13 target PPCP standards (acylation and silylation), but silylation proved to be better in sensitivity as it detected all of the analytes under investigation. Samples were extracted using an ultrasonicator, concentrated and re-dissolved in 100 mL water, then cleaned-up using C18 cartridges before silylation that preceded the Gas chromatography-mass Spectrometry detector (GC–MS) analyses. The optimized method provided a linear response over the range of 10–400 ng·g⁻¹ with r² > 0.992 and satisfactory recoveries (>45.6%) for the 13 compounds of interest. In this study, the variation of the sonication temperature, type of organic solvent for extraction, and types of cartridge were used to optimize the extraction procedure. A good repeatability (within day) and reproducibility (between days) with a relative standard deviation (RSD) that was equal or less than 13% for all the PPCPs were achieved with the developed extraction procedures for the irrigated soil and sewage sludge samples. The limits of detection (LODs) of the tested compounds varied from 0.1 ng·g⁻¹ (aspirin) to 1.4 ng·g⁻¹ (doxycycline) and from 0.1 ng·g⁻¹ (codiene) to 1.7 ng·g⁻¹ (doxycycline) for soils and sewage sludge samples, respectively. The method was successfully applied to the sludge of wastewater treatment plants and soils of an irrigated golf course. Among the tested emerging pollutants, paracetamol showed the highest concentration value of 98.9 ng·g⁻¹ in the sludge, and for the irrigated soil (0 to 10 cm), the concentration ranged from 1.16 ng·g⁻¹ (aspirin) to 8.57 ng·g⁻¹ (ibuprofen).

Olive mill sludge may reduce water contamination by 4-chloro-2-methylphenoxyacetic acid (MCPA) in non-flooding but enhance it in flooding rice cropping agroecosystems

A field experiment covering three years was conducted to evaluate how composted olive mill sludge (OS) influenced MCPA's environmental fate in rice soils under six combinations of tillage and irrigation cultivation techniques: tillage and sprinkler irrigation without (TS) or with (TSOS) the addition of OS (80 Mg ha^-1), no-tillage and sprinkler irrigation without (NTS) or with (NTSOS) OS, and tillage and continuous flooding without (TF) or with (TFOS) OS. The measurements made in the first and third years after OS application were taken to constitute the "direct" and "residual" effects, respectively. After OS amendment, K_d (partition coefficients) values in the direct year were lower by factors of 1.1, 1.3, and 1.9 in TSOS, NTSOS, and TFOS, respectively, relative to the corresponding unamended soils, and in the residual year by factors of 1.1 and 1.5 in TSOS and NTOS, but greater by a factor of 1.5 in TFOS, than in the corresponding unamended soils, respectively. The dissipation of MCPA was very fast under both anaerobic (t_1/2 = 1.80-5.29 d) and aerobic (t_1/2 = 2.23-9.42 d) incubation conditions. The field application of OS led to a decrease in MCPA persistence under both incubation conditions, especially in the TF case. However, while under aerobic conditions the half-life (t_1/2) decreased after OS addition in the direct and residual years, under anaerobic condition it only decreased in the direct year. While the application of OS in TS and NTS led to less leaching of MCPA, in TF it led to 1.4 and 1.2 times more leaching losses of the herbicide for the direct and residual years, respectively. Therefore, the use of OS in rice production could be considered an effective strategy for reducing water contamination by MCPA in at least the short- and medium-terms after its application, but only under non-flooding crop management regimes irrespective of the tillage practice implemented.

Interaction and coexistence characteristics of dissolved organic matter with toxic metals and pesticides in shallow groundwater

The long-term and large-scale utilization of fertilizers and pesticides in facility agriculture leads to groundwater pollution. However, the coexistence and interactions between organic fertilizers (i.e., organic matter), toxic metals, and pesticides in shallow groundwater have seldom been studied. Thus, the study sought to characterize said interactions via fluorescence, ultraviolet-visible spectroscopy (UV-Vis), and Fourier-transform infrared spectroscopy coupled with two-dimensional correlation spectroscopy and chemometric techniques. The results indicated that groundwater DOM was comprised of protein-, polysaccharide-, and lignin-like substances derived from organic fertilizers. Protein-like substances accounted for the binding of Co, Ni, and Fe, while polysaccharide- and lignin-like substances were mainly responsible for Cr and Mo complexation. Moreover, lignin- and polysaccharide-like substances played a key role in the binding of pesticides (i.e., dichlorodiphenyltrichloroethane [DDT], endosulfan, γ-hexachlorocyclohexane [γ-HCH], monocrotophos, chlorpyrifos, and chlorfenvinphos), rendering the conversion of γ-HCH to β-hexachlorocyclohexane (β-HCH) and the degradation of DDT to dichlorobenzene dichloroethylene (DDE) ineffective. However, the presence of protein-like substances in groundwater benefited the degradation and conversion of γ-HCH and α-endosulfan. Redundancy analyses showed that lignin- and polysaccharide-like matter had the most impacts on the coexistence of DOM with toxic metals and pesticides.

Environmental fate of bensulfuron-methyl and MCPA in aerobic and anaerobic rice-cropping systems

Bensulfuron-methyl (BM) and 4-chloro-2-methylphenoxyacetic acid (MCPA) are herbicides widely used in rice agroecosystems, and are commonly found in their environments, especially in water resources. The objective of this study was to evaluate the sorption-desorption, leaching, and dissipation of BM and MCPA under aerobic and anaerobic rice cropping conditions. For this purpose, a three-year field experiment was conducted in SW Spain using four management systems: aerobic with sprinkler irrigation and tillage (ST), sprinkler irrigation and no-tillage (SNT), long-term sprinkler irrigation and no-tillage (SNT^LT), and anaerobic with flooding and tillage (FT). At the end of the experiment, the partition coefficients (K_d-values) in ST were (2.7, 3.1, and 3.9) and (1.2, 1.5, and 1.9) times significantly lower than the values in {SNT, SNT^LT, and FT} for BM and MCPA, respectively. Greater sorption was related to lower values of soil pH for both herbicides and to higher contents in humic acids for BM and fulvic acids for MCPA. The persistence was much longer for BM (t_1/2 = 26.9-52.1 days) than for MCPA (t_1/2 = 1.54-21.1 days) in all management systems, and both herbicides' dissipation rates were generally greater under aerobic than under anaerobic conditions. The mobility of MCPA was much greater than that of BM. Compared with SNT and SNT^LT, leaching losses of the applied BM were greater by 51% for ST, and of the applied MCPA by 55% and 99% for ST and FT, respectively. Therefore, only aerobic rice production with no-tillage in the short- or long-terms could be considered as alternative management strategies with which to reduce water contamination by BM and MCPA in rice-growing environments.

Enhanced phosphate sequestration by Fe(iii) modified biochar derived from coconut shell

In this work, a novel Fe-modified coconut shell biochar (Fe-CSB) was synthesized and utilized to remove phosphate from aqueous solution. Characterization results confirmed that the iron in the Fe(iii)-impregnated CSB existed mainly in the amorphous phase, as ferrihydrite and amorphous hydroxide, which substantially enhanced the phosphate adsorption. Batch experiments indicated that phosphate adsorption on the Fe-CSB was highly dependent on the pH, the humic acid, and temperature, while it was less affected by the nitrate. Phosphate adsorption by the CSB and Fe-CSB could be well described by the pseudo n-th order and Langmuir–Freundlich models. The fitting of the experimental data with the intra-particle diffusion model revealed that surface adsorption and inner-sphere diffusion were involved in the phosphate adsorption process, and that the latter was the rate-controlling step. Batch adsorption experiments and post-adsorption characterization results revealed that the phosphate adsorption by Fe-CSB was primarily governed by four mechanisms: ligand exchange, electrostatic attraction, chemical precipitation, and inner-sphere complexation. This work demonstrated that the modified Fe-CSB is an environmentally friendly and cost-effective bioretention medium and could open up new pathways for the removal of phosphorus from stormwater, as well as solve the problem of waste biomass pollution.

In this work, a novel Fe-modified coconut shell biochar (Fe-CSB) was synthesized and utilized to remove phosphate from aqueous solution.

Influence of physicochemical properties of various soil types on iodide and iodate sorption

Studies that deal with iodine mobility in uncontaminated agricultural soils are scarce and unique. Therefore, in this article, we have evaluated the sorption behavior of two most abundant naturally occurring inorganic iodine species - iodide and iodate - in several soil types. Our results showed that the sorption process is extremely slow with equilibrium achieved after ten days. The sorption of both iodine species is well described by Freundlich isotherm. The affinity of iodine for all investigated soils in the observed concentration range is relatively low. Our results showed that besides iodine speciation, sorption efficiency is highly dependent on soil types and their characteristics. While in mineral soils with low organic carbon content iodide sorption is dominant, organic rich soils are more favorable for iodate sorption. Organic carbon, clay content, pH and the abundance of iron, aluminum and manganese oxides and hydroxides showed to be the most important soil properties controlling iodine sorption. Our results provide new insight into the complex iodine behavior and retention in soils. This is crucial for better understanding of iodine mobility and the ability to enter the food chain.

Influence of dissolved organic matter on sorption and desorption of MCPA in ferralsol

MCPA (4-chloro-2-methylphenoxyacetic acid) is an acidic herbicide, widely used in paddy fields. The presence of dissolved organic matter (DOM) modifies the sorption-desorption of herbicides in soils. In this study, effects of DOM on sorption- desorption of MCPA were tested using three typical ferralsol soil types from China: rhodic ferralsol, haplic ferralsol and paddy soil. DOM preparations were extracted from the paddy soil (DOM_P), from a compost mixture of cassava stems with chicken manure (DOM_C), and from rice straw (DOM_R). Sorption-desorption of MCPA in the tested soil types was shown to follow pseudo first-order kinetics, and the calculated isotherm data fitted well with a Freundlich equilibrium model in the range of the studied concentrations. MCPA was weakly sorbed by the soils, producing low Freundlich coefficient values (K_f) (0.854 to 4.237). The presence of DOM reduced the K_f whereby DOM_C had the strongest and DOM_R the weakest effect. Presence of DOM also promoted MCPA desorption from the soils, again with DOM_C having the strongest effect and DOM_R the weakest. DOM coating changed the soil particle surface, as demonstrated by electron microscopy, and DOM also directly interacted with MCPA, as shown by Fourier-transform infrared spectroscopy. The experimental data were interpreted to suggest a competing sorption of DOM to ferralsol and an increased solubility of MCPA in the presence of DOM. The results indicate that the environmental risk of MCPA leaching to groundwater and surface flow is increased by presence of DOM, for instance as a result of organic fertilizer use.

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 K_F values that ranged from 0.7 to 8.8Lⁿ µmol^1-nkg^-1 and K_D 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.

Sorption and desorption of glyphosate, MCPA and tetracycline and their mixtures in soil as influenced by phosphate

Phosphate fertilizers and herbicides such as glyphosate and MCPA are commonly applied to agricultural land, and antibiotics such as tetracycline have been detected in soils following the application of livestock manures and biosolids to agricultural land. Utilizing a range of batch equilibrium experiments, this research examined the competitive sorption interactions of these chemicals in soil. Soil samples (0-15 cm) collected from long-term experimental plots contained Olsen P concentrations in the typical (13 to 20 mg kg-1) and elevated (81 to 99 mg kg-1) range of build-up phosphate in agricultural soils. The elevated Olsen P concentrations in field soils significantly reduced glyphosate sorption up to 50%, but had no significant impact on MCPA and tetracycline sorption. Fresh phosphate additions in the laboratory, introduced to soil prior to, or at the same time with the other chemical applications, had a greater impact on reducing glyphosate sorption (up to 45%) than on reducing tetracycline (up to 13%) and MCPA (up to 8%) sorption. The impact of fresh phosphate additions on the desorption of these three chemicals was also statistically significant, but numerically very small namely < 1% for glyphosate and tetracycline and 3% for MCPA. The presence of MCPA significantly reduced sorption and increased desorption of glyphosate, but only when MCPA was present at concentrations much greater than environmentally relevant and there was no phosphate added to the MCPA solution. Tetracycline addition had no significant effect on glyphosate sorption and desorption in soil. For the four chemicals studied, we conclude that when mixtures of phosphate, herbicides and antibiotics are present in soil, the greatest influence of their competitive interactions is phosphate decreasing glyphosate sorption and the presence of phosphate in solution lessens the potential impact of MCPA on glyphosate sorption. The presence of chemical mixtures in soil solution has an overall greater impact on the sorption than desorption of individual organic chemicals in soil.

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.

Adsorption and degradation of phenoxyalkanoic acid herbicides in soils: A review

The primary aim of the present review on phenoxyalkanoic acid herbicides-2-(2,4-dichlorophenoxy) acetic acid (2,4-D), 2-(4-chloro-2-methylphenoxy) acetic acid (MCPA), (2R)-2-(2,4-dichlorophenoxy) propanoic acid (dichlorprop-P), (2R)-2-(4-chloro-2-methylphenoxy) propanoic acid (mecoprop-P), 4-(2,4-dichlorophenoxy) butanoic acid (2,4-DB), and 4-(4-chloro-2-methylphenoxy) butanoic acid (MCPB)-was to compare the extent of their adsorption in soils and degradation rates to assess their potential for groundwater contamination. The authors found that adsorption decreased in the sequence of 2,4-DB > 2,4-D > MCPA > dichlorprop-P > mecoprop-P. Herbicides are predominantly adsorbed as anions-on organic matter and through a water-bridging mechanism with adsorbed Fe cations-and their neutral forms are adsorbed mainly on organic matter. Adsorption of anions of 2,4-D, MCPA, dichlorprop-P, and mecoprop-P is inversely correlated with their lipophilicity values, and modeling of adsorption of the compounds based on this relationship is possible. The predominant dissipation mechanism of herbicides in soils is bacterial degradation. The contribution of other mechanisms, such as degradation by fungi, photodegradation, or volatilization from soils, is much smaller. The rate of bacterial degradation decreased in the following order: 2,4-D > MCPA > mecoprop-P > dichlorprop-P. It was found that 2,4-D and MCPA have the lowest potential for leaching into groundwater and that mecoprop-P and dichlorprop-P have slightly higher potential. Because of limited data on adsorption and degradation of 2,4-DB and MCPB, estimation of their leaching potential was not possible.

Influence of substrate water saturation on pesticide dissipation in constructed wetlands

Constructed wetlands are an effective and practical option for removing pesticide pollution from runoff or subsurface drainage water. The objective of this study was to assess the efficiencies of a ditch with a bundle of straw placed in its centre and a vegetated pond installed in grass cover bands at downstream of a drained plot. The dissipation rates of three herbicides and three fungicides were monitored on four substrates commonly found in constructed wetlands (two soils, sediment and straw). The influence of water content was determined in a sequence of three steps (flooded-unsaturated-flooded) over 120 days. The pesticide dissipation rates observed during the 120 days of incubation ranged from 1.4 to 100%. Isoproturon and 2,4-MCPA (MCPA) showed the highest dissipation rates, which ranged from 61.0 to 100% of the applied quantities during the 120 days of incubation. In contrast, boscalid and tebuconazole showed the lowest dissipation rates, which ranged from 1.4 to 43.9% of the applied quantities during the 120 days of incubation. The estimated DT50 values ranged from 20.5 days to more than 1 year and were influenced by the substrate water content. The soil and straw substrates had the lowest DT50 values during the unsaturated conditions, whereas the sediments had the lowest DT50 values during the flooded conditions. These results could be explained by an adaptation of microbial communities to their environmental conditions. Thus, the most favourable conditions of dissipation for soils and straw are observable when the drainage ceases (spring and summer). However, favourable conditions occur all year for the sediments, except when the constructed wetlands are dry. The results suggest that the dissipation of pesticides in constructed wetlands contributes to the long-term effectiveness of these buffer zones for reducing water pollution.

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.

A laboratory-scale column study comparing organic micropollutant removal and microbial diversity for two soil types

This study investigated sorption and biodegradation behaviour of 20 organic micropollutants (OMPs) in lab-scale columns filled with two types of soil (fed with the same water quality) simulating river bank filtration (RBF) under oxic conditions. Retardation factors and OMP biodegradation rates were similar for the two soils that were characterised by a different cationic exchange capacity, organic matter and sand/silt/clay content. This result was supported by the microbial community composition (richness, evenness) of the two soils that became more similar as a result of feeding both columns with the same water quality. This indicates that microbial community composition and thereby OMP removal in soils is primarily determined by the composition of the aqueous phase (organic matter quantity and quality, nutrients) rather than the soil phase. These results indicate that different RBF sites located along the same river may show similar OMP removal (in case of similar water quality and residence time).

CAPSULE

This study shows that the microbial community composition and thus OMP removal is primarily determined by the aqueous phase (water quality) rather than the soil phase.

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.

Adsorption of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) by goethite

Interaction between the goethite surface and 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was studied using density functional theory (DFT) calculations combined with molecular dynamics (MD). The important step made here lies in the use of a periodic DFT method enabling the study of a mineral surface of different protonation states, in strong contrast with previous molecular modeling studies limited to single protonation state corresponding to the point of zero charge. Different surface OH groups and MCPA proton states were used to mimic the strong effects of pH on the outer- and inner-sphere surface complexes that are theoretically possible, together with their binding energies, and their bond lengths. Modeling both a solvated and a protonated (110) goethite surface provided a major breakthrough in the acidic adsorption regime. An outer-sphere complex and a monodentate inner-sphere complex with the neutral MCPA molecule were found to be the most energetically stable adsorbate forms. MD modeling predicted that the latter forms via the sharing of the carbonyl oxygen between the MCPA carboxylate group and a singly coordinated surface hydroxyl group, releasing an H2O molecule. All the other complexes, including the bidentate inner-sphere complex, had higher relative energies and were therefore less likely. The two most likely DFT-optimized structures were used to constrain a surface complexation model applying the charge distribution multisite complexation (CD-MUSIC) approach. The adsorption constants for the complexes were successfully fitted to experimental batch equilibrium data.

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.

Sorption of selected pesticides on soils, sediment and straw from a constructed agricultural drainage ditch or pond

Buffer zones such as ponds and ditches are used to reduce field-scale losses of pesticides from subsurface drainage waters to surface waters. The objective of this study was to assess the efficiency of these buffer zones, in particular constructed wetlands, focusing specifically on sorption processes. We modelled the sorption processes of three herbicides [2-methyl-4-chlorophenoxyacetic acid (2,4-MCPA), isoproturon and napropamide] and three fungicides (boscalid, prochloraz and tebuconazole) on four substrates (two soils, sediment and straw) commonly found in a pond and ditch in Lorraine (France). A wide range of Freundlich coefficient (K fads) values was obtained, from 0.74 to 442.63 mg(1 - n) L (n) kg(-1), and the corresponding K foc values ranged from 56 to 3,725 mg(1 - n) L (n) kg(-1). Based on potential retention, the substrates may be classified as straw >> sediments > soils. These results show the importance of organic carbon content and nature in the process of sorption. Similarly, the studied pesticides could be classified according to their adsorption capacity as follows: prochloraz >> tebuconazole-boscalid > napropamide >> MCPA-isoproturon. This classification is strongly influenced by the physico-chemical properties of pesticides, especially solubility and K oc. Straw exhibited the largest quantity of non-desorbable pesticide residues, from 12.1 to 224.2 mg/L for all pesticides. The presence of plants could increase soil-sediment sorption capacity. Thus, establishment and maintenance of plants and straw filters should be promoted to optimise sorption processes and the efficiency of ponds and ditches in reducing surface water pollution.

Degradation of polar organic micropollutants during riverbank filtration: complementary results from spatiotemporal sampling and push-pull tests

The fate of polar organic micropollutants (logDOW (pH 7) between -4.2 and +3.5) during riverbank filtration (RBF) at the river Thur was studied using both spatiotemporally resolved sampling and single-well push-pull tests (PPT), followed by LC-MS/MS analysis. The Thur is a dynamic prealpine river with an alluvial sandy-gravel aquifer, which is characterized by short groundwater travel times (a few days) from surface water infiltration to groundwater extraction. The spatiotemporal sampling allowed tracing concentration dynamics in the river and the groundwater and revealed persistence for the drug carbamazepine, while the herbicide MCPA (2-methyl-4-chloro-phenoxyacetic acid) and the drug 4-acetamidoantipyrine were very quickly degraded under the prevalent aerobic conditions. The corrosion inhibitor 1H-benzotriazole was degraded slightly, particularly in a transect influenced by river restoration measures. For the first time in situ first-order degradation rate constants for three pesticides and two pharmaceuticals were determined by PPTs, which confirmed the results of the spatiotemporal sampling. Atenolol was transformed almost completely to atenolol acid. Rate constants of 0.1-1.3 h(-1) for MCPA, 2,4-D, mecoprop, atenolol, and diclofenac, corresponding to half-lives of 0.6-6.3 h, demonstrated the great potential of RBF systems to degrade organic micropollutants and simultaneously the applicability of PPTs for micropollutants in such dynamic systems.

Behavior of MCPA in four intensive cropping soils amended with fresh, composted, and aged olive mill waste

An evaluation was made of the impact of olive mill waste and its organic matter transformation on the sorption, desorption, leaching, and degradation of the herbicide MCPA when the waste was applied to four Mediterranean soils. The soils were amended in the laboratory with fresh, composted, and field-aged olive mill waste (OW, COW, and AOW treatments, respectively). It was found that the greater the amount of OW applied to the soils, but especially the greater its organic matter maturity, the greater the adsorption of MCPA. Compared with unamended soils, at the 5% rate of application the adsorption capacity increased by between 9.8% and 40%, 148% and 224%, and by 258% for the OW, COW, and AOW amended soils, respectively. The hysteresis coefficients were significantly lower in the OW-amended soils than in AOW or COW-amended soils, indicating that the adsorbed MCPA could be easily desorbed in OW-amended soils if the amendment is not aged or composted. While the OW addition greatly extended the persistence of MCPA, the application of COW enhanced MCPA degradation in all the soils, as corresponded to the increased soil microbial activity indicated by the higher levels of soil dehydrogenase activity. Fresh OW amendment significantly increased the amount of MCPA leached (from 13.7% in the most alkaline soil to 36.7% in the most acidic, at the 5% rate of application), favored by the higher levels of water soluble organic carbon content. However, leaching losses of the herbicide were reduced by up to 39.9% and 55.3% in the COW- and AOW-amended soils at the 5% loading rate, respectively. The use of OW with a high degree of organic matter maturity may be regarded as a potentially useful management practice to reduce MCPA leaching in soils with low organic matter content. The application of fresh OW, however, could well increase the risk of groundwater contamination by this herbicide, especially in acidic soils.

Kinetics of degradation and adsorption-desorption isotherms of thiobencarb and oxadiargyl in calcareous paddy fields

Herbicides are an important source of contamination in paddy fields. Monitoring their fate and chemical interactions is therefore imperative for sustaining the environment and human health. To meet this purpose, field experiments were conducted to investigate kinetics of thiobencarb and oxadiargyl dissipation in soil and water of two paddy fields. Their adsorption and desorption isotherms were also determined in the soil samples. Variation in concentration was monitored for 60d in soil solution phase and for 315d in soil solid phase. In soil solution, concentrations of both herbicides were rapidly reduced within 5d and reached steady state within 20-30d. Analysis of experimental data resolved a half-life ≈2-4d for both herbicides. In soil solid phase, adsorption reaction played a dominant role in the first 10d. Afterwards, degradation reactions regulated the process. Variation in concentration was minimized after about 150d for thiobencarb and 80d for oxadiargyl. The half-lives were calculated ≈50d for thiobencarb and ≈20d for oxadiargyl, indicating that association with soil particles protect them effectively against degradation reactions. Adsorption isotherms confirmed that both herbicides were strongly adsorbed on soil particles. Furthermore, desorption data indicated that after four successive desorption steps, less than 9% thiobencarb and 1% oxadiargyl were released. This denotes that electrolyte ions in solution cannot adequately compete with and replace adsorbed thiobencarb and oxadiargyl molecules. This would lead to a considerable hysteresis between adsorption and desorption isotherms as was observed experimentally. Overall, it was concluded that both herbicides are among non-persistent and immobile herbicides in the paddy soils.

Phenoxyalkanoic acid herbicide sorption and the effect of co-application in a Haplic Cambisol with contrasting management

The adsorption and desorption behaviour of two phenoxyalkanoic acid herbicides (MCPA and mecoprop-p) in a Haplic Cambisol with tillage and grassland management was examined using a batch equilibrium method. Additionally, the effect on adsorption of the simultaneous presence of the two herbicides was also studied. The sorption equilibrium was reached within 24h for adsorption and desorption in both soils. The experimental sorption data for MCPA and mecoprop-p fitted the Freundlich and the linear adsorption isotherms very well (R(2)>0.99). The Freundlich exponent values of the adsorption isotherm ranged from 0.91 to 0.98 indicating a non-linear and a linear adsorption of the two chemicals studied. Generally, mecoprop-p showed lower adsorption than MCPA, although the adsorption of both phenoxyalkanoic acid herbicides was low. The adsorption process was not fully reversed during one washing cycle, as the K(f) values for desorption were greater than corresponding K(f) values for adsorption. The Freundlich exponent (1/n) of the MCPA adsorption isotherm was affected by the simultaneous presence of both herbicides and tended more towards non-linearity, whilst the mecoprop-p adsorption exponent remained unaltered. The Freundlich and the linear adsorption coefficients calculated in the mix study were not that different from the adsorption coefficients calculated in the single compound study, and therefore single compound adsorption data can be used when modelling the fate of simultaneously applied phenoxyalkanoic acid herbicides. The study also indicated that both herbicides were poorly sorbed by the soils studied, and therefore may pose a risk of surface and/or groundwater pollution in Ireland.

Differences in sorption behavior of the herbicide 4-chloro-2-methylphenoxyacetic acid on artificial soils as a function of soil pre-aging

PURPOSE

The sorption behavior of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) to three different artificial soil mixtures was investigated. Artificial soils serve as model systems for improving understanding of sorption phenomena.

MATERIALS AND METHODS

The soils consisted of quartz, ferrihydrite, illite, montmorillonite, and charcoal. In a previous study, several selected mixtures had been inoculated with organic matter, and microbial aging (incubation) had been performed for different periods of time (3, 12, and 18 months) before conducting the sorption experiments. The effect of this pre-incubation time on the sorption behavior was determined. Interaction of MCPA with soil surfaces was monitored by aqueous phase sorption experiments, using high-performance liquid chromatography/ultraviolet and in selected cases Fourier-transformed infrared spectroscopy.

RESULTS AND DISCUSSION

The sorption behavior showed large differences between differently aged soils; Freundlich and linear sorption model fits (with sorption constants K_f , 1/n exponents, and K_d values, respectively) were given for pH = 3 and the unbuffered pH of ∼7. The largest extent of sorption from diluted solutions was found on the surfaces with a pre-incubation time of 3 months. Sorption increased at acidic pH values.

CONCLUSIONS

Regarding the influence of aging of artificial soils, the following conclusions were drawn: young artificial soils exhibit stronger sorption at lower concentrations, with a larger K_f value than aged soils. A correlation with organic carbon content was not confirmed. Thus, the sorption characteristics of the soils are more influenced by the aging of the organic carbon than by the organic carbon content itself.