Fate Of Pesticides Research Articles

Modelling herbicides mobility in amended soils: Calibration and test of PRZM and MACRO

Addition of organic residues to soil is a current farming practice but it is not considered in the modelling studies for pesticide risk assessment at regulatory level despite its potential impact on the pesticide dynamics in soil. Thus, the objective of this work was to examine and to compare the ability of PRZM and MACRO pesticide fate models to simulate soil water content, and bromide (Br−, tracer), chlorotoluron and flufenacet concentrations in the soil profiles (0–100 cm) of one agricultural soil, unamended (control soil, S), amended with spent mushroom substrate (S + SMS) or amended with green compost (S + GC). Based on a two-year field-scale dataset, the models were first calibrated against measurements of water and solutes contents in the soil profiles (first year) and then tested without any further model calibration by comparison with the field observations of the second year. In general, the performance of MACRO to simulate the whole dataset in the three soil treatments was higher than that of PRZM. MACRO simulated satisfactorily the water dynamics along the soil profiles whereas it was poorly described by the capacity model PRZM. Both models predicted very well the Br− mobility in control and amended soils after dispersion parameters were fitted to observations. No calibration was necessary to reproduce correctly herbicides vertical distribution in the control soil profile. In the amended soils, MACRO simulations were highly correlated to the observed vertical distribution of flufenacet and chlorotoluron, but calibration of the Kd of chlorotoluron was needed. On the contrary, modelling with PRZM required calibration of Kd and DT50 of both herbicides to obtain an acceptable agreement between observations and predictions in the amended soils. Kd and DT50 calibration was based on the initial dissolved organic carbon contents (DOC) of amended soils. It allowed to take into account the processes that decrease the herbicides sorption on the soil and enhance their bioavailability, but that are not described in PRZM and MACRO (such as the formation of herbicide-DOC mobile complexes). This work showed that models such as PRZM and MACRO are able to simulate the fate of pesticides in amended soils. However, before using these models as predictive tools in large amended soil conditions, and especially in the regulatory context, further modelling studies should focus on other pedoclimatic-pesticides-organic residues combinations, and on longer periods.

Sensitivity analysis of the aquatic pesticide fate models in SYNOPS and their parametrization for Switzerland.

The model SYNOPS was developed to calculate national risk indicators for assessing the aquatic and terrestrial risk potential of pesticides in Germany. For Switzerland, a national aquatic risk indicator is currently being developed based on SYNOPS. It aims at evaluating long-term trends in aquatic risks based on changing pesticide usage and risk mitigation measures. In a first step, parameters of the fate models of SYNOPS were parametrized for the Swiss geographical context. Apart from data about pesticides and their specific usage, SYNOPS requires information about climate, soil and site-specific properties and crop stage. Based on these inputs, SYNOPS calculates the predicted environmental concentrations (PEC) of pesticides in water bodies and the associated exposure-toxicity-ratios (i.e., risks). To consider the effects of risk mitigation measures in risk indicators, a realistic representation of the contribution of different routes of entry (run-off, erosion, drainage, drift) is essential. To parametrize SYNOPS, a sensitivity analysis of the aquatic transport and fate models of SYNOPS was conducted: realistic ranges of Swiss-specific parameters and their combinations were defined and used as input for the sensitivity analysis. The impacts of input parameters on total PEC values and on the contribution of different routes of entry were analyzed. The sensitivity analysis revealed that slope and KOC were the parameters with the highest impact on pesticide concentration and that run-off was the dominant route of entry in most tested scenarios. From over 40,000 tested environmental scenarios, a reduced set of 75-113 environmental scenarios was finally selected, which predicted similar PEC values and comparable contributions of different routes of entry compared with the full set. With the parametrization and reduction of used environmental scenarios, fate calculations became more efficient and realistic for Swiss conditions. The findings of this study provide a solid basis for developing a national aquatic risk indicator using SYNOPS.

Hydrological tracers for assessing transport and dissipation processes of pesticides in a model constructed wetland system

Abstract. Studies that have used hydrological tracers to investigate the fate and transport of pesticides in constructed wetlands have often considered such systems as a “black box”. Consequently, internal temporal and spatial mechanisms that dominate pesticide transport and dissipation (e.g., sorption, transformation and plant uptake) are still not fully understood. Here we present a novel approach that combines the use of tracers with different sorptive and reactive properties – i.e., bromide (Br−), uranine (UR) and sulforhodamine B (SRB) – with high vertical resolution sampling and monitoring to evaluate transport and dissipation processes of three selected pesticides (boscalid, penconazole and metazachlor) inside a model constructed wetland system on a long-term basis and detailed spatial scale. Moreover, the influence of vegetation and alternating different hydrologic conditions on transport and dissipation processes was evaluated by comparing a vegetated with a non-vegetated section and by alternating periods of saturation and drying. Breakthrough curves obtained at different sampling depths pointed out that the solutes were not equally distributed within the constructed wetland. Data revealed that a higher mass of solutes was transported to the vegetated part of the uppermost layer, which was associated with possible lateral transport at or near the surface and/or a shortcut effect produced by the roots. In contrast, the middle layers showed retardation, most likely due to the presence of water-filled pores before the injections and low pore connectivity in the vicinity of the sampling ports. The strong temporal and spatial correlation found between Br−, UR and metazachlor indicated that transport was the dominant process for these solutes. Conversely, SRB, boscalid and penconazole most likely underwent sorption, as evidenced by their absence in the middle layers, the rapid decrease in their concentrations after the injections and the gradual increase in accumulated mass recovery at the outlet. The overall tracer mass balance allowed us to identify three dissipation pathways: sorption, transformation and plant uptake. The detection of metazachlor transformation products (TPs) confirmed the contribution of transformation to metazachlor dissipation, whereas no TPs for boscalid and penconazole were detected; however, their transformation could not be ruled out in the present study. Hot spots of sorption and transformation were found in the uppermost layer, whereas hot moments were detected at the beginning of the experiment for sorption and after promoting aerated conditions for transformation. The use of hydrological tracers coupled with high vertical resolution sampling and monitoring proved to provide valuable information about the transport vectors and dissipation processes of pesticides inside a constructed wetland. This study represents a first approximation, and further experiments need to be carried under field conditions in combination with modeling.

Application and prospects of fugacity models in the fate of pesticides in lake watershed

Application and prospects of fugacity models in the fate of pesticides in lake watershed

Crop residue ashes reduce leaching, persistence and bioavailability of sulfosulfuron and pretilachlor used in the succeeding crop

Ash produced during burning of crop biomass may affect the behaviour of herbicides applied in the crops sown after burning. Therefore, the effect of wheat straw ash (WSA) on pretilachlor and rice straw ash (RSA) on sulfosulfuron leaching, degradation and bioactivity in soils was studied. Both ash types reduced downward mobility of respective herbicides, but the effect varied with soil type and dose of ash. Effect was greater in the sandy loam soil because masking of ash was observed in the clay loam soil. Pretilachlor degradation studies indicated that the WSA enhanced degradation and effect was greater in the flooded soil where 0.2% ash reduced the half-life (t1/2) by nearly half, whereas increasing the ash content to 0.5% slightly increased the t1/2 values. The effect of RSA on sulfosulfuron degradation was significant in the sandy loam soil. A pot culture study in wheat also confirmed these results. The effect of the WSA on the bioavailability of sulfosulfuron was assayed by observing its effect on mustard seedlings and results suggested that even 0.1% WSA reduced herbicide availability. Burning of crop residues on field is a major concern due to air pollution, but also affects the fate of soil-applied herbicides. Our study has implications in assaying the role of crop ashes on pesticide fate in soils where crop residues are burned regularly.

Humic Substances and their Relation to Pesticide Sorption in Eight Volcanic Soils

ABSTRACT: Pesticide soil sorption is a primary factor that influences the fate of pesticides in the environment, affecting regulation of microbiological and chemical degradation, volatilization and leaching. The main goal of this research was to study the effect of the organic phase of volcanic soils on sorption of agricultural pesticides. Sorption and desorption of eight agricultural pesticides were studied on eight volcanic soils that varied in the fulvic and humic constituents of their organic matter. For all pesticides, sorption was well described by a Freundlich isotherm where 1/nads values indicated that the sorption mechanism could be mainly explained by physical reactions in all soils. Kf values for carbaryl and flumioxazin were the highest with average values of 7.78 and 7.16 mL g-1, respectively. By contrast, hexazinone and metsulfuron-methyl had the lowest average Kf: 0.86 and 0.81 mL g-1, respectively, indicating that they were the least attracted to the soils. The organic fraction of the soil was the main soil factor related to the sorption of all study pesticides. Particularly, humic acid content regulated the sorption between pesticide and soil, especially through the carboxylic groups.

Sobol Global Sensitivity Analysis of a Coupled Surface/Subsurface Water Flow and Reactive Solute Transfer Model on a Real Hillslope

The migration and fate of pesticides in natural environments is highly complex. At the hillslope scale, the quantification of contaminant fluxes and concentrations requires a physically based model. This class of model has recently been extended to include coupling between the surface and the subsurface domains for both the water flow and solute transport regimes. Due to their novelty, the relative importance of and interactions between the main model parameters has not yet been fully investigated. In this study, a global Sobol sensitivity analysis is performed on a vineyard hillslope for a one hour intensive rain event with the CATHY (CATchment HYdrology) integrated surface/subsurface model. The event-based simulation involves runoff generation, infiltration, surface and subsurface solute transfers, and shallow groundwater flow. The results highlight the importance of the saturated hydraulic conductivity K s and the retention curve shape parameter n and they reveal a strong role for parameter interactions associated with the exchange processes represented in the model. The mass conservation errors generated by the model are lower than 1% in 99.7% of the simulations. Boostrapping analysis of sampling methods and errors associated with the Sobol indices highlights the relevance of choosing a large sampling size (at least N = 1000) and raises issues associated with rare but extreme output results.

Organochlorine pesticides and dissolved organic matter within a system of urban exorheic lakes.

Urban lakes represent the most extensive water bodies in cities and provide blue ecosystem services, by retaining pollutants, offering cultural services, and mitigating climate change. Human activities threaten to decrease the supply of ecosystem services associated with urban lakes. Exorheic lakes play an essential role in reducing and changing the characteristics of pollutants and organic matter along the environmental continuum. This study aims to gain further understanding on the distribution and fate of organochlorine pesticides (OCPs) in relation to fluorescent dissolved organic matter (DOM) within an exorheic lake system, located along Colentina river, Bucharest. Results indicated a historical usage of HCHs, which were present in lake water and sediment samples, in concentrations exceeding the regulatory limits, with potential eco-toxicity on aquatic biota. Decades of intense applications along the river, before OCPs ban, led to their accumulation in sediments and their re-mobilization, each year, after the lakes were drained, dredged, and refilled. Fluorescence measurements revealed that DOM accumulated in certain lakes due to wastewater discharges, and surface runoff, but decreased towards the end of the exorheic lakes through dilution, sedimentation, and biodegradation. The results also showed that fluorescent DOM may have a substantial impact on OCPs cycle in urban lakes and may help to determine the conditions and effectiveness of removing OCPs from water and sediments. These issues contribute to the decrease of ecosystem services supply associated with urban lakes, having multiple hidden consequences on the urban environment.

Error Models for the Kinetic Evaluation of Chemical Degradation Data

In the kinetic evaluation of chemical degradation data, degradation models are fitted to the data by varying degradation model parameters to obtain the best possible fit. Today, constant variance of the deviations of the observed data from the model is frequently assumed (error model “constant variance”). Allowing for a different variance for each observed variable (“variance by variable”) has been shown to be a useful refinement. On the other hand, experience gained in analytical chemistry shows that the absolute magnitude of the analytical error often increases with the magnitude of the observed value, which can be explained by an error component which is proportional to the true value. Therefore, kinetic evaluations of chemical degradation data using a two-component error model with a constant component (absolute error) and a component increasing with the observed values (relative error) are newly proposed here as a third possibility. In order to check which of the three error models is most adequate, they have been used in the evaluation of datasets obtained from pesticide evaluation dossiers published by the European Food Safety Authority (EFSA). For quantitative comparisons of the fits, the Akaike information criterion (AIC) was used, as the commonly used error level defined by the FOrum for the Coordination of pesticide fate models and their USe(FOCUS) is based on the assumption of constant variance. A set of fitting routines was developed within the mkin software package that allow for robust fitting of all three error models. Comparisons using parent only degradation datasets, as well as datasets with the formation and decline of transformation products showed that in many cases, the two-component error model proposed here provides the most adequate description of the error structure. While it was confirmed that the variance by variable error model often provides an improved representation of the error structure in kinetic fits with metabolites, it could be shown that in many cases, the two-component error model leads to a further improvement. In addition, it can be applied to parent only fits, potentially improving the accuracy of the fit towards the end of the decline curve, where concentration levels are lower.

Emission estimation and fate modelling of three typical pesticides in Dongjiang River basin, China

Pesticides are widely and intensively used in the world for crops protection. High pesticide loadings can potentially pollute the water resource. However, little is known about the usage, environmental emission and fate of pesticides in river basins. Here, we firstly established a pesticide emission estimation method, and investigated the environmental fate of three commonly used pesticides (chlorpyrifos, triazophos, and isoprothiolane) in Dongjiang River basin, southern China using mathematical modelling approach in combination with field monitoring. The distributed hydrological model SWAT (Soil and Water Assessment Tool) was applied to model the emission of the target pesticides from farmland to stream water, and their fate in the basin. A satisfactory model calibration for flow and suspended sediment was obtained based on eight-year observation data of four hydrological monitoring stations in Dongjiang River basin. The differences between the simulation and observation of pesticides were almost within an order of magnitude, including more than 53% differences within 0.5 order of magnitude. In the river basin, 78860 kg of chlorpyrifos, 54990 kg of triazophos and 35320 kg of isoprothiolane were sprayed onto the crops, the estimated annual emissions of the basin come up to 1801 kg, 3779 kg, and 2330 kg under the conditions of rainfall, surface runoff and percolation. After a series of environmental processes including settlement and degradation within the channels, the predicted export masses for chlorpyrifos, triazophos and isoprothiolane were reduced to 266 kg, 1858 kg, 1350 kg, respectively. Successful prediction suggests that the reliable estimation method combing the SWAT modelling can help us understand the source, concentration levels and fate of pesticides in river basin in different scales. Combing the method of emission and fate modelling method we proposed, countries and regions lacking pesticide-application database can facilitate better management of pesticides.

A critical review of different factors governing the fate of pesticides in soil under biochar application

Pesticides are extensively used in the modern agricultural system. The inefficient and extensive use of pesticides during the last 5 to 6 decades inadvertently led to serious deterioration of environmental quality with health risk to living organisms, including humans. It is important to use some environmentally-friendly and sustainable approaches to remediate, restore and maintain soil quality. Biochar has gained considerable attention globally as a promising soil amendment because it has the ability to adsorb and as such minimize the bioavailability of pesticides in soils. This review emphasizes the recent trends and implications of biochar in pesticide-contaminated soils, as well as highlights need of the pesticides use and associated environmental issues in context of the biochar application. The overarching aim of this review is to signify the role of biochar on primary processes such as effect of biochar on the persistence, mineralization, leaching and efficacy of pesticides in soil. Notably, the effects of biochar on pesticide adsorption-desorption, degradation and bioavailability under various operating/production conditions are critically discussed. This review delineates the indirect impact of biochar on pesticides persistence in soils and proposes key recommendations for future research which are essential for the remediation and restoration of pesticides-impacted soils.

Research and application progresses on rice water quality (RICEWQ)model.

Rice production presents a unique environmental condition, with the diseases, insects and weeds being serious during production process. Many kinds of pesticides are used with high frequency. Some pesticides will leach into surrounding water, which shows a high risk for pollution. With the increasing costs of pesticide monitoring and field experiments, mathematical models have become an indispensable part during the process of pesticide registration. As the most reliable and widely used model for pesticide exposure assessment in European paddy fields, rice water quality (RICEWQ) model was mainly used to predict pesticide concentrations in flooded paddy fields and water, and had been preliminarily applied in China. In this review, system structure, the main processes of pesticide fate involved, input and output of RICEWQ model were briefly introduced, and the research progress at home and abroad were summarized. This review would promote the application of RICEWQ model in China and provide reference for related research.

A sensitivity analysis of pesticide concentrations in California Central Valley vernal pools

Vernal pools are ephemeral wetlands that provide critical habitat to many listed species. Pesticide fate in vernal pools is poorly understood because of uncertainties in the amount of pesticide entering these ecosystems and their bioavailability throughout cycles of wet and dry periods. The Pesticide Water Calculator (PWC), a model used for the regulation of pesticides in the US, was used to predict surface water and sediment pore water pesticide concentrations in vernal pool habitats. The PWC model (version 1.59) was implemented with deterministic and probabilistic approaches and parameterized for three agricultural vernal pool watersheds located in the San Joaquin River basin in the Central Valley of California. Exposure concentrations for chlorpyrifos, diazinon and malathion were simulated. The deterministic approach used default values and professional judgment to calculate point values of estimated concentrations. In the probabilistic approach, Monte Carlo (MC) simulations were conducted across the full input parameter space with a sensitivity analysis that quantified the parameter contribution to model prediction uncertainty. Partial correlation coefficients were used as the primary sensitivity metric for analyzing model outputs. Conditioned daily sensitivity analysis indicates curve number (CN) and the universal soil loss equation (USLE) parameters as the most important environmental parameters. Therefore, exposure estimation can be improved efficiently by focusing parameterization efforts on these driving processes, and agricultural pesticide inputs in these critical habitats can be reduced by best management practices focused on runoff and sediment reductions.

Reaction pathways, kinetics and toxicity assessment during the photocatalytic degradation of glyphosate and myclobutanil pesticides: Influence of the aqueous matrix

Assessment of reaction pathways, kinetics and water toxicity during the photocatalytic degradation of glyphosate and myclobutanil pesticides has been performed in different aqueous matrices of increasing complexity, from the single pesticides to the mix of their commercial formulations. Using Aeroxide® TiO2-P25 as reference UV-A (Ultraviolet A) light photocatalyst, the ability of photocatalysis to degrade glyphosate and myclobutanil pesticides in water was evidenced independently of the aqueous matrix complexity, complete mineralization into CO2, phosphate and chloride ions being achieved. Further, an unusual volcano-like TOC evolution profile resulting from the proposed glyphosate degradation pathway was observed whatever the aqueous matrix. Increasing the water matrix complexity from single pesticides to the commercial formulation mix reduced the degradation kinetics and consequently extended the time necessary for complete mineralization but, did not influence the overall pesticide fate profiles. This behavior was associated to the competitive adsorption of the organic matter onto the catalyst and to the presence of ions and inorganic matter. The co-presence of glyphosate and to lesser extent of Roundup® formulation additives strongly impacted the myclobutanil fate profile, due to preferential adsorption/degradation of glyphosate. By contrast, despite the impact in the degradation pathway, the inorganic additives of the Systhane® formulation influenced less both the myclobutanil removal duration and the TOC removal than the glyphosate pesticide and its organic additives from Roundup® do. The treatment allowed for most of the cases a strong reduction of acute toxicity to aquatic invertebrate test organisms (D. magna) whatever the water matrix complexity, while the ecotoxicity was reduced by half for the complex formulation mix.

Processing Induced Degradation Routes of Prochloraz in Rapeseed Oil.

Analyzing the fate of substances in complex matrices, such as processed food, is a major challenge in modern analytical chemistry. However, current regulatory procedures for pesticides only include high temperature hydrolysis of the active substance in water (OECD 507) to simulate food processing. This study shows that heating radiolabeled [imidazolyl-2-14C]prochloraz in virgin rapeseed oil at temperatures up to 240 °C leads to an extensive degradation of the active substance. In total, 11 degradation products were identified. Several of these products were formed by reactions of the active substance with ingredients from the oil. 2-[(1-H-Imidazole-1-carbonyl)(propyl)amino]ethyl oleate (icpame-oleate), a reaction product of an oleic acid moiety and the prochloraz backbone, was identified for the first time. The quantification of prochloraz, icpame-oleate, imidazole, and 2,4,6-trichlorophenol demonstrated the dependency of the degradation process on temperature, heating duration, and type of oil. The obtained results in this study show the enormous impact of high temperature food processing on the fate of pesticides. The necessity to consider matrix related reactions in pesticide regulation is emphasized, and the suitability of the OECD 507 guideline is questioned. Concerning possible toxicological risks of novel degradation products, future studies will have to assess potential hazards or opportunities of food processing, ultimately yielding in safer food.

PestTox: An object oriented model for modeling fate and transport of pesticides in the environment and their effects on population dynamics of non-target organisms

Pesticides are toxic chemicals/products that are widely used for pest control. The most widely used type of pesticides is insecticides, fungicides and herbicides. Their continued use has been associated with undesired effects to non-target organisms thus raising environmental concerns worldwide. The problem however, is complex to integrate as there are number of processes that could contribute to the undesired effects. One of the problems is the lack of object-oriented and open source ecological tools that could be used to model the complex interaction of pesticides in the environment and their effects to non-target organisms e.g., frogs. Ecological models could save time as they could be used for management of complex interaction in the environment. The aim of the present study was therefore to add to the available literature, an ecological modeling tool that could be used to model this complex interaction of pesticides and the environment either for research or registration purposes. In this view, PestTox, which is an object-oriented and open-source model, was developed. The model is written in standard C++ language to model this complex interaction. PestTox adopted PestLCI model so that sub-models (objects) could be integrated to it. New equations for modeling washoff, photo-degradation, and pesticide-induced mortality rates were added to PestTox. The model runs on Linux, OS X, and Windows operating systems. It utilizes open source programs; Universal simulator, R, and Notepad, as such it remains open source. This model could be of interest to those involved in ecological modeling, modeling fate and transport of pesticides, data science, and management framework to evaluate potential effects of using pesticides in agricultural settings.

Mapping Geospatial Processes Affecting the Environmental Fate of Agricultural Pesticides in Africa.

The application of agricultural pesticides in Africa can have negative effects on human health and the environment. The aim of this study was to identify African environments that are vulnerable to the accumulation of pesticides by mapping geospatial processes affecting pesticide fate. The study modelled processes associated with the environmental fate of agricultural pesticides using publicly available geospatial datasets. Key geospatial processes affecting the environmental fate of agricultural pesticides were selected after a review of pesticide fate models and maps for leaching, surface runoff, sedimentation, soil storage and filtering capacity, and volatilization were created. The potential and limitations of these maps are discussed. We then compiled a database of studies that measured pesticide residues in Africa. The database contains 10,076 observations, but only a limited number of observations remained when a standard dataset for one compound was extracted for validation. Despite the need for more in-situ data on pesticide residues and application, this study provides a first spatial overview of key processes affecting pesticide fate that can be used to identify areas potentially vulnerable to pesticide accumulation.

Sensitivity analysis of the Pesticide in Water Calculator model for applications in the Pampa region of Argentina

Despite the widespread use of pesticides in the Pampa region of Argentina, mathematical models are rarely employed to predict pesticide fate due to the lack of regionally tested models and the absence of readily available databases to run such models. The objective of the current study was to perform a sensitivity analysis of the Pesticide in Water Calculator (PWC) model for the Pampa Region of Argentina. The sensitivity analysis was performed while simulating applications of 2,4-D (mobile, low Kd) and glyphosate (soil-binding, high Kd) in five localities of the Pampa region: Anguil, Paraná, Marcos Juárez, Pergamino and Tres Arroyos. The sensitivity of the various parameters involved in PWC modelling was evaluated though a two-steps sensitivity analysis which included a first screening of less sensitive parameters with Morris method, followed by a fully global sensitivity analysis of the remaining parameters using Sobol method. When ran under soil and climate conditions typical of the Pampa region of Argentina, PWC was most sensitive to 25% of the parameters evaluated. The sensitive parameters identified depended mainly on the nature of the pesticide molecule being modelled; the location and endpoint considered having much less influence on the sensitivity results. Sensitive parameters belonged to two main grand categories: (i) degradation rates of the pesticide in soil and water, and (ii) parameters descriptive of soil binding, runoff and erosion. The sensitivity analysis of the model PWC performed in the current study represents a crucial first step towards the development and expansion of probabilistic pesticide risk assessment in Argentina, and provides important parameterization criteria that will help obtaining more certain modelling results from PWC in Argentina and elsewhere.

Influence of water chemistry on colloid-size Cu-based pesticides particles: A case of Cu(OH)2 commercial fungicide/bactericide

The intensive, widespread, and ever-increasing applications of Cu-based pesticides in agriculture could potentially increase environmental exposures via different routes. Unlike ionic/bulk forms, the fate, transport, and toxicity of colloid-size Cu-based pesticides are not well studied. This paper provides evaluation outcomes of granule and dispersion characterizations, stability, and dissolution of colloid-size particles of Cu(OH)2 commercial pesticide product at a range of water chemistry. The evaluated product contained about 35% weight of metallic Cu equivalent and Cu(OH)2 particles with sizes < 1 μm of which a fraction of nanoscale particles exist. The presence of Ca2+ at ionic strengths of >0.01 M and 0.001–0.2 M significantly influenced (p < 0.001) particle size (PS) and ζ-potential values, respectively at all investigated pH values. Cu dissolution at pH 5.5 was significant (p < 0.001) and exceeded Cu dissolutions at pH 7.0 by 87–90% and at pH 8.5 by 87–95% in all dispersions. The order of Cu dissolution was pH 5.5 > pH 7.0 > pH 8.5 in all dispersions. Cu dissolution was relatively reduced by 53% by increasing HA from 0 to 5 mg L−1 and enhanced by 55% by increasing HA from 5 to 15 mg L−1, however, the overall Cu dissolution was decreased by 27% by increasing HA from 0 to 15 mg L−1. Thus, HAs reduced the dissolution of Cu at pH < 7. The findings provide an insight into how water chemistry influences the fate and transport of colloid-size Cu-based pesticides particles.

Quantifying dynamic desorption of 3,5,6-trichloro-2-pyridinol in loamy farmland soils.

Reliable estimate of the release of adsorbed pesticide from soil particles is crucial to evaluating the pesticide fate, mobility, efficacy, and remediation. In this study, the dynamics of TCP (3,5,6-trichloro-2-pyridinol) desorption, the main degradation product of chlorpyrifos and triclopyr, is explored quantitatively by the breakthrough curve (BTC) experiment with the tracer of Br- in the loamy farmland purple soil sampled from Sichuan Basin of southwestern China. TCP in the outflow originates from two sources: dissolved TCP in pore water and desorbed TCP from soil particles by infiltrating water. The dissolved TCP is considered proportional to the amount of Br- because both TCP and Br- are dissolved in water uniformly. According to the mass balance equation, the desorbed TCP are estimated and the typical patterns of dynamic TCP desorption are revealed. Characteristics of TCP desorption are compared between packed and undisturbed soil columns as well as between different planting types. The dynamics of the proportion of desorbed TCP during the breakthrough process are characterized. In particular, the high heterogeneity of the undisturbed soil may be responsible for the observed fluctuation of desorbed TCP in the outflow. Additionally, the obtained increase-decrease pattern of the desorbed rate of TCP released from the soil shows that most models proposed to simulate the desorption processes are not appropriate, because these models display a monotone decreasing trend, such as the Noyes-Whitney Rule and other release kinetic models (zero order, first order, Higuchi and Korsmeyer-Peppas model, etc.). After a comparison among linear model, Gamma distribution and Weibull distribution, the CDF of gamma distribution is identified as a better method to describe the proportion of desorbed TCP in outflow. Therefore, this study provides an alternative method to measure the dynamic desorption process of TCP in different environment of the purple soil, and their affecting factors are also identified. These results are useful in quantifying the leaching of the TCP in the field, in support of the prevention of agricultural non-point pollution of pesticides.