Initial Pesticide Concentration Research Articles

Oxidation kinetics of two pesticides in natural waters by ozonation and ozone combined with hydrogen peroxide

The oxidation of bromoxynil and trifluralin was investigated using ozone (O 3) and O 3 combined with hydrogen peroxide (H 2O 2) in natural waters using batch reactors. The results indicated that these pesticides could not be completely degraded during ozonation, achieving degradation levels lower than 50%. An enhancement of the level of degradation was observed using O 3/H 2O 2 process. A biphasic behaviour of O 3 was also observed. Depending on the experimental conditions, the rate constant for O 3 decomposition was estimated to be between 7.4 × 10 −4 s −1 to 5.8 × 10 −2 s −1, and 3.2 × 10 −3 s −1 to 4.2 × 10 −2 s −1 for bromoxynil and trifluralin samples, respectively. Acute toxicity analysis performed using Microtox ® showed a decrease in the toxic effects of the samples on the luminescent bacteria during the first few minutes of treatment, followed by an increase of the toxic effects at the end of the reaction for both pesticides. The quantification of oxidation by-products generated during treatment was also addressed. The total molar balances of the degradation by-products versus the initial pesticide concentrations ranged from 60 to 103% under different experimental conditions.

Mineralization of isoproturon, mecoprop and acetochlor in a deep unsaturated limestone and sandy aquifer

Isoproturon ( N, N-dimethyl- N′-[4-(1-methylethyl)phenyl]urea), mecoprop (MCPP) (2-(4-chloro-2-methylphenoxy)propanoic acid) and acetochlor (2-chloro-N-(2-ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide) are agricultural pesticides that may leach through the vadose zone down to groundwater. Sediment samples were collected from intact sediment cores from 0 to 59 m below surface, including soil, unsaturated limestone and aquifer sand. In the unsaturated limestone, the initial pesticide concentrations (0.5–100 μg kg −1) did not systematically affect the proportion of mineralized pesticides or the kinetics. However, in the aquifer, mecoprop and to some degree isoproturon mineralization was found to increase with increasing initial concentration (0.5–100 μg L −1 equivalent to 1–220 μg kg −1) demonstrating the importance of using environmentally relevant concentrations when predicting pesticide fate. The mineralization of isoproturon, mecoprop and acetochlor was studied in 40 samples at low concentrations (1–3 μg L −1) and specific pesticide-mineralizing bacteria were enumerated using 14C-MPN. Presence of the mineralizers documented a degradation potential of the pesticides within the catchment. The number of mineralizers varied from <0.18 to >16 000 g −1 and was not found to correlate with depth. Mecoprop, isoproturon and acetochlor were substantially mineralized in the soils (19–44% after 8 months incubation at 1 μg kg −1), in sub-surface unsaturated limestone samples (≤2% for acetochlor, ≤21% for isoproturon and ≤31% for mecoprop) and in aquifer samples (4–28% for mecoprop, ≤4.7% for isoproturon and ≤5.6% for acetochlor). The finding of isoproturon and acetochlor mineralization in deep aquifers is novel and important for the evaluation of the fate of these pesticides, as even low mineralization rates can be important in aquifers exhibiting long residence times.

Removal of nitrophenol pesticides from aqueous solutions by layered double hydroxides and their calcined products

The ability of MgAl layered double hydroxides (LDHs) and their calcined products to adsorb the water contaminants 2,4-dinitrophenol (DNP) and 2-methyl-4,6-dinitrophenol (DNOC) was assessed. Adsorption tests were conducted on LDHs with variable Mg/Al ratios (and variable layer charge), pH values, contact times and initial pesticide concentrations to identify the optimum conditions for the intended purpose. Adsorbents and adsorption products were characterized by X-ray diffraction and FT-IR spectroscopy as well as atomic absorption spectroscopy and thermal analyses. The amounts of pesticides removed from water were determined by UV–Vis spectrophotometry. All adsorbents except the carbonate-containing hydrotalcite possessed a very high adsorption capacity for both contaminants.

Influence of initial pesticide concentrations and plant population density on dimethomorph toxicity and removal by two duckweed species

Aquatic plants take up, transform and sequester organic contaminants and may therefore be used in phytoremediation for the removal of pollutants from wastewaters. A better understanding of factors affecting the rate of contaminant uptake by aquatic plants is needed to improve engineered systems for removal of pollutants from wastewaters. This work focused on the influence of initial concentrations of pesticide and population density of plants on toxicity and uptake of the fungicide dimethomorph by two duckweed species. An increased sensitivity to dimethomorph was observed with increasing duckweed population density. Less light, due to crowding, may explain this higher sensitivity and reduced removal rate. A positive relationship was also found between toxicity or contaminant uptake and initial pesticide concentration with a maximal removal of 41 and 26 µg g − 1 fresh weight of dimethomorph (at 600 µg L − 1 of dimethomorph and an initial density of 0.10 g E-flask − 1 ) by Lemna minor and Spirodela polyrhiza, respectively. This research also indicated that these aquatic plants can efficiently eliminate organic contaminants and may ultimately serve as phytoremediation agents in the natural environment.

Adsorption of Methyl Parathion from Aqueous Solutions Using Mango Kernels: Equilibrium, Kinetic and Thermodynamic Studies

ABSTRACT The adsorption of methyl parathion from aqueous solutions by the low-cost and abundant adsorbent mango kernel was studied in a batch adsorption system. The adsorption was studied as a function of pH, contact time, initial pesticide concentration, adsorbent dose, and temperature. A maximum adsorption of 98% ± 1% was achieved. Physicochemical characterization of the adsorbent was carried out by EDXRF, BET, and CHNS analysis. Freundlich, Langmuir, and Dubinin-Radushkevich isotherms were employed to evaluate the adsorption capacity of the adsorbent. Lagergren, Morris-Weber, and Reichenberg equations were employed to study the kinetics of the adsorption process. Thermodynamic parameters Δ H, Δ S, and Δ G were computed. The developed adsorption method was applied to real environmental samples.

Effect of the adsorbate (Bromacil) equilibrium concentration in water on its adsorption on powdered activated carbon. Part 2: Kinetic parameters

The application of several monosolute equilibrium models has previously shown that Bromacil adsorption on SA-UF (Norit) powdered activated carbon (PAC) is probably effective on two types of sites. High reactivity sites were found to be 10–20 less present in a carbon surface than lower reactivity sites, according to the q m values calculated by isotherm models. The aims of this work were trying, primarily, to identify the kinetic-determinant stage of the sorption of Bromacil at a wide range of initial pesticide concentrations (∼5 to ∼500 μg L −1 at pH 7.8), and secondly, to specify the rate constants and other useful design parameters for the application in water treatment. It was therefore not possible to specify a priori whether the diffusion or surface reaction is the key step. It shows that many of the tested models which describe the stage of distribution or the surface reaction are correctly applied. However, the diffusivity values ( D and D 0) were found to be constant only constants for some specific experimental concentrations. The HSDM model of surface diffusion in pores was also applied but the values of the diffusion coefficient of surface ( D s) were widely scattered and reduce significantly with the initial concentration or the equilibrium concentration in Bromacil. The model of surface reaction of pseudo-second order fitted particularly well and led to constant values which are independent of the equilibrium concentration, except for the low concentrations where the constants become significantly more important. This last observation confirms perfectly the hypothesis based on two types of sites as concluded by the equilibrium data (part 1).

Effect of the adsorbate (Bromacil) equilibrium concentration in water on its adsorption on powdered activated carbon. Part 1. Equilibrium parameters

This study was carried out to investigate the adsorption equilibrium and kinetics of a pesticide of the uracil group on powdered activated carbon (PAC). The experiments were conducted at a wide range of initial pesticide concentrations (∼5 μg L −1 to ∼500 μg L −1 at pH 7.8), corresponding to equilibrium concentrations of less than 0.1 μg L −1 for the weakest, which is compatible with the tolerance limits of drinking water. Such a very broad range of initial solute concentrations resulting powdered activated carbon (PAC) concentrations (0.1–5 mg L −1) is the main particularity of our study. The application of several monosolute equilibrium models (two, three or more parameters) has generally shown that Bromacil adsorption is probably effective on two types of sites. High reactivity sites ( K L ∼ 10 3 L mg −1) which are 10–20 less present in a carbon surface than lower reactivity sites ( K L ∼ 10 L mg −1), according to the q m values calculated by two- or three-parameter models. The maximum capacity of the studied powdered activated carbon (PAC), corresponding to monolayer adsorption, compared to the Bromacil molecule surface, would be between 170 mg g −1 and 190 mg g −1. This theoretical value is very close to the experimental q m values obtained when using linearized forms of Langmuir, Tóth and Fritz–Schluender models.

Mitigation Assessment of Vegetated Drainage Ditches for Collecting Irrigation Runoff in California

Widespread contamination of California water bodies by the organophosphate insecticides diazinon and chlorpyrifos is well documented. While their usage has decreased over the last few years, a concomitant increase in pyrethroid usage (e.g., permethrin) (replacement insecticides) has occurred. Vegetated agricultural drainage ditches (VADD) have been proposed as a potential economical and environmentally efficient management practice to mitigate the effects of pesticides in irrigation and storm runoff. Three ditches were constructed in Yolo County, California for a field trial. A U-shaped vegetated ditch, a V-shaped vegetated ditch, and a V-shaped unvegetated ditch were each amended for 8 h with a mixture of diazinon, permethrin, and suspended sediment simulating an irrigation runoff event. Water, sediment, and plant samples were collected spatially and temporally and analyzed for diazinon and permethrin concentrations. Pesticide half-lives were similar between ditches and pesticides, ranging from 2.4 to 6.4 h. Differences in half-distances (distance required to reduce initial pesticide concentration by 50%) among pesticides and ditches were present, indicating importance of vegetation in mitigation. Cis-permethrin half-distances in V ditches ranged from 22 m (V-vegetated) to 50 m (V-unvegetated). Half-distances for trans-permethrin were similar, ranging from 21 m (V-vegetated) to 55 m (V-unvegetated). Diazinon half-distances demonstrated the greatest differences (55 m for V-vegetated and 158 m for V-unvegetated). Such economical and environmentally successful management practices will offer farmers, ranchers, and landowners a viable alternative to more conventional (and sometimes expensive) practices.

Effects of chlorine on organophosphorus pesticides adsorbed on activated carbon: Desorption and oxon formation

We investigated effects of chlorination on four organophosphorus pesticides (diazinon, isoxathion, malathion, and tolclofos-methyl) adsorbed on powdered activated carbon (PAC). Following adsorption of each pesticide on 10 mg/L of PAC in water, chlorine was added. After 30 min of chlorination, the corresponding oxons were detected in the water, but the parent compounds were not detected. Molar ratios of the oxon concentration in solution after 30 min of chlorine addition to the initial pesticide concentration before the adsorption process were 4.1% and 7.9% for diazinon, 3.9% and 5.8% for isoxathion, 1.2% and 1.7% for malathion, and 1.4% and 1.4% for tolchlofos-methyl, in the case of 2 and 5 mg/L of chlorine addition. The results suggested that the oxons were desorbed from the PAC by chlorination. The concentrations of the desorbed oxons gradually decreased with time, apparently owing to their readsorption by the PAC. Results from additional experiments suggest the following sequence of events: (i) adsorbed pesticides are oxidized by chlorine on the surface of the PAC and transformed into corresponding oxons; (ii) the oxons are released from the PAC; (iii) the released oxons are gradually readsorbed by the PAC, decreasing their concentrations in the water phase.

Bioremediation of lindane-contaminated soil by Streptomyces sp. M7 and its effects on Zea mays growth

The objective of the present study was to study the lindane bioremediation abilities of Streptomyces sp. M7 in soil samples and to know the pesticide effects on maize plants seeded in lindane-contaminated soil previously inoculated with Streptomyces sp. M7. When different initial pesticide concentrations (100, 150, 200, and 300 μg kg −1) were added to sterile soil, the microbial growth observed was similar to the control without lindane. A decrease of the residual lindane concentration was detected in soils samples in relation to the abiotic controls (29.1%, 78.03%, 38.81%, and 14.42%, respectively). The optimum Streptomyces sp M7 inoculum was selected in sterile soil spiked with lindane 100 μg kg −1soil; it was 2 g kg −1 soil for obtaining the most efficient bioremediation process (56% removal). Lindane concentrations of 100, 200, and 400 μg kg −1 soil did not affect the germination and vigor index of maize plants seeded in contaminated soils without Streptomyces sp. M7. When this microorganism was inoculated at the same conditions a better vigor index was observed and 68% of lindane removal. These results confirm the lindane-contaminated soil bioremediation potential of Streptomyces sp. M7.

Natural organic matter (NOM) and pesticides removal using a combination of ion exchange resin and powdered activated carbon (PAC)

The combination of anion exchange resins (AERs) and powdered activated carbon (PAC) was studied to remove both natural organic matter (NOM) and pesticides. Experiments were conducted with high dissolved organic carbon (DOC) surface water (about 6.0 mg DOC/L) spiked with both atrazine and isoproturon. AERs, like MIEX ® and IRA938 ®, showed up to 75% removal of DOC after 30 min contact time. The addition of PAC after treatment with these AERs only slightly decreased the residual DOC from 1.4 to 1.2 mg/L. Experiments conducted with high (200 μg/L) and low (1 μg/L) initial pesticide concentrations showed that simultaneous and successive combinations of AER and PAC significantly improve the removal of both pesticides compared with PAC treatment on raw water. The improvement of short-term adsorption kinetics was explained by the adsorption of pesticides on AERs (about 5%) and the removal of high molecular weight (MW) NOM structures by AERs that reduce pore blockage phenomena. For 24 h contact time with PAC (adsorption isotherms), the benefit of AER treatment was lower, which indicates that the refractory DOC to AER treatment still competes through direct site competition mechanism. MIEX ® resin had a distinct behavior since the simultaneous treatment with PAC showed no benefit on pesticide adsorption. The presence of fine residues of MIEX ® was shown to interfere with PAC adsorption.

Detoxification of wastewater containing five common pesticides by solar AOPs–biological coupled system

A mixture of five pesticides commonly used in intensive agriculture in the southeast of Spain, Methomyl, Dimethoate, Oxamyl, Cymoxanil and Pyrimethanil, has been completely mineralized in a combined solar photocatalytic–biological pilot plant. Two advanced oxidation processes (AOPs: TiO 2 and photo-Fenton) were employed for enhancing the biodegradability of wastewater and an aerobic immobilised biomass reactor (IBR) was used for the following continuous biological treatment. TiO 2 photocatalysis experiments were performed in a 35-L solar pilot plant made up of three compound parabolic collectors (CPCs), whereas photo-Fenton tests were carried out in a 75-L solar pilot plant with four CPCs units. The initial pesticide concentrations in the mixture were 50 mg L −1 each. The TiO 2 catalyst concentration employed was 200 mg L −1, and two different Fe 2+ concentrations, 20 mg L −1 and 55 mg L −1, were used in the photo-Fenton tests. Toxicity ( Vibrio fischeri) and biodegradability assays (Zahn-Wellens test) were also performed to monitor toxicity and biodegradability of samples at different stages of photo-Fenton treatment. Biodegradable compounds generated during the preliminary oxidative process were mineralized in a 60-L activated sludge biological reactor filled with 30 L of propylene Pall Ring supports. Total disappearance of the parent compounds, more than 90% mineralization and complete nitrification were achieved by the combined system.

Treatment of pesticide contaminated surface water for production of potable water by a coagulation-adsorption-nanofiltration approach

The surface water bodies have become very much susceptible to pollution by pesticides due to their increased application in agriculture. The production of potable water from pesticide contaminated lake and river water was investigated by a coagulation-adsorption-nanofiltration approach. Isoproturon (IPU) was selected as a target pesticide and spiked in distilled water and then in surface water. Coagulation was done before adsorption and coagulant dosage was selected on the basis of turbidity removal. Various adsorbents such as powdered activated charcoal (PAC), bentonite, chitosan were tried at different dosages to evaluate their efficiency in IPU removal. The effect of initial pesticide concentration was studied on percent removal of pesticide when treated with selected adsorbent at a particular dosage. The values of adsorption capacity calculated from Langmuir and Freundlich equations were 104.21 mg/g and 69.4 mg/g respectively indicating favorable adsorption of IPU on powdered activated charcoal surface. After optimizing the coagulation and adsorption protocol, nanofiltration (NF) was performed on pretreated water in a test cell in dead end mode. The NF permeate was analyzed for pH, turbidity, TDS, COD, TOC, conductivity, hardness, and colony count. Reverse osmosis (RO) was done after NF if required. The quality of NF/RO permeate was found comparable to the standards of drinking water.

Photocatalytic Degradation of Monolinuron and Linuron in an Aqueous Suspension of Titanium Dioxide Under Simulated Solar Irradiation

The photocatalytic degradation of two phenylurea herbicides, monolinuron (MLN) and linuron (LN), was investigated in an aqueous suspension of TiO2 using simulated solar irradiation. The objective of the study was to compare their photocatalytic reactivity and to assess the influence of various parameters such as initial pesticide concentration, catalyst concentration and photonic flux on the photocatalytic degradation rate of MLN and LN. A comparative study of the photocatalytic degradation kinetics of both herbicides showed that these two compounds have a comparable reactivity with TiO2/simulated sun light. Under the operating conditions of this study, the photocatalytic degradation of MLN and LN followed pseudo first-order decay kinetics. The kobs values indicated an inverse dependence on the initial herbicide concentration and were fitted to the Langmuir-Hinshelwood equation. Photocatalytic degradation rates increased with TiO2 dosage, but overdoses did not necessarily increase the photocatalytic efficiency. The degradation rate of MLN increased with radiant flux until an optimum at 580 W m‑2 was reached and then decreased. Under these conditions, an electron-hole recombination was favored. Finally, the photocatalytic degradation rate depended on pH, where an optimum was found at a pH value close to the pH of the point of zero charge (pH = 6).

Heterogeneous photocatalytic degradation of prometryn in aqueous solutions under UV–Vis irradiation

In this study, the heterogeneous photocatalytic degradation of prometryn using TiO(2) as photocatalyst was investigated. The main objectives of the study were: (I) to evaluate the kinetics of the pesticide disappearance, (II) to compare the photocatalytic efficiency of two different types of TiO(2), (III) to examine the influence of various parameters such as initial concentration of pesticide or catalyst and presence of oxidants (H(2)O(2) and K(2)S(2)O(8)), (IV) to evaluate the degree of mineralization and (V) to assess the detoxification efficiency of the studied processes. The experiments were carried out in a 500 ml pyrex UV reactor equipped with a 125 W high-pressure mercury lamp surrounded by a pyrex filter blocking wavelengths below 290 nm. Prometryn concentration was determined using HPLC. It was found that the degradation of the pesticide follows the first order kinetics according to the Langmuir-Hinshelwood model. Parameters like the type and concentration of the catalyst affect the degradation rate. A synergistic effect was observed when an oxidant was added in the TiO(2) suspensions increasing the reaction rate of photodegradation. In order to examine the extent of pesticide mineralization, DOC measurements were carried out. After 6h of illumination, mineralization was achieved up to almost 70%. The toxicity of the treated solution was evaluated using the Microtox test based on the luminescent bacteria Vibrio fisheri, in order to compare the acute toxicity of prometryn and its photoproducts. The detoxification efficiency was found to be dependent on the studied system and it did not follow the rate of pesticide disappearance.

Solar photocatalytic degradation of some hazardous water-soluble pesticides at pilot-plant scale

The technical feasibility and performance of photocatalytic degradation of six water-soluble pesticides (cymoxanil, methomyl, oxamyl, dimethoate, pyrimethanil and telone) have been studied at pilot-plant scale in two well-defined systems which are of special interest because natural solar UV light can be used: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. TiO 2 photocatalysis tests were performed in a 35 L solar pilot plant with three Compound Parabolic Collectors (CPCs) under natural illumination and a 75 L solar pilot plant with four CPC units was used for homogeneous photocatalysis tests. The initial pesticide concentration studied was 50 mg L −1 and the catalyst concentrations employed were 200 mg L −1 of TiO 2 and 20 mg L −1 of iron. Both toxicity ( Vibrio fischeri, Biofix ®) and biodegradability (Zahn–Wellens test) of the initial pesticide solutions were also measured. Total disappearance of the parent compounds and nearly complete mineralization were attained with all pesticides tested. Treatment time, hydrogen peroxide consumption and release of heteroatoms are discussed.

Degradation of Pesticides in Nursery Recycling Pond Waters

Recycling or collection ponds are often used in outdoor container nursery production to capture and recycle runoff water and fertilizers. Waters in recycling ponds generally have high concentrations of nutrients, pesticides, and dissolved organic matter, as well as elevated salinity and turbidity. Little is known about pesticide degradation behavior in the unique environment of nursery recycling ponds. In this study, degradation of four commonly used pesticides diazinon, chlorpyrifos, chlorothalonil, and pendimethalin in waters from two nursery recycling ponds was investigated at an initial pesticide concentration of 50 microg/L. Results showed that the persistence of diazinon and chlorpyrifos appeared to be prolonged in recycling pond waters as compared to surface streamwaters, possibly due to decreased contribution from biotic transformation, while degradation of chlorothalonil and pendimethalin was enhanced. Activation energies of biotic degradation of all four pesticides were lower than abiotic degradation, indicating that microbial transformation was less affected by temperature than chemical transformation. Overall, the pesticide degradation capacity of recycling ponds was better buffered against temperature changes than that of surface streamwaters.

Removal of atrazine, lindane and diazinone from water by organo-zeolites

Systematic adsorption tests were carried out to determine the efficiency of organo-zeolite (OZ) for removal of atrazine, lindane and diazinone from water. The hydrophobic character of OZ-pesticide interactions was confirmed by measuring the amount of pesticides sorbed on zeolite samples modified with 25, 50, 75 and 150 mmol of stearyldimethylbenzylammoniumchloride (SDBAC)/kg of zeolite. The effects of adsorbent particle size, solid content in the suspension and the initial pesticide concentration in the solutions were also investigated. For effective adsorption of diazinone onto an OZ, it is necessary for the SDBAC/diazinon ratio to be higher than 25. The adsorption capacities, calculated by fitting the experimental data to the Langmuir–Freundlich equation, were 2.0 μmol/g (atrazine), 4.4 μmol/g (diazinone) and 3.4 μmol/g (lindan). At lower initial concentrations of pesticide solution, a linear dependence existed between the amount adsorbed and the equilibrium concentration of pesticide. Column experiments showed that at volumetric flow of 6 cm 3/min, the breakthrough points (at C / C 0 = 0.1 ) were 560 bed volume (BV) for lindane and 620 for diazinone.

Evaluation of Simplifying Assumptions on Pesticide Degradation in Soil

There is evidence that degradation of pesticides in simple laboratory systems may differ from that in the field, but it is not clear which of the simplifications inherent in laboratory studies present serious shortcomings. Laboratory experiments evaluated several simplifying assumptions for a clay loam soil and contrasting pesticides. Degradation of cyanazine [2-(4-chloro-6-ethylamino-1,3,5-triazin-2-ylamino)-2-methylpropiononitrile] and bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] at fluctuating temperature and moisture was predicted reasonably well based on parameters derived from degradation under constant conditions. There was a tendency for slower degradation of cyanazine and bentazone in soil aggregates of 3 to 5 mm in diameter (DT50 at 15 degrees C and 40% maximum water holding capacity of 25.1 and 58.2 d, where DT50 is the time for 50% decline of the initial pesticide concentration) than in soil sieved to <3 mm (DT50 of 19.1 and 37.6 d), but the differences were not significant for most datasets. Degradation of cyanazine, isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea], and chlorotoluron [3-(3-chloro-p-tolyl)-1,1-dimethylurea] was measured in soil amended with different amounts of lignin. The effect of lignin on degradation was small despite considerable differences in sorption. The DT50 values of cyanazine, isoproturon, and chlorotoluron were 16.2, 18.6, and 33.0 d, respectively, in soil without lignin and 19.0, 23.4, and 34.6 d, respectively, in soil amended with 2% lignin. Degradation of bentazone and cyanazine in repacked soil columns was similar under static and flow conditions with 50.1 and 47.2% of applied bentazone and 74.7 and 73.6% of applied cyanazine, respectively, degraded within 20 d of application. Thus, the assumptions underpinning laboratory to field extrapolation tested here were considered to hold for our experimental system. Additional work is required before general conclusions can be drawn.

Removal of the herbicide 2,4-dichlorophenoxyacetate from water to zinc–aluminium–chloride layered double hydroxides

Batch sorption studies were conducted to investigate the potential of [Zn–Al–Cl] layered double hydroxides (LDHs) for the removal of the herbicide 2,4-dichlorophenoxyacetate (2,4-D) from contaminated aqueous solutions. Experiments were performed at different pH values, initial pesticide concentration, solid/pesticide ratio and anion exchange capacity of LDHs. The LDH samples evaluated had very high retention capacity for 2,4-D whose removal was a rapid process, as a quasi-equilibrium state was reached after 1-h reaction time. The adsorption can be described by Langmuir-type isotherms, with an average affinity constant of 12.5 L mmol −1. At initial 2,4-D concentrations between 0.08 and 4 mmol L −1, the solids removed up to 98% of the pesticide. Physicochemical characterization of the LDH solids, both fresh and after removal of 2,4-D, by X-ray diffraction, infrared spectroscopy and thermogravimetry, indicates that the retention of 2,4-D is done by adsorption on the surface of the solid for low 2,4-D concentrations. However, a combination of surface adsorption and interlayer ion exchange takes place when the 2,4-D concentration is high.