Sorption Of Chlorpyrifos Research Articles

Magnet-assisted nanoscale zerovalent iron soil washing in chlorpyrifos-contaminated soil remediation: Proof of concept

Chlorpyrifos (CPF)––a widely used organophosphate pesticide––is banned in many countries due to its persistence in the environment and high toxicity. Residue levels often vastly exceed safety thresholds, posing significant risks to human health and ecosystems. This persistent contamination challenges farmers, especially those transitioning to organic practices. Here, we propose magnet-assisted soil washing with nanoscale zerovalent iron (nZVI) for the rapid remediation of CPF-contaminated soil. Soil mixed with water and nZVI facilitates CPF adsorption and degradation, with the CPF-sorbed nZVI being magnetically separated. We tested various nZVI conditions (inactivated [IZ] and activated [AZ], with and without hydrogen peroxide [H2O2]) against controls, including untreated soil and conventionally washed soil. The control experiments showed that conventional washing without nZVI removed 50.54 ± 3.48 % of the CPF via volatilization, leaving CPF residues in the soil (25.44 ± 2.12 %) that were above the maximum contamination level (MCL). Inactivated nZVI increased the removal by 24.38 ± 0.78 % via CPF sorption, but the MCL was still exceeded. However, AZ or nZVI with H2O2 achieved complete CPF removal (>99.95 %) within 180 min, reducing its concentration to below the MCL (<0.03 mg/kg). Thus, CPF sorption followed by either reductive dechlorination or oxidative degradation proved effective. Additionally, nZVI demonstrated reusability for three rounds while mitigating CPF toxicity, improving seed germination and plant growth. This method offers a promising solution for rapid soil decontamination, supporting the transition to organic farming.

Biosynthesized CS-MgO/zeolite hybrid material: An efficient adsorbent for chlorpyrifos removal - Kinetic studies and response surface methodology

The prevalence of organophosphate pesticides in aquatic environments raises severe concerns on a global scale. Chlorpyrifos, an insecticide, is included in a class of organophosphate pesticides. It is widely used on agricultural lands to control pests in cotton, fruit, and vegetables. The acute toxicity of chlorpyrifos is still dangerous to all aquatic living organisms. Then the treatment of water contaminated with chlorpyrifos is an important aspect. The recent decade has witnessed adsorption technology emerging as an advanced organophosphate pesticide wastewater treatment with great potential and a grand blueprint, in which the specific surface area and active sites of the adsorbent are considered to be the two most important characteristics largely impacting the adsorption performance. In this study, a CS-MgO/Zeolite composite was prepared by the microbial method as an effective adsorbent for the removal of chlorpyrifos from an aqueous solution. The adsorbent's properties were carefully characterized using X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The refinement of experimental conditions, encompassing variations in adsorbent dosage, contact time, and chlorpyrifos concentration at five discrete levels, was systematically undertaken through the utilization of a composite central design rooted in response surface methodology. The solution pH played a key role in chlorpyrifos removal, and a pH of 7.0 was selected according to its high adsorption ability. The highest removal (80.9%) of chlorpyrifos by CS-MgO/Zeolite was obtained at an optimum pH of 7, a contact time of 40 min, an adsorbent dosage of 0.4 g/L, and a chlorpyrifos concentration of 5 mg/L−1. The adsorption results were highly fitted with the Freundlich adsorption isotherm model, and the maximum adsorption was 83.3 mg/g. Kinetic studies indicate that the removal of chlorpyrifos followed the pseudo-second-order model of adsorption (0.994). The thermodynamic parameters indicate the spontaneous and endothermic nature of chlorpyrifos sorption on CS-MgO/Zeolite sorbent. The results revealed that introducing chitosan could improve the adsorption capacity and rate effectively even though it sacrificed part of the specific surface areas of the MgO/Zeolite, indicating that active sites might play a dominant role during chlorpyrifos adsorption. The fabricated CS-MgO/Zeolite adsorbent nanocomposite displayed high reusability based on the elution and simultaneous regeneration ability. Therefore, as a cheap green nanocomposite adsorbent with high adsorption performance for chlorpyrifos, the CS-MgO/Zeolite nanocomposite adsorbent is expected to become one of the best candidate materials for chlorpyrifos removal aqueous solutions.

Induced effects of gamma irradiation on activated carbon derived from Hyphaene Thebaica husks as a potential adsorbent for chlorpyrifos pesticide-air purification

In the current study, Doum palm husk of Hyphaene Thebaica (HT), a local agro-waste, was utilized as a new source to produce activated carbon (HT-AC). The thermally prepared adsorber was chemically activated by phosphoric acid aqueous solution and exposed to γ-ray at doses of 2.5-10 Grays (Gy) for capacity enhancement. Characterization of the obtained products were tested using FT-IR, SEM-EDX, XRD, BET and Raman spectroscopy. The carbon species were then utilized in the ambient air purification from the chlorpyrifos (trade name, Ictafos) pesticide air pollutant. Results showed the development of very high surface area of 1439, 1702 and 1561 m2/g for the parent HT-AC and its HT-AC2.5Gy and HT-AC5Gy irradiated forms, respectively. The experimental and theoretical results clarified the best fitting of pseudo-first-order model in describing the Chlorpyrifos sorption reaction. Thermodynamic analysis revealed physical sorption of the hazardous material onto the surfaces of the activated carbons with exothermic process of non-spontaneous nature. Experimental kinetics presented that, HT-AC2.5Gy had excellent fitting to the Langmuir isotherm model, wherein the adsorption was proceeded in a monolayer manner with a uniform surface energy. Conversely, Freundlich isotherm was perfectly fitted to the original HT-AC and HT-AC5Gy, where the multilayer and heterogeneous adsorption mechanism was exhibited.

Dual metal zeolitic imidazolate frameworks as an organometallic polymer for effective adsorption of chlorpyrifos in aqueous solution

In this work for the first time, green technique-solvent free synthesis Dual metallic Zeolitic imidazolate frameworks (ZIF-2M) consisting of cobalt and zinc metals (ZIF-2M) at room temperature was performed. The synthesized compound was used as an efficient adsorbent for the adsorption of chlorpyrifos. The presence of second metal led to the improving in both chemical as well as physical properties such as crystal structure, porosity, specific area and magnetic property together keeping basic structure of ZIFs. In order to comparison ZIF-2M with ZIF-8 both of them were applied for removal of chlorpyrifos in aqueous solution. Comparison of removal efficiency was investigated for both nanoparticles under optimized conditions. The main factors which can potentially effect on the adsorption process are dosage of adsorbent, pH and contact time. Those factors were considered in statistical studies. The optimum conditions were achieved by BOX-Behnken design(BBD). Results revealed that the removal efficiency of ZIF-2M (97%) is more than that of ZIF-8 (90%). Also, Langmuir and Freundlich isotherms for chlorpyrifos sorption by ZIF-2M in optimal conditions were studied and discussed.

Sorption of chlorpyrifos onto zinc oxide nanoparticles impregnated Pea peels (Pisum sativum L): Equilibrium, kinetic and thermodynamic studies

Abstract This study was focused on the sorption of chlorpyrifos from aqueous media utilizing synthesized zinc oxide nanoparticles impregnated Pea peels (ZnONPs-IPPs) in batch mode under the impact of pH of solution, dosage of sorbent, time of contact, temperature and initial pesticide concentration. The prepared composite was characterized by SEM, EDX, Surface area pore size analyzer and FTIR before and after sorption of chlorpyrifos. It was observed that the sorption of chlorpyrifos depends upon pH and maximal sorption (56%) was occurred at pH 2. The data of sorption process were fitted into Freundlich, Langmuir, Temkin and Dubinin–Radushkevich (D–R) isotherm models and the results indicate that Temkin isotherm is a suitable choice to describe the data owing to higher R2 value (0.99). Monolayer sorption capacity of ZnONPs-IPPs for chlorpyrifos of the Langmuir isotherm was found to be 47.846 mg g−1. Kinetics of sorption were described by fitting data into pseudo-1st-order, pseudo-2nd-order, Elovich, intraparticle and liquid film diffusion models and the results showed that pseudo-2nd order interprets the data well owing to the higher R2 (0.99) well as the close agreement between the calculated and experimental sorption capacity. Thermodynamic parameters ( Δ G ∘ is negative and Δ H ∘ is positive) imply that sorption process of chlorpyrifos utilizing ZnONPs-IPPs is spontaneous and endothermic in nature. The prepared composite is an economical and eco-friendly biomass and may be efficiently used for the removal of other pollutants.

Characteristics and mechanisms of chlorpyrifos and chlorpyrifos-methyl adsorption onto biochars: Influence of deashing and low molecular weight organic acid (LMWOA) aging and co-existence

The effects of inherent minerals in biochars and low molecular weight organic acids (LMWOAs) on chlorpyrifos and chlorpyrifos-methyl adsorption by biochars are unclear. We examined the sorption of chlorpyrifos and chlorpyrifos-methyl onto giant reed-derived biochars before and after deashing or LMWOA aging. The effect of citric acid (CA) as a co-solute on the sorption of chlorpyrifos and chlorpyrifos-methyl was also investigated. With increasing temperature (300–600 °C), the adsorption capacity of biochars increased from 4.32 to 14.8 mg/g for chlorpyrifos and from 15.0 to 50.5 mg/g for chlorpyrifos-methyl. This can be explained by the fact that higher temperature biochar had more aromatic units and pores for capturing more sorbates. The deashing and LMWOA aging treatments exposed more carbon surfaces and improved the porosity of biochar, thus favoring sorption. Further, the deashing treatment resulted in greater sorption enhancement, when compared with the LMWOA aging treatment. At pH 6.5, CA2− and CA3− chelated Ca2+ via bridging at CA concentration below 10 mmol/L, thus reducing the competition of Ca2+ for aromatic surfaces and COO−/OH groups. When the CA concentration was above 20 mmol/L, CA2−, CA3−, and [Ca(CA)2]x− inhibited the sorption of chlorpyrifos and chlorpyrifos-methyl by competing for carbon sites and pores of biochar. These findings will help guide the practical application of biochar in pesticide-contaminated water and soil, and to better understand the role of biochar in the transport, fate, and bioavailability of organophosphorus pesticides in the rhizosphere.

Soil organic amendments: impacts on sorption of organophosphate pesticides on an alluvial soil

Soil organic carbon enrichment by addition of organic amendments (OAs) is a common agricultural and gardening practice. Such amendments can cause ambiguous environmental effects; it could enhance the sorption of pesticides by increasing soil organic carbon content, and on the contrary, dissolved organic matter (DOM) from OAs could facilitate their leaching. This study evaluated the influence of OAs, mixed waste compost, and dried goat organic manure on the sorption of organophosphates, dichlorvos, and chlorpyrifos. Soil (15 cm depth) was collected from an agricultural field and stored. Dissolved organic matter (DOM) extracted from the amendments and the amended soils was characterized by fluorescence spectroscopy and Fourier transform infrared spectroscopy (FT-IR). Initially, studies were carried out to evaluate the effect of DOM from organic amendments (OA-DOM) and dissolved humic acids (HAs) as model DOM on the sorption of selected pesticides. In the later part, OAs (2.5 and 5% w/w) were added to the soil, and sorption experiments were carried out using amended soil to understand the combined effects of insoluble and soluble organic carbon fraction. As dichlorvos sorption was found to be very low, desorption experiments were conducted only for chlorpyrifos using 0.01 M CaCl2 and DOM solutions. The spectroscopic characterization of OA-DOM revealed that it mainly contained large amounts of highly humified and aromatic material. OA-DOM and HAs had a similar effect on pesticide sorption leading to a slight but not significant increase in dichlorvos sorption while a substantial reduction in chlorpyrifos sorption was observed. Surface tension analysis highlighted that OA-DOM and HAs might have caused greater solubilization of chlorpyrifos, thus reducing sorption. Further, it also promoted greater desorption of adsorbed chlorpyrifos. These results seem to be related to the humified and aromatic nature of OA-DOM and HAs, determining the interactions between hydrophobic chlorpyrifos and DOM. On the contrary, the addition of OAs to soil promoted greater chlorpyrifos and dichlorvos sorption, but a clear correlation between increase in soil organic carbon and pesticide sorption could not be established. The study highlighted that the net effect of OA application was an increase in pesticide sorption that depended on the nature of DOM and pesticide properties. The interactions of hydrophobic chlorpyrifos with DOM can lead to a significant reduction in sorption to such an extent that the sorption in the presence of substantial DOM concentration can be less than the sorption without it.

Characterization of soil organic matter by FT-IR spectroscopy and its relationship with chlorpyrifos sorption

Sorption of non-ionic organic compounds to soil is usually expressed as the carbon-normalized partition coefficient (KOC) assuming that the main factor that influences the amount sorbed is the organic carbon content (OC) of the soil. However, KOC can vary across a range of soils. The influence of certain soil characteristics on the chlorpyrifos KOC values variation for 12 representative soils of the Northpatagonian Argentinian region with different physicochemical properties was investigated for this study. The chlorpyrifos sorption coefficients normalized by the OC content were experimentally obtained using the batch equilibrium method; the KOC values ranged between 9000–20,000 L kg−1. The soil characteristics assessed were pH, clay content and spectral data indicative of soil organic matter (SOM) quality measured by FT-IR on the whole soil. The bands considered in the spectroscopic analyses were those corresponding to the aliphatic components, 2947–2858 cm−1 (band A) and the hydrophilic components, 1647–1633 cm−1 (band B). A significant relationship was found (R2 = 0.66) between chlorpyrifos sorption (KOC) and the variables pH and A/B height band ratio. The correlation between the values predicted by the derived model and the experimental data was significant (r = 0.89 p < 0.05). Thus, this methodology could be used to estimate chlorpyrifos sorption coefficient through the use of a simple, rapid, and environmentally-friendly measurement. KOC analysis in relation to soil properties represents a valuable contribution to the understanding of the attenuation phenomena of the organic contaminants off-site migration in the environment.

Contribution of Soil Components on the Sorption of Chlorpyrifos

It is generally assumed that the sorption of a nonionic pesticide on soil depends mainly on the content of soil organic matter (SOM); however, there are other factors that can contribute to this process. The possible causes of variation in the carbon-normalized partition coefficient (K OC) for chlorpyrifos (CPF) for a diverse set of ten soils have been investigated. On the one hand, the analysis of the chemical composition of the SOM was analyzed, and on the other hand, the likely interactions between the organic matter and the mineral phase were assessed. Sorption experiments of CPF were performed on whole soil, on soils treated with 2% hydrofluoric acid (HF), and onto calcined soil at 550 °C. Organic matter chemistry of soil was determined by 13C CP/MAS NMR spectroscopy; K OC values were positively correlated with aryl C relative proportion and negatively correlated with alkyl C and O-aryl C proportions and prediction equation of K OC was found (R 2 = 0.82, p < 0.001). To evaluate possible organo-mineral interactions, a mathematical model was proposed which calculates the concentration of CPF at equilibrium (C cal) considering adsorption coefficients for the organic (K DHF) and inorganic (K D550 °C) soil constituents, separately. The comparison between C cal and the equilibrium concentration obtained from experimental data (C exp) onto whole soil allowed us to confirm that interactions between the OM and clay affect the adsorption of CPF in whole soil. Such findings should be taken into account in the development of predictive models for the evaluation of the fate and transport of this pesticide in soil.

Toxicity Persistence of Chlorpyrifos in Runoff from Experimental Soybean Plots to the Non-target Amphipod Hyalella curvispina: Effect of Crop Management.

Toxicity persistence to the nontarget amphipod Hyalella curvispina in runoff events following chlorpyrifos applications to soy experimental plots was compared in conventional and no-till management. Two application scenarios were compared: an early-season application with the soil almost bare and a late-season application after the foliage had attained complete soil cover. H. curvispina was exposed to chlorpyrifos using two different test systems: a short-term (48h) runoff water exposure and a long-term (10 days) soil exposure. Both commonly used crop management practices for soybean production resulted in runoff toxicity following pesticide applications and represent a toxicity risk for adjacent inland waters. Toxicity persistence was longer after the earlier than the late season application, likely because of higher volatilization and photodecomposition losses from the soy canopy than from the soil. For the early-season application, toxicity persisted longer in the no-till plots than in the conventional tillage plots. Suspended matter was higher in the conventional treatment. Chlorpyrifos sorption to suspended matter likely contributed to the shorter persistence. For the late-season application, toxicity persisted longer in the conventional treatment. The causes remain conjectural. The soil organic carbon content was higher in the no-till treatment. Sorption to organic matter might have contributed to the shorter chlorpyrifos toxicity persistence in no-till management. Late applications are more frequent and prevail longer throughout the soy growing season. Overall, the no-till management practice seems preferably because shorter toxicity persistence in runoff represents a lower environmental risk for the adjacent inland waters.

Feasibility of Using Drinking Water Treatment Residuals as a Novel Chlorpyrifos Adsorbent

Recent efforts have increasingly focused on the development of low-cost adsorbents for pesticide retention. In this work, the novel reuse of drinking water treatment residuals (WTRs), a nonhazardous ubiquitous byproduct, as an adsorbent for chlorpyrifos was investigated. Results showed that the kinetics and isothermal processes of chlorpyrifos sorption to WTRs were better described by a pseudo-second-order model and by the Freundlich equation, respectively. Moreover, compared with paddy soil and other documented absorbents, the WTRs exhibited a greater affinity for chlorpyrifos (log Koc = 4.76-4.90) and a higher chlorpyrifos sorption capacity (KF = 5967 mg(1-n)·L·kg(-1)) owing to the character and high content of organic matter. Further investigation demonstrated that the pH had a slight but statistically insignificant effect on chlorpyrifos sorption to WTRs; solution ionic strength and the presence of low molecular weight organic acids both resulted in concentration-dependent inhibition effects. Overall, these results confirmed the feasibility of using WTRs as a novel chlorpyrifos adsorbent.

Sorption and photodegradation of chlorpyrifos on riparian and aquatic macrophytes

Surface water bodies may become contaminated via spray drift following pesticide application. In this investigation, the photodegradation and sorption of chlorpyrifos was studied in four riparian macrophytes representative of Mediterranean flora (Phragmites australis, Iris pseudacorus, Equisetum pratense and Typha latifolia). The results of experiments with both the active ingredient and the formulation DURSBAN 48® EC confirm the ability of these species to interact with chemicals such as chlorpyrifos. The maximum sorption of chlorpyrifos at equilibrium was observed in Phragmites australis (22%). And, the maximum instantaneous sorption of chlorpyrifos was observed in the dried biomass of Phragmites australis (49%). The epicuticular waxes present on leaves influence photodegradation processes, resulting in a decrease in chlorpyrifos persistence depending on the nature of the extract. The half-life of chlorpyrifos residues in leaf waxes decreased from 34 to 99 minutes when irradiated.

Partitioning of chlorpyrifos to soil and plants in vegetated agricultural drainage ditches

Constructed wetlands and vegetated agricultural drainage ditches (VADD) have been proposed as structural best management practices for the mitigation of chlorpyrifos contamination in agriculturally dominated watersheds. Sorption to soil and submergent aquatic plants has been measured as an important sink for chlorpyrifos; however, sorption to emergent plants has not been well characterized. Sorption isotherms for two soils and five emergent plants were determined by batch equilibrium technique. Sorption to whole plant stems ( K d = 570–1300 L kg −1) was more than 10 times higher than to soil ( K d = 40–71 L kg −1). Chopped plant material had K d values 7.6–96.2% greater than whole stems. Wetland plants with high internal surface area due to porous tissues had greater linear partitioning coefficients than terrestrial plants with a hollow structure. Chlorpyrifos sorption reached pseudo-equilibrium rapidly, indicating that partitioning will be an important mechanism in vegetated natural treatment systems for mitigating peak concentrations in surface waters and allowing time for attenuation by slower degradation reactions.

Sorption of Chlorpyrifos to Selected Minerals and the Effect of Humic Acid

Sorption of chlorpyrifos (CPF) from 2.85 microM (1 mg/L) aqueous solutions in 0.01 M NaCl to montmorillonite, kaolinite, and gibbsite was investigated at 25 degrees C. Uptake of CPF by kaolinite and gibbsite was generally <10%, with pH having at most a small effect. Sorption to montmorillonite was significantly greater, with approximately 50% of the initial CPF being removed from solution below pH 5. Above pH 5 the sorption decreased to about 30%. About 70% of CPF was sorbed to kaolinite and gibbsite after 30 min, whereas on montmorillonite only 50% sorbed in an initial rapid uptake (approximately 30 min) followed by slower sorption, with a maximum achieved by 24 h. Although CPF desorbed completely from kaolinite in methanol, only about two-thirds was desorbed from montmorillonite. CPF has only a weak affinity for the surfaces of kaolinite and gibbsite. In the case of montmorillonite, sorption is significantly stronger and may involve a combination of sorption to external surfaces and diffusion into microporous regions. At pH >6 increased negative surface charge results in a lower affinity of CPF for the external surface. In the presence of 50 mg/L humic acid (HA) the amount of CPF sorbed on gibbsite and kaolinite was 3-4 times greater than that in the binary systems. The HA forms an organic coating on the mineral surface, providing a more hydrophobic environment, leading to enhanced CPF uptake. The HA coating on montmorillonite may reduce access of CPF to microporous regions, with CPF tending to accumulate within the HA coating.

Sorption and Degradation of Pesticides in Nursery Recycling Ponds

Knowledge of pesticide distribution and persistence in nursery recycling pond water and sediment is critical for preventing phytotoxicity of pesticides during water reuse and to assess their impacts to the environment. In this study, sorption and degradation of four commonly used pesticides (diazinon, chlorpyrifos, chlorothalonil, and pendimethalin) in sediments from two nursery recycling ponds was investigated. Results showed that diazinon and chlorothalonil were moderately sorbed [K(OC) (soil organic carbon distribution coefficient) from 732 to 2.45 x 10(3) mL g(-1)] to the sediments, and their sorption was mainly attributable to organic matter content, whereas chlorpyrifos and pendimethalin were strongly sorbed (K(OC) > or = 7.43 x 10(3) mL g(-1)) to the sediments, and their sorption was related to both organic matter content and sediment texture. The persistence of diazinon and chlorpyrifos was moderate under aerobic conditions (half-lives = 8 to 32 d), and increased under anaerobic conditions (half-lives = 12 to 53 d). In contrast, chlorothalonil and pendimethalin were quickly degraded under aerobic conditions with half-lives < 2.8 d, and their degradation was further enhanced under anaerobic conditions (half-lives < 1.9 d). The strong sorption of chlorpyrifos and pendimethalin by the sediments suggests that the practice of recycling nursery runoff would effectively retain these compounds in the recycling pond, minimizing their offsite movement. The prolonged persistence of diazinon and chlorpyrifos, however, implies that incidental spills, such as overflows caused by storm events, may contribute significant loads of such pesticides into downstream surface water bodies.

Determining Kinetic and Nonequilibrium Sorption Behavior for Chlopyrifos Using a Hybrid Batch/Column Experiment

Pesticide mobility in soil is strongly coupled to the chemical's sorption characteristics. A modified soil column batch experiment was conducted to measure the transient nature of chlorpyrifos sorption and desorption from Cecil soil. This experimental system minimizes many shortcomings associated with obtaining sorption parameters by fitting soil column data to an advective-dispersive transport equation. Several chlorpyrifos formulations were investigated to determine how formulations affect soil sorption, and if this effect is adequately described using transient sorption/desorption algorithms. Both a second-order sorption with first-order desorption kinetic model and the two-site kinetic/equilibrium model were found to yield reasonable comparisons to experimental observations. In general, the formulation temporarily decreases the sorptivity of chlorpyrifos and alters the time for equilibrium to be achieved. Care must be exercised when extrapolating sorption data for a pure molecule in a laboratory setting to formulated materials used in field applications when environmental fate predictions are sought.

Contrasting behaviour of chlorpyrifos and its primary metabolite, TCP (3,5,6-trichloro-2-pyridinol), with depth in soil profiles

Regulatory agencies and natural resource managers are increasingly recognising the role of pesticide metabolites in the overall risk to non-target organisms. However, the environment fate data on pesticide metabolites are relatively meagre. We report the sorption and degradation behaviour of chlorpyrifos and its primary metabolite, TCP (3,5,6-trichloro-2-pyridinol), with depth in 2 Australian soil profiles. Sorption isotherms were determined by batch equilibrium method and the degradation was studied under controlled incubation conditions. Sorption of chlorpyrifos (Kd = 40.3–209.6 L/kg) was found to be about 100 times higher than that of TCP (Kd = 0.45–2.86 L/kg) in both the soil profiles. A significant correlation (r2�=�0.88**) was found between sorption of chlorpyrifos and the soil organic carbon content, but not in the case of TCP. However, in the case of TCP a significant inverse relationship was observed with pH (r2�=�0.81**). The rate of degradation of chlorpyrifos increased with depth in the soil profile, whereas the converse was true for TCP. The time for 50% loss of chlorpyrifos (DT50) was found to be 23–28 days in the surface soils (acidic pH) and only 7–16 days in the subsurface (alkaline pH). The DT50 values for TCP in the surface soils ranged from 42 to 49 days and in subsurface soils from 64 to 117 days. The contrasting behaviour of chlorpyrifos and TCP in soil profiles is clearly evident from the study. Due to its lower sorption and longer persistence, TCP has a much greater leaching potential than chlorpyrifos.

Effects of dissolved organic matter from animal waste effluent on chlorpyrifos sorption by soils.

The increased use of animal waste-derived effluents for irrigation could result in the enhanced movement of pesticides through complexation with dissolved organic materials. Batch equilibrium studies were conducted to measure the interaction among soil, chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate], and dissolved organic matter (DOM) from poultry, swine, and cow waste-derived lagoon effluents. All DOM was found to have a strong affinity for chlorpyrifos, resulting in reduced sorption of chlorpyrifos by soil, thus the potential for DOM-enhanced mobility. Effluent DOM was observed to sorb to soils. Thus, for increasingly higher soil mass to solution volume ratios, the effect of chlorpyrifos association with water-borne DOM on sorption decreases significantly. For high soil mass to solution volume ratios typical of soil profiles in the landscape, the potential for DOM-enhanced transport will be greatly attenuated. Dissolved organic matter concentration and the nonpolar nature of DOM in the lagoon effluent decreased with increasing residence time in the cells of the lagoon system, thus reducing the potential for DOM-enhanced transport.

Sorption of chlorpyrifos and fonofos on four soils and turfgrass thatch using membrane filters

Abstract Chemical transport in soil is a major factor influencing soil and water contamination. Four soils and turfgrass thatch, representing a wide range of organic carbon OC content were studied to determine sorption Kd and Kf parameters for the insecticides chlorpyrifos and fonofos. The batch equilibrium method was used. The concentration of insecticide was measured in the solution as well as in the solid phase to determine the most accurate sorption data. Four soils and thatch were equilibrated for 24 h at 22 ± 1OC with aqueous insecticide solutions. Four concentrations of the insecticides, each <50% of their respective water solubilities, were selected for the experiments. After extraction with an organic solvent, the concentration of insecticides in the aqueous solution was determined by gas liquid chromatography using electron capture detection for chlorpyrifos, and nitrogen/phosphorus detection for fonofos. Data obtained were fitted to the log and simple linear form of the Freundlich equation. Mass balance Freundlich isotherm exponents n ranged between 0.82 and 0.93 for chlorpyrifos. 0.82 and 1.21 for fonofos, with r2 ≥ 0.97. Koc (percent of organic carbon %OC normalized Sorption coefficient) values were calculated by using experimentally developed Kd and Kf coefficients in relation to OC levels from 0.29 to 34.85%. Kd and Kf coefficients of both insecticides were positively correlated with OC (r2 ≥ 0.96). organic matter OM (r2 ≥ 0.96), and cation exchange capacity CEC (r2 ≥ 0.90).