Priority pesticide dichlorvos removal from water by ozonation process: Reactivity, transformation products and associated toxicity

Rapid analysis of dichlorvos via releasing the phosphate core

Monitoring the residual dichlorvos (O,O-dimethyl-O-2,2-dichlorovinylphosphate, DDVP) in food has received extensive attention owing to its large consumption in agriculture. However, the previous sensing methods are not time-efficient enough due to the long incubation time for enzyme inhibition (tens of minutes to hours) or bottlenecked by the complicated procedures for senor fabrication. Herein, a novel sensing strategy is proposed based on the hydrolysis of DDVP into PO43-. By using alkaline phosphatase for hydrolysis, a certain portion of DDVP was transformed to PO43- within only 8 min. Then, the released PO43- was detected by a fluorescent terbium metal-organic framework (Tb-MOF). The coordination of the naked P-O groups to the metal nodes of the Tb-MOF disturbed the antenna effects of its ligands. Thus, DDVP was quantified by the decrease of the fluorescence of Tb ions. Based on this method, DDVP residues on plum surfaces were collected by swabs and successfully detected. The recovery of DDVP was determined in the range from 105 % to 115 %, demonstrating the quantification accuracy of this method. The detection limit reached 4.7 μM, which was lower than the restricted amount in fruit set by the National Standard of China. The present method provides an efficient and user-friendly way for the detection of DDVP and many other organophosphorus pesticides in food.

Insight into the application of supercritical water oxidation for dichlorvos degradation: experimental and simulation aspects

Dichlorvos or 2,2-dichlorovinyl dimethyl phosphate (DDVP) ( C 4 H 7 C l 2 O 4 P ) is a chlorinated organophosphorus pesticide, which is frequently detected in agricultural wastewater. Herein, a batch reactor was used to carry out the supercritical water oxidation (SCWO) of a synthetic wastewater containing dichlorvos as a very hazardous agricultural pollutant. To do so, the impact of four operating parameters including dichlorvos concentration (100-500 ppm), oxidant coefficient (0.7-2), temperature (300-500°C) and time (0-100 s) on dichlorvos removal was optimized by the response surface method (RSM). According to the obtained results, at optimal conditions (i.e. initial concentration of dichlorvos 107.5 ppm, oxidation ratio 1.9234, temperature 419.9°C and time 79.94 s), as an index for dichlorvos removal, the chemical oxygen demand (COD) was found to be about 96.34%. Also, the results of high-performance liquid chromatography test showed that dichloroacetaldehyde (C2CL2H2O) and dichloroacetic acid (C2CL2H2O2) were created as intermediate substances during the dichlorvos degradation. Further, the molecular dynamics simulation was performed using ReaxFF force field to show the reaction path and products obtained in each step of the dichlorvos removal. Finally, as an indication, the simulation results indicated a good coordination with the experimental results.

Guidance document on the impact of water treatment processes on residues of active substances or their metabolites in water abstracted for the production of drinking water

This guidance document provides a tiered framework for risk assessors and facilitates risk managers in making decisions concerning the approval of active substances (AS) that are chemicals in plant protection products (PPPs) and biocidal products, and authorisation of the products. Based on the approaches presented in this document, a conclusion can be drawn on the impact of water treatment processes on residues of the AS or its metabolites in surface water and/or groundwater abstracted for the production of drinking water, i.e. the formation of transformation products (TPs). This guidance enables the identification of actual public health concerns from exposure to harmful compounds generated during the processing of water for the production of drinking water, and it focuses on water treatment methods commonly used in the European Union (EU). The tiered framework determines whether residues from PPP use or residues from biocidal product use can be present in water at water abstraction locations. Approaches, including experimental methods, are described that can be used to assess whether harmful TPs may form during water treatment and, if so, how to assess the impact of exposure to these water treatment TPs (tTPs) and other residues including environmental TPs (eTPs) on human and domesticated animal health through the consumption of TPs via drinking water. The types of studies or information that would be required are described while avoiding vertebrate testing as much as possible. The framework integrates the use of weight-of-evidence and, when possible alternative (new approach) methods to avoid as far as possible the need for additional testing.

Photocatalytic activity of graphene oxide-TiO2 nanocomposite on dichlorvos and malathion and assessment of toxicity changes due to photodegradation

Heterogeneous photocatalysis was used for the removal of two widely used organophosphorus pesticides, dichlorvos, and malathion from water. Graphene oxide-TiO₂ nanocomposite (GOT) was synthesized and used as a photocatalyst for the removal of these pesticides. Batch studies for optimizing photocatalytic degradation and mineralization of pesticides over 80 min were conducted by varying the pH (2-10), catalyst dose (20 mg/L-200 mg/L), and initial pesticide concentration (0.5 mg/L-20 mg/L), and the irradiation source (125 W UV and visible lamp). Degradation kinetics for the pesticides were evaluated. Ellman assay was used to estimate the toxic effect of pesticides and evaluate toxicity reduction due to treatment. The highest degradation and mineralization of dichlorvos and malathion was observed at pH 6 and the optimum catalyst dose was 60 mg/L. Under UV irradiation, 80% and 90% degradation were observed for dichlorvos and malathion, respectively for 0.5 mg/L initial pesticide concentration. The photocatalytic degradation reaction followed Langmuir-Hinshelwood kinetics. A high degree of mineralization was achieved for both the pesticides. Analysis of the results revealed that the residual toxic effect after photocatalysis was primarily due to the residual parent compound. A comparative study revealed that GOT yielded better pesticide degradation compared to commercially available TiO₂ under both UV and visible irradiation.

Degradation of malathion and carbosulfan by ozone water and analysis of their by-products

BACKGROUND

Treatment by ozone water is an emerging technology for the degradation of pesticide residues in vegetables. The ozone dissolved in water generates hydroxyl radicals (^· OH), which are highly effective in decomposing organic substances, such as malathion and carbosulfan.

RESULTS

We found that washing pak choi with 2.0 mg L^-1 ozone water for 30 min resulted in 58.3% and 38.2% degradation of the malathion and carbosulfan contents respectively, and the degradation rates of these pure pesticides were 83.0% and 66.3% respectively. In addition, the 'first + first'-order reaction kinetic model was found to predict the trend in the pesticide content during ozone water treatment. Based on investigations by gas chromatography-mass spectrometry combined with the structures of the pesticides, the by-products generated were identified. More specifically, the ozonation-based degradation of carbosulfan generated carbofuran and benzofuranol, whereas malathion produced succinic acid and phosphoric acid. Although some new harmful compounds were formed during degradation of the parent pesticides, these were only present in trace quantities and were transient intermediates that eventually disappeared during the reaction.

CONCLUSION

Our results, therefore, indicate that ozone water treatment technology for pesticide residue degradation is worthy of popularization and application. © 2022 Society of Chemical Industry.

Synthesis and application of a carbon composite containing molecularly imprinted poly(methacrylic acid) for efficient removal of fenpyroximate pesticide

This work describes fabrication steps of the carbon composite based on molecular imprinted poly(methacrylic acid) (MIP-CC) as a new adsorbent for the selective removal of fenpiroxymate pesticide (Fen). The prepared composite was characterized using Brunauer-Emmett-Teller (BET), zeta sizer and Field Emission Scanning Electron Microscopy (FESEM) techniques. The influence of operational parameters such as solution pH, contact time, amount MIP for preparation of carbon composite and amount MIP- CC toward removal of Fen have been evaluated and optimized via central composite design (CCD) as an optimization tool of response surface method. The optimum removal (87%) was achieved at pH 6.5, 1.53 g/L carbon composite prepared with 3.4 wt % MIP at 70 min. The maximum adsorption of Fen by the fabricated MIP-CC was 254 mg/g. Compared with the corresponding non-imprinted polymer (NIP-CC), the MIP-CC exhibited higher adsorption capacity and outstanding selectivity toward Fen. Langmuir isotherm best fitted the adsorption equilibrium data of MIP-CC and the kinetics followed a pseudo-second-order model. The calculated thermodynamic parameters showed that adsorption of Fen pesticide was spontaneous and exothermic under the studied conditions.

Evaluation of Ozonation Technique for Pesticide Residue Removal in Okra and Green Chili Using GC-ECD and LC-MS/MS

The indiscriminate use of pesticides in agricultural commodities has become a global health concern. Various household methods are employed to remove pesticide residues from agricultural commodities, e.g., water and ozone. Many ozone-based commercial pesticide removal machines are available in the market for the general public. The current study compares the pesticide removal efficiency of ozone-based washing of fruits and vegetables to simple tap water through commercially available machines and its health risk assessment to different age groups of consumers. The okra and green chili fruits were treated with acetamiprid and ethion as foliar application at the fruiting stage, using the recommended dose (RD) and double to the recommended dose (2RD), respectively. A modified QuEChERS-based pesticide extraction method was verified for its accuracy, precision, linearity, and sensitivity. The treated samples were washed with tap and ozonated water at different intervals, i.e., 3, 8, and 10 min using a commercial food purifier. Washing with ozonized water for 3 min recorded the maximum removal of acetamiprid and ethion from okra and chili fruits. Further, the risk quotient values (RQ) obtained were lower than one at both doses. Thus, washing vegetables with ozonized water for 3 min ensures vegetables are safer for general consumption without any health risk to Indian consumers.

Reactions of bisphenol F and bisphenol S with ozone and hydroxyl radical: Kinetics and mechanisms

Bisphenol F (BPF) and bisphenol S (BPS) are the most employed substitutes of bisphenol A (BPA), after being restricted by legislation in different countries because of its endocrine disrupting behaviour. In the present work, a deep study was performed about the reactivity of BPF and BPS with ozone and hydroxyl radical. Firstly, the second order rate constants of ozone with the di-protonated, mono-protonated and deprotonated species of both bisphenols were determined to be 2.38 × 10⁴, 1.31 × 10⁹ and 1.43 × 10⁹ M^-1 s^-1 for BPF and 5.01, 2.82 × 10⁷ and 1.09 × 10⁹ M^-1 s^-1 for BPS. Then, the second order rate constants for the reaction of hydroxyl radical with BPF and BPS were established through UV/H₂O₂ and UV experiments at pH 7, resulting in the values of 8.60 × 10⁹ and 6.60 × 10⁹ M^-1 s^-1, respectively. Finally, a study regarding the transformation products (TPs) from the reaction of both bisphenols with molecular ozone and hydroxyl radical was also performed. Hydroxylation in the ortho position of the phenol rings was observed as main degradation pathway. Additionally, most of the TPs were accumulated over the reactions at relatively high oxidant doses.

Role of cytochrome P450 genes of Trichoderma atroviride T23 on the resistance and degradation of dichlorvos

The Trichoderma has been extensively used to degrade the xenobiotics. In the present study, thirty-nine open reading frames of cytochrome P450 genes from T. atroviride T23 genome was cloned and it was found to be distributed in 29 families under 21 clades. Among them, 21 cytochrome P450 genes were involved in the degradation of xenobiotics. The quantitative expression of P450 genes in the presence of dichlorvos at 24 h showed 7 different expression patterns in the presence of 100 μg/mL, 300 μg/mL, 500 μg/mL and 1000 μg/mL of dichlorvos. The relative expression of P450 genes belongs to the family of TaCyp548, TaCyp620, TaCyp52, TaCyp528, TaCyp504 were upregulated at least 1-fold compared to the control. Significantly, the deletion of TaCyp548-2 reduced the concentration of 2,2-dichloroethanol. Further, it was observed that TaCyp548-2 belongs to the ω-hydroxylase family was responsible for fatty acid oxidation and the production of acetic acid, propionic acid, isobutyric acid and dibutyric acid to convert the 2,2-dichloroethanol to 2,2-dichloroethanolacetate. This study evidenced the involvement of Trichoderma P450 genes on dichlorvos degradation as an environmentally significant Biological control agent for the sustainable agriculture.

Chlorpyrifos in environment and food: a critical review of detection methods and degradation pathways

Chlorpyrifos (CP) is a class of organophosphorus (OP) pesticides, which find extensive applications as acaricide, insecticide and termiticide. The use of CP has been indicated in environmental contamination and disturbance in the biogeochemical cycles. CP has been reported to be neurotoxic and has a detrimental effect on immunological and psychological health. Therefore, it is necessary to design and develop effective degradation methods for the removal of CP from the environment. In the past few years, physicochemical (advanced oxidation process) and biological treatment approaches have been widely employed for the pesticide removal. However, the byproducts of this process are more toxic than the parent compound and along with an incomplete degradation of CP. This review focuses on the toxicity of CP, the sources of contamination, degradation pathways, physicochemical, biological, and nano-technology based methods employed for the degradation of CP. In addition, consolidated information on various detection methods and materials used for the detection have been provided in this review.

Profiles and risk assessment of legacy and current use pesticides in urban rivers in Beijing, China

Pesticides in the environment can pose serious risks to aquatic ecosystems. This study focused on the existence of 27 pesticides, including 13 pesticides regulated by the Stockholm Convention as persistent organic pollutants (POPs) and 14 commonly used pesticides in three urban rivers in Beijing that receive effluents from three municipal wastewater treatment plants (MWTPs). Among the 27 pesticides, 12 were detected at least once over a period of 4 seasons. Atrazine, aldrin and dieldrin were universally found in the three rivers, with the highest concentrations being 311, 163 and 23.3 ng/L, respectively. HCHs, DDTs, heptachlor and endosulfan, which are POPs, were detected at lower concentrations (ND-16.7 ng/L). Most of the insecticides and some of the herbicides in the rivers originated from MWTP effluents. The risk assessment results showed that aldrin posed medium risk (0.1 ≤ RQ < 1) to fish, and atrazine exhibited medium risk to both fish and algae. Despite the implementation of the Stockholm Convention and the upgrades of MWTPs emitting ozone, high loads of aldrin, atrazine and dieldrin were discharged to the rivers. Efforts should be devoted to identifying POP pesticide sources and upgrading MWTPs with other technologies to ensure the ecological safety of rivers.

Occurrence and risk evaluation of organophosphorus pesticides in typical water bodies of Beijing, China

AbstractHuman activities, particularly in large cities, can lead to pollution caused by micropollutants such as pesticides in water bodies, which have been recognized as serious threats to the environment and human health. The pollution level of six organophosphorus pesticides, three herbicides, and one bactericide in groundwater and the Wenyu River, and their fates in three sewage treatment plants (STPs) and a hospital were investigated in this study. The concentrations of the ten detected pesticides ranged from not detected (ND) to 323.44 ng L^-1 in different water samples from Beijing; metalaxyl was detected to have the highest concentration (89.58 ng L^-1), and the detection frequencies of atrazine and metalaxyl were 100%. The maximum concentrations of pesticides in the Wenyu River, STPs, and the hospital were 1-2 orders of magnitude higher than those in the groundwater. Good removal efficiencies by the treatment processes were observed for ametryn (100%), while the removal efficiencies for atrazine and omethoate were the lowest in the three STPs (- 9.6% and 12.67%, respectively). Finally, risk quotient (RQ) values of each contaminant were estimated from the maximum values determined for typical urban to assess the ecology and health effects. In the case of environmental toxicity, the highest RQ values (> 1) were obtained for dichlorvos and omethoate. In the case of health toxicity, the RQ values show that the pesticides found in groundwater pose no potential health risks to humans at current concentrations.

Occurrence, source and ecotoxicological risk assessment of pesticides in surface water of Wujin District (northwest of Taihu Lake), China

This study investigated the occurrence and distribution of pesticides in surface water (lakes, major rivers and tributaries) and potential discharge sources (fish ponds, livestock and poultry farms, and sewage treatment plants) in Wujin District (northwest of Taihu Lake), Jiangsu province, China. An analytical liquid chromatography-tandem mass spectrometry method was developed for 38 pesticides, which was applied in the monitoring of 240 surface water samples and 76 potential discharge source samples. Eleven insecticides and five fungicides with temporal and spatial variation were detected in surface water. The total pesticide concentrations in surface water in different seasons were as follows: March > August > June > November. The two most polluting and widespread pesticides were carbendazim (maximum concentration 508 ng L^-1, detection rate 100%) and imidacloprid (maximum concentration 438 ng L^-1, detection rate 88%). Gehu Lake (S46) and Sanshangang River (S12) were seriously polluted water bodies. Seven insecticides and four fungicides were detected in the potential discharge sources; and their composition changed significantly with the seasons. The concentrations of detected organophosphorus pesticides and neonicotinoids (e.g. acetamiprid in March and dichlorvos in November) in a few non-agricultural planting sources were far greater than those detected in surface water, and hence a few fish ponds, livestock and poultry farms, and sewage treatment plants might be the potential discharge sources of pesticides in the surrounding surface water. The estimated input flux of the studied pesticides from upstream rivers to Taihu Lake was 141.95 kg a^-1. Furthermore, more attention should be paid to the medium or high aquatic ecotoxicological risk presented by the levels of organophosphorus pesticides, carbamates, and benzimidazoles.

Ozone treatment pak choi for the removal of malathion and carbosulfan pesticide residues

Since the beginning of the widespread use of pesticides, their removal from food has become a serious concern. In this study, the removal of residual pesticides (malathion and carbosulfan) from pak choi via treatment with ozonated water was investigated. Under the optimal treatment conditions, i.e., 2.0 mg/L ozonated water and a treatment duration of 15 min, malathion and carbosulfan were degraded by 53.0 and 33.0%, respectively, without any significant changes in color. Even though there was a slight decrease in vitamin C content (~7.9 mg/100 g) following the treatments, a significant decrease in the microbial colonies on the vegetables was observed. Additionally, the pesticide degradation mechanism showed good fitting with a "first + first"-order kinetic model (R² > 0.9), and the slope (k) indicated that ozone had a more prominent degradation effect on malathion than on carbosulfan. Therefore, this study provides a theoretical basis for controlling agricultural pesticide residues in household applications.

Ipomoea aquatica extract reduces hepatotoxicity by antioxidative properties following dichlorvos administration in rats

Ipomoea aquatica (IA) with antioxidant properties is used in therapeutic trends. An organophosphate, dichlorvos (Dich), is a common insecticide with various side effects on living tissues. This study examines the role of IA on Dich-induced hepatotoxicity in male rats. Sixty-four male rats were divided into eight groups including sham, Dich (4 mg/kg/day, intraperitoneally), IA 1, 2, and 3 (250, 500, and 1000 mg/kg/day, respectively, orally), and Dich + IA 1, 2, and 3. All treatments were applied daily for 60 days. At the end of the treatment, the animals were sacrificed. The histopathological changes, leukocyte infiltration, and apoptosis were assessed by light and fluorescent microscopy. The serum levels of hepatic enzymes, nitrite oxide (NO), and total antioxidant capacity (TAC) were evaluated biochemically. Dich statistically significantly increased the NO level, hepatic enzyme activity, apoptosis, leukocyte infiltration, the mean diameter of hepatocytes (DHs), and central hepatic vein diameter (CHVD) and also decreased the TAC, mean weight of liver, and the total weight of rats compared to the sham group (P < 0.01). In all IA and Dich + IA groups, a statistically significant decrease was detected in apoptosis, leukocyte infiltration, hepatic enzyme activity, NO level, mean DH, and CHVD, whereas an increase in TAC level, mean liver weight, and total weight was detected compared to the Dich group (P < 0.01). IA, due to the antioxidant property, recovers the Dich-related catastrophic changes in liver.

Sono-coprecipitation synthesis of ZnO/CuO nanophotocatalyst for removal of parathion from wastewater

Semiconductor photocatalysis is an effective method used to degrade organophosphorus compounds. Here, the potential of a commonly mixed oxide semiconductor, ZnO/CuO, has been examined to degrade methyl parathion. Sono-coprecipitation method was used to provide ZnO/CuO nanocomposites, and it was applied to photocatalytic and sono-photocatalytic degradation of methyl parathion under solar light irradiation. Powder x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), the Brunauer-Emmett-Teller (BET) surface area, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) were used to characterize the synthesized samples. The optimal experimental conditions such as ZnO/CuO photocatalyst 90:10 M ratios, the initial concentration of 20 mg/L parathion, 1 g/L photocatalyst loading, no compressed air sparging, pH of 8, and ultrasonic power (60 W and 80 kHz) were used to degrade the parathion effectively. The parathion was fully (100% removal) degraded after 60 min sono-photoirradiation in the optimal experimental conditions. A real water sample was used to examine the ability of the ZnO/CuO photocatalyst 90:10 to remove the parathion in the water-soluble ions. Graphical abstract.

Transformation pathway and toxicity assessment of malathion in aqueous solution during UV photolysis and photocatalysis

In drinking water treatment, complete mineralization of organophosphorus pesticides (OPPs) by UV-based advanced oxidation processes (UV AOPs) is rarely achieved. The formation of intermediate oxidation byproducts would likely have some profound effects on toxicity of the reaction solutions. This study investigated the intermediate oxidation byproducts, transformation pathway and toxicity of malathion solutions during the treatment processes of UV alone, UV/H₂O₂, UV/TiO₂ and UV/Fenton. The main intermediate oxidation byproducts were derived using ultra-performance liquid chromatography - electrospray - time-of-flight mass spectrometry. Thereby the transformation pathway for each of these treatment processes was proposed. The results indicate that in UV photolysis, the transformation pathway of malathion proceeded initially via cleavage of the phosphorus-sulfur bonds while in photocatalysis, the desulfurization from a PS bond to a PO bond was the primary degradation pathway. Interestingly, only in the UV/TiO₂ process a small fraction of malathion was found decomposed via a demethylation reaction. At the same time, a toxicity assessment of the treated solutions was conducted by both luminescence inhibition of Vibrio fischeri and inhibition of acetylcholinesterase (AChE). It was found that after UV AOP treatment, the toxicity of the malathion aqueous solution increased sharply. In contrast, no increase in toxicity was observed for the malathion aqueous solution after UV alone treatment. This study demonstrates that the high removal efficiency achieved by OPPs does not imply that detoxification of the water solution has been achieved. On the contrary, the toxicity of the treated solutions by OPPs may be increased significantly depending on the selected treatment processes.

The pathway of 2,2-dichlorovinyl dimethyl phosphate (DDVP) degradation by Trichoderma atroviride strain T23 and characterization of a paraoxonase-like enzyme

Dichlorvos (DDVP) is widely applied in the agricultural industry, and its residues are considered hazardous to the environment. Microbial bioremediation is an innovative technology with the potential to mitigate such pollution. Trichoderma atroviride strain T23, a filamentous fungus, is very efficient at degrading DDVP. Therefore, we used DDVP as a model organophosphate pesticide to study the mechanism by which Trichoderma degrades organophosphate pesticides, with the aim of attaining a global understanding of the molecular mechanism of enzymatic degradation of organophosphate pesticides by beneficial fungi. DDVP can be biodegraded via two routes, and the primary one involves hydrolysis of the P-O bond, which can result in the production of the novel degradation intermediate trichloroethanol. TaPon1-like showed continuously high expression during 120 h, and deletion of the gene decreased the efficiency of P-O bond hydrolysis. The enzyme produced by TaPon1-like had a low K_m for DDVP (0.23 mM) and a high k_cat (204.3 s^-1). The enzyme was able to hydrolyze broad substrates such as organophosphate oxons and lactone and maintain stable activity in a wide range of pH and temperature values. The TaPon1-like hydrolase played an important role in the first step of DDVP degradation by strain T23 and contributed to a comprehensive understanding of the mechanism of organophosphate pesticide degradation.

Sunlight and UVC-254 irradiation induced photodegradation of organophosphorus pesticide dichlorvos in aqueous matrices

Dichlorvos (DDVP) is an organophosphorus pesticide that has been classified as highly hazardous chemical by the World Health organization. In this study, the fate of the pesticide DDVP in natural water compartments was examined under simulated sunlight. Moreover, the effect of UV-254 irradiation on DDVP depletion was also studied. In deionized water, DDVP was photodegraded only in the presence of dissolved molecular oxygen. The photodegradation during the first 6 h of sunlight irradiation occurred with pseudo first-order kinetics, and the rate constants were 0.040 h^-1 at pH 7 and 0.064 h^-1 at pH 3. A reaction mechanism for the generation of reactive oxygen species (ROS) via DDVP photoabsorption was proposed. Humic acids (HA) played a double role as photosensitizer and inhibitor, observing an enhancement on DDVP photodegradation at low HA concentration (TOC = 2 mg L^-1). The depletion of DDVP under 254 nm UV irradiation was ascribed to direct photodegradation and oxygen mediated photoinduced reactions. Direct photodegradation of DDVP decreased with 254 nm irradiation reduction, highlighting the importance of radical mediated mechanisms at low irradiation doses. Based on LC/MS data, the main photoproducts under simulated solar light and UV-C irradiation were identified and potential reaction pathways were postulated. The three main identified products were o-methyl 2,2-dichlorovinyl phosphate, dichloroacetaldehyde and dimethylphosphate. Moreover, the toxicity of samples was evaluated along the irradiation exposure time using Microtox® assays. This study brings new insights into the role of oxygen in the photodegradation of DDVP and the induced and inhibition mechanisms involved in the presence of the humic acids in natural waters.