Environmental Fate Of Pesticides Research Articles

Impact of biochar on the degradation rates of three pesticides by vegetables and its effects on soil bacterial communities under greenhouse conditions

A 28 days pesticide degradation experiment was conducted for broccoli (Brassica oleracea L. var. italica Planch) and pakchoi (Brassica chinensis L.) with three pesticides (chlorantraniliprole (CAP), haloxyfop-etotyl (HPM), and indoxacarb (IXB)) to explore the effects of biochar on pesticide environmental fate and rhizosphere soil diversity. Rice straw biochar (RB) was applied to soil at a 25.00 t ha−1 dosage under greenhouse conditions, and its effects on the degradation of three pesticides in vegetables and in soil were investigated individually. Overall, RB application effectively facilitated CAP and HPM degradation in broccoli by 13.51–39.42% and in broccoli soil by 23.80–74.10%, respectively. RB application slowed the degradation of CAP, HPM and IXB in pakchoi by 0.00–57.17% and slowed the degradation of CAP in pakchoi by 37.32–43.40%. The results showed that the effect of RB application on pesticide degradation in crops and soil was related to biochar properties, pesticide solubility, plant growth status, and soil characteristics. Rhizosphere soil microorganisms were also investigated, and the results showed that biochar application may be valuable for altering bacterial richness and diversity. The effect of biochar application on pesticide residues in crops and soil was influenced by the vegetable variety first, and the second was pesticide characteristics. RB applied to soil at a 25.00 t ha−1 dosage under greenhouse conditions is recommended for broccoli production to ensure food safety. Our results suggested that biochar application in soil could reduce pesticide non-point source pollution, especially for highly soluble pesticides, and could affect soil microorganisms.

Modeling Environmental Fate, Transport, and Transformation of Pesticides: First-Order Kinetic Models for Regional and Global Applications

Predicting pesticide residue masses in environments requires time- and cost-efficient fate models, particularly for high-throughput simulations of hundreds of active ingredients registered for use in agriculture. Due to the adaptability of first-order kinetics-based models for simulating the fate of pesticides in environments of varying scales, we conduct a review of these models in the present investigation. We discuss the application of first-order kinetics-based fate models in different types of compartments, such as environmental media, plant tissues, and animal bodies, and at different levels, such as the product-oriented life cycle impact assessment and the chemical-oriented health risk assessment. In addition, the first-order kinetics-based rate constants of pesticides provide process- and scenario-specific information on the fate, transport, and transformation of pesticides, which is essential for predicting pesticide residue masses in different environmental compartments. By varying the level of model complexity and site-specific rate constants of pesticides, the first-order kinetics-based fate models can be used as either comparable or absolute tools for conducting the life cycle impact assessment or the health risk assessment of pesticides, respectively. Bioconcentration, bioaccumulation, and biomagnification of pesticides may be evaluated with the aid of an inventory database of rate constants based on first-order kinetics in future research. We suggest incorporating non-first-order kinetic processes into the first-order kinetics-based model to advance risk assessment, as well as approximating non-first-order kinetic processes using first-order kinetics to facilitate life cycle impact or screening-level risk assessments.

Insight into the effect of microplastics on the adsorption and degradation behavior of thiamethoxam in agricultural soils

Thiamethoxam and microplastics are both common pollutants in farmland soil; however, few studies have focused on the interaction between thiamethoxam and microplastics in soil. Here, a batch experiment and soil incubation experiment were performed to explore the mechanism and effects of microplastics on the adsorption and degradation behaviors of thiamethoxam in soil, respectively. First, the batch experimental results indicated that the adsorption process of thiamethoxam on the microplastic/soil mixtures and soil-only systems mainly relies on chemical interactions. All sorption processes had moderate intensities of adsorption, and the sorption process occurred on the heterogeneous surface. In addition, the particle size and dose of microplastics could both affect the adsorption behavior of thiamethoxam onto microplastics/soil systems. The sorption capacity of thiamethoxam in soil decreases as the particle size of microplastics increases, but the sorption capacity increases as the dose of microplastics increases. Second, the results of the soil incubation experiment showed that the half-lives of thiamethoxam ranged from 57.7 d to 86.6 d, from 86.6 d to 173.3 d, and 115 d in the biodegradable microplastic/soil systems, nondegradable microplastic/soil systems, soil-only systems, respectively. These results indicate that biodegradable microplastics promoted the degradation of thiamethoxam, while nondegradable microplastics delayed the degradation process of thiamethoxam in soil. Overall, microplastics could change the degradation behaviors, sorption capacity and adsorption efficiency, and then affect the mobility and persistence of thiamethoxam in the soil environment. These findings contribute to understanding the influence of microplastics on the environmental fate of pesticides in the soil environment.

Atmospheric degradation of two pesticides mixed with volatile organic compounds emitted by citrus trees. Ozone and secondary organic aerosol production

Once pesticides are released into the environment, their active ingredient and other formulation compounds, such as coadjuvants or solvents, may undergo biological and chemical degradation, and form a range of products that could be even more hazardous than their precursors. These degradation products may also interact with the natural biogenic compounds emitted by treated crops, which leads to secondary air pollutants, such as ozone (O3) or fine particulate matter, which directly affect human health and climate warming. This research provides evidence for the atmospheric process influencing the atmospheric and environmental fate of pesticides, active substance chloropicrin and commercially formulated chlorpyriphos, which interact with biogenic volatile organic compounds (α-pinene and a mixture of monoterpenes) simulating mixtures of terpenes emitted by orange trees at the large outdoor European PHOto-REactor (EUPHORE). Significant SOA formations were observed during the photolysis and/or ozonolysis of both pesticides in the presence of biogenic volatile organic compounds. For the photolysis of chloropicrin in the presence of α-pinene, the aerosol and O3 formation yields ranged from 6 to 16% and 167–338%, respectively, depending on the initial conditions. For the photolysis of commercial chlorpyrifos in the presence of a mixture of terpenes, the formed aerosol yield was 24%, higher than those obtained by the photolysis of the terpenes in the absence of pesticides. Both pesticides in combination with terpenes increased O3 formation. O3 reacted with those terpenes, which increased particulate matter formation and may pose atmospheric issues on local and global scales.

Runoff of Hexazinone and Diuron in Green Cane Systems

Sugarcane is a major crop in Brazil as well as other tropical areas. The rise of green cane systems that maintain straw on the soil surface after mechanical harvesting alongside extreme precipitation has changed the use and environmental fate of pesticides, mainly herbicides. The goal of this research was to evaluate the effects of straw amounts (0, 7, and 14 t ha−1), soil water contents (10 and 18%, volumetric basis), and herbicide incubation time (0 and 3 days) on the runoff of hexazinone and diuron in green cane systems, under a heavy rainfall event of 120 mm that is becoming more frequent over the decades in tropical areas. A rainfall event of 80 mm h−1 during 1.5 h was simulated over a 1 m2 area, using a rainfall simulator with a structure designed to collect runoff. Herbicides in water runoff were determined by ultra performance liquid chromatography with mass spectrometry (UPLC ESI QTOF/MS), while herbicides attached to sediments were estimated using Kd values. Sugarcane straw on the soil surface decreased water, sediments, and diuron runoffs, but barely affected hexazinone losses. Crop residues cannot prevent runoff of highly soluble molecules, such as hexazinone. Herbicides’ runoffs were much higher in the aqueous phase and at higher soil moisture content. Maintaining 7 t ha−1 of sugarcane straw on the soil surface was enough to mitigate water, sediments, and diuron runoff, but 3-day herbicide incubation did not affect both herbicides runoffs. Diuron and hexazinone are heavily used herbicides that can reach concerning concentrations in the runoff and contaminate surface waters in vulnerable areas if no control measures are taken.

Environmental fate of pesticides in open field and greenhouse tomato production regions from Colombia

The environmental fate of pesticides has been widely studied in temperate regions but not in tropical regions. In Colombia, tomato is an important commodity characterized by the excessive use of pesticides; however, the environmental fate of pesticides has not yet been determined. Residues for 30 pesticides were analyzed in fruits, leaves, and soils samples, as well as residues for 490 pesticides in water and sediments, from two open field and greenhouse tomato production regions, by direct sampling in the field and subsequent laboratory analysis through liquid or gas chromatography coupled to mass spectrophotometry. A total of 22 pesticides were detected, being the highest concentrations for thiocyclam in fruits (0.79 mg kg−1), indoxacarb in leaves (24.81 mg kg−1) and dimethomorph in soils (44.45 mg kg−1), however no residues were detected in water or sediments. At least one pesticide was detected in 66.7% of the samples. Methomyl and dimethomorph were common in fruits, leaves and soils for both regions; in addition, seven pesticides exceeded the Maximum Residue Limits. The results showed a high presence and affinity of pesticides in the environmental compartments of high-Andean tomato production regions, mainly in soils and open field productive systems.

Temperature Dependence of Henry's Law Constants of Fenpropidin and Pyrimethanil: Impact on their Atmospheric Partitionnings and Lifetimes

Henry's law constants (HLC) play a key role in the environmental fate of pesticides and their distribution between the different phases, i.e., between air, water and soil. For certain compounds such as fenpropidin and pyrimethanil, HLC values are poorly documented in the literature and in particular their temperature dependence. This work reports the experimental HLC values of two pesticides, namely fenpropidin and pyrimethanil, determined by means of a dynamic equilibrium system coupled to an off-line analysis performed by Gas Chromatography–Photoionisation Detection (GC–PID). The measurements were conducted over the range 278–293 K. In pure water, the experimental average values of HLC at 293 K were: HLC293K(fenpropidin) = (10.0 ± 3.1) × 104 M atm–1, HLC293K(pyrimethanil) = (8.2 ± 0.7) × 104 M atm–1. The obtained data were used to derive the following Arrhenius expressions where the quoted errors represent 2σ: ln HLC (fenpropidin) = (6060 ± 2420)/T – (9.1 ± 8.3); ln HLC (pyrimethanil) = (14570 ± 1800)/T – (38.4 ± 6.2). The environmental implications are then discussed in terms of lifetime or partitionning between the different atmospheric compartments.

Evluation of Pesticide Environmental Fate at the Watershed Scale: A New Simulation Framework

Evluation of Pesticide Environmental Fate at the Watershed Scale: A New Simulation Framework

Inverse modeling of laboratory experiment to assess parameter transferability of pesticide environmental fate into outdoor experiments under paddy test systems.

Extraction of environmental fate parameters for pesticides by inverse modeling in laboratory experiments has evolved to become a common practice in higher tier exposure modeling. This study focuses on flooded paddy soil conditions using a simple container test system. Four active ingredients of paddy herbicide were tested. The results were parameterized and transferred to analyze the effect of formulation types on the outdoor experimental data via inverse analyses of two structurally-compatible mathematical models, namely: pesticide concentration in paddy field for laboratory (PCPF-LR) and PCPF for outdoors (PCPF-1Rv1.1 ). After in-laboratory calibration, the PCPF-LR model revealed statistically acceptable or ideal simulations of pesticide concentrations in both the aqueous and soil phases (e.g. Nash-Sutcliffe efficiency > 0.7), in addition to determining the apparent sorption from the laboratory data. The extracted persistence indicators (degradation half-life, DegT50 ) in the aqueous phase were 1.4-38.7 times higher than those of the dissipation (DT50 ) due to the exclusion of partitioning and phase transfer processes (diffusion and sorption). In the outdoor experiment, 72% of the outdoor-calibrated simulations of the PCPF-1Rv1.1 model, showed statistically acceptable representations of the concentrations in paddy water. Furthermore, the DegT50 as 'bulk' degradation in paddy water was statistically insignificant between the formulation types; however, the DT50 demonstrated statistically different results. The laboratory/outdoor data interconnections using proposed modeling approach facilitate the data-specific model calibration and analysis. These can be useful in the exposure modeling of paddy pesticide by manipulating the parameter uncertainties associated with the experimental constraints. © 2020 Society of Chemical Industry.

Agricultural uses of chitin polymers

Due to strict legislation which governs the use of pesticides, fertilizers and plant growth regulators, there is a demand for organic alternatives. Potential risks for people, possible long-term health effects, and pesticide environmental fate resulted in a widespread societal issue. Because sustainable agriculture interconnects the economically and socially, the use of environmentally sound compounds has become popular. Improving plant growth using natural compounds such as chitin, a carbohydrate chain polymer, and its derivatives is a promising sustainable agriculture strategy. Chitin and its derivatives exhibit a unique mode of action being at the same time safe and non-toxic by nature. They are recognized as promising soil amendments for improving soil quality, induce abiotic and biotic plant stress tolerance, boost defense mechanism of plants against invading microorganisms, elicit the production of secondary metabolites, and protect the safety of edible products. Here, we review beneficial effects of chitin as a fertilizer, soil conditioning agent, plant disease control agent, antitranspirant, ripening retardant, and seed and fruit coating.

Addressing bystander exposure to agricultural pesticides in life cycle impact assessment

Residents living near agricultural fields may be exposed to pesticides drifting from the fields after application to different field crops. To address this currently missing exposure pathway in life cycle assessment (LCA), we developed a modeling framework for quantifying exposure of bystanders to pesticide spray drift from agricultural fields. Our framework consists of three parts addressing: (1) loss of pesticides from an agricultural field via spray drift; (2) environmental fate of pesticide in air outside of the treated field; and (3) exposure of bystanders to pesticides via inhalation. A comparison with measured data in a case study on pesticides applied to potato fields shows that our model gives good predictions of pesticide air concentrations. We compared our bystander exposure estimates with pathways currently included in LCA, namely aggregated inhalation and ingestion exposure mediated via the environment for the general population, and general population exposure via ingestion of pesticide residues in consumed food crops. The results show that exposure of bystanders is limited relative to total population exposure from ingestion of pesticide residues in crops, but that the exposure magnitude of individual bystanders can be substantially larger than the exposure of populations not living in the proximity to agricultural fields. Our framework for assessing bystander exposure to pesticide applications closes a relevant gap in the exposure assessment included in LCA for agricultural pesticides. This inclusion aids decision-making based on LCA as previously restricted knowledge about exposure of bystanders can now be taken into account.

Fate and Impact of Pesticides

Fate and Impact of Pesticides

Characterization of spectral responses of dissolved organic matter (DOM) for atrazine binding during the sorption process onto black soil

This study was aim to investigate the interaction between soil-derived dissolved organic matter (DOM) and atrazine as a kind of pesticides during the sorption process onto black soil. According to the experimental data, the adsorption capacity of Soil + DOM, Soil and DOM were 41.80, 31.45 and 9.35 mg kg−1, separately, which indicated that DOM significantly enhanced the adsorption efficiency of atrazine by soil. Data implied that the pseudo-second-order kinetic equation could well explain the adsorption process. The adsorption isotherms (R2 > 0.99) had a satisfactory fit in both Langmuir and Freundlich models. Three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence, two-dimensional correlation spectroscopy (2D-COS) and Fourier transform infrared spectroscopy (FT-IR) were selected to analyze the interaction between DOM and atrazine. 3D-EEM showed that humic acid-like substances were the main component of DOM. The fluorescence of DOM samples were gradually quenched with the increased of atrazine concentrations. Synchronous fluorescence spectra showed that static fluorescence quenching was the main quenching process. 2D-COS indicated that the order of the spectral changes were as following: 336 nm > 282 nm. Furthermore, the fluorescence quenching of humic-like fraction occurred earlier than that of protein-like fraction under atrazine surroundings. FT-IR spectra indicated that main compositions of soil DOM include proteins, polysaccharides and humic substances. The findings of this study are significant to reveal DOM played an important role in the environmental fate of pesticides during sorption process onto black soil and also provide more useful information for understanding the interaction between DOM and pesticides by using spectral responses.

An assessment of environmental and toxicological risk to pesticide exposure based on a case-based approach to computing

Pesticide environmental fate and toxicity depends on its physical and chemical features, the soil composition, soil adsorption, as well as residues that may be found in different soil slots. Indeed, pesticide degradation in soil may be influenced by either biotic or abiotic factors. In addition, the toxicity of pesticides for living organisms depends on their adsorption, distribution, biotransformation, dissemination of metabolites together with interaction with cellular macromolecules and excretion. Biotransformation may result in the formation of less toxic and/or more toxic metabolites, while other processes determine the balance between toxic and a nontoxic upcoming. Aggregate exposure and risk assessment involve multiple pathways and routes, including the potential for pesticide residues in food and drinking water, in addition to residues from pesticide use in residential and non-occupational environments. Therefore, this work will focus on the development of a decision support system to assess the environmental and toxicological risk to pesticide exposure, built on top of a Logic Programming approach to Knowledge Representation and Reasoning, complemented with a Case Based attitude to computing. The proposed solution is unique in itself, once it caters for the explicit treatment of incomplete, unknown, or even self-contradictory information, either in terms of a qualitative or quantitative setting.

Impact of Spent Mushroom Substrates on the Fate of Pesticides in Soil, and Their Use for Preventing and/or Controlling Soil and Water Contamination: A Review.

Intensive crop production involves a high consumption of pesticides. This is a cause of major environmental concern because the presence of pesticides in water is becoming increasingly common. Physicochemical methods based on soil modification with organic residues have been developed to enhance the immobilization and/or degradation of pesticides in agricultural soils, which may control both the diffuse and the point pollution of soils and waters. This review summarizes the influence of spent mushroom substrate (SMS) on the environmental fate of pesticides when both are simultaneously applied in agriculture. The processes of adsorption, leaching and dissipation of these compounds in SMS-amended soils were evaluated at laboratory and field scale. Relationships were established between the experimental parameters obtained and the properties of the soils, the SMS, and the pesticides in order to determine the effect that the application of SMS in agricultural soils has on the environmental impact of pesticides. Accordingly, this review highlights the use of SMS as a strategy for the prevention and/or control of soil and water contamination by pesticides to strike a balance between agricultural development and the use of these compounds.

Pesticide regulatory risk assessment, monitoring, and fate studies in the northern zone: recommendations from a Nordic-Baltic workshop.

The recent revision of the legal framework for authorization of use of plant protection products and pesticides within the European Union/European Economic Area (EU/EEA; Regulation EC 1107/2009, Directive 2009/128/EC) imposes a need for close collaboration across country borders within the three pesticide authorization zones (designated the north, central, and south zones) in Europe. The principles of zonal evaluation and mutual recognition embedded in Regulation EC 1107/2009 concerning marketing of plant protection products are intended to reduce the approval times for pesticides. However, the three authorization zones represent a very simplified view compared to the 16 climatic zones/scenarios that have been outlined for pesticide modeling in Europe (Blenkinsop et al. 2008; Fig. 1). Pedoclimatic or agricultural constraints could entitle the individual states to adopt restrictions on the use of pesticides approved within their zone or even to refuse approval. Fig. 1 Zones for pesticide authorization overlaid on climatic zones for pesticide modeling (reprinted from Blenkinsop et al. 2008 with permission from Elsevier) in Europe To achieve a sound scientific basis for zonal evaluation and collaboration on a regulatory level, it is also necessary to increase research collaboration and knowledge exchange within the scientific community. Here, we report the main conclusions and recommendations from a Nordic-Baltic workshop on the environmental fate of pesticides, which was conducted in As, Norway, in September 2014 with the aim of promoting knowledge exchange, network building, and a common agenda for future research within the northern zone. Pesticide regulatory risk assessment in the northern zone Zonal evaluation and mutual recognition The “Guidance document on work sharing in the Northern zone in the authorization of plant protection products” (Anonymous 2015) states that the northern zone cooperation includes the EU member states Denmark, Sweden, Finland, Estonia, Latvia, and Lithuania, as well as the European Economic Community/European Free Trade Association (EEC/EFTA) members Norway and Iceland. The guidance document was implemented in all countries within the zone from January 2015. Climatic zones for pesticide modeling (Blenkinsop et al. 2008) reflect the complexity of the different authorization zones within Europe (Fig. 1). According to this classification, the northern zone countries cover seven of the 16 climatic zones (Table ​(Table1).1). The variation within the northern zone is further illustrated by the 13 environmental zones representing an aggregation of the environmental stratification of Europe (Metzger et al. 2005; Jongman et al. 2006), five of which are covered by the northern zone countries (Table ​(Table2).2). The duration of the growing season and the sum of active temperatures are doubled when moving southward from the alpine north to the Atlantic north. This will inevitably affect the possibility of harmonizing risk assessment procedures and/or requirements between the countries within the northern zone, and it will also influence the commercial viability of the pesticide industry. Table 1 Climate zones for pesticide modeling (Blenkinsop et al. 2008) in the northern zone countries Table 2 Growing season characteristics in the northern zone based on the environmental stratification of Europe (Metzger et al. 2005; Jongman et al. 2006) Due to the strict limits of the timeline for the zonal evaluation (SANCO/13169/2010 rev. 9), there must be good agreement between the countries in the northern zone to ensure a satisfactory risk assessment. The time frame during which the member states are to appraise specific national concerns comprises a period of 6 weeks for commenting on the draft regulatory report and 120 days for assessment after the initial zonal evaluation.

Dissipation of fomesafen in biochar-amended soil and its availability to corn (Zea mays L.) and earthworm (Eisenia fetida)

Purpose Biochar application has been shown to be effective in improving soil fertility and sequestering soil contaminants. However, the impact of biochar amendments on the environmental fate of pesticides and the bioavailability of pesticides to living organisms in the soil environment is still not fully understood.

Nature and decomposition degree of cover crops influence pesticide sorption: Quantification and modelling

This study quantifies and models the influence of the type and the degree of decomposition of cover crops (CC) on three pesticides sorption: epoxiconazole (EPX), S-metolachlor (SMOC) and glyphosate (GLY). Residues of four cover crop species were incubated for 0, 6, 28 or 56d in controlled conditions. For each incubation time, adsorption of pesticides on CC residues was measured in batch experiments. Additionally, the biochemical and elemental composition (Van Soest fractionation, C:N, 13C NMR spectroscopy) of CC was characterized. Mineralization of CC residues was monitored at all incubation times using CO2 trapping. Results showed that the adsorption of pesticides differed significantly according to (i) the type of molecule, (ii) the type of CC, (iii) the degree of CC decomposition and the interaction CC×decomposition time. EPX and GLY were the most (Kd ranging from 188 to 267Lkg−1) and the least (Kd ranging from 18 to 28Lkg−1) sorbed pesticides respectively. With increasing decomposition of the CC residue, sorption increased by 1.6- to 4.7-fold according to the type of pesticide and cover crop. It was significantly correlated with the net cumulative mineralization (ρ>0.7) and other indicators of biochemical composition such as C:N ratio (ρ<−0.7), the Van Soest neutral detergent soluble fraction (ρ>0.5) and the alkyl/O-alkyl C ratio determined by NMR. An innovative model based on net cumulative mineralization of CC residues is proposed to describe the pesticide sorption and appears to be a promising approach to account for the effects of decaying plant residues on the environmental fate of pesticides.

Crop protection: new strategies for sustainable development

GFP 2012 was the 42nd congress organized by the French Group of Pesticide research (“Groupe Francais des Pesticides”, GFP), an association created in 1977 by a group of scientists from several French universities and research institutes. Initially, this conference was held twice a year, but nowadays, the adopted rhythm is once a year over a period of 3 days, usually in May. All scientific and technical aspects of the synthesis, reactivity, mode of action, toxicology, ecotoxicology, and environmental fate of pesticides are discussed. In this special issue, ESPR publishes 17 articles that are based on oral presentations at GFP 2012 in Poitiers. It covers the latest advances in the field of pesticide research with a special focus on innovative strategies for plant protection. This key theme was chosen by the organizing team according to the main research conducted in the location hosting the conference, namely, original strategies to confer systemicity to nonmobile compounds. The purpose of this research is to improve the bioavailability of active compounds, thereby reducing the quantity of pesticides used and pollution. It also aims at managing parasites that remain uncontrolled because of their location, e.g., fungi responsible for grapevine trunk diseases. In 2008, France, which is the fourth largest market, behind the USA, Brazil, and Japan, has implemented an action plan called “Ecophyto”. The Ecophyto plan embodies the commitment given by the authorities, industry professionals, and representatives of civil society to cut the nationwide use of pesticides by 50 % within 10 years, if possible (Ministere de l’Agriculture et de la Peche 2008). The most notable goal of Ecophyto is to reduce the dependency of farms on plant protection products, without affecting agricultural yields and maintaining high levels both in terms of quality and quantity. In this context, the aim of the conference was to provide some answers to current societal challenges, i.e., producing larger amounts of food for an exponentially growing population while reducing agronomic inputs for pest and weed control, thereby reducing pollution as well as potential toxicity to the environment or human health. In order to achieve these various objectives, GFP 2012 was organized in four sessions as follows:

The role of indirect photochemical degradation in the environmental fate of pesticides: a review

Photochemical degradation contributes to the environmental fate of many pesticides in surface waters. A better understanding of the role of direct and indirect photochemical degradation of pesticides is necessary in order to predict their environmental fate and persistence. This review includes all major pesticide classes and focuses on the importance of dissolved organic matter (DOM) as a sensitizer in indirect photodegradation within aquatic systems. Photochemical studies conducted under environmentally relevant conditions (i.e., aqueous solutions with irradiation wavelengths >290 nm) are included. Comparisons are made between observed photodegradation rates in pure or buffered water and in water containing DOM to assess the extent of pesticide susceptibility to DOM-sensitized indirect photolysis. When data is available, the role of specific reactive species in indirect photodegradation is described. While it is possible to assess the relative importance of direct and indirect photodegradation on a pesticide-by-pesticide basis in many cases, it is often difficult to make generalizations based on compound class. Knowledge gaps and inconstancies in the current body of literature are discussed and areas that require additional research are described.