Pesticides in Water, Soil, and Sediments

C H A P T E R

9 Pesticides in Water, Soil, and Sediments Victoria Ochoa and Britt Maestroni Food and Environmental Protection Laboratory, Joint FAO/IAEA Division of Nuclear Applications in Food and Agriculture, International Atomic Energy Agency, Vienna, Austria

INTRODUCTION The use of pesticides to control weeds, insects, and other pests has resulted in a range of benefits, including increased food production and reduction of insect-borne disease, but also raises questions about possible adverse effects on the environment, including water quality. Despite more stringent legislation, consumer awareness, and increased efficacy of pesticides that currently allow lower amounts to be applied per ha, pesticides are still a significant cause of contamination of environmental resources. Changing climatic conditions, differing soil type, land uses, intrinsic chemical
physical properties of the chemicals as well as point sources are crucial factors influencing the overall pesticides balance within a catchment (Kreuger, 1998; Capel et al., 2001). The concentration of pesticides in each environmental compartment (water, soil, and air) determines the exposure and consequently the impact of pesticides on target and nontarget organisms. Understanding the environmental fate and transport mechanisms of pesticides is essential to undertake environmental risk assessment and therefore be able to implement risk management strategies at catchment level.

ENVIRONMENTAL FATE PROCESSES OF PESTICIDES The environmental fate of any agrochemical starts with its application onto agricultural fields. The fate of substances in the environment is affected by chemical, physical, biological, and hydro-meteorological processes in soil, water, and air (Gassman, 2013); these are illustrated graphically in Fig. 9.1. The major environmental processes related to pesticides are transport, degradation, and uptake by plants and organisms. Transport processes refer to the translocation of pesticides away from their application point. Wind drift can contaminate nontarget areas during pesticide application. In water, pesticides can be transported in dissolved form or attached to soil particles or sediments (Gassman, 2013). After application, pesticides may be washed off plants and crops to the soil surface by rainfall (Wauchope et al., 2004). Surface runoff is the major pathway for river contamination (Schulz 2001; Shipitalo and Owens; 2003; Gassman, 2013). Leaching of pollutants may contaminate groundwater (Djodjic et al., 2004; Fava et al., 2005; Gassman, 2013). Preferential transport in combination with tile drains are important sources of freshwater contamination and act as shortcuts for the transport of pesticides toward surface water (Doppler et al., 2012; Gassman, 2013). Direct evaporation of organic compounds from surface water, soil, and plants is also possible via volatilization (Mackay and Yuen, 1980; Gassman, 2013). Degradation processes lead to changes in structure of a pesticide. Resulting transformation products may be more mobile in the environment and more resistant to degradation. Transformation is of major importance in determining the persistence of a chemical. The most common transformation processes in the environment are photolysis, microbial degradation, and hydrolysis (Holt, 2000; Gassman, 2013). Each pesticide has its own speed of degradation, which depends on the active ingredient, the formulation and environmental conditions.

Integrated Analytical Approaches for Pesticide Management. DOI: https://doi.org/10.1016/B978-0-12-816155-5.00009-9

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FIGURE 9.1 Environmental transport and degradation processes of pesticides applied to an apple orchard.

Uptake by organisms refers to the incorporation of pesticides and/or their degradation products into a target or nontarget organism. Two different modes of uptake can be distinguished, passive uptake and active uptake. For aquatic fauna active uptake occurs through feeding, passive uptake occurs via the skin and gills. For plants, uptake may occur through passive uptake from water or air via the leaves but also through active uptake from pore water via the roots (Holt, 2000). In general, uptake by organisms leads to bioconcentration and bioaccumulation. Those are the effects of dietary uptake through “food” consumption (Miyamoto et al., 1990). The effect of each of these processes on the concentration of a chemical in any given environmental compartment (such as water, air, soil, sediment, biomass) depends on the physicochemical properties of the pesticide and the hydrology, geochemistry, and biological characteristics of the receiving environment (Holt, 2000).

FATE OF PESTICIDES IN SOIL Once pesticides reach the soil compartment they can either be “sorbed” to the soil and therefore become temporarily unavailable, or they can move and be transported together with soil particles through erosion processes, for example, they can also be transported through runoff, transformed into other simpler molecules (degradation products) through degradation mechanisms induced by soil microorganisms or through other physical events such as photolysis and hydrolysis. Many factors have an influence on the transport processes of pesticides in soils: These are described later. The fate of a pesticide in soil depends first on the application method. With application by spraying, pesticides are applied to the foliage of plants and unintentionally varying proportions of the spray are intercepted by the crop canopy and/or the bare soil surface. This implies that the most likely transportation processes for pesticides are surface runoff, volatilization, movement with eroded soil particles, and photo-decomposition. On the other hand, direct application of pesticides by injection into the soil or incorporated into plant seed will result in pesticides being “well fixed” to the soil structure and thereby able to correctly carry out their “agrochemical” function. The fate of a pesticide in soil may also depend on the pesticide’s physicochemical properties. Adsorption of pesticides to soil particles increases with the soil volume and surface area (Sabljic et al., 1995; Mamy and Barriuso, 2005). In addition the electronic structure of the pesticide determines its interaction with soils through

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donor
acceptor electron and hydrogen bonds (Calvet, 1989). In general, the sorption of cations is strong on negatively charged surfaces like clays, oxides, hydroxides, humic substances, and the sorption of anions is high in soils with positive charges, like tropical soils. The fate of a pesticide in soil may also depend on the balance between its hydrophilicity and its hydrophobicity. In general terms, the adsorption of pesticides onto soil is reduced when they show high water solubility (hydrophilicity) and high affinity for the water phase. On the other hand, the probability of adsorption to soil increases with the hydrophobicity of the pesticide. However, the adsorption of polar compounds does not always decrease with increased water solubility (Calvet, 1989). Glyphosate is an example: This is a polar herbicide but due to its amphoteric molecular properties it is highly soluble in water but also strongly sorbed to soils (Barriuso et al., 2008). The fate of a pesticide in soil may also depend on the intrinsic properties of the soil. In general, clay soils are more prone to sorption due to the presence of a large number of hydroxyl groups and exchangeable cations thus creating the conditions for hydrophilic surfaces. In addition the higher the content of organic matter, the higher the sorption of selected pesticides to soil particles (Calvet, 1989). This is attributed to the high chemical reactivity of the soil toward both mineral surfaces and organic molecules. Pesticide adsorption will increase (or decrease) with pH depending on the charge of the pesticide. For example, the retention of glyphosate increases as pH decreases because the number of negative charges on the molecule decreases, allowing the adsorption on negatively charged adsorbents like clay or organic matter (Chaplain et al., 2011). The fate of a pesticide in soil may also depend on the environmental conditions, e.g., water balance and temperature, which influence soil moisture content. The adsorption of pesticides increases with high soil moisture content as water facilitates pesticide diffusion to sorption sites. In general, the higher the organic matter, the higher the number of bonding sites via hydrophilic interactions and the greater the sorption of hydrophilic pesticides to soil (Roy et al., 2000). It was also observed that the adsorption of pesticides onto soil generally decreases when temperatures increase (Hulscher and Cornelissen, 1996). Pesticide degradation is the process by which a pesticide is transformed into simpler compounds such as water, carbon dioxide, and ammonia as a result of chemical reactions like hydrolysis, photolysis and biodegradation. Several factors control the biodegradation in soil. The most important are their physicochemical properties, such as vapor pressure, stability, and solubility. However, there is no general rule about the relationship between the chemical properties of a pesticide and its rate of degradation because of the large variety of pesticides and the phenomena involved in their degradation (Calvet, 1989). Degradation of pesticides can be influenced by environmental conditions influencing the soil moisture. Soil moisture affects the diversity of soil biota and their activity (Bouseba et al., 2009). Generally, aerobic microbial activity increases with soil water content up to a maximum point before decreasing (Linn and Doran, 1984). Low water content in soil reduces soil microbial activity and this may favor long-term undisturbed sorption of pesticides to soil (Cox and Walker, 1999). This explains why pesticide degradation is reduced (with increase in persistence) in areas with elevated temperature and limited rainfall (arid areas) (Bouseba et al., 2009). Finally the degradation of pesticides can be influenced by the distribution of microorganisms in soil. The spatial distribution of microorganisms in heterogeneous soil structure plays an important role in microbial processes and in the persistence and degradation of organic compounds in soil (Strong et al., 1998), by affecting the probability of contact between the degraders (the microorganisms) and the soil substrate, including the pesticides (Pallud et al., 2004).

PESTICIDES IN WATER Entry of pesticides into aquatic resources can be the result of direct application for pest prevention programs that require their application into or near aquatic environments. An example is the application of insecticides to rice crops. Nonpoint source pollution of water resources by pesticides may occur through a number of mechanisms, the most important being through runoff, soil erosion, and wind deposition. Several factors affect the fate of pesticide in aquatic systems. The most important are: • Physicochemical properties of the pesticides: Water solubility, volatility, stability against degradation by abiotic (hydrolysis, photodecomposition), and biotic (microbial degradation) factors. • pH: Organophosphorus and carbamate insecticides are generally stable at lower pH (5
7), but rapidly hydrolyzed at higher pH (7
10), and triazines herbicides are most stable at pH . 7. • Temperature: Generally an increased temperature results in increased rates of chemical reactions such as solubilization, adsorption, volatilization, biological degradation.

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Biological degradation is a continuous process in aquatic environments (Pagga, 1997). Surface waters are good environments for pesticide breakdown, especially when microorganisms are able to anchor on surfaces, such as the sediment
water interface, rocks and plants. In natural systems, the pathways and rates of microbial degradation of pesticides will depend on the type of substrate, temperature, dissolved oxygen availability, nutrient supply, similarity of the agrochemical to other food sources, resistance mechanisms to the pesticides and other environmental conditions that control the microbial population growth (Warren et al., 2003). Natural sorbents, like sediments, can indirectly control processes in the water phase by release or uptake of pesticides through adsorption processes. Organic carbon is the dominant component that acts as a sorbent in sediments (Holvoet et al., 2007). Sorption is often described by a “sorption constant” normalized for the organic carbon content called Koc (Warren et al., 2003, Holvoet et al., 2007). For sediments with low organic carbon content, the sorption of polar compounds (acids/bases) is proportional to the cation exchange capacity of the sediment/soil specific surface and to the pH. Important to note is that the process of desorption of pesticides from sediments involves a relatively fast initial release of sorbed pesticides followed by a prolonged and increasingly slower release as desorption proceeds (Gao et al., 1998).

PESTICIDES INTO AIR During field applications, pesticides may enter air as tiny droplets or vapor drift. Spray drift is the movement of droplets of pesticide spray that through wind are taken away from the target application area. Wind, droplet size, temperature, and height of spraying nozzle are some of the factors influencing the amount of spray drift released in the environment. Volatilization is the most likely movement of pesticides into the atmosphere after field spraying. It relates to the pesticide vapor pressure and its tendency to volatilize from dilute aqueous solutions. The volatilization effect is directly proportional to the temperature and increases at higher temperatures.

MONITORING AND MODELING PESTICIDE TRANSPORT AT CATCHMENT SCALE For monitoring of nonpoint source pollution from pesticides at catchment scale the authors recommend an integrated monitoring approach as described in Chapter 2, Generic Guidelines on Integrated Analytical Approaches to Assess Indicators of Pesticide Management Practices at a Catchment Scale. Black-Box Monitoring and the Laboratory’s Role in Fostering Good Agricultural Practice, and Chapter 15, Integrated Analytical Monitoring. It emphasizes the complementarities achieved by coordinated monitoring activities comprising chemical and biological measurements in a variety of environmental media. Biological monitoring techniques (through biomarkers, biosensors, biological early warning systems and whole-organism bioassays), and chemical monitoring by a range of analytical methods may provide a time integrated estimation of bioavailable fractions of pesticides in surface water (Holvoet et al., 2007). Sampling and monitoring, however, are challenged by the temporal and spatial variations in pesticide distribution; hence the need for pesticide residue data over several seasons and from strategically identified sampling points. The combined information from catchment characteristics, main transport mechanisms, target substances (either pesticides or their transformation products), target matrices (water, air, soil, sediment, biomass matrices), and off-site pesticide balance through initial monitoring are essential to build a first model approximation and start predicting pesticide transport at catchment scale. Refinement of the model should occur once additional monitoring data are available. According to Allan et al. (2006), it is very important to combine the use of monitoring data and models to optimize sampling strategies for a more representative and cost-effective assessment of pesticides in surface water.

REGULATIONS FOR PROTECTION OF WATER RESOURCES Pesticides are regulated worldwide due to their toxicity; in particular, the introduction of new pesticides and their uses are strictly regulated by country-specific registration procedures and authorizations for specific uses. The risk assessment procedures assist establishing maximum residue limits (MRLs) for pesticides in food thus aiming at the protection of not only farmers and consumers worldwide, but also the soil and water resources and ecosystems.

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FAO (2015) has published country reports on the status of pesticide management and MRLs setting. Detailed information for Bangladesh, Cambodia, China, Indonesia, Japan, Korea DPR, Lao PDR, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Singapore, Sri Lanka, Thailand, and Vietnam can be accessed through the FAO website. With regards to water quality standards, several international comparisons have been published on the World Wide Web and regulatory limits are available (David Suzuki Foundation, 2006; UNEP, 2007; WHO, 2013; Safe Drinking Water Foundation, 2015).

EUROPE Pesticides are strictly regulated in Europe and rigorous scientific assessment must ensure that their use is safe for human health and a sustainable environment. The core legislation regulating the authorization for placing of pesticides on EU markets is Regulation (EC) No. 1107/2009, directly applicable in member states. This regulation targets health and environmental protection over agricultural production. Active substances are approved by the European Commission following advice from the Risk Assessment Unit of the European Food Safety Authority (EFSA). Council Directive 98/83/EC (Drinking Water Directive) regulates the maximum pesticide concentration in drinking water. The Water Framework Directive 200/62/EC intends to simplify the legislation in order to assure a more effective implementation of the water policy. In relation to agricultural use of water for irrigation the Water Framework Directive contains a number of important aspects: • • • •

River basin management Cost recovery for water services Participation of public sector in the planning process Protection of groundwater and wetlands Other European legislation related to pesticides includes:

• • • • • •

Directive 2009/128/EC establishing a framework for sustainable use of pesticides Regulation (EC) No. 1185/2009 concerning statistics on plant protection products Regulation (EC) No. 396/2005 on maximum residue levels of pesticides in or on food and feed Regulation (EC) No. 1272/2008 on product classification, labeling and packaging Directive 2006/118/EC on the protection of groundwater Directive 2004/35/CE on environmental liability A useful infographic on how Europe ensures pesticides are safe is available at the EFSA website (EFSA, 2016).

UNITED STATES The Environmental Protection Agency (EPA) is responsible for regulating pesticide uses in the United States under the authority of two Federal statutes: • Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) which regulates the regulation, sale, distribution, and use of pesticides in the United States • Federal Food, Drug, and Cosmetic Act (FFDCA) which authorizes EPA to set maximum residue levels, or tolerances, for pesticides used in or on foods or animal feed In addition a number of other federal laws regulate the use, storage, disposal, and transportation of pesticides in the United States: • The Food Quality Protection Act (FQPA) amended FIFRA and FFDCA, setting safety standards for new and old pesticides and to make uniform requirements regarding processed and unprocessed foods. • The Clean Water Act which aims at protecting waterways from both point and nonpoint sources of pollution. • The Safe Drinking Water Act designed to ensure that public water systems provide water meeting the minimum national standards or protection of public health.

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• The Occupational Safety and Health Act mandates protection of workers, including farm workers applying pesticides to crops and workers in pesticide manufacturing plants from all hazards in the workplace. • The Federal Endangered Species Act aims at protecting endangered species from harmful effects of pesticides, restricting the use of agrochemicals in areas where endangered species are likely to be exposed. • The US Department of Transportation (DOT) controls the mode of transportation of pesticides and other hazardous substances.

AUSTRALIA The Australian Pesticides and Veterinary Medicines Authority (APVMA) is the regulatory body responsible for the import, manufacture, registration, packaging, labeling, distribution, and retail sale of pesticides in Australia. The States and Territories of Australia are responsible for the control of pesticide uses. The MRLs are set in Australia by the APVMA. The Australian Government National Health and Medical Research Council (NHMRC) is responsible for drinking water quality standards, developing the Australian Drinking Water Guidelines. The National Water Quality Management Strategy (NWQMS) is a joint national approach to improve water quality in Australian and New Zealand waterways. The NWQMS aims to protect the nation’s water resources by improving water quality while supporting the business, industry, environment and communities that depend on water for their continued development. It provides policies, a process and a series of national guidelines for water quality management (Government of Australia, 2015).

CHILE In Chile the Agricultural and Livestock Service (SAG) regulates the manufacture, formulation, distribution and application of pesticides through Decree Law 3557 (Anon., 2015). Chile’s pesticide registration regulatory framework is based on the Food and Agriculture Organization’s guidelines. The Ministry of Agriculture, through Resolution No. 1117 establishes the toxicological classification of pesticides for agricultural uses based on the WHO recommendations. The Official Chilean Standard 409 establishes the physical, chemical, radioactive and bacteriological requirements for drinking water and sets the maximum permissible concentration of certain pesticides in water resources (Anon., 1984).

WATER MONITORING USING PASSIVE SAMPLING TECHNOLOGY The application of passive sampling technology for monitoring pesticides and other micropollutants in surface water is accepted worldwide (USGS, 2010). Two of the most common passive samplers for organic contaminants are the semipermeable membrane device (SPMD) and the polar organic chemical integrative sampler (POCIS). The principle of these techniques is based on the accumulation of pesticides by passive diffusion onto a receiving phase. This can be a liquid or a solid absorbent that has a specific affinity for a particular class of pollutant. The sorbents used in SPMD and POCIS are respectively triolein and Oasis HLB phase. Equilibrium passive samplers should be left for an average of 20
30 d in the water body to absorb the pollutant. The SPMD is employed to target neutral organic chemicals with a log octanol
water partition coefficient (Kow) greater than three (lipophilic substances). POCIS are employed to target the more water soluble organic chemicals with a log octanol
water partition coefficient (Kow) less than three (polar substances). Both types of passive samplers can be used together and placed in a canister that in turn is anchored to a stable hook in the field (see Fig. 9.2). Passive samplers can be deployed to catch episodic events such as surface runoff, and other nonpoint source contamination events independently from the time when these events happen. The cumulative response from passive samplers can be used in combination with the information from grab sampling. Morin et al. (2012) compiled information from numerous references involving POCIS passive samplers and critically reviewed the analytical protocols.

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FIGURE 9.2 A scientist in Ecuador collects passive samplers (POCIS) that had been placed for 25 days in a river flowing through a palm oil plantation (Photograph from B. Maestroni, FAO/IAEA).

Remove the SPMD type membrane from the canister and to remove particulate matter or biofilm gently rinse using a brush, quickly submerging in diluted acid, rinse with distilled water, follow by a rinse with acetone and hexane. Place the clean SPMD in a beaker and cover the membrane with n-hexane. Place the dialysis beaker in an incubator at 18ºC for 24 h

Remove the SPMD and put it into a second container. Cover the membrane completely with n-hexane. Place the dialysis beaker in an incubator at 18ºC for 24 h

Combine both n-hexane extracts; concentrate under nitrogen stream, solvent exchange

Inject the extract into GC/MSD

FIGURE 9.3 Outline of the general method for recovery of pesticides from SPMD type membranes.

A relatively easy method for recovering absorbed pesticides from SPMD is briefly described in Fig. 9.3 (USGS, 2010; Narvaez et al., 2013). The recovery for SPMD membranes essentially consists of dialysis and for POCIS membranes it consists of a solvent extraction procedure. Note that the general method as described in Fig. 9.3 should be validated in the analytical laboratory and adapted to the range of pesticides analyzed. For example, the dialysis solvent may be changed to n-hexane: dichloromethane (95:5); the combined n-hexane extract may be subjected to additional clean-up using alumina and/or silica columns. When performing a solvent exchange it is important to ensure that the target pesticides are soluble in the final solvent. The method for recovering the chemicals from POCIS membranes is briefly described in Fig. 9.4 (USGS, 2010; Narvaez et al., 2013). The POCIS membranes need to be open and the internal sorbent needs to be transferred for column extraction. The extraction method for the recovery of pesticides from POCIS or SPMD membranes depends on the equipment available at the laboratory. Method adaptation and validation are essential to ensure that the method is “fit for purpose.”

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Remove the POCIS types membranes from the holders; to remove particulate matter or biofilm, gently rinse using distilled water

Separate the membranes and using a spatula, collect the POCIS sorbent and transfer to an empty solid phase extraction cartridge. Use methanol or water to quantitatively transfer all sorbent to the column

Add 20 mL ethyl acetate, followed by 50 mL of a mixture of methanol:toluene:dichloromethane (1:1:8, v/v), followed by 20 mL ethyl acetate

Concentrate under nitrogen stream, solvent exchange

Inject the extract into the analytical instrument (i.e. LC-MS)

FIGURE 9.4 Brief description of method for recovery of pesticides from POCIS type membranes.

In 2014 the Norman Network hosted a workshop on passive sampling techniques for monitoring contaminants in the aquatic environment. A position paper was then prepared highlighting a set of recommendations to enable the future use of passive sampling for regulatory monitoring of contaminants in aquatic environments and for its acceptance by policymakers (Norman Network, 2014).

ANALYTICAL METHODS FOR WATER, SOIL AND SEDIMENTS Several analytical options exist for the analysis of environmental matrices, such as water, soil, and sediments, the choice depending on the objective of the analysis, the regulatory limits in place in the country, on the target pesticides and the instruments and equipment available. A guidance table for analysis of pesticides in water, based on a literature review for the year 2014, is presented in Table 9.1. In most laboratories the multiresidue method can be set up having prior information on the pesticides used in the field and applying such information to the Pesticide Impact Rating Index (PIRI) for early “screening” and selecting possible pesticides. For example, if the PIRI output (see Chapter 13: Environmental Risk Indicators: Their Potential Utility in Pesticide Risk Management and Communication) shows that only few pesticides have an impact on the environment in terms of mobility and toxicity then the analytical chemical monitoring should start focusing on those few pesticides, thereby narrowing the scope of the multiresidue procedure. Such an approach helps target scarce resources at the priority problem and maximizes the utility of expensive analytical resources. A complete method for pesticide analysis in environmental samples such as water, soil, and sediments, always includes a sample preparation method and a pesticide detection method. In the following paragraphs, several methodologies are presented for the analysis of pesticides in water and soil matrices.

DETERMINATION OF PESTICIDES IN WATER In order to be able to detect pesticides at trace levels in a water sample, it is important to work toward concentrating the extract. Alternatively, it is important to have access to a very sensitive last generation analytical instrument that allows detection even at very low levels. Concentration can be achieved by using liquid
liquid extraction (LLE) or solid
phase extraction (SPE). LLE is a very common sample preparation method used widely in the analytical community. The principle of separation for LLE is the difference in solubility of the pesticide molecules between the organic and water layers.

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TABLE 9.1 Compiled Literature Review for the Year 2014 for the Analysis of Selected Pesticides in Water Samples Analyte

Matrix

Instrument

Method

Reference

Metaldehyde, Isoproturon, Simazine, Chlorotoluron, Atrazine, Epoxiconazole, Chlorpyrifos, Cypermethrin, Permethrin

Water samples

GS-MS

Solid
phase extraction (SPE)

Zhang et al., 2014

PCB-28, PCB-52, PCB-101, PCB-118, PCB-153, PCB-138, PCB-180, o,p0 -DDE, p, p0 -DDE, o,p0 -DDD, p,p0 -DDD, o,p0 -DDT, p,p0 -DDT, α-HCH, β-HCH, γ-HCH, δ-HCH

Seawater samples

GC
ECD or GC
Ms/MS

Membrane-assisted solvent extraction (MASE)

Shi et al., 2014

Difenoconazole, Epoxiconazole, Tebuconazole, Atrazine, Azoxystrobin, Picoxystrobin, Pyraclostrobin, Trifloxystrobin, Chlorpyrifos, Profenofos, Fipronil, Carbendazim

Drinking waters

LC-Ms/MS

SPE using Oasis HLB (Waters, Milford, USA), Strata SAX (Phenomenex, Torrance, USA), C18 Envi-18 (Supelco, Bellefonte, USA) and Envi Carb (Supelco, Bellefonte, USA)

Montagner et al., 2014

α-HCH, HCB, β-HCH, ϒ-HCH, PCNB, δ-HCH, HEPT, aldrin, heptachlorn epoxide (HCE), trans-chlordane, cis-chlordane, dieldrin, endrin, β-endosulfan, PP-DDD, o,p0 dichlorodiphenyltrichloroethane, and p,p0 -DDT

Snow water

GC-ECD

Low-densitysolvent based dispersive liquid
liquid microextraction (LDS-DLLME)

Zhao et al., 2014

Thionazin, Sulfotep, Phorate, Dimethoate, Disulfoton, Methyl-Parathion, Fenitrothion, Malathion, Parathion, O,O,O-TEPT, Ethion, Famophos

Water sample

GC-MS

Magnetic multiwalled carbon nanotubes nanocomposites (MMWCNTs)

Nedaei et al., 2014

EPTC, Butylate, Vernolate, Tebuthiuron, Etridiazole, Molinate, Propachlor, Cycloate, Fluridone, Fenarimol, Terbacil, Chlorpropham, Trifluralin, Atraton, Prometon, Simazine, Atrazine, Propazine, Pronamide, Simetryn, Metribuzine, Alachlor, Ametryn, Napropamide, Metolachlor, Triadimefon, Diphenamid, MGK-264, Butachlor, Norflurazon, Hexazinone, Alpha-BHC, Endrin

Water simple

GC-MS

SPE

El
Osmani et al., 2014

Organophosphate, herbicide, fungicides, insecticides

Rice paddy water

GC-Ms/MS

Solid
phase microextraction (SPME)

Pereira et al., 2014

Simazine, Chlortoluron, Norflurazon, Azoxystrobin, Atrazine, Dimethomorph 3,4-dichloroaniline, Isoproturon, Procymidon, Metolachlor, Linuron, Fenitrothion, Tebuconazole, Chlorfenvinphos, Acetochlor, Diflufenican, Chlorpyrifos-ethyl Flufenoxuron

Fresh water

GC-Ms/MS

SBSE

Assoumani et al., 2014

Diazinon and Fenthion

Water sample

GC
CD
IMS

SPME fiber

Jafari et al., 2014

α-BHC, β-BHC, γ-BHC, heptachlor, δ-BHC, aldrin, heptachlor epoxide, γ-chlordane, α-chlordane, α-endosulfan, 4,40 -DDE, dieldrin, endrin, 4,40 -DDD, β-endosulfan, endrin aldehyde, 4,40 -DDT, endosulfan sulfate, and methoxychlor

Water sample and fruit

GC
ECD

Homogeneous liquid
liquid extraction (HLLE)

Yazdanfar et al., 2014

organophosphorus (chlorpyrifos, dichlorvos and trichlorfon), dinitroanilines (trifluralin), anilide (propanil), substituted urea (diuron), and organochlorines (endosulfan alpha, endosulfan beta, endosulfan sulfate and lindane)

Water sample

GC-QqQ-Ms/ MS

Dispersive liquid
liquid microextraction (DLLME)

Martins et al., 2014.

OC Ps (endosulfan I, p,p dichlorodiphenyldichloroethylene (p,p DDE), dieldrin, p,p dichlorodiphenyldichloroethane (p,p DDD), endosulfan II, o,p dichlorodiphenyldichloroethane (o,p DDD), p,p dichlorodiphenyltrichloroethane (p,p DDT), methoxychlor,and endrin

Water samples

GC-ECD

Dispersive liquid
liquid microextraction based on solidification of floating organic drop (DLLME-SFO)

Mirzaei and Rakh 2014

Atrazine, Lindane, Terbuthylazine, Aldrin

Natural waters

GC-Micro ECD

Solvent bar microextraction technique (SBME)

Vergel et al., 2014

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To 1 L fortified water, add internal standard (i.e. Sulfotep 1 ng/µl), 20 g NaCl and 20 mL nhexane. Stir for 10 min.

Allow to stand for 5 min and insert the micro-separator device (see Figure 9.7)

Slowly add about 130 mL pure water and collect the enriched n-hexane through 2.5 g NaSO4

Evaporate the n-hexane extract to 1 mL on rotary evaporator

Inject the extract into GC/MSD

FIGURE 9.5 Method for the extraction of nonpolar pesticides in water using n-hexane.

FIGURE 9.6 Bottle and microextractor device (Photograph by B. Maestroni, FAO/IAEA).

Nonpolar target compounds partition better into the organic fraction, and subsequently they can be concentrated by evaporation and analyzed. Depending on the type of analytes, different solvents or other conditions may be used. Advantages of LLE include the need for minimal equipment, simplicity, detection of a large range of possible pesticides, and reliability. On the other hand the large volumes used in LLE may render it a less environmentally friendly method. An example of a method for nonpolar pesticides in water samples is briefly described in Fig. 9.5. This is a modified LLE method (DIN, 1993) and validated at the analytical laboratory. In this case, a microextractor device is necessary for the separation of phases. The microextractor is presented in Fig. 9.6. In this modified LLE method the volume of organic solvent was only 20 mL of n-hexane. The method is useful for the determination of nonpolar pesticides such as the organochlorines or when used in combination with gas chromatography coupled to mass selective detector.

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Condition octadecyl C18 extraction sorbent with methanol (10 mL) followed by water (10 mL)

Apply 1 L water to the conditioned C18 sorbent and elute with ethyl acetate:acetone (1:1) (20 mL)

Evaporate to 1 mL (40ºC, nitrogen flow)

Inject the extract into GC/MSD

FIGURE 9.7 Adapted method for the analysis of a range of pesticides in water having intermediate to high polarities.

SOLID
PHASE EXTRACTION SPE is a widely used technique available to chemists to bridge the gap that exists between the sampling and the analytical determination of pesticides in water. SPE is similar to LLE in the sense that a partitioning of the pesticide takes place between the water and a sorbent, toward which the pesticides show more affinity for or are trapped. Sorbents available include the common inorganic adsorbents such as silica gel, carbon sorbents such as graphitized carbon black, bonded silica phases such as octadecyl (C18) and octyl silica (C8), polymers such as styrene-divinylbenzene and mixed phases. A typical SPE sample preparation is a stepwise procedure that involves sorbent activation, application of the sample (water), removal of interferences by rinsing, elution of the analytes of interest from the sorbent, concentration of the analytes by evaporation, and reconstitution of the extract into a solvent suitable for chromatographic determination. The exact conditions and the choice of solvents are usually specified by the manufacturer. Advantages of SPE include use of small amounts of solvents, and opportunity to work in the field. Water samples can be processed in remote sampling areas, and only the SPE cartridges need to be transported under cooled conditions to the laboratory. On the other hand, it is important to work under standardized conditions (i.e., constant flow rate of loading and elution) and to work with filtered water samples as solids and salts may block the SPE cartridge. Filtering water samples is usually very important; however, filtered suspended solids and sediments require additional sample preparation and analysis. Pesticides such as hydrophobic compounds may be associated with suspended solids, sediments, and soils. The determination of pesticides in soil and sediments is discussed later in this chapter. An example of a SPE method for the analysis of a range of pesticides in water, with intermediate to high polarities is presented in Fig. 9.7 (Fortuny et al., 2013). The combined extraction procedure with two extraction steps applied in series (one relies on the extraction of the more nonpolar compounds using n-hexane, a second one utilizes C18 octadecyl discs to recover middle polar compounds from the water phase) is very fast and doesn’t necessitate sophisticated equipment; it is therefore recommended for application in many laboratories provided that the method is first validated and performance criteria meet requirements. In general, the challenges for determining pesticides in water rely on the sensitivity of the methods and their reliability at low levels of concentration for the analytes. Analysts may want to explore the option of loading more matrix (water) with the SPE methods using the appropriate amounts of sorbent. Peristaltic pumps, for example, may be used to provide the option of loading more than 1 L water to SPE cartridges, thereby “concentrating the analytes” in the sorbent. The sensitivity of the method is not increased, but the analytes can be detected at higher levels, therefore peak identification is improved and false positive results can be reduced.

DETERMINATION OF PESTICIDES IN SOIL AND SEDIMENTS Pesticides differ in their physicochemical characteristics. This has a consequence on their affinity for soil, water or air, and also affects their mobility in those environmental compartments. As mentioned earlier, some

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9. PESTICIDES IN WATER, SOIL, AND SEDIMENTS

TABLE 9.2 Classification of Pesticides Into Different Mobility Classes Depending on the Value of the Soil Organic Carbon Distribution Coefficient (Koc) Koc

Mobility scale

Examples of pesticides

0
50

Very highly mobile

Acrolein, aldicarb, 2,4-D, dimethoate, mevinphos, dichlorvos

50
150

Highly mobile

Atrazine, simazine, bromacil, 2,4,5-T

150
500

Medium mobility

Carbaryl, diuron, monuron, propachlor, diazinon

500
2000

Slightly mobile

Chlorothalonil, malathion, linuron, diallate

2000
5000

Low mobility

Endosulfan, glyphospate, parathion-methyl

. 5000

Immobile

Dieldrin, DDT, trifluralin, paraquat, deltamethrin, chlorpyrifos, abamectin

Adapted from McCall et al. 1980.

pesticides seem to have little affinity to bind to soil, and if they have come in contact with soil through water, they may continue flowing undisturbed; they may leach through the soil profile to reach groundwater resources or they may be washed out from soil with irrigation or rainwater and finally reach surface waters under runoff events. At the other extreme, some pesticides may bind very strongly to soil particles, and remain attached to them even if the particles are carried somewhere else through water or erosion mechanisms. The same can occur for pesticides in sediments and suspended particles. Most pesticides fall somewhere in between these two extremes. The extent to which pesticides bind to soil (or sediments) depends, among others, on their physicochemical characteristics (e.g., ionic or nonionic, polarity, presence of functional groups, water solubility, lipophilicity, volatility, molecular size, and spatial distribution); the pH of the media, the amount of water and the characteristics of the soil in terms of the amount and composition of clay (clay minerals differ in the type of reactive sites and their cation-exchange capacity); on humic substances (organic colloids) and ageing (the increased contact time between a pesticide and the soil which can allow a compound to become more strongly associated with the soil); and on the origin of organic matter and the presence of other soil minerals (through hydrophobic effects). Pesticides have been characterized for their mobility in soil using the distribution coefficient (Kd for sorption or desorption). Since soil organic matter is responsible for binding many pesticides, the distribution coefficient is often expressed in terms of the organic carbon content of the soil as Koc, referred to as the soil organic carbon distribution coefficient. McCall et al. (1980) suggested a scale of mobility classes as shown in Table 9.2. Therefore a desk exercise may be very helpful to work out a list of possible target pesticides for a multiresidue procedure for soil analysis. Information about pesticide water solubility, n-octanol water partitioning coefficient, and other soil properties as discussed earlier, may help understand the fate of target pesticides and their possible presence/absence from the soil. In other words, as in the case of water, it is recommended to use screening information and tools (e.g., PIRI) to help target scarce resource at the priority problem and maximize the utility of expensive analytical resources. The analytical challenge in the case of soil is the efficiency of extraction. When a pesticide “enters” a soil it is sorbed to the soil phases. “Free” residues can be extracted from the soil without altering their chemical structure; “bound residues” are resistant to this extraction. In addition, an increased contact time (ageing) of pesticide with the soil may result in the formation of stronger bonds (covalent bonds), physical entrapment within the soil organic matter or mineral components and diffusion into micro- and macropores. Therefore the analytical procedure should consider all these elements and be adequate for the type of pesticides and soil properties. In general, laboratories have no choice than to apply multiresidue procedures in attempting to recover what is possibly “recoverable” with a generic method. Tadeo et al. (2012) reviewed sample preparation techniques for analyzing pesticide residues in soil. An example of a multiresidue method using extraction in an ultrasonic water bath with ethyl acetate is outlined in Fig. 9.5. Depending on the pesticide analyzed, the method can be modified to allow extraction of compounds with different physicochemical properties using a first extraction with ethyl acetate which removes the less polar compounds, followed by a second extraction with methanol which removes the more polar compounds. Validation of the method and establishment of its scope and performance criteria remain essential (Fig. 9.8).

5. EXPOSURE ASSESSMENT

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After sampling, the soil samples are dried, sieved (2 mm) and frozen until analysis

5 g sieved soil placed over 2 g anhydrous sodium sulphate in a plastic tube over two filter paper circles

Add 5 mL ethyl acetate and place in an ultrasonic water bath at room temperature for 15 min

Collect the solvent from the first extraction Repeat extraction with a further 4 mL ethyl acetate in an ultrasonic water bath at room temperature for 15 min

Collect the second solvent fraction; rinse the soil with additional 1 mL solvent

Evaporate the combined extracts to an appropriate volume

Inject the extract into GC/MSD

FIGURE 9.8 Brief description of a method for pesticides in soil according to Tadeo et al. (2012).

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