Development of a Passive Sampling Technique for Measuring

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Development of a Passive Sampling Technique for Measuring Pesticides in Waters and Soils Yanying Li, Chang-Er L. Chen, Wei Chen, Jingwen Chen, Xiyun Cai, Kevin C Jones, and Hao Zhang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.9b00040 • Publication Date (Web): 08 May 2019 Downloaded from http://pubs.acs.org on May 9, 2019

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Journal of Agricultural and Food Chemistry

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Development of a Passive Sampling Technique for

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Measuring Pesticides in Waters and Soils

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Yanying Li1, Chang-Er L. Chen1,^, Wei Chen1#, Jingwen Chen2, Xiyun Cai2, Kevin C. Jones1*,

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Hao Zhang1*

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1. Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK

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2. Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Linggong Road 2, Dalian 116024, China

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^ Current address: Environmental Research Institute, MOE Key Laboratory of Environmental Theoretical Chemistry, South China Normal University, Guangzhou, 510006, China

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# Current address: State Key Laboratory of Environmental and Biological Analysis, Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, China.

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* corresponding authors

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E-mail: [email protected]; Tel: 44-1524 510230; [email protected]; Tel: +44 1524

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593899.

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1 ACS Paragon Plus Environment


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For TOC only

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ABSTRACT

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It is essential to monitor pesticides in the environment to help ensure water and soil quality. The

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diffusive gradients in thin-films (DGT) technique can measure quantitative in-situ labile (available)

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concentrations of chemicals in water, soil and sediments. This study describes the systematic

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development of the DGT technique for 9 current pesticides, selected to be representative of

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different classes with a wide range of properties, with two types of resins (HLB (hydrophilic-

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lipophilic-balanced) and XAD 18) as binding layer materials. The masses of pesticides

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accumulated by DGT devices were proportional to the deployment time and in inverse proportion

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to the thickness of the diffusive layer, in line with DGT theoretical predictions. DGT with both

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resin gels were tested in the laboratory for the effects of typical environmental factors on the DGT

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measurements. DGT performance was independent of: pH in the range of 4.7 - 8.2; dissolved

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organic matter concentrations 99% remaining in soils.6 This may cause unintended

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environmental effects as pesticides can be hazardous to the indigenous microorganisms, including

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beneficial competitors, predators and parasites of target pest insects.7 Studies have shown that

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pesticides inhibit soil microbial diversity and activities,8, 9 adversely influence soil biochemical

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processes and disturb soil ecosystems.10 In recent decades there has been increasing concern that

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pesticides constitute a risk to humans by entering the food chain,11 through direct contact with soil,

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inhalation of volatile pesticides,12 and through groundwater contamination by pesticides leaching

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from soils.

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It is clear that measurements of pesticides in soils are needed to understand their fate and

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dissipation. These are usually performed using various extraction methods,13 which can be

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complicated, expensive, laborious and time-consuming.14 These extraction methods usually focus

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on the ‘total concentration’, although some of them could be related to the bioavailable fraction,

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which is more relevant in risk assessment.15 However, they cannot provide any kinetic parameters

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of in situ soil processes of pesticides, such as i) exchange between soil solution and solid phase

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and ii) resupply kinetics in response to biological uptake. Therefore, a technique which considers

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kinetic aspects and bioavailability would be of great benefit.

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However, their potential adverse effects on the


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Pesticides can enter surface waters through diffuse pollution and leaching.16 There are

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requirements to monitor pesticides to assess water quality. Grab sampling, which is widely used

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in water monitoring, is an effective way to measure the occurrence of organic contaminants in

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aquatic systems, but it only provides snapshot information at the time of sample collection;

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episodic contaminant events may be missed.17,18 The development of passive sampling approaches,

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which can give time-weighted average (TWA) concentrations, has therefore increased in recent

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years, as summarised below.

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Passive samplers are able to retain trace analytes by pre-concentration; the in situ sampling does

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not affect the environment.19 Passive samplers also limit the degradation of trapped chemicals

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during transport and storage.20 Techniques such as POCIS (polar organic chemical integrative

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sampler), Chemcatcher21, 22, ceramic dosimeters23 and microporous samplers24 are currently used

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for the measurement of pesticides in waters. However, they are dependent on hydrodynamic

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conditions during field deployment and/or rely on a laboratory calibration and losses of

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performance reference compounds to estimate sampling rates.25 DGT (diffusive gradients in thin-

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films) is a passive sampling technique which can be used for field deployment without the need

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for field calibration in a solution of similar matrix.26 It just requires that the diffusion coefficient

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is known for the compound of interest in the DGT diffusive gel. The thick diffusion gel layer

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which controls the uptake of analytes into the receiving phase limits the influence of hydrodynamic

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conditions by minimizing the effect of the diffusive boundary layer (DBL).27 It is also a ‘dynamic’

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technique that has been shown to sample the bioavailable fraction of trace metals and nutrients in

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soils.28-30

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The development and use of DGT for inorganics has a long and well-published pedigree. The

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principles were first published in 1994 in Nature31 and now over 800 peer-reviewed papers have



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been published on developing, testing and applying the technique in different environmental media,

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such as waters,32, 33 soils34 and sediments.35 Until recently, the focus has been on metals, nutrients

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and radionuclides. DGT typically utilizes a three-layer system: a resin-impregnated hydrogel layer,

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a hydrogel diffusion-layer and a filter membrane. Uptake and pre-concentration is balanced against

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exposure time to yield sufficient time-intergated mass of analytes(s) for detection.31

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The principle of DGT is based on Fick’s first law,31 such that the DGT measured-concentration

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(CDGT) of target chemicals in solution can be calculated using Equation 1:

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CDGT =

M (∆g + δ ) D𝑒At

(1)

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where, M is the mass of analyte accumulated in the binding gel, t is the exposure time, De is the

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diffusion coefficient of the analyte in the diffusive layer, A represents the sampling area of DGT,

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Δg is the diffusion length through which the analyte passes before being taken up by the binding

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phase, and δ is the thickness of the DBL.

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The first application of DGT to organic compounds was published in 2012 by Chen et al.26 They

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investigated the performance characteristics of DGT for quantifying polar organic compounds

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(with logKow value 80% of

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Maximum Water Holding Capacity) before deployment. The details of soil properties, soil

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collection and treatments, and DGT deployment in soils are listed in SI and Table S5.

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Quality assurance/control (QA/QC)

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All DGT deployments in the laboratory and field were carried out in triplicate and the results

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expressed as the average ± standard deviation (SD). Three DGT devices were retieved prior to

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each deployment as blank samples. Control samples (test solution without DGT devices) were

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performed in each experiment to prevent possible interference during the experiment. All the SPE

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samples were replicated, no target compounds were found in the blank SPE samples.

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RESULTS AND DISCUSSION

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Sorption by DGT holder, filter membrane and diffusive gels

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There was no appreciable sorption of target compounds on the two types of diffusive gels or DGT

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mouldings as shown in Figure S1(a). However, compounds were sorbed substantially by PES, NL,

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OE and ME filter membranes (Figure S1(b)). Sorption to the PES filters was marked (>50%) –

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this filter type has been used for POCIS19 and Chemcatcher.22 Loss on the ME filter was also



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considerable. The PES filters were also used in DGT devices for other medium polar chemicals in

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other studies and the adsorption effect was negligible. PC and GHP showed little sorption of the

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compounds; PC membrane performed the best, with

Development of a Passive Sampling Technique for Measuring

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