Investigation and Application of a New Passive Sampling Technique

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Investigation and application of a new passive sampling technique for in-situ monitoring of illicit drugs in waste waters and rivers Changsheng Guo, Tingting Zhang, Song Hou, Jiapei Lv, Yuan Zhang, Fengchang Wu, Zhendong Hua, Wei Meng, Hao Zhang, and Jian Xu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b00731 • Publication Date (Web): 24 Jul 2017 Downloaded from http://pubs.acs.org on July 24, 2017

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Environmental Science & Technology

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Investigation and application of a new passive sampling technique for in-situ monitoring of illicit

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drugs in waste waters and rivers

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Changsheng Guo†, Tingting Zhang‡, Song Hou†, Jiapei Lv†, Yuan Zhang†, Fengchang Wu†,

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Zhendong Hua‡*, Wei Meng†, Hao Zhang§, Jian Xu†*

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† State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research

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Academy of Environmental Sciences, 100012 Beijing, China

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‡ National Narcotics Laboratory, Drug Intelligence and Forensic Center of the Ministry of Public

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Security, Beijing 100193, China

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§ Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom

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ACS Paragon Plus Environment

Environmental Science & Technology 10

TOC art

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Contents brief

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DGT technique has been developed and applied for the first time as passive samplers to

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quantitatively measure illicit drugs in situ in waste waters and rivers.

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ABSTRACT

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Illicit drugs constitute a class of emerging contaminants that has been drawing significant

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concern due to its potent pharmacological and biological activities. In this study, an in situ passive

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sampling approach that uses diffusive gradients in thin films (DGT) was successfully tested for

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measuring ketamine (KET), methamphetamine (METH), and amphetamine (AMP) in water. The

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diffusion coefficients of KET, METH, and AMP in diffusive gel were (8.13±0.12)×10−6,

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(8.55±0.14)×10−6, and (7.72±0.18)×10−6 cm2 s−1 at 22 °C, respectively. The capacities of an XAD

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binding gel for KET, METH, and AMP were 92, 57, and 45 µg per binding gel disc, which were

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suitable for long-term environmental monitoring. The DGT measurement of these drugs was not

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influenced by the pH (4 to 9) and the ionic strength (0.001 M - 0.1 M) and unaffected by the water

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flow, demonstrating the effectiveness of the XAD-based DGT for the in situ monitoring of illicit

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drugs. DGT samplers were deployed in a WWTP influent and natural rivers in Beijing, China. The

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ng L−1 levels of the drugs were high in the wastewater influent and low in river waters, with an

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insignificant fluctuation during the seven-day monitoring. The DGT-measured concentrations were

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comparable to the average concentrations determined by SPE method, which suggested that the

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average data measured by DGT could be substituted for high-frequency grab sampling. This study

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has demonstrated systematically for the first time that DGT is effective and accurate for monitoring

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illicit drugs in wastewater and surface waters, and provides a powerful tool to investigating the

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presence, transport, and environmental behaviors of these drugs in the aquatic ecosystem.

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INTRODUCTION

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Synthetic illicit drugs constitute a heterogeneous group of substances that has entered the drug

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market around the world in the past quarter of a century.1,2 Although their use in some areas is lower

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than that of traditional illicit drugs, such as cocaine, opium, heroin, and cannabis, they have the 3



potential to spread in some populations, particularly among young people during social events,

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which can result in significant problems. Data from surveys on populations indicate that each year

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approximately 230 million people consume drugs of abuse worldwide.3 By the end of 2014, the

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registered users in China has reached up to 2.9 million, two times more than the registered

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population in 2008.4 However, the total number of drug users is approximately 5 times of the

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number of the registered users. The actual population of drug users in China exceeded 14 million in

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2014.4 The direct economic loss caused by drug abuse is 78.6 billion per year.4

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A recently proposed approach for estimating the use of methamphetamine (METH) and other

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illicit drugs in populations by measuring their metabolic residues in urban wastewater5–7 might

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provide information on these synthetic drugs. The monitoring of illicit drug concentrations in

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wastewater treatment plant (WWTP) influents is proposed to estimate the consumption of these

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psychoactive substances at the community level.5,7,8

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Limited studies were conducted to investigate the eco-toxicological impacts of drugs of abuse

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at the chronic low levels in the aquatic environment.9–11 Similarly, reports of the ecotoxicological

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impacts of illicit drugs at environmentally relevant concentrations have been few.12,13 Because of

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their intrinsic psychoactive characteristics and possible adverse effects to the non-target biota, the

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presence of drugs of abuse in the environment has been redeemed as an important issue requiring

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much attention.

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Many studies have been carried out to study the fluctuations in drug concentrations in the

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aquatic environment during weekends and holidays using traditional discrete sampling methods

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because of the known use of these substances for leisure.6,14 Nevertheless, inconsistent daily and

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seasonal variations were reported by these studies, resulting in unclear conclusions. Few data of the

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time-averaged concentrations of these drugs in the receiving river waters or WWTP influents are 4


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available. Grab and composite sampling, which are traditional water-sampling approaches, are

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effective for measuring the presence of illicit drugs, however, these sampling approaches only

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provide data at the sampling time and cannot reflect the circumstance changes, for instance, the

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changes of the flow rate, chemical inputs, and the precipitation influence.11 The polar organic

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chemical integrative sampler (POCIS) was developed to sample trace organic compounds, including

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METH and amphetamine (AMP).11,15,16 However, this approach has limitations as well; for instance,

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the environmental conditions such as water flow, the turbulence, and temperature can influence the

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sampling rates and hence the concentration accuracy of the target compounds in water.

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The diffusive gradients in thin films (DGT) technique was developed to measure labile

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inorganic species and trace organic compounds in situ in aquatic environments.17 It has been

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reported that DGT can measure 55 elements simultaneously at the detection limits from 0.001 to 1

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ng mL-1 after a 24-h deployment.18 A total of 34 pharmaceuticals and pesticides could be measured

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by DGT.19 Its robustness, simplicity, independence on flow to use, and apparent high stability

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against outside interference make it attractive for measuring the time-integrated concentrations of

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trace organics in waters, without tedious laboratory calibrations.17-19 DGT has been used recently for

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both the qualitative and quantitative evaluations of antibiotics

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and soil environment, which has provided alternatives for the DGT application to monitor organic

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compounds in the aquatic environment.

20,21

and bisphenols

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in aqueous

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China Narcotics Bureau stated that METH and ketamine (KET) account for the largest share

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(>99%) of synthetic illicit drugs in the Chinese drug consumption market.4 Du et al. 6 collected

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water samples from 36 WWTPs in eighteen big cities covering major geographic areas of China to

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determine the consumption of METH and KET. Wide occurrence of METH in the country was

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observed, but there was no clear trend geographically. For KET, its usage was generally greater in 5



the southern China than in the northern China. In previous studies, the active grab-sampling

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technique followed by the solid-phase extraction (SPE) was used for quantifying the concentration

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of drugs. One recent work using o-DGT to measure a diverse suite of polar organic compounds

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including pharmaceutical drugs was carried out, in which the diffusion coefficients and the diffusive

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boundary layers were measured, and the o-DGT was calibrated in the laboratory solution, without

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considering its performance under wide range of environmental conditions.19 Although DGT is a

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well-established technique in its fundamental theory and principle, it cannot be applied to illicit

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drugs without systematic investigations if the technique is to be used for fully quantitative

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measurement of in situ chemical concentrations. The illicit drug compounds are different in

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chemical properties, structures and functions from antibiotics and other pharmaceutical compounds

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tested by DGT. The aim of the current research was to develop DGT as a passive sampling

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technique for accurately measuring the concentrations of illicit drugs, namely, KET, METH and

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AMP, in situ. Different parameters and environmental conditions and their effects on DGT

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performance were tested and investigated systematically. Finally, the developed DGT technique was

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applied and validated in field conditions by the deployment of DGT devices in situ in a WWTP

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influent and in the surface water of rivers.

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EXPERIMENTAL SECTION

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Chemicals and Reagents.

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KET, AMP, METH, and their deuterated internal standards (KET-d4, AMP-d8, and METH-d8)

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were obtained from Cerilliant Corporation (Round Rock, TX). The properties of the drugs are

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provided in Supporting Information (SI) Table S1. Stock solutions of KET, AMP, or METH at 100

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mg L−1 were prepared in methanol [MeOH, high-performance liquid chromatography grade] and

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stored at −20 °C in the amber bottles. MeOH and acetonitrile (ACN) were obtained from Fisher 6


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Scientific (Poole, UK). Deionized water was prepared by a Milli-Q system (Millipore, MA, US).

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SPE cartridges (Oasis MCX, 60 mg, 3 mL) were obtained from Waters Corporation (Milford, MA,

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US). Polyethersulfone (PES) filter membrane was purchased from Pall Co., US. Mixed cellulose

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ester (MCE), hydrophilic polytetrafluoroethylene (PTFE), and nylon (NL) filter membranes were

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purchased from Shanghai Anpel Scientific Instrument Co., China. All membranes are 25 mm in

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diameter and 0.45 µm in pore size.

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DGT and Gel Preparation

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Standard DGT devices for trace organics were purchased from DGT Research Ltd., UK. The

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standard DGT consists of an XAD 18 agarose binding layer (0.5-mm thickness), an agarose

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diffusive layer (0.8-mm thickness), and a PES filter membrane (0.14-mm thickness). The area of the

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exposure window of the DGT plastic molding is 3.1 cm2. The preparation of binding and diffusive

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gels followed the well-established procedures.20,22 To prepare the XAD layer, in 10 mL of hot

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agarose solution 2 grams of XAD18 powder were added, and the solution was well mixed. The

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solution was then poured into the space between two hot glasses, and cooled down at ambient

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temperature to form the gel. The gels were put into the milli-Q water for hydration, and stored in the

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salt solution (0.05 M NaCl).

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Assessment of Adsorption by Sampling Apparatus and Materials.

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Four different filters and two diffusive layers were soaked in 10 mL solutions containing 20 µg

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L−1 KET, METH, or AMP. The solution was shaken for 12 h. DGT plastic moldings were soaked in

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200 mL solutions of 20 µg L−1 KET, METH, or AMP because of their large size. The adsorbed mass

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of the illicit drugs was calculated by the difference of drug concentrations before and after the

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deployment of the testing materials.

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Uptake Kinetics and Elution Efficiencies. 7



The XAD binding gel discs were placed in 10 mL solution containing 20 µg L−1 KET, METH,

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or AMP with a background NaCl concentration of 0.01 M, and shaken for different time (0.5 min to

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24 h). The optimal elution conditions were obtained by calculating the elution efficiencies of the

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illicit drugs by eluting the XAD layers in 10 mL of MeOH, ACN, 5% ammonia solution in MeOH,

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or ethyl acetate for at least 1 d. Masses of target drugs in the eluents and the immersion solution

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were used for elution efficiency calculation.

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Diffusion Coefficient Measurements.

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A diaphragm diffusion cell, which comprised two chambers that were linked by a 1.5-cm

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circular window that housed a 0.80-mm thick agarose-based diffusive layer, was employed to

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measure the diffusion coefficients of the drug compounds. The two chambers were washed first with

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MeOH and then with Milli-Q water before use. The concentration gradient was the sole driving

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force for the analyte transfer between the two chambers. The matrix-matched solutions in both

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chambers were the same (50 mL, the same pH and ionic strength), except that the source chamber

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contained 2 mg L−1 KET, METH, or AMP, while no illicit drugs were present in the receptor

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chamber. The solutions in the two chambers were well stirred throughout the experiment. For at

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least 3 h, 0.2 mL samples of solutions were taken at 15-min intervals from each chamber. The

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diffusion coefficient D was calculated by the slope of the linear plot of the measured masses of each

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drug in the receptor chamber versus time, as follows:

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D = ( slope)

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where A is the area of the window linking two chambers, C is the drugs concentration in the source

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chamber, and ∆g is the thickness of the diffusive layer.

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Calculation of DGT Measured Concentrations.

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∆g , CA

(1)

After the deployment time (t, sec), the accumulated mass (M, in ng) of the analyte in the 8


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binding layer can be related to its solution concentration (i.e., CDGT, µg/L) according to Eq. (2).

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CDGT =

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where ∆g (cm) is the thickness of both the filters and the diffusive gel, D is the diffusion coefficient

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(cm2 s−1), and A is the area (cm2) of the DGT’s exposure window.

(2)

M is calculated by Eq. (3) if it can be eluted with a known volume of eluent (Ve, L).

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M ∆g , DAt

M=

Ce (Ve + Vgel ) fe

,

(3)

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where Ce (µg/L) is the analyte concentration in the eluate; Vgel (L) is the volume of the binding gel,

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which is typically 0.15 mL; and fe is the elution efficiency of the analyte from the binding gel.

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Effects of Ionic Strength, pH, and Deployment Time

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The effects of pH and ionic strength on DGT performance was tested by deploying the

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standard DGT devices in different solutions: (1) 2.5 L of 20 µg L−1 KET, METH, or AMP solution

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(pH 7) with varying NaCl levels (0.001- 0.5 M), and (2) 2.5 L solution with 0.01 M of NaCl and 20

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µg L−1 KET, METH, or AMP at different pH values. The DGT devices were placed in 2.5 L

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solutions (pH 7) containing 20 µg L−1 KET, METH, or AMP and 0.01 M of NaCl, and withdrawn at

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various time intervals (12- 96 h) to evaluate the effect of deployment times. The relationship

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between the DGT-accumulated mass and the thickness of diffusive gels was determined by

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deploying the DGT devices equipped with different thickness diffusive gels (0.05 cm to 0.175 cm)

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in the 2.5 L solution for 12 h containing 20 µg L−1 KET, METH, or AMP and 0.01 M of NaCl.

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Capacity and Competition Effects.

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The capacity of the XAD binding gels assembled in the DGT devices for the uptake of illicit

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drugs were measured by immersing the devices in the solutions for 12 h containing 0.01 M of NaCl

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and different levels of drugs: KET (0.02 mg L−1 to 25 mg L−1), METH (0.02 mg L−1 to 25 mg L−1),

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or AMP (0.02 mg L−1 to 20 mg L−1). 9



The competition effects among three illicit drugs in the solution were determined at various

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solution concentrations. DGT device was placed for 12 h in different solutions containing 0.01 M of

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NaCl: (1) KET or METH at 10 µg L−1, and the other two at 100 or 1000 µg L−1; (2) AMP at 10 µg

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L−1, and KET and METH at 100 or 1000 µg L−1.

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DGT Application and Validation in Field Conditions.

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Four DGT devices were fixed together, with the exposure windows outward, to compare the

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DGT measured concentrations and the SPE measured concentrations. The DGT devices, together

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with temperature button data loggers (Maxim Integrated Products, United States) set to record

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temperature every 2 h, were deployed in WWTP influents and urban rivers (located in Beijing,

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China) for 7 days. The WWTP is in the south of Beijing City, which can treat 400,000 tons of

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domestic wastewater per day. The WWTP covers an area of approximately 160 km2, serving

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810,000 people. The treatment techniques of the WWTP include primary treatments and two

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separate secondary treatment procedures, namely, traditional and reversed A2/O, each of which has a

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domestic wastewater capacity of 200,000 tons per day. Surface water samples were collected in 15

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urban river sites in Beijing, as shown in Figure S1. The Wenyu River and its tributaries (Sha River,

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Beixiao River, Qing River, Ba River, and Tonghui River) cover an area of 2478 km2 and are

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receiving rivers of most wastewater from the urban areas of Beijing. Wastewater samples were

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collected at 10:00 and 16:00 each day. A previous study indicated that although the levels of METH

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and AMP in a sewage pipeline varied significantly from 22:00 to 6:00, their concentrations in the

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influents of several WWTPs in Beijing were relatively stable.23 All samples were transferred within

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30 min to the laboratory, where the concentrations of drugs in the water samples (filtered by

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Whatman GF/F filters) were determined with the established method (details in Supporting

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Information) after the pre-concentration of 100 mL of water samples by SPE using an Oasis MCX 10


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cartridge (60 mg, 3 mL). The retrieved XAD binding gels from the DGT devices were soaked in 10

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mL of MeOH for 24 h. Before instrumental analysis, the eluents from both the SPE cartridges and

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DGT gels were passed through 0.22-µm membranes, followed by transferring to the HPLC sample

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vials.

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Instrumental Analysis.

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The target compound analysis procedures by ultra-performance liquid chromatography tandem

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mass spectrometry (UPLC-MS/MS, AB SCIEX, USA) are provided in the SI.

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RESULTS AND DISCUSSION

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Adsorption by DGT Moldings, Diffusive Layers, and Filter Membranes

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The possible adsorption of drugs by the standard DGT moldings, diffusive gels, and filter

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membranes was assessed. The results presented in Figure 1 shows minimal adsorption of drugs onto

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the DGT moldings and two diffusive gels (agarose and PAM) (40%) and MCE (>20%). They were minimally absorbed on the

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PES membranes (METH > AMP (Figure S3), which was in accordance with the order of the logKow values of

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these compounds. The average uptake rates in the first half hour for KET, METH, and AMP were 11



1.75, 1.45, and 1.03 ng cm−2 min−1, respectively, which were faster than the uptake rate required by

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DGT devices to establish the concentration gradients. Hence, the DGT technique could be applied.

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Diffusion Coefficients.

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The time dependence of the masses of the three drugs diffused through an open-pore agarose

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gel in the diffusion cell is shown in Figure S4. The masses of the drugs in the receptor chamber

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increased linearly with time, whereas the drug concentrations in the source chamber were constant.

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The slope of the mass plot in the receptor chamber versus time (Figure S4) allowed the calculation

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of D values for the three drugs at the experimental temperature (22 °C). The obtained D values were

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(8.13 ± 0.12) × 10−6, (8.55 ± 0.14) × 10−6, and (7.72 ± 0.18) × 10−6 cm2 s−1 for KET, METH, and

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AMP, respectively. The diffusion coefficient at 25 °C can be calculated from measured D with the

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following equation:17,20,22

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log DT =

D (273 + T ) 1.37023(T − 25) + 8.36 ×10−4 (T − 25)2 + log 25 (4) 109 + T 298

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where DT (cm2 s−1) is the analyte diffusion coefficient at temperature T (°C), and D25 (cm2 s−1) is the

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analyte diffusion coefficient at 25 °C.

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Elution Efficiencies and Capacity.

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Four different eluents were tested to elute the drugs from the XAD binding gels that were

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preloaded with the chemicals (Table S4). The average elution efficiencies of the three drugs were

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more than 90% using 10 mL of MeOH (A) or ACN (B) in 6 h. For eluent C, that is, 10 mL of

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MeOH with 5% ammonia solution, a similar performance was reported when eluting these illicit

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drugs from mixed reverse-phase cation exchange cartridges.6,7 The elution efficiencies we obtained

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for KET and METH were 89.5% and 85.6%, respectively. The use of ammonia solution had a small

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effect on the elution efficiency of KET and METH, but a significant decrease for AMP, from 97% to

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56-72%. When ethyl acetate (D) was used, the elution efficiencies were very low (0.05), and an insignificant difference was also observed between the weekend and

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weekday measurements (p>0.05). Of the three studied compounds in the influent, METH and AMP

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were ubiquitous with high concentrations. As shown in Figure 2, METH was detected in all samples

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with concentrations ranging from 101.7 ng·L−1 to 181.1 ng·L−1, which implied that the abuse of

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METH is popular in Beijing. AMP was also detected in all influents, with concentrations at tens of

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ng·L−1 levels. In contrast to a previous research in which no KET was detected in the WWTPs in

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Beijing,23,27 the use of KET among Beijing inhabitants was found in the current study, with

310

concentrations at several ng·L−1 levels (Figure 2).

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To estimate the drug consumption at the community level, the concentrations of the target

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compounds in the influent of WWTP were measured and used. 5,7,27 The amount of the drugs (grams)

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discharged per day was obtained by using the average concentrations of the selected drugs in the 15



untreated wastewater samples and the daily flow rates in the WWTP. The amount of drugs excreted

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in the wastewater each person each day was estimated by dividing the total amount of drugs in the

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influent by the number of population served by the WWTP. The value is generally normalized as

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grams per day per 1000 people. The consumption data of each drug in the community were obtained

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by the fraction of the excreted drugs in the urine samples proposed by Zuccato et al. 5 The daily

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influent load of a drug residue that enters a certain WWTP can be calculated with the following

320

equation:

mg ) 1000 ⋅ day

Influent load of a chemical residue (

321

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=

Concentration of chemical residue(ng ⋅ L−1 ) × Influent flow( L ⋅ d −1 ) 1 mg × 6 ( ). Population served 10 ng 1000

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The mass loads of METH in sewage influents ranged from 50.2 mg (1000 inh)−1 d−1 to 89.3 mg

324

(1000 inh)−1 d−1 (Table 1). The high level of METH in the influent loading was in accordance with

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the seizure data for illicit drugs released by Chinese authority, that the number of seized METH in

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China rose eightfold from 2007 to 2011.34 As the metabolite of METH, AMP has been detected in

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the influents in other three WWTPs in Beijing.27 In this study, the estimated dose of AMP varied

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from 19.6 mg (1000 inh)−1 d−1 to 26.8 mg (1000 inh)−1 d−1. The AMP traces in sewage influents with

329

concentrations no more than 10% those of METH concentrations were deemed to have come from

330

the metabolism of METH (other than AMP consumption itself).5 Thus, the AMP in the wastewater

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influents from most cities in China came from METH degradation, which indicated that AMP

332

consumption can be neglected in China. This finding is in contrast to the results in European

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countries, where more AMP was found compared with METH.35-37 In the sewage samples AMP may

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potentially come from the illicit use of METH and AMP, clinical use of METH and AMP, and

335

clinical use of AMP precursors.38 In China, neither AMP nor METH are clinically used; therefore, 16


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the presence of AMP in the influents are likely resulted from the illicit uses of both METH and AMP,

337

and the clinical use of selegiline, which is the AMP precursor used in China.23,27

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The loads of KET in this study ranged from 2.6 mg (1000 inh)−1 d−1 to 3.7 mg (1000 inh)−1 d−1

339

(Table 1). The highest mean KET loads were found on Sundays. The concentrations of KET were

340

higher during weekends (mean 7.2 ng L−1) than weekdays (mean 5.8 ng L−1), which implied the

341

high usage of KET during weekends. Several early studies also reported the increased use of KET

342

during weekends.24,35,39 The comparison of the three drug concentrations with the levels in the

343

literature is provided in the SI.

344

In Situ Profiling of Illicit drugs in River Water in Beijing

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DGT devices were deployed in a river system for monitoring in January of 2016 to extend the

346

application of the developed technique in this study. No report on the illicit drugs in the urban river

347

waters of Beijing exists. Fifteen sampling sites in six urban rivers in Beijing were selected, and

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DGT devices were deployed for 7 days. Over these 7 days, composite water samples were also

349

collected in the same way as described earlier. The water temperature during sampling was in the

350

range of 3.3 ± 0.7 °C (Figure S10). Field blanks were analyzed and were too low to be quantifiable.

351

The concentrations of the three illicit drugs were generally at the ng L−1 level in the river waters.

352

The average DGT concentrations of the three illicit drugs (Figures 3a and S11) were close to the

353

average concentrations measured by SPE method, which demonstrated that the average

354

concentrations measured by DGT can be substituted for the high-frequency active sampling. The

355

masses of drugs in the DGT sampler linearly increased during the 7-day deployment, which

356

indicated that the devices could be deployed for at least 7 days to obtain reliable and accurate

357

measurements (Figure 3b). The concentrations were relatively stable during the DGT deployment,

358

as shown by the grab sample data in Figure 3b. METH was detected by the SPE and DGT methods 17



in all sampling sites, with the highest concentrations ranging from 4.37 ng L−1 to 57.36 ng L−1.

360

These values were higher than those of the METH detected in other rivers, such as Jarama and

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Manzanares Rivers (3.1 ng L−1 to 5.0 ng L−1) in Spain,40 River Lambro (2.1 ng L−1) in Italy,41 and

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Yellow River (1.3 ng L−1), Songhua River (2.2 ng L−1), and Yangze River (1.9 ng L−1) in China,48

363

and lower than those in Taiwan (n.d.-917 ng L−1) 14,29 and downstream (62.6 ng L−1) of a WWTP at

364

Hasting, Nebraska,11 but comparable with that in Pear River (31.1 ng L−1).42 The high

365

concentrations and detection frequencies of METH in the surface water in Beijing were consistent

366

with the seizure data from the Chinese authorities, which showed that METH and KET are the two

367

major drugs with increasing abuse dosages in China.4 However, the measurements in the Beijing

368

surface water in this study showed very low concentrations of KET (n.d.-3.85 ng L−1) throughout

369

the sampling survey, which is consistent with the effluent data from the Beijing sewage treatment

370

plants.23,27 It is the first application of well tested DGT method for measuring the three illicit drugs

371

in situ in a WWTP and in river waters with good performance and convincing results.

372

Environmental Significance

373

Grab sampling is the sampling method currently used most widely due to its easy use without

374

special requirement on equipment. Results obtained from the grab sampling however, may be

375

misleading because of the combination of the high variations in concentration and low in sampling

376

frequency. In the rivers and WWTPs where the point sources and rains may result in significant

377

fluctuations of water flow, grab sampling for water quality monitoring should be paid more attention.

378

Grab sampling is also likely to miss discharging event, such as the consumption of illicit drugs at

379

entertainment venues, such as pubs, bars, and nightclubs, at any given time when the sample

380

collection usually is not carried out.

381

Passive sampling, which can measure a time-weighted concentration of contaminants, has been 18


Page 18 of 30

Page 19 of 30


382

developed and applied to deal with the above concern. POCIS has been used to collect

383

pharmaceutical and illicit drugs in water, which is able to overcome the drawbacks of traditional

384

sampling and provide time-averaged result.

385

semi-quantitative analysis as its sampling rate is affected by environmental conditions such as water

386

flow.11,15 DGT is superior over other passive sampling approaches, particularly in terms of its steady

387

accumulating rates, which are unaffected by the flow rate of water. The sampling rates (RS/A) for

388

METH and AMP by POCIS were 5.3 and 6.3 mL d−1 cm−2 with a surface area of ∼41 cm2, 11 and the

389

RS/A values by DGT were 7.86 and 7.10 mL d−1 cm−2, respectively. The higher sampling rates of

390

DGT suggest a shorter deployment time for achieving the same detection limit. This study

391

demonstrates that DGT is a better sampling technique than conventional active sampling methods

392

for investigation on the behaviors of illicit drugs in the water environment. It is the first time we

393

could confidently recommend a simple, robust and reliable method for illicit drug measurements

394

and monitoring to the government authority. Although DGT was only tested for measuring three

395

specific illicit drugs in this study, it is probably able to measure other illicit drugs, which requires

396

further investigation.

397

Supporting Information. Sampling sites in Beijing urban rivers, details on analysis methods,

398

including water sample pre-treatment, instrumental analysis, QA/QCs, uptake kinetics of illicit

399

drugs by XAD gels, elution efficiencies of illicit drugs by various eluents, DGT capacity,

400

relationship between DGT measurement of illicit drugs and the deployment time or the thickness of

401

diffusion gels, effect of solution pH and ionic strength on the DGT performance, temperature during

402

DGT deployment, competing effects, and physicochemical properties of illicit drugs.

403

AUTHOR INFORMATION

404

Corresponding Author

11,15,16

However, POCIS is only effective for

19



Tel:

86-10-84915103;

Fax:

86-10-84926073.

E-mail:

Page 20 of 30

405

*

406

[email protected] (H.Z.)

407

Notes

408

The authors declare no competing financial interest.

409

ACKNOWLEDGMENT

410

This work was funded by the National Science Foundation of China (No. 41673120), Special Fund

411

for Basic Scientific Research of Central Public Research Institutes (2016YSKY-030), and Beijing

412

Natural Science Foundation (8173058).

413

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414

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25



Page 26 of 30

Table 1. Median or mean influent loads and concentrations of METH, AMP and KET from WWTPs in China and elsewhere

523 Location

METH

AMP

KET

Year

References

Load,

Concentration,

Load,

Concentration,

Load,

Concentration,

mg (1000 inh)-1 day-1

ng L-1

mg (1000 inh)-1 day-1

ng L-1

mg (1000 inh)-1 day-1

ng L-1

65.42±15.0

132.48±30.42

21.94±2.62

44.44±5.31

3.27±0.37

6.63±0.74

2015

Shanghai

31.2-35.2

n.r.

4.8-5.2

n.r.

2.5-2.9

13

2012

27

Guangzhou

33.5-48.4

n.r.

3.8-40.5

n.r.

33.6

89

2012

27

Shenzhen

121.7

n.r.

21.9

n.r.

38.7

500

2012

27

Beijing

8.6-1014.6

n.r.

Investigation and Application of a New Passive Sampling Technique

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