Effect of E‑waste Recycling on Urinary Metabolites ofOrganophosphate Flame Retardants and Plasticizers and TheirAssociation with Oxidative StressShao-you Lu,†,‡,§,@ Yan-xi Li,†,@ Tao Zhang,*,†,§ Dan Cai,† Ju-jun Ruan,† Ming-zhi Huang,∥ Lei Wang,⊥

Jian-qing Zhang,‡ and Rong-liang Qiu†

†School of Environmental Science and Engineering, Sun Yat-Sen University; Guangdong Provincial Key Laboratory of EnvironmentalPollution Control and Remediation Technology (Sun Yat-Sen University), Guangzhou 510275, China‡Shenzhen Center for Disease Control and Prevention, Shenzhen 518055, PR China§Guangzhou Key Laboratory of Environmental Exposure and Health, School of Environment, Jinan University, Guangzhou 510632,China∥School of Geograghy and Planning, Guangdong Provincial Key Laboratory of Urbanization and Geo-simulation, Sun Yat-senUniversity, Guangzhou 510275, PR China

⊥College of Environmental Science and Engineering, Nankai University, Tianjin 300350, PR China

*S Supporting Information

ABSTRACT: In this study, three chlorinated (Cl−mOPs) and five non-chlorinated (NCl−mOPs) organophosphate metabolites were determined inurine samples collected from participants living in an electronic waste (e-waste)dismantling area (n = 175) and two reference areas (rural, n = 29 and urban,n = 17) in southern China. Bis(2-chloroethyl) phosphate [BCEP, geometricmean (GM): 0.72 ng/mL] was the most abundant Cl−mOP, and diphenylphosphate (DPHP, 0.55 ng/mL) was the most abundant NCl−mOP. The GMconcentrations of mOPs in the e-waste dismantling sites were higher thanthose in the rural control site. These differences were significant for BCEP(p < 0.05) and DPHP (p < 0.01). Results suggested that e-waste dismantlingactivities contributed to human exposure to OPs. In the e-waste sites, theurinary concentrations of bis(2-chloro-isopropyl) phosphate (r = 0.484, p <0.01), BCEP (r = 0.504, p < 0.01), dibutyl phosphate (r = 0.214, p < 0.05), andDPHP (r = 0.440, p < 0.01) were significantly increased as the concentration of 8-hydroxy-2′-deoxyguanosine (8-OHdG), amarker of DNA oxidative stress, increased. Our results also suggested that human exposure to OPs might be correlated withDNA oxidative stress for residents in e-waste dismantling areas. To our knowledge, this study is the first to report the urinarylevels of mOPs in China and examine the association between OP exposure and 8-OHdG in humans.

■ INTRODUCTION

Concerns over the persistence, bioaccumulation, and toxicity ofpolybrominated diphenyl ethers (PBDEs) have resulted in thephasing out or restriction of their use since the mid-2000’s.1−3

With the growing market demand for flame retardants (FRs),the use of alternative FRs has increased. Organophosphates(OPs) are commonly used as PBDE alternatives for consumerproducts containing polyurethane foam.1−3 For example,chlorinated OPs (Cl−OPs), including tris(2-chloroethyl) phos-phate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), andtris(1,3-dichloro-2-propyl) phosphate (TDCIPP), are used asreplacements for penta-BDE.1−3 In addition, triphenyl phosphate(TPHP) is a potential deca-BDE alternative. OPs are not onlyapplied in FRs but also widely used as plasticizers in variousproducts; for instance, nonchlorinated OPs (NCl−OPs),including tris(2-butoxyethyl) phosphate, tri-n-butyl phosphate(TNBP), and TPHP, are applied as plasticizer additives in baby

products, electronic products (e-products), and polyvinylchloride (PVC).3 The global market for OPs used in FRsand plasticizers was estimated at 150000 t in 2010.4

OPs used as additives in materials are not chemically bonded;hence, OPs may easily be released into the environment overtime.3 As a consequence, they have been widely detected inair particles, house dust, drinking water, and baby food; thiscontamination leads to human exposure.5−12 Limited animalstudies have suggested that certain OPs may be neurotoxic,carcinogenic, and endocrine disruptors.13−16 TNBP was deter-mined as a neurotoxic agent after chronic exposure in rodent.13

Cl−OPs are suspected carcinogens; for example, TCEP was

Received: October 28, 2016Revised: January 13, 2017Accepted: January 17, 2017Published: January 17, 2017

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related to tumor growth in the kidney and thyroid, andTDCIPP might cause cancer in the brain, liver, and testes.14

TDCIPP was also identified as a mutagen in the Salmonella-mammalian tissue homogenate test after it has been activatedby mouse liver homogenate and has also been recentlyidentified as a potential endocrine disruptor in adult zebra-fish.15,16 Furthermore, high OP concentrations in house dustwere related to altered hormone levels and decreased spermquality in men aged 18 to 54 years (yrs) old from the U.S.17

Thus, concerns on human exposure to OPs should be addressedto determine potential health risks.Electronic waste (e-waste) dismantling area has been exten-

sively investigated because of its ensuing environmental pollutionand health hazards to human body. Primitive recycling ofFR- or plasticizer-containing e-waste exacerbates the chance offugitive emissions of FRs or plasticizers contaminating theenvironment.18−21 Atmospheric PBDE concentrations (3260−8760 ng/m3) observed in Longtang and Guiyu towns, twoe-waste recycling areas in China, were higher than those innonpolluted areas of other countries.18−20 High PBDE levelswere also found in soil from Guiyu (acid-leaching site, 2720−4250 ng/g and e-waste dumping site, 893−2890 ng/g).21

However, varying FR compositions were observed in an e-wastesite environment where the concentrations of OP FRs insediment, indoor dust, and air particle samples were higher thanthose of PBDE FRs.5,8,22 Furthermore, Bi et al. found thatTPHP was the major organic component in air particlesemitted during printed circuit board recycling.7 Home-produced eggs from an e-waste recycling area contained higherconcentrations of TCEP and TCIPP than those from a ruralcontrol area.23 Thus, human health might be threatened byOP exposure. Nevertheless, limited information is availableregarding human exposure to OPs in e-waste recycling areas.The mechanism of pollutant-induced health effects possibly

involves oxidative stress.24 Limited animal and in vitro studieshave shown that TCEP and TPHP caused oxidative stress inmouse liver and TM3 Leydig cells from testes.25,26 TDCIPPalso induces oxidative stress in PC12 cells from adrenal gland,although reduced cell viability is not observed.27 Nonetheless,the association between OP exposure and DNA oxidative stressremains unclear, and studies have yet to examine such asso-ciation in humans. 8-Hydroxy-2′-deoxyguanosine (8-OHdG),a product of damaged DNA, is widely used as a biomarkerof DNA oxidative stress.24,27,28 Furthermore, OPs are rapidlymetabolized to their diester metabolites [common OPs andtheir metabolites (mOPs) are shown in Table S1] in thebody,30 and urinary mOPs are widely used as an indicator ofOP exposure.6,9,31,32 In our study, human exposure to OP inan e-waste dismantling area and two reference areas wereinvestigated and the correlation between OP exposure andDNA oxidative stress was examined by measuring the urinarylevels of eight mOPs and 8-OHdG (Table S1).

■ MATERIALS AND METHODSReagents and Solvents. The native standards of

bis(2-chloroethyl) phosphate (BCEP), bis(1-chloro-2-propyl)phosphate (BCIPP), bis(1,3-dichloro-2-propyl) phosphate(BDCIPP), bis(2-butoxyethyl) phosphate (BBOEP), dibutylphosphate (DBP), di-o-cresyl phosphate (DoCP), di-p-cresylphosphate (DpCP), and diphenyl phosphate (DPHP) (theirparent compounds are shown in Table S1) and their corre-sponding internal standards of d8-BCEP, d12-BCIPP, d10-BDCIPP,d8-BBOEP, d18-DBP, d14-DoCP, d14-DpCP, and d10-DPHP were

obtained from Toronto Research Chemicals (all had >97%purity, Toronto, Canada). 8-OHdG (>97% purity) was pur-chased from Sigma-Aldrich (St. Louis, MO).15 N5-8-OHdG(98% purity) was purchased from Cambridge IsotopeLaboratories (Andover, MA). Methanol was high-performanceliquid chromatography (HPLC)-grade and was obtained fromMerck (Darmstadt, Germany). Deionized water was used inall experiments through a Millipore system (Billerica, MA).Formic acid, ammonium acetate, and ammonia were purchasedfrom Fisher Scientific (Houston, TX). Solid-phase extraction(SPE) cartridges (CNW P-WAX, 60 mg/3 mL) for mOPsanalysis was obtained from Anpel (Shanghai, China).

Study Areas and Sample Collection. The e-wastedismantling areas involved in this study are located in LongtangTown, Qingyuan City (Figure S1). Detailed information on thesampling sites has been previously provided.33 In this study,two villages in Longtang Town were selected based on thedifferent scale of e-waste dismantling workshops. Village #1 hasa large number of e-waste workshops (>50% of families havee-waste workshops) mainly involved in equipment dismantlingand plastic sorting, whereas village #2 has similar types ofworkshops but less dense (approximately 20% of families). Thedistance between village #1 and #2 is approximately 0.5 km. Inaddition, a village located 80 km northwest of Longtang Town,having no e-waste dismantling operation, was selected as a ruralreference site (Figure S1). The two e-waste dismantling villagesand the rural reference village mentioned above are all locatedin Qingyuan City. Guangzhou, located 60 km southeast ofLongtang Town, is the capital city of Guangdong Province.It does not have any e-waste dismantling operation and thuswas chosen as the urban reference site (Figure S1).Urine sample collection was carried out in July 2014. First

morning voids were collected from residents living in village #1(total, n = 98; males, n = 56; and age range, 3−86 yrs) and #2(total, n = 77; males, n = 40; and age range, 0.4−87 yrs) locatedin the e-waste dismantling area. First morning voids were alsocollected from study participants in the rural (total, n = 29;males, n = 16; and age range, 3−78 yrs) and urban (total, n =17; males, n = 9; and age range, 18−58 yrs) reference areas.Sample collection method was approved by the ethics com-mittee of Sun Yat-sen University, China. All the participantsand guardians of the children consented to participate. Beforesample collection, each participant was required to complete aquestionnaire, which covered personal information on sex,age, and place of residence. Detailed information is shown inTable S2. All participants were healthy and without anyinfectious disease. No female participant was on their menstrualperiod during urine sample collection. Local residents werechosen in the e-waste dismantling and rural reference sites;participants living in the urban reference site were required tohave resided in Guangzhou for more than three years. Approxi-mately 50 mL of urine sample was collected in a polypropylenetube and stored at −20 °C until chemical analysis.

Sample Preparation. Urine samples were prepared formOPs analysis as follows. Briefly, 2 mL of urine sample wastransferred to a glass tube and spiked with 10 μL of internalstandard solution (0.25 ng/μL). The pH value of each samplewas adjusted to 3.0 using 12 μL formic acid. Then, the urinesample was sequentially loaded onto a CNW P-WAX SPEcartridge conditioning using 2.0 mL of methanol (containing5% ammonia) and 3.0 mL of 0.6% formic acid. Then, aftersample loading, the cartridge was rinsed with 2.0 mL of30% methanol to remove any potential interfering matrix

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components, and the mOPs were eluted with 2.0 mL ofmethanol (containing 5% ammonia). The eluted solution wasconcentrated to 200 μL under nitrogen gas and filtered with a0.22 μm nylon filter for instrumental analysis.Instrumental Analysis. Concentrations of mOPs in urine

samples were measured using a 20A HPLC system (Shimadzu,Japan) coupled with a Q-Trap 5500 mass spectrometer(Applied Biosystems, Foster City, CA). Each analyte wasquantified with its own deuterated internal standard (Table S1).All analytes were separated on an XTerra-C18 column (5 μm,4.6 × 250 mm, Waters). Water containing 10 mM ammoniumacetate and methanol were used as mobile phases. The gradientelution program was set as follows: 0−5 min, 55% methanol;5−18 min, 55%−68% methanol; 18−20 min, 68%−100%methanol; 20−25 min, 100% methanol; 25−27 min, 100%−55% methanol; and 27−30 min, 55% methanol. The flow ratewas set at 0.6 mL/min, and the column temperature wasmaintained at 40 °C. A 10 μL of extract was injected for eachsample.Electrospray ionization was operated in negative mode.

The multiple reaction monitoring mode was used for thequantification of all mOPs with a dwell time of 50 ms.The ionization voltage was −4500 V, and the source temper-ature was 450 °C. Other optimized mass spectrometric param-eters, including precursor ion, product ion, declusteringpotential, entrance potential, collision energies, and collisioncell exit potential for each compound, as well as the corre-sponding internal standard, are listed in Table S1. An examplechromatogram of mOPs in human urine is shown in Figure S2.No measures of specific gravity and creatinine were available foranalyzed urine samples.For the 8-OHdG analysis, urine samples were prepared

according to a previously described procedure.29 Briefly, 0.1 mLof urine was diluted 5-fold with Milli-Q water, 20 ng of labeledinternal standard (15N5−8-OHdG) was added, and the samplewas analyzed through HPLC−MS/MS.Quality Assurance and Quality Control. Calibration

curves were obtained using standard solutions of the targetanalytes over a concentration range of 0.01−100.0 μg/L.The calibration curves for all the individual mOPs exhibitedexcellent linearity with regression coefficients (r2) above 0.99.Mixed internal standard solution with moderate levels was usedto check for the stability of detector response during instru-mental analysis. Relative standard deviation was confirmed tobe less than 10%. The limits of quantification, defined asten times the signal-to-noise (S/N) ratio, ranged from 0.010−0.10 ng/mL. Under the chromatographic conditions describedabove, DoCP and DpCP were metabolites of the same OP(i.e., tricresyl phosphate) and could not be completely sepa-rated from each other; therefore, both chemicals were referredto as DoCP+DpCP.Eight corresponding internal standards were spiked into

samples prior to preparation (Table S1). We quantified mOPsin studied samples through isotope dilution. Matrix-spikerecoveries of individual mOPs through the analytical procedurewere determined by spiking eight mOPs into randomly selectedurine samples. Recoveries of mOPs were calculated by sub-tracting the background levels from the spike levels. Meanrecoveries of mOPs spiked into urine samples ranged from75 ± 9% (DBP) to 127 ± 20% (BCEP) when the spiking levelwas at 0.25 ng/mL in sample (n = 4) and ranged from 76 ± 5%(DBP) to 97 ± 12% (BCIPP) when the spiking level was at2.5 ng/mL (n = 4). The recoveries of mOPs in Milli-Q water

blank spikes (n = 8, 2.5 ng/mL in water) ranged from 91 ±13% (BDCIPP) to 121 ± 18% (BCIPP). Procedural blanks andsolvent blanks were analyzed in each batch of ten urine samplesto check for potential contamination in the laboratory, andall blanks were free of detectable concentrations of the targetmOPs analyzed.

Statistical Analysis. The sum concentration of all Cl−mOPsand NCl−mOPs was denoted as ΣCl−mOPs and ΣNCl−mOPs.In the present study, the concentrations of mOPs and 8-OHdGin urine samples were not normally distributed (Kolmogorov−Smirnov test). However, the data set became normally distri-buted after log transformation. Therefore, Pearson correlationcoefficients were used to test the associations between variables.One-way ANOVA was used to investigate the differences bet-ween groups when the data were distributed normally; otherwise,Mann−Whitney U test was used. The statistical significance levelwas set as p < 0.05.

■ RESULTS AND DISCUSSIONTable 1 shows concentrations (GM, median, mean, and range)of mOPs in human urine samples collected from e-wasterecycling sites and two reference sites in southern China.

Urinary OP Metabolite Concentrations. To our knowl-edge, the present study is the first to report on urinary levels ofmOPs in China. Among participants (n = 221), NCl−mOPs(i.e., DoCP+DpCP, 90%; BBOEP, 93%; DBP, 99%; andDPHP, 100%) had high detection frequencies in urine atgreater than 90% (Table 1), whereas relatively low-detectionfrequencies (50%−80%) were observed for Cl−mOPs (i.e.,BCIPP, 56%; BCEP, 71%; and BDCIPP, 76%). Low detectionfrequencies of Cl−mOPs might be partly due to high LOQsobtained for these chemicals (0.05−0.10 ng/mL for Cl−mOPsand 0.01−0.06 ng/mL for NCl−mOPs). Among analyzedCl−mOPs, highest GM concentration in all participants wasobserved with BCEP (0.72 ng/mL), followed by BCIPP(0.094 ng/mL) and BDCIPP (0.091 ng/mL); DPHP(0.55 ng/mL) exhibited highest GM level among all NCl−mOPs, followed by DBP (0.29 ng/mL), BBOEP (0.065 ng/mL),and DoCP+DpCP (0.012 ng/mL; Table 1). Human exposureto OPs are thus widespread in e-waste dismantling areas andrural and urban reference areas in southern China.In e-waste dismantling areas, urinary concentration of

ΣCl−mOPs varied and ranged from < LOQ to 58 ng/mL;GM value (1.7 ng/mL) was significantly higher (Mann−Whitney U test, p < 0.05) than that in rural (0.93 ng/mL)and urban (0.56 ng/mL) reference areas. Concentrations ofindividual Cl−mOPs (Table 1) were all higher in residentsexposed to e-waste than those in two reference areas; differ-ences were significant for BCEP (Mann−Whitney U test, p <0.05) between e-waste and rural sites and for BCEP (p < 0.05),BCIPP (p < 0.05), and BDCIPP (p < 0.01) between e-wasteand urban sites (Table 1). Notably, participants from urbancontrol area aged from >18 to 60 yrs old, while donors livingin e-waste sites aged from 0.4 to 87 yrs old (Table S2).We therefore compared urinary levels of mOPs for 18−60 agegroup between e-waste sites and the urban areas; similarly,18−60 age group in e-waste sites had significant higher urinaryconcentrations of BCEP (p < 0.05; 0.76 vs 0.43 ng/mL),BCIPP (p < 0.01; 0.089 vs 0.028 ng/mL), and BDCIPP(p < 0.01; 0.075 vs 0.019 ng/mL) than those in participantsfrom the urban areas (Table S3). Although limited sample sizepossibly contributed to bias of urinary mOP concentrations inreference areas, these comparisons suggest that participants

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living in e-waste sites had high possibility of exposure toCl−OPs. Cl−OPs are mostly used as FRs and are thereforetypically added to widely used materials in e-products.1−3 Forexample, TCEP (parent compound of BCEP) and TDCIPP(parent compound of BDCIPP) are used as FRs in plastic;TCEP, TCIPP (parent compound of BCIPP), and TDCIPP areused in polyurethane foam.2,3 Thus, primitive e-waste recyclingactivities can result in emission of Cl−OPs into the environ-ment.10,23 He et al. observed that house dust from e-wastedismantling area contained much higher median levels ofTCIPP (4.77 μg/g) and TDCIPP (0.41 μg/g) than those fromrural (TCIPP, 1.22 μg/g and TDCIPP, 0.15 μg/g) and urban

(TCIPP, 0.75 μg/g and TDCIPP, 0.13 μg/g) reference areas.10

Furthermore, in home-produced eggs, median levels of TCEPand TCIPP were higher in three e-waste dismantling villages(TCEP, 0.67−1.08 μg/g and TCIPP, 0.33−0.56 μg/g) than inthe control village (TCEP, 0.65 μg/g and TCIPP, 0.17 μg/g).23

As observed in present study, in e-waste sites, elevated urinaryconcentrations of ΣCl−mOPs are consistent with reportedenvironmental pollution of Cl−OPs in e-waste sites, implyinghuman exposure to OPs. Meanwhile, individual Cl−mOP con-centrations were all lower in urban area than in rural referencearea (Mann−Whitney U test, p < 0.05 for BCIPP and BDCIPP;Table 1 and Table S3) when the entire data set from all

Table 1. Urinary Concentrations (ng/mL) of Organophosphate Metabolites in Participants Living in E-waste Dismantling andReference Areas in China

chlorinated OP metabolites nonchlorinated OP metabolites

BCEP BCIPP BDCIPP ΣCl-mOPsf BBOEP DBP DoCP+DpCP DPHP ΣNCl-mOPsg

all areas (ne = 221)DRa (%) 71 56 76 84 93 99 90 100 100GMb 0.72c 0.094 0.091 1.4 0.065 0.29 0.012 0.55 1.3median 1.1 0.097 0.11 1.7 0.071 0.15 0.015 0.53 1.1mean 3.0 0.43 0.25 3.6 0.093 1.2 0.020 0.85 2.2min <LOQd <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ 0.10 0.23max 57 23 4.5 58 2.1 7.8 0.27 36 36e-waste dismantling area (total: n = 175)DR (%) 73 60 81 89 91 99 90 100 100GM 0.81 0.11 0.11 1.7 0.065 0.38 0.012 0.57 1.5median 1.3 0.14 0.12 2.0 0.073 0.20 0.015 0.56 1.4mean 3.2 0.51 0.29 4.0 0.088 1.5 0.021 0.72 2.3min <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ 0.10 0.32max 57 23 4.5 58 0.33 7.8 0.27 5.1 8.4e-waste dismantling area (village #1: n = 98)DR (%) 64 72 93 90 99 99 95 100 100GM 0.77 0.16 0.15 1.6 0.073 0.42 0.013 0.59 1.6median 1.1 0.19 0.13 2.1 0.076 0.19 0.015 0.59 1.5mean 3.2 0.70 0.36 4.2 0.086 1.8 0.016 0.79 2.7min <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ 0.12 0.21max 27 23 4.5 33 0.33 7.8 0.050 5.1 8.4e-waste dismantling area (village #2: n = 77)DR (%) 83 44 66 80 82 99 84 100 100GM 1.0 0.071 0.074 1.7 0.056 0.34 0.013 0.56 1.4median 1.3 <LOQ 0.11 1.7 0.070 0.20 0.016 0.54 1.2mean 3.3 0.27 0.19 3.8 0.090 1.2 0.027 0.64 1.9min <LOQ <LOQ <LOQ <LOQ <LOQ 0.016 <LOQ 0.10 0.41max 57 3.6 2.3 58 0.32 4.4 0.27 2.6 5.2rural reference area (n = 29)DR (%) 69 55 76 80 100 100 93 100 100GM 0.50 0.069 0.069 0.93 0.052 0.10 0.012 0.37 0.60median 0.61 0.049 0.075 1.1 0.041 0.11 0.015 0.36 0.55mean 1.8 0.15 0.15 2.1 0.12 0.12 0.014 0.49 0.74min <LOQ <LOQ <LOQ <LOQ 0.022 0.041 <LOQ 0.13 0.23max 15 0.77 0.75 16 2.1 0.29 0.024 2.4 2.6urban reference area (n = 17)DR (%) 59 12 29 70 100 100 88 100 100GM 0.43 0.028 0.019 0.56 0.093 0.10 0.012 0.67 0.96median 0.67 <LOQ <LOQ 0.70 0.091 0.090 0.016 0.53 0.77mean 1.9 0.068 0.033 2.0 0.10 0.12 0.016 2.8 3.0min <LOQ <LOQ <LOQ <LOQ 0.051 0.043 <LOQ 0.15 0.69max 10 0.56 0.14 10 0.20 0.34 0.034 36 36

aDR, detection rates. Bold font are GM values used for comparison among different areas, and have presented the mOPs concentrations as GM value inthis paper. bGM, geometric mean values. cTwo effective digits have been used in this study. d<LOQ, concentrations value lower than LOQ. en, thenumber of samples. fΣCl-mOPs represented the sum urinary concentrations of all three chlorinated OP metabolites. gΣNCl-mOPs represented thesum urinary concentrations of all four nonchlorinated OP metabolites.

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age groups (or 18−60 age group) was collectively analyzed.TCIPP and TDCIPP are commonly used in similar prod-ucts (e.g., polymers, resins, latexes, and foams). This findingwas unexpected and inconsistent with prevailing perceptionthat urban people are more frequently in contact withCl−OP-containing products than rural people. Many OPs(e.g., TCEP, TNBP, and TPHP) have high vapor pressures andsolubility in water,3 thus OPs release from a point source mayexhibit more extensive environmental transport to the adjacentenvironment. In this study, however, air samples were notcollected, and concentrations of Cl−OPs were not measured;therefore, further research is needed to explore origins ofhuman exposure to Cl−OPs in rural areas in China.Urinary concentration of ΣNCl−mOPs was within 0.32−

8.4 ng/mL in e-waste area. Urinary levels of ΣNCl−mOPs(GM, 1.5 ng/mL) and DPHP (0.57 ng/mL) were significantlyhigher in participants from e-waste area (Mann−Whitney Utest, p < 0.01) than those from rural reference area (ΣNCl−mOPs, 0.60 ng/mL and DPHP, 0.37 ng/mL). TPHP (parentcompound of DPHP) and TCP (parent compound of DoCP+DpCP) are widely used as plasticizers in e-products, andTNBP (parent compound of DBP) is used as a plasticizerin plastic.1−3 Thus, NCl−OPs may also be released fromuncontrolled e-waste recycling activities because the e-product(e.g., air conditioner, television, fridge, washing machine, andcomputer) contains 20%−50% plastic by weight.34 Bi et al.analyzed chemical constituents of air particle samples fromworkshops engaged in recycling printed circuit board waste anddiscovered that major organic compounds were OPs consistingmainly of TPHP.7 In addition, e-waste recycling area located inLongtang Town had higher indoor dust levels of NCl−OPs[i.e., TPHP, ethylhexyl diphenyl phosphate (EHDPP), TNBP,and TCP] than in rural reference area;10 in the present study,consistency was noted with geographic difference in NCl−OPconcentrations in indoor dust samples and NCl−mOP concen-trations in urine between e-waste recycling and rural referencesites. Thus, e-waste dismantling activities may contribute tohuman exposure to NCl−OPs. However, in the present study,significant differences (Mann−Whitney U test, p = 0.100−0.830) were not observed between e-waste and urban sites inurinary concentrations of individual NCl−mOPs and ΣNCl−mOPs, when the entire data set from all age groups (or 18−60 agegroup) was collectively analyzed (Table 1 and Table S3).Urinary levels of mOPs were not previously compared betweene-waste and urban sites, whereas in outdoor air particles,comparable NCl−OP levels were previously observed betweene-waste dismantling area located in Qingyuan (126 ng/m3)and urban reference area (i.e., Guangzhou, 132 ng/m3).5

These findings indicate that NCl−OPs are not only containedin e-products but also are applied in various commercialand consumer products. For example, TPHP and EHDPPare commonly used in hydraulic fluid and PVC, and tris(2-butoxyethyl) phosphate (TBOEP) is widely used in dailyplastic products, floor polishes, rubber, and lacquers.3 Peopleliving in urban areas are more frequently in contact with NCl−OP-containing products than those living in rural areas; thiscondition increases urinary levels of NCl−mOPs in urbandwellers. This observation is supported by our present study, inwhich higher concentration of ΣNCl−mOPs was calculated inurban area (GM, 0.96 ng/mL) than in rural reference area(GM, 0.60 ng/mL; Table 1).Interestingly, although urinary levels of ΣCl-mOPs and ΣNCl-

mOPs observed in e-waste dismantling area were significantly

(Mann−Whitney U test, p < 0.05) higher than those observedin rural control areas (Table 1), comparable urinary levels ofΣCl-mOPs (p = 0.952; 1.6 vs 1.7 ng/mL) and ΣNCl-mOPs(p = 0.281; 1.6 vs 1.4 ng/mL) were obtained between village#1 (>50% of families have e-waste workshops) and #2 (approxi-mately 20% of families) (Table 1). Thus, the scale of e-wasterecycling activities seem to have no associations with humanOPs exposure; however, we need to emphasize that villages#1 and #2 were at a distance of less than 1.0 km, environmentaltransport of OPs generated from e-waste dismantling may be areason for the comparable urinary mOPs levels obtainedbetween both villages. As we mentioned before, OPs (e.g.,TCEP, TNBP, and TPHP) have high vapor pressures and goodwater solubility.3 Therefore, e-waste dismantling activities invillages #1 and #2 may cause environmental pollution of OPsfor each other. Similar, no significant differences (Mann−Whitney U test, p = 0.311−0.836) on urinary levels of indi-vidual mOPs (except BCIPP and BDCIPP) were found betweenvillages #1 and #2. Nevertheless, the urinary concentrations ofBCIPP and BDCIPP obtained in village #1 (GM: BCIPP,0.16 ng/mL and BDCIPP, 0.15 ng/mL) were significantly(p < 0.05) higher than those observed in village #2 (GM:BCIPP, 0.071 ng/mL and BDCIPP, 0.074 ng/mL). The vaporpressure (2.6 × 10−9 mm Hg) and solubility in water (1.50 mg/L)of TDCIPP are several orders of magnitude lower than otherOPs (e.g., TNBP, TCEP, and TPHP),3 and these propertiesreduce the mobility of TDCIPP in the environment. This maylead to residents living in village #1 having higher urinaryBDCIPP concentrations than people living in village #2.

Comparison of OP Metabolite Concentrations inUrine with Previously Reported Concentrations. Urinaryconcentrations of mOPs were also reported for residents fromU.S., Canada, Norway, Germany, and Australia.9,31,32,35−44

In several studies, specific gravity-corrected concentrations werereported,31,38,41,43,44 while urinary levels of mOPs were notcorrected in this study. We therefore compared uncorrectedurinary mOPs observed in China (present study) with thoseuncorrected mOPs levels reported in other countries (previousstudies; Table 2). In general, BDCIPP and DPHP were the twomost common mOPs analyzed in previous studies (Table 2).In the present study, among adults living in rural and urbanreference areas, BDCIPP and DPHP urinary levels were lessthan those observed in adults from other countries (Table 2).Similarly, adults from our reference areas also had lower orcomparable urinary concentrations of other mOPs (i.e., BCEP,BCIPP, BBOEP, DBP, and DoCP+DpCP) than those reportedfrom other countries (Table 2). These findings imply that OPsare not used in large quantities in household products insouthern China.Although e-waste dismantling activities were associated with

elevated urinary levels of mOPs in the present study (Table 1and Table 2), concentrations of mOPs in adults living ine-waste sites in China were lower than or comparable to thosereported in U.S., Canada, and Australia (Table 2). Thesefindings were inconsistent with our speculation that urinarymOP levels in adults from e-waste recycling sites in China arehigher than or in line with those in developed countries becausea considerable proportion of e-waste processed in China comesfrom overseas. Possibly, in the e-waste site, unexpectedlylow levels of mOPs were caused by addition of OPs, whichprobably decreased in concentration during the lifetime of thetreated products; therefore, percentage composition of OPs ine-waste may be much lower than those in new e-products.3

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2431

Table

2.Com

parisonof

Urinary

GM

(Median/Mean)

Organop

hosphate

Metabolites

Con

centration

s(ng/mL)

inAdu

ltParticipantsfrom

China

withTho

seUrinary

Con

centration

sReportedfrom

Other

Location

sarou

ndtheWorld

chlorin

ated

OPmetabolites

nonchlorinated

OPmetabolites

countries

populatio

nna

samplingdate

BCEP

BCIPP

BDCIPP

BBOEP

DBP

DoC

P+DpC

PbDPH

Preference

China

adults(e-waste)c

121

2014

0.61

(0.98/2.6)f

0.087

(0.085/0.30)

0.079(0.11/0.18)

0.065

(0.072/0.091)

0.41

(0.20/1.6)

0.015

(0.016/0.025)

0.52

(0.53/0.62)

thisstud

y

China

adults

(reference)d

392014

0.39

(0.54/2.0)

0.060

(0.020/0.15)

0.050

(0.057/0.11)

0.067(0.056/0.14)

0.11 (0.11/0.13)

0.011

(0.015/0.014)

0.45

(0.36/1.7)

thisstud

y

UnitedStates

adults

132016e

3.4(1.3/3.8)

0.4(0.3/0.9)

2.5(2.4/3.4)

NA

NA

NA

1.5(1.5/2.0)

37UnitedStates

adults

162011

NC

(0.63/0.76)

NC

(NA/0.17)

NC

(0.09/0.46)

NC

(ND/N

D)

NC

(0.11/0.16)

NA

NC

(0.44/1.10)

42UnitedStates

adults

532012−2013

NA

NA

0.37

(NC/N

C)

NA

NA

NA

1.02

(NC/N

C)

9UnitedStates

pregnant

wom

en39

2012−2013

NA

NA

1.3(1.1/N

C)

NA

NA

NA

1.9(1.6/N

C)

40Canada

pregnant

wom

an24

2010−2012

0.37

(0.46/NC)

0.41

(0.46/NC)

0.27

(0.26/NC)

0.38

(<0.08/N

C)

NA

0.64

(0.69/NC)

2.88

(2.94/NC)

39Germany

14−85

yrs

192011e

NA

NA

NA

NA

NA

NA

NC

(1.3/N

C)

36Germany

11−68

yrs

302009

NC

(<0.10/

NC)

NA

NA

NA

NA

NC

(<1.0/NC)

NC

(<0.50/N

C)

35

Australia

notavailable

282010−2013

NA

NA

1.00

(NC/N

C)

<0.35(N

C/N

C)

<0.43(N

C/N

C)

NA

24.4

(NC/N

C)

32Australia

notavailable

232010−2013

NA

NA

0.66

(NC/N

C)

ND

(NC/N

C)

<0.43(N

C/N

C)

NA

63.4

(NC/N

C)

32UnitedStatesj

adults

402015

NAg

NDh(N

D/N

Ci )

2.321(2.061/N

A)

NA

NA

NA

1.137

(1.160/N

A)

41

UnitedStatesj

adults

92011e

NA

NA

0.148(0.083/N

C)

NA

NA

NA

1.074

(0.803/N

C)

43

UnitedStatesj

adultfemales

222013−2015

NA

ND

(NC/N

C)

2.4(N

C/N

C)

NA

NA

NA

1.9(N

C/N

C)

45UnitedStatesj

adultmales

452002−2007

NA

NA

0.13

(0.12/NC)

NA

NA

NA

0.31

(0.27/NC)

38Norwayj

adultfemales

224

2012

NA

NA

NC

(0.08/0.25)

NC

(0.11/0.12)

NC

(0.08/0.08)

NA

NC

(0.63/1.44)

31aThe

numberof

collected

samples.B

oldfont

indicatesthattheurinarymOPs

concentrations

obtained

inourstudy.b“D

oCP+

DpC

P”representedthesum

concentrations

ofDoC

PandDpC

P.c “Adults

(e-waste)”

representedalladultsfrom

thee-waste

dism

antling

area.d“Adults

(reference)”

representedalladultsfrom

thereferenceareas.e Publisheddate

was

show

nforthesereferences

dueto

the

samplingdate

beingunavailable.f These

values

representedGM

(median/mean)

concentrationof

individualOPF

Rmetabolite

reported

inotherstudies.gNA=notanalyzed

(i.e.,thischem

icalwas

not

analyzed

inthisreference).hND

=notdetected

(i.e.,thischem

icalwas

notdetected

inallsamples).i NC

=notcalculated

(i.e.,thischem

icalwas

analyzed,butthisvaluewas

notcalculated

inthis

reference).jSpecificgravity-corrected

concentrations

ofmOPs

inurinewerereported

inthesestudies,andwethereforeexcluded

thesestudieswhencomparin

gthisstudywith

otherstudies.

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2432

Furthermore, nonoccupational residents of e-waste sites areexposed to OPs mainly through the food chain or inhalation ofpolluted air. However, contact with OP-containing products isconsidered an important route of OP exposure for people livingin unpolluted areas.45−47 Hence, in the present study, indirectexposure to OP-containing e-waste also possibly resulted inrelatively lower or comparable levels of urinary mOPs ine-waste dismantling areas compared with those in developedcountries (Table 2). Human urine and indoor dust sampleshave rarely been investigated in the same sampling area of othercountries,9; lower or comparable levels of TDCIPP and TPHPin house dust were found in e-waste sites (i.e., Qingyuan city)of China (median: TDCIPP, 0.41 μg/g; TPHP, 1.09 μg/g)compared with those obtained in the U.S. (GM: TDCIPP,1.39 μg/g; TPHP, 1.02 μg/g),9,10 thus, the geographicdifference in mOPs concentrations in urine coincide with thatin house dust between China and the U.S.9,10

Gender- and Age-Related Patterns of Urinary OPMetabolite Levels. We also examined gender-related patternsof urinary mOP concentrations in e-waste and two referencesites. Significant gender-related differences were not observed(Mann−Whitney U test, p > 0.05) for all mOPs across allsampling sites.Associations between age (in years) and log-transformed

mOPs were analyzed in e-waste sites (Pearson’s Correlationtest), whereas reference areas were excluded because of limitedsample size (Table 1 and Figure S3). Increasing age wasassociated with significant decreases in BCEP (r = −0.208,p < 0.05), BCIPP (r = −0.235, p < 0.05), BDCIPP (r = −0.245,p < 0.01), and DPHP (r = −0.419, p < 0.001) concentrations.On the other hand, urinary concentrations of BBOEP, DBP,and DoCP+DpCP exhibited nonsignificant negative correla-tions with age (r = −0.039−0.079, p > 0.05) (Table 1). Similarage-related patterns were also found for each mOPs, whenurinary mOPs concentrations were presented for different agegroups (i.e., 0−6, > 6−18, > 18−60, and >60 yrs) (Figure S3).In a previous study from Australia, urinary levels of BCIPP andDPHP were significantly higher in children than in adults,suggesting higher exposure to OPs of young children.32 In U.S.,children also had higher urinary levels of BDCIPP and DPHPcompared with their mothers and BDCIPP levels in infantswere substantially higher than those in adults.44,46 Possibly,significant negative correlations of urinary mOPs with age maybe related to increased hand−mouth contact and elevated dustexposure of children;44 children showed an order of magnitudehigher daily intake of OPs via dust ingestion than in adults.8,10

Children’s products that contain polyurethane foam are alsocommonly treated with OPs; Hoffman et al. observed that thenumber of infant products owned was strongly associated withurinary BDCIPP,46 thus the use of OP-containing children’sproducts may be another reason for negative associations ofurinary mOPs with age.Sources Analysis of Human Exposure to OPs. Pearson’s

correlation analysis was used to test associations betweenindividual urinary mOPs (log-transformed) in e-waste andreference areas. On the basis of statistical results (Table 3 andFigure S4), significant and positive correlations were calculatedbetween 14 of 21 pairs of urinary mOPs in e-waste sites,and coefficients ranged from 0.180 (p < 0.05 for DBP:BDCIPP)to 0.551 (p < 0.01 for BCIPP:BDCIPP). By contrast, signifi-cant relationships were discovered in 6 of 21 pairs of mOPs(r values, 0.485−0.607) in rural areas, and no significantassociations were obtained in urban reference area (Table 3). Table

3.Pearson

’sCorrelation

CoefficientsAmon

gIndividu

alOrganop

hosphate

Metabolites

inUrine

Samples

Collected

inSouthern

China,as

Stratified

bySampling

Location

sa

BCEP

BCIPP

BDCIPP

BBOEP

DBP

O&

Page

BCEP

BCIPP

BDCIPP

BBOEP

DBP

O&P

BCEP

BCIPP

BDCIPP

BBOEP

DBP

O&P

e-waste

dism

antling

area

ruralreferencearead

urbanreferencearead

BCEP

11

NAb

BCIPP

0.378**

10.607*

1NA

NA

BDCIPP

0.311**

0.551**

10.313

0.553*

1NA

NA

NA

BBOEP

0.185*

0.434**

0.110

10.357

0.556*

0.027

1NA

NA

NA

1

DBP

0.118

0.412**

0.180*

0.156

10.485*

0.647**

0.512*

0.220

1NA

NA

NA

0.431

1

O&Pc

0.034

0.157

0.159

−0.033

0.483**

10.009

−0.109

−0.190

−0.224

−0.202

1NA

NA

NA

0.149

0.124

1

DPH

P0.468**

0.529**

0.290**

0.284**

0.417**

0.216**

0.006

0.146

0.026

−0.030

0.364

0.178

NA

NA

NA

0.062

0.438

−0.103

age

-0.208*

-0.235*

-0.245**

−0.039

−0.079

0.059

-0.419**

a*p

<0.05,*

*p<0.01;concentrationvalues

less

than

LOQ

wereexcluded

from

theseanalyses;log-transformed

concentrations

wereused

fortheanalysis.B

oldfont

indicatessignificant

associations

(p<0.05).bNA=notavailable,theserelatio

nships

werenotanalyzeddueto

lowdetectionratesobtained

forBCIPP(12%

)andBDCIPP(29%

)intheurbanreferencearea.cO&P=DoC

P&DpC

P.dThe

associations

betweenurinarymOPs

levelsandagewerenotanalyzed

inreferenceareasdueto

limitedsamplesize.

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2433

These results imply that sources of human exposure to OPs arecommon or related to e-waste areas, whereas diverse sources ofOPs exist in rural and urban areas.As we mentioned above, OPs were widely used in e-products

for decades;1−3 limited studies showed that crude e-wasterecycling activities release OPs into environment.7,10,23 Ine-waste sites, exposure to OPs by participants can be viainhalation of polluted air, dermal contact with contaminateddust, or ingestion of food produced (or grown) in OP-pollutedenvironment.8−10,23 Thus, significant associations in e-wasteareas resulted from release of OPs during e-waste recycling.In addition to e-products, OPs are also used to treat manyconsumer products, such as furniture, baby products, andconstruction materials, that contain polyurethane foam.3

Stapleton et al. observed high prevalence of TCIPP andTDCPP in furniture foam samples, which were collected fromcouches, chairs, mattress pads, and pillows.48 In a previousstudy on OPs in baby products, common FR detected wasTDCPP; TCEP was also widely found as an impurity in babyproducts. OP emissions from OP-containing products were alsoidentified, suggesting that the use of OP-treated products mayaffect indoor air quality and is a possible route of OP exposurefor humans.46−48 Overall, OPs are used in a wide range ofcommercial products, suggesting that multiple sources may beresponsible for OPs detected in participants in rural and urbanreference areas. Interestingly, BCIPP correlated well withBCEP, BDCIPP, BBOEP, and DBP in both e-waste and ruralreference areas. TCIPP is an important OP (global production:30000 tons), representing approximately 60% of Cl−OPs and iswidely used in polyurethane foam. Several OPs are commonlyused in some products,3,46,48 thus our results indicate that otherOPs (e.g., TCEP, TDCIPP, TBOEP, and TNBP) may be usedin electronic and other commercial products as mixtures ofTCIPP.Difficulty arises from identifying a valid indicator for human

OP exposure because OPs are used in a wide range of products,resulting in diverse exposure sources. All mOP compoundswere less probable to be a useful indicator of human exposureto OPs in reference areas because of weak and nonsignificantcorrelations observed among mOPs. On the other hand, bothDPHP and BCIPP had significant positive associations withall other mOPs in e-waste sites, except that BCIPP didnot correlate well with DoCP+DpCP (Table 3). DPHP andBCIPP are possible indicators for OP exposure in the e-wastedismantling area, but they pose several disadvantages when oneof them was used as an indicator. For example, BCIPP showeda low detection rate and concentration (GM concentration,0.11 ng/mL and detection rate, 60%) (Table 1); DPHP can bepresent in many products as the parent compound and is also ametabolite of a variety of plasticizers, lubricants, and FRs.3 There-fore, combination of BCIPP and DPHP may be a more suitableindicator strategy for OP exposure in e-waste dismantling areas.Associations between OP Exposure and Oxidative

Stress. 8-OHdG is a marker for oxidative damage to DNA andoxidative stress.28,29 In the present study, we evaluatedcorrelation between urinary concentrations (log-transformed)of individual mOPs and 8-OHdG by Pearson’s correlationanalysis for e-waste and rural reference area, respectively. Theseresults are important because they provide a first-hand report,using data from the human population, of associations betweenelevated OP exposure and oxidative stress.In all the participants, 8-OHdG was found be significantly

correlated with BCIPP (r = 0.394, p < 0.001), DBP (r = 0.230,

p < 0.01), and DPHP (r = 0.338, p < 0.001). We also observedthat urinary 8-OHdG levels significantly increased withincreasing levels of BCIPP in e-waste sites (r = 0.484, p <0.01) and rural (r = 0.610, p < 0.05) reference area (Figure 1).

Furthermore, data in e-waste recycling area showed significantassociation between urinary concentrations of 8-OHdG andBCEP (r = 0.504, p < 0.01), DBP (r = 0.214, p < 0.05), andDPHP (r = 0.440, p < 0.01), whereas no such associationswere obtained in the rural reference area (Figure 1). Both areasdemonstrated nonsignificant associations between urinary8-OHdG and BDCIPP, BBOEP, and DoCP+DpCP (Figure 1).These results suggest that TCIPP exposure is correlated withoxidative damage to DNA across sampling sites, and thathuman exposure to TCEP, TNBP, and TPHP (or EHDPP)were correlated with elevated oxidative stress in e-wastedismantling sites. Notably, limited sample size possibly affected

Figure 1. Pearson correlations of urinary OP metabolites concen-trations with urinary 8-OHdG in participants living in e-wastedismantling [plot (a−d)] and rural reference [plot (e−h)] areas.Concentration values less than LOQ were excluded from theseassociation analyses, and we used log-transformed urinary concen-trations for these analyses. The blue dotted lines representedsignificant correlations, gray dotted lines represented nonsignificantassociations. Relationship between urinary BDCIPP, BBOEP, andDoCP+DpCP levels and 8-OHdG were not significant (p > 0.05) inboth of sampling areas and thus were not shown.

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2434

statistical power of association analysis. Therefore, in the ruralreference area (n = 29), association results between mOPs and8-OHdG should be interpreted with caution.Although no previous study explored the association between

OP exposure and 8-OHdG in humans, limited animal or in vitrostudies were performed to examine OP-induced oxidativestress.25−27 Chen et al. evaluated effects of TPHP (300 mg/kgbody weight) and TCEP (100 mg/kg body weight) on induc-tion of oxidative stress in the livers of male mice and witnessedthat oral administration evidently affected the oxidative status.25

Similarly, TPHP (60 μg/mL in cell culture) and TCEP(300 μg/mL in cell culture) also induced oxidative stress inTM3 cells.26 In a study from Duke University, an in vitro model(i.e., PC12 cells) was used to assess developmental neurotoxicityof TCIPP, TCEP, and TDCIPP; TDCIPP (50 μmol/L in cellculture) resulted in elevated oxidative stress but was insufficientto compromise cell viability.27 Furthermore, few studies exploredthe underlying mechanism of OP-induced oxidative stress,25 butinformation on the mechanism remains lacking for OPs.Notably, urinary levels of mOPs (GM weight concentra-

tions: 0.012 to 0.81 ng/mL; GM molar concentrations: 0.057 to3.6 nmol/L) obtained in participants by the present study wereseveral orders of magnitude less than the effect of values of OPsspiked into studied animal or cell.25−27 In accordance withprevious reports,7,10,23,33,49−51 e-waste dismantling activities notonly release OPs but also release other toxicants into theenvironment. Thus, high oxidative stress may also resultfrom many other pollutants produced by e-waste recycling.In our previous studies, increased urinary levels of bisphenols(BPs) and monohydroxy-polycyclic aromatic hydrocarbons(OH-PAHs) were obtained from participants in the sameinvestigated e-waste site and indicated that bisphenol A andPAH exposures are correlated with high oxidative stress.33,49 Niet al. and Wen et al. further reported an association betweenexposure to polychlorinated dibenzo-p-dioxin and dibenzofur-an, PBDEs, and heavy metals and increased urinary 8-OHdGlevels in e-waste dismantling areas.50,51 Furthermore, associa-tions of urinary concentrations between 8-OHdG and mOPs[and other pollutants (i.e, BPs and OH-PAHs)] were alsoestimated by the linear regression model (Table S4), and ourresults showed that NCl-mOPs may be the main contributor tooxidative stress among these types of pollutants. However,coexposure to more e-waste-pollutants should be considered toinvestigate their associations with oxidative stress.In summary, this study is the first to report urinary levels of

mOPs in China. Participants living in e-waste dismantling areasyielded significantly higher concentrations of BCEP and DPHPthan those in rural reference areas. These findings suggested ahigh possibility of exposure to TCEP and TPHP or EHDPP ine-waste sites. Age is a possible factor influencing OP exposurebecause of the negative correlation of urinary BCEP, BCIPP,BDCIPP, and DPHP with age (p < 0.05). Our findings alsosuggested that sources of human exposure to OPs were commonin or related to e-waste sites. Furthermore, correlation wasobserved in human exposure to TCIPP, TCEP, TNBP, andTPHP (or EDHPP) and high oxidative stress in e-wastedismantling sites. This study provided novel information onassociation between OP exposure and oxidative stress in humans.

■ ASSOCIATED CONTENT*S Supporting InformationSupporting Information as noted in text is available free ofcharge via the Internet at The Supporting Information is

available free of charge on the ACS Publications website atDOI: 10.1021/acs.est.6b05462.

Optimized MS/MS parameters for target organophos-phate metabolites, detailed information of recruited studysubjects, geometric mean urinary concentrations oforganophosphate metabolites, associations betweenurinary 8-OHdG levels and sum urinary concentrations,map of Guangdong Province, HPLC−MS/MS chroma-togram, geometric mean urinary mOPs levels, andPearson correlations among individual organophosphatemetabolites in urine samples collected in southern China(PDF)

■ AUTHOR INFORMATIONCorresponding Author*Address: School of Environmental Science and Engineering,Sun Yat-Sen University, 135 Xingang West Street, Guangzhou510275, China; phone: 86-20-84113454; fax: 86-20-84113454;email: zhangt47@mail.sysu.edu.cn.ORCIDTao Zhang: 0000-0002-4424-0423Author Contributions@S.-y.L. and Y.-x.L. contributed equally to this work.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThe Natural Science Foundation of China (Grants 41225014and 41303094), Pear River S&T Nova Program of Guangzhou,and the Fundamental Research Funds for the CentralUniversities are acknowledged for their partial research support.The present study was also supported by the Guangzhou KeyLaboratory of Environmental Exposure and Health (GrantGZKLEEH201606). We gratefully acknowledge the donorswho contributed the urine samples for this study.

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