Human Exposure to Short- and Medium-Chain Chlorinated Paraffins

Dec 8, 2016 - *(L.G.) Phone: +861062849356; fax: +861062923563; e-mail: ... The high CP concentrations found in Chinese mothers' milk should raise ...
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Human Exposure to Short- and Medium-Chain Chlorinated Paraffins via Mothers’ Milk in Chinese Urban Population Dan Xia, Lirong Gao, Minghui Zheng, Jingguang Li, Lei Zhang, Yongning Wu, Qichang Tian, Huiting Huang, and Lin Qiao Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04246 • Publication Date (Web): 08 Dec 2016 Downloaded from http://pubs.acs.org on December 8, 2016

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Human Exposure to Short- and Medium-Chain Chlorinated Paraffins via Mothers’ Milk in Chinese Urban Population

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Dan Xia,†,‡ Lirong Gao,*,† Minghui Zheng,† Jingguang Li,§,║ Lei Zhang,§,║ Yongning Wu*§,║

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Qichang Tian,† Huiting Huang,†,‡ and Lin Qiao†,‡

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Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

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University of Chinese Academy of Sciences, Beijing 100085, China

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§

The Key Laboratory of Food Safety Risk Assessment, Ministry of Health, China National

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for

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Center of Food Safety and Risk Assessment, Beijing 100021, China

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Prevention, 29 Nanwei Road, Beijing 100050, China

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*Corresponding author: Lirong Gao, Tel.: +861062849356, Fax: +861062923563, E-mail

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address: [email protected]; Yongning Wu, Tel. & Fax: +861052165589, E-mail address:

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[email protected]

National Institute of Nutrition and Food Safety, Chinese Center for Disease Control and

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ABSTRACT: Chlorinated paraffins (CPs) are high production volume synthetic chemicals,

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found ubiquitously in various environmental matrices. However, little information is

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available on CP contamination in mothers’ milk. In this study, 1,370 urban mothers’ milk

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samples were collected from 12 Chinese provinces in 2007 and 16 provinces in 2011. CP

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geographical distribution and congener group profiles were studied to assess the CP levels

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and figure out the source of exposure in humans. Twenty-eight pooled samples were analyzed

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for 48 short-chain CP (SCCP) and medium-chain CP (MCCP) congener groups using the

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GC×GC-ECNI-HRTOFMS method. The median concentrations of SCCPs were 681 and 733

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ng/g lipid in 2007 and 2011, respectively; median concentrations of MCCPs were 60.4 and

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64.3 ng/g lipid in 2007 and 2011, respectively. Variations of more than 2 orders of magnitude

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in CP exposure levels were found between different provinces. The levels of CPs increased

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from 2007 to 2011, which indicates that CP production and use may be an important exposure

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source. This is the first global comprehensive and large-scale investigation of CPs in mothers’

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milk, and it lays foundations for improving our understanding of the metabolism of CPs in

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humans. The high CP concentrations found in Chinese mothers’ milk should raise concern

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about potential toxic effects in both mothers and breastfeeding infants.

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INTRODUCTION

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Chlorinated paraffins (CPs) are known as the most complex groups of organohalogen

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pollutants in the environment, with homologues and isomers far exceeding 10,000.1

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Commercial mixtures of CPs are produced by chlorination of n-alkane feedstocks and are

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classified into short-chain CPs (SCCPs, C10–13), medium-chain CPs (MCCPs, C14–17), and

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long-chain CPs (LCCPs, C18–30) based on their carbon chain length, with chlorination degree

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varying from 30% to 70%. CPs are used in many applications, mainly as lubricant, cutting

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fluid, flame retardants and plasticizers in PVC, rubber, paints, coatings, and sealants.2

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Persistent organic pollutants (POPs) are toxic chemicals that persist in the environment and

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adversely affect human health and the environment.3 Studies have shown that CPs persist in

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the environment and could be prone to long-range atmospheric transport because of their

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semi-volatile properties. SCCPs can bioaccumulate and biomagnify through food webs, likely

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posing ecological and health risks to wildlife and humans.4-6 SCCPs have been listed as

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candidate POPs under the Stockholm Convention,3 and have also been placed on the Toxics

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Release Inventory (TRI) in the European Union, Japan, and Canada, and classified as priority

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toxic substances in the United States.6

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The global cumulative production of CPs has been approximately seven million tons

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since the 1930s, and no other anthropogenic persistent organic chemical has been produced in

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such quantities.7 Although some information is available on the global occurrence of CPs in

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various environmental matrices, human exposure data remain scarcer, mainly because of the

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complexity of CP mixtures and analytical difficulties encountered when studying them.8,9

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Mothers’ milk is a unique biological matrix for investigating the human exposure pathways 3

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of certain environmental contaminants, because it can provide exposure information for both

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the mother and breastfeeding infant.10 The significance of mothers’ milk as an exposure

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medium for humans has been shown for polychlorinated dibenzodioxins/furans (PCDD/Fs),11

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polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs).12,13

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However, human exposure to CPs though mothers’ milk has rarely been investigated. A study

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on three mothers’ milk samples from Quebec, Canada, was the first to show the presence of

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SCCPs in mothers’ milk.14 Thomas et al. reported levels of SCCPs and MCCPs in mothers’

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milk samples from Lancaster and London, U.K..15 The sampling was limited geographically,

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and the congener group patterns and exposure sources of CPs remain unclear. Moreover, no

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comprehensive and large-scale investigation of CPs exposure levels in mothers’ milk has yet

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been conducted.

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China is the largest producer and consumer of CP-based products in the world. CP

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production volume has been continuously and rapidly growing during the past decade, from

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about 0.6 million tons in 2007 to about 1 million tons in 2010.7,16 Three main commercial CP

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mixtures (CP-42, CP-52, and CP-70) are produced and used on a large scale.17 In recent years,

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CPs have been found to be prevalent in the environment in China. One study indicated that

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relatively high SCCPs concentrations were found in aquatic organisms from Liaodong Bay,

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North China.18 Zhou et al. also reported high levels of CPs in wildlife in Yangtze River

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Delta.19 Harada et al. found, by analyzing composite food samples (a sample being all the

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food and drinks a participant consumed in a 24 h period), that dietary intakes of SCCPs in

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Beijing increased by two orders of magnitude between 1993 and 2009, and may be related to

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the increasing production and use of CPs in China.20 Human exposure for CPs though 4

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mothers’ milk may also be great in this country with continued heavy production and

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consumption of CPs. To better understand the occurrence, sources, and accumulation of CPs

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in mothers’ milk, this study focused on CP exposure status in China, the most typical

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CP-polluted country.

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In this study, 1,370 individual urban mothers’ milk samples were collected and analyzed

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for SCCPs and MCCPs simultaneously using the comprehensive two dimensional gas

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chromatography coupled to electron capture negative ionization high-resolution time-of-flight

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mass spectrometry (GC×GC-ECNI-HRTOFMS) method for the first time.21 With increased

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chromatographic separation and high resolution of mass spectrometry, this method can

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effectively exclude interference from other CP congeners and organohalogen compounds,

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thus providing more accurate and precise analytical results for concentrations and congener

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group profiles of CPs in mothers’ milk.

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The objective of this study was to conduct the first comprehensive and large-scale

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investigation of CP exposure in mothers’ milk. The national geographical distribution and

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congener profiles of CPs were studied to assess the levels, and figure out the sources of CPs

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exposure in humans. In addition, the CP concentrations in mother’s milk in 2007 and 2011

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were compared, and the changes were assessed in relation to CP production and use.

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EXPERIMENTAL SECTION

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Sample collection. Individual mothers’ milk samples were collected from urban areas in

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12 Chinese provinces in 2007 and 16 provinces in 2011. The approach for mothers selection

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and mothers’ milk sampling followed the “Guidelines for Developing a National Protocol” of

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the Fourth WHO-Coordinated Survey of Mothers’ milk for Persistent Organic Pollutants in 5

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Cooperation with UNEP.22,23 The locations of the 16 provinces in China are shown in Figure

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1, and the 12 provinces from 2007 were also part of sampling provinces in 2011. Other

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relevant sampling information regarding donor ages and sample collection is detailed in the

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Table 1. Fifty donors were selected in urban sites in each province, and at least 50 mL of milk

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for each participant, was collected directly to the pre-washed glass jars. A total of 570

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mothers’ milk samples from 12 provinces in 2007 and 800 samples from 16 provinces in

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2011 were obtained. The samples were stored at −20°C until analysis. The fifty individual

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samples from each province were pooled to give one pooled sample before analysis, resulting

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in 12 pooled samples in 2007 and 16 pooled samples in 2011.

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Sample preparation. Briefly, approximately 30 mL of pooled mothers’ milk sample 13

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was freeze-dried and spiked with 2.5 ng of

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Cambridge Isotope Laboratories), then extracted with a 1:1 mixture of dichloromethane and

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n-hexane using an ASE 350 extraction unit (Dionex, Sunnyvale, CA, USA). Lipid content

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was determined gravimetrically after solvent evaporation. Gel permeation chromatography

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was used to remove lipids from the extract, which was then cleaned through a multi-layered

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column, from bottom to top, 3 g of activated Florisil, 2 g of activated silica gel, 5 g of

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acidified silica gel (containing 30% w/w of concentrated sulfuric acid), and 4 g of anhydrous

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sodium sulfate. The cleaned extract was concentrated, solvent-exchanged into cyclohexane,

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evaporated to approximately 50 µL in a vial containing 2.5 ng of ε-hexachlorocyclohexane

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(obtained from Dr. Ehrenstorfer). Sample extraction and cleanup procedures of CPs are

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detailed in the Supplemental Material.

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Analytical

quantification.

C10-labeled trans-chlordane (purchased from

Instrumental

analysis

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conducted

using

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GC×GC-ECNI-HRTOF-MS (a GC instrument (Agilent, Santa Clara, CA, USA) coupled to a

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HRTOF-MS instrument (Tofwerk, Thun, Switzerland) which operated in ECNI mode).

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Forty-eight SCCPs (C10−13Cl5−10) and MCCPs (C14−17Cl5−10) formula congener groups were

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quantified in one injection. Detailed information about the identification and quantification

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procedures was given in our previous work about the GC×GC-ECNI-HRTOF-MS method

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development,21 and detailed in the Supplemental Material.

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Quality assurance/quality control. To minimize contamination, all glassware used in

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this study was heated to 450°C before usage. Seven mothers’ milk samples were analyzed in

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each batch, and one procedural blank was also performed in each batch. These procedural

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blanks were extracted and analyzed in the same way as the samples. Levels in blanks were on

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average 8.1 ng/sample for SCCPs and 2.4 ng/sample for MCCPs. The method detection limit

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(MDL) for SCCPs and MCCPs was calculated by tripling the standard deviation of the

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average levels of seven blanks samples. The MDLs were estimated to about 5.6 ng/g lipid for

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SCCPs and 2.0 ng/g lipid for MCCPs, respectively. As the mean concentrations of the blanks

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were lower than one-tenth of the SCCP and MCCP concentrations in mothers’ milk samples,

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results were not blank corrected. The recoveries of

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milk samples were in the range of 57%−119%, with an average of 92%.

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C10-labeled trans-chlordane from the

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Statistical analysis. Statistical analysis was performed with IBM SPSS Statistics 22.0,

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and statistical significance was accepted at p-Values < 0.05. Correlations between the

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concentrations of SCCPs and MCCPs were analyzed using the spearman correlation analysis.

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RESULTS AND DISCUSSION

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CP levels in mothers’ milk. The concentrations of total SCCPs, MCCPs, and different 7

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carbon chain length homologues (C10-17) are summarized in Table 2. SCCPs and MCCPs

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were detectable in all mothers’ milk samples. Total SCCP concentrations measured in 2007

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ranged from 170 ng/g lipid (in Sichuan Province) to 6,150 ng/g lipid (in Hebei Province),

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with a median value of 681 ng/g lipid. MCCP concentrations were between 18.7 ng/g lipid (in

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Sichuan Province) and 350 ng/g lipid (in Hebei Province), with median of 60.4 ng/g lipid. In

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2011, the median SCCP concentration was 733 ng/g lipid, and values ranged from 131 ng/g

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lipid (in Neimenggu Province) to 16,100 ng/g lipid (in Hebei Province). MCCP concentration

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were in the range of 22.3 ng/g lipid (in Neimenggu Province) and 1,501 ng/g lipid (in Hebei

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Province), with a median value of 137 ng/g lipid. The ubiquitous detection of CPs in mothers’

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milk suggested that both SCCPs and MCCPs can reach to human to a large extent.

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The CP concentrations we found in mothers’ milk were typically present at the highest

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levels compared with other POPs reported in mothers’ milk in China. These CPs levels were

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higher than levels reported for dichloro-diphenyl-trichloroethanes (DDTs) (mean, 526 ng/g

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lipid), and are 1–3 orders of magnitude higher than those found for PBDEs (median, 1.49

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ng/g lipid) and indicator PCBs concentrations (median, 10.5 ng/g lipid) in mothers’ milk from

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the same 2007 samples.23,24 Globally, higher PCBs levels were found in mothers’ milk from

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Europe and Northern America than those in other areas, which may related to the PCBs

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production and usage.25 The large amounts of CPs produced and used in China could partly

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explain why the SCCP and MCCP concentrations in the samples were much higher than the

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concentrations of other POPs that have been found in mothers’ milk.

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Difficulties in analyzing complex CP mixtures are responsible for the lack of data on

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SCCP and MCCP levels in human mothers’ milk. SCCP levels in human mothers’ milk were 8

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determined only in two countries (Canada and the U.K.), while MCCP levels were measured

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only in the U.K..14,15 Compared with these two studies, CP levels in this study are up to 1–2

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orders of magnitude higher than those found in Canada (11.0–17.0 ng/g lipid) and the U.K.

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(49–820 ng/g lipid) for SCCPs, and 0.81–14.0 ng/g lipid for MCCPs in the U.K. The high CP

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concentrations we found in mothers’ milk were in line with the high CP concentrations that

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have been found in sediment (320 to 6,600 ng/g dry weight (dw) for SCCPs and 880 to

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38,000 ng/g dw for MCCPs) and biota (280 to 3,900 ng/g dw for SCCPs and 530 to 23,000

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ng/g dw for MCCPs) in China.16,26

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Generally, significant correlations between SCCP and MCCP concentrations were found

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in Chinese mothers’ milk samples (R2 = 0.82, 2007; R2 = 0.85, 2011, p < 0.001). This

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suggests that the two contaminants groups may have similar sources and undergo similar

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uptake pathways. Similar positive correlations between SCCP and MCCP concentrations

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were also found in dolphins and porpoises in the South China Sea.26 The possible reason for

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these observations is that n-alkane feedstocks used to produce CPs are not strictly grouped by

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carbon chain length, meaning that commercial products used in China are mixtures of SCCPs

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and MCCPs with different carbon chain lengths.17

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SCCP concentrations were much higher than those of MCCPs in all mothers’ milk

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samples in the two sampling years. Higher SCCP concentrations were also found in samples

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in the U.K. mothers’ milk samples and indoor air and dust samples in Sweden.15,27 The

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transfer of contaminants to humans is the result of exposure from various sources, including

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emissions during production, processing and use, food, and in vivo metabolism processes.15

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The results of modeling and laboratory studies indicate that SCCPs and MCCPs are 9

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hydrophobic (with log octanol–water partition coefficients of 5.9–8.1) that can

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bioaccumulate.28 Exposure experiments using fish have indicated that CP bioaccumulation

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potentials generally increase with the chain length and chlorine content of the CP.29 Humans

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could be exposed to CPs through the diet and the inhalation of indoor air and dust. Human

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exposure to CPs through inhaling indoor air and dust could be an important reason for the

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SCCP concentrations being higher than the MCCP concentrations in the mothers’ milk

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samples. Differences in the metabolisms of humans and other biota and differences in the

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overall transfer efficiencies of SCCPs and MCCPs in humans could also account for these

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results. Overall, this topic deserves further investigation.

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Geographical distribution differences. We collected samples from 12 provinces in

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2007 and 16 provinces in 2011. Spatial distribution of SCCPs and MCCPs in mothers’ milk

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samples is important, as for the assessment of its sources. Figure 2 shows that variations of

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more than 2 orders of magnitude in SCCP and MCCP concentrations were found among

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different provinces.

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The highest SCCP levels were found in Hebei and Henan provinces in both sampling

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years. Based on background distribution information of CP-manufacturing plants in China,30

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Hebei and Henan provinces are the major Chinese production bases of CPs, and are

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characterized by high industrialization. Overall, there is a good correlation between the

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regional distribution of CP production and the high CPs levels found in this study. With most

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of the CPs manufacturing plants located in eastern China, high CP concentrations were found

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in eastern parts, such as Jiangxi province, Liaoning province, and the city of Shanghai. The

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release of CPs into the environment could occur during production, storage, transportation, 10

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and industrial use of manufactured products.31 CPs can enter the aquatic environment in

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runoff, biomagnify through the food chain, and finally be transferred to humans. The release

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of CPs from materials in which they are present is a source of CPs to humans in the indoor

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environment. 27 Increases in the production and use of CPs will increase the amounts of CPs

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released into the environment in urban areas. The production and use of CPs in urban areas

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may therefore be important sources of CPs found in mothers’ milk in those areas.

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Levels of SCCPs and MCCPs from Neimenggu, Qinghai, Sichuan, and Ningxia

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Provinces were much lower than those in other provinces. There are few or no CP

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manufacturing plants and industrial activities in these provinces. Low CP levels in these areas

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may result from long-range atmospheric transport of CPs. For future studies, these locations

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may be regarded as background areas for national POPs monitoring.

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Congener group profiles of SCCPs and MCCPs. Figures 3 show the SCCP and

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MCCP congener patterns of 28 pooled mothers’ milk samples from different provinces for

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both sampling years. Both the carbon and chlorine congener group profiles are shown. In

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general, the congener group patterns of SCCP and MCCP in all samples were similar among

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the sampling provinces, although the SCCPs and MCCPs concentrations varied between

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provinces. The most abundant SCCP congener groups were C10 and C11, which accounted for

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approximately 47% and 31% of total SCCPs, respectively. For MCCPs, the most abundant

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group was C14, accounting for approximately 70% of total MCCPs. For the chlorine congener

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group profiles of SCCPs, Cl6-CPs and Cl7-CPs dominated in most mothers’ milk samples,

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contributed to the total abundance of SCCPs were 31% and 43%. For MCCPs, the main

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congeners Cl7-CPs and Cl8-CPs showed notably higher mean abundance than other chlorine 11

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atom congeners, accounting for approximately 34% and 40% of total MCCPs.

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Congener patterns of SCCPs and MCCPs in mothers’ milk are a function of exposure

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and metabolism processes. The SCCP congener group patterns we found were different from

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those reported in mothers’ milk samples in the U.K.,15 where CPs were dominated by C11 and

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C12 homologues. The difference indicates that exposure sources may differ between the U.K.

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and China. The SCCP congener group patterns were similar to those in dolphins and

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porpoises collected from Chinese marine areas, where C10-CPs and C11-CPs predominated.26

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Congener patterns in the environment can also reflect those in commercial CP mixtures.32

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Consistent with this, SCCP congener profiles identified in the present study reflect the two

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major industrial CP mixtures manufactured in China, CP-42 and CP-52, which are dominated

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by C10-CPs and C11-CPs;33 while in the U.K., the technical mixtures were dominated by

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C11-CPs and C12-CPs.

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For lower CP exposure areas, such as Guangdong and Qinghai provinces, the congeners

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of the carbon chains was dominated by C10, accounting for 60.75% and 69.75%, respectively.

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The Cl6 and Cl7 groups were the most abundant chlorine congener groups. CPs with fewer

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carbon chains and lower chlorine numbers have relatively higher vapor pressures, and are

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more favorable for long-range atmospheric transport. This further suggests that long-range

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atmospheric transport of CPs may be the most important source for areas that lack industrial

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CP production plants. Meanwhile, the release of CPs from materials containing CPs is also a

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source of CP exposure in the indoor environment.27 Compared with the low-CP exposure

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areas, the abundance of longer-chain SCCPs (C11-CPs, C12-CPs and C13-CPs) and higher

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chlorinated congeners (Cl7−10) significantly increased in the high-CP exposure areas such as 12

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Hebei and Liaoning provinces. These specific congener distributions may be influenced by

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the difference in constitution of CP technical mixtures produced and used in China. The

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relative contribution of carbon chain groups to SCCP totals in mothers’ milk in Hebei

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Province in 2011 (C10 = 35%, C11 = 33%, C12 = 16%, C13 = 15%) is similar to results reported

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for technical CP-52 samples (C10 = 35%, C11 = 34%, C12 = 24%, C13 = 7%).34 This pattern

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from other mothers’ milk samples further indicate that production is a source of CP exposure

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in Chinese human mothers’ milk.

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Comparison of CP concentrations in mothers’ milk in 2007 and 2011. Between the

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two sampling years, the SCCPs and MCCPs concentrations in 2007 samples were lower than

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those measured in 2011 samples (Figure 4). SCCP and MCCP median concentrations increase

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between 2007 (681 ng/g lipid for SCCPs and 60.4 ng/g lipid for MCCPs) and 2011 (733 ng/g

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lipid for SCCPs and 64.3 ng/g lipid for MCCPs) with rates of increase of 7.1% and 6.1%,

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respectively.

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The increase in CP levels found in mothers’ milk are in accordance with the increasing

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production volumes and use of CPs during this period. These results are also in good

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agreement with increasing CP deposition concentrations found in sediment cores in China,35

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and the significant increase observed in marine mammals (porpoises and dolphins) over the

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past decade in the South China Sea.26 In addition, the increases in CP concentrations in

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mothers’ milk were consistent with the increases in the concentrations of other POPs, such as

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PBDEs and perfluorinated compounds, in various environmental matrices related to marked

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increases in the production and use of those compounds. 36,37

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SCCPs have been listed as priority hazardous substances by the European Union, and 13

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the production of SCCPs has been voluntarily reduced from 13,000 tons in 1994 to 4,000 tons

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in 1998 by the European industrial sector.9 Although SCCPs have been under review by the

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Stockholm Convention as candidate POPs since 2007, the production and use of CPs in

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China is currently not restricted in industrial activity. Annual production output grew

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five-fold between 2004 and 2009, and reached a new high in 2015.30 The increase of SCCP

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and MCCP levels in Chinese mothers’ milk are in good agreement with the history of CP

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production and use in China over the past decade. Meanwhile, it can be inferred that

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increasing production and use of CPs would further increase environmental release in regions

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with rapid economic development and industrial activities.

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Variations in both SCCP and MCCP carbon chain lengths and congener group profiles in

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the samples were also observed between the two sampling periods (Figure 3). An increase

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was observed for total abundances of C10 and C11 SCCPs in 2011 relative to 2007 in high-CP

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exposure areas, such as Hebei and Henan provinces. This finding may be linked to the

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continuing production of CP-42 and CP-52 in technical mixtures during this period. There

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were no significant changes in the MCCP homologue pattern observed in the samples. C14

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was the most abundant MCCP homologue group in both sampling years. Overall, the increase

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in CP concentrations in Chinese mothers’ milk, combined with the prevalence of C10 and C11

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SCCPs in both sampling years may indicate that emissions from urban production and use

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may still be the most important source of CP exposure in China.

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Environmental implications. This is the first comprehensive and large-scale

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investigation of CP exposure levels in mothers’ milk, and also the first report of SCCPs and

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MCCPs in mothers’ milk in China. Concentrations of SCCPs and MCCPs in Chinese mothers’ 14

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milk were much higher than those reported in other countries, and higher than other

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contaminants of concern, such as OCPs, PBDEs, PCDD/Fs, and PCBs in the same samples.

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SCCPs have been found to be hepatotoxic in trout at high levels of exposure.38 Carcinogenic

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effects in rats and mice have also been observed for SCCPs.39 Considering the persistence

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and bioaccumulative properties of these contaminants, detection of high levels CPs in

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Chinese mothers’ milk should raise concern for potential toxicity to both the mother and

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breastfeeding infant.

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Nationwide geographical differences of SCCP and MCCP exposure levels in urban

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mothers’ milk were observed in 16 provinces. CP production may be an important source of

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CP exposure in some urban areas, while the atmospheric transport of CPs is likely the source

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in low-CP exposure areas. SCCP and MCCP levels in 2011 samples were higher than those in

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2007 samples. This may be explained by increasing CP production and related urban

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industrial activities. Increasing levels of these contaminants may pose a risk, especially to the

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developing fetus and breastfeeding infant. Therefore, regulatory actions governing these

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contaminants may be needed to reduce emissions of CPs and human exposure in China. In

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the meantime, more detailed studies are required to determine the major human exposure

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pathways in the general population, such as indoor air, dust and food, along with an

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evaluation of the metabolic pathways and possible biological effects involved at these levels

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of exposure.

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ASSOCIATED CONTENT

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Supporting Information

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Additional information is available as noted in the text. This material is available free of

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charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

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Corresponding Author

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*E-mail: [email protected]; [email protected]

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Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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This research was funded by the National 973 program (No. 2015CB453100), the National

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Natural Science Foundation of China (Nos. 21377140, 21361140359, 21577152, 21537001

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and 21321004) and the Strategic Priority Research Program of the Chinese Academy of

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Sciences (No. XDB14010100 and XDB14020102).

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Figure 1. The sampling provinces in 2007 and 2011 in China.

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Figure 2. Spatial distributions of SCCP and MCCP concentrations (ng/g lipid) in urban

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mothers’ milk from 16 provinces in China. (Two colors were indicated for two contaminant

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groups in both years. Blue was indicated for SCCPs and yellow for MCCP in 2007; green

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was indicated for SCCPs and red for MCCP in 2007)

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Figure 3. Carbon and chlorine congener group profiles of SCCPs (A) and MCCPs (B) in 28

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pooled Chinese urban mothers’ milk samples from 16 provinces in 2007 and 2011.

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Figure 4. Boxes-and whiskers plot of SCCP and MCCP concentrations (ng/g lipid) in

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Chinese urban mothers’ milk samples in 2007 and 2011.

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Table 1. Characteristics and description of the participants (the number of participants and the age range in each province) Provinces 2007 Heilongjiang Liaoning Hebei Ningxia Henan Shanxi Shanghai Sichuan Hubei Jiangxi Fujian Guangxi Mean 2011 Heilongjiang Jilin Liaoning Neimenggu Hebei Ningxia Qinghai Henan Shanxi Shanghai Sichuan Hubei Jiangxi Fujian Guangxi Guangdong Mean

Number of participants

Age Average age

Age range

50 50 40 50 50 50 50 30 50 50 50 50 -

25.8 26.4 27.7 25.2 27.6 26.9 27.1 24.2 25.7 23.9 26.0 28.1 26.2

21-30 20-31 21-35 20-36 21-35 21-35 23-35 20-29 19-30 18-33 21-29 23-34 -

50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 -

29.4 28.0 28.1 26.2 26.5 24.6 27 22.5 25.6 26.8 24.9 26.8 24.3 27.0 27.5 28.2 26.5

22-37 22-35 22-35 21-35 20-32 18-35 20-36 20-35 20-29 22-35 18-39 22-36 17-29 22-35 21-34 22-36 -

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Table 2. Concentrations (ng/g lipid) of SCCPs, MCCPs, and congener groups in mothers’

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milk samples from 12 Chinese provinces in 2007 and 16 provinces in 2011 Provinces

2007 Heilongjiang Liaoning Hebei Ningxia Henan Shanxi Shanghai Sichuan Hubei Jiangxi Fujian Guangxi Minimum Maximum Mean Median 2011 Heilongjiang Jilin Liaoning Neimenggu Hebei Ningxia Qinghai Henan Shanxi Shanghai Sichuan Hubei Jiangxi Fujian Guangxi Guangdong Minimum Maximum Mean Median

Percent lipid

∑SCCPs

∑MCCPs

SCCPs concentration ∑C10

∑C11

∑C12

∑C13

MCCPs concentration ∑C14

∑C15

∑C16

∑C17

3.5 3.3 3.0 4.5 2.8 3.9 3.5 2.7 3.0 4.1 3.9 5.0 2.7 5 3.6 3.5

366 1550 6150 175 3010 721 1140 170 215 1230 641 263 170 6150 1300 681

213 677 2180 106 1740 375 460 35.6 112 607 225 174 35.6 2180 575 300

111 392 2040 48.1 796 261 326 75.5 45.4 393 222 63.9 45.4 2040 397 241

32.9 278 1010 15.1 276 64.5 194 42.7 36.4 140 104 15.1 15.1 1010 184 84.2

8.72 202 905 6.39 195 21.0 157 16.0 21.0 91.4 89.9 9.53 6.39 905 143 55.4

21.4 170 350 19.5 243 91.3 107 18.7 26.7 76.0 44.9 26.6 18.7 350 99.6 60.4

17.76 153 274 17.0 184 62.3 97.4 13.8 22.9 57.5 40.2 16.8 13.8 274 79.7 48.8

2.30 11.7 58.3 1.80 46.0 16.6 7.78 2.64 3.02 14.4 3.34 3.78 1.80 58.3 14.3 6.48

0.64 2.75 14.8 0.56 10.4 1.50 1.22 1.25 0.55 3.43 0.62 3.18 0.55 14.8 3.41 2.12

0.21 2.07 2.73 0.17 1.82 10.8 0.38 1.00 0.22 0.72 0.70 2.77 0.17 10.8 1.97 1.08

3.5 3.2 3.4 4.3 3.2 4.4 4.5 3.0 3.9 3.5 2.9 3.0 3.9 3.9 4.5 4.0 2.9 4.5 3.7 3.7

489 368 2180 131 16100 478 203 7060 977 2530 465 1180 1981 1650 342 355 131 16100 2280 733

342 204 1230 16.9 6820 252 124 4210 501 607 135 370 983 613 175 248 16.9 6820 1050 356

126 108 681 26.3 5870 162 50.1 2270 318 839 206 504 541 644 98.2 82.0 26.3 5870 783 262

17.1 37.8 155 33.3 2170 34.5 18.3 453 126 699 88.6 230 290 199 44.0 17.3 17.1 2070 288 107.3

3.43 18.8 114 31.4 1230 29.1 11.4 190 32.2 389 34.5 75.7 167 193 23.8 8.13 3.43 1230 159 33.3

28.5 63.9 409 22.3 1501 40.2 47 736 64.8 355.7 37.3 108 126 102 43.5 47.5 22.3 1501 233 64.3

22.8 41.4 321 13.4 1110 27.5 35.0 651 50.6 327.4 24.7 88.2 91.2 80.2 26.2 35.3 13.4 1110 184 46.0

4.28 10.4 43.6 5.20 171 6.15 5.36 72.8 8.79 20.1 5.57 13.0 21.8 16.9 7.12 5.42 4.28 171 26.0 9.59

1.14 7.42 23.5 2.88 102 2.63 3.19 10.6 3.10 5.70 3.95 4.38 9.18 3.56 5.64 3.22 1.14 102 12.0 5.40

0.29 4.68 23.5 0.85 113 3.96 3.55 2.07 2.33 2.51 3.09 2.40 3.95 0.80 4.50 3.59 0.29 113 10.9 3.57

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