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Significance of Anthropogenic Factors to Freely Dissolved Polycyclic Aromatic Hydrocarbons in Freshwater of China Yao Yao, Chun-Li Huang, Ji-Zhong Wang, Hong-Gang Ni, ZeYu Yang, Zhi-Yong Huang, Lian-Jun Bao, and Eddy Y. Zeng Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 27 Jun 2017 Downloaded from http://pubs.acs.org on June 27, 2017

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Environmental Science & Technology

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Significance of Anthropogenic Factors to Freely Dissolved

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Polycyclic Aromatic Hydrocarbons in Freshwater of China

3 4

Yao Yao,†,¥ Chun-Li Huang,‡ Ji-Zhong Wang,§ Hong-Gang Ni,║ Ze-Yu Yang,⊥

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Zhi-Yong Huang,‡ Lian-Jun Bao,*,‡ and Eddy Y. Zeng†,‡

6

†

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Chinese Academy of Sciences, Guangzhou 510640, China

8

‡

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and Guangdong Key Laboratory of Environmental Pollution and Health, Jinan University,

State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry,

School of Environment, Guangzhou Key Laboratory of Environmental Exposure and Health

10

Guangzhou 510632, China

11

§

12

Hefei, 230009, China

13

║

14

University, Shenzhen 518055, China

15

⊥

16

Ottawa, K1A0H3, Canada

17

¥

School of Resources and Environmental Engineering, Hefei University of Technology,

Shenzhen Key Laboratory of Circular Economy, Shenzhen Graduate School, Peking

Emergencies Science and Technology Section, Environment and Climate Change Canada,

University of Chinese Academy of Sciences, Beijing, 100049, China.

18 19

ABSTRACT: Assessment of surface water pollution by organic pollutants is a top priority

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in many parts of the world, as it provides critical information for implementing effective

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measures to ensure drinking water safety. This is particularly important in China, where

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insufficient data of national scale have been acquired on the occurrence of any organic

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pollutants in the country’s water bodies. To fill the knowledge gap, we employed passive

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samplers to survey polycyclic aromatic hydrocarbons (PAHs) in 42 freshwaters throughout 1 Environment ACS Paragon Plus


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the country. The dissolved ∑24PAH concentrations ranged from 0.28 to 538 ng L-1, with the

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highest and lowest values obtained in Southern Lake in Wuhan and in the Nam Co Lake in

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Tibet, respectively. Average ∑24PAH concentrations in West, Central and East China

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correlated well with the population densities in these regions. The composition profiles of

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PAHs showed a mixed PAH source of coal combustion, fossil fuel combustion and oil spills.

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In addition, all dissolved PAH concentrations were below the water guidelines developed by

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the U.S. Environmental Protection Agency, the European Union and the Canadian

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government, except for anthracene in Southern Lake. Our results also demonstrated the

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feasibility of establishing a global network of monitoring organic pollutants in the aquatic

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environment with passive sampling techniques.

2 Environment ACS Paragon Plus

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INTRODUCTION The United Nations estimates that more than two-thirds of the global population will

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live in cities by 2050.1 Rapid urbanization has created overpopulated metropolis, resulting in

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inadequate waste treatment and disposal capacity, deterioration of water quality, shortage of

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drinking water and other health issues.2-6 Intensified human activities have aggravated water

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pollution, because organic pollutants of anthropogenic origin can deposit in marine and

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freshwater systems through effluent discharge, atmospheric fallout, surface runoff and other

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means.7 One of the most important groups of organic contaminants, polycyclic aromatic

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hydrocarbons (PAHs), have been shown to cause adverse effects on humans and wildlife

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because of their widespread occurrence, toxic potency and bioaccumulative ability through

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the aquatic food web.8-10 In many cases, often the freely dissolved or bioavailable

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concentration instead of total concentration is directly related to bioaccumulation and human

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exposure to organic contaminants.11-13

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Yet measurement of freely dissolved organic contaminants on a large spatial scale,

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which is critical for identifying trends and patterns, is no trivial task. Passive sampling

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approach, capable of simultaneously sampling in a large range of areas, is beneficial in this

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aspect.11 Among the available passive samplers, devices with low density polyethylene

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(LDPE) as the sorbent phase have been recommended as a preferred alternative for sensing

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organic contaminants in aquatic environments because they are consistent, biomimetic,

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inexpensive, and convenient for field deployment.14-16

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Enormous economic development and urbanization in China has created severe water

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pollution issues, which however has not been adequately monitored.12, 17 One of the reasons

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is obviously that China’s vast territorial area, amounting to more than 960 million square

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kilometers, is posing a great challenge to any monitoring effort. On the other hand, China’s

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variable geographical settings and population distribution patterns present an unparalleled



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opportunity for examining whether freshwater quality has been significantly impacted by

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anthropogenic activities. Building on our previous efforts in development of robust passive

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samplers for sensing organic contaminants in open waters,18, 19 we conducted a large-scale

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survey to examine water quality in China using passive sampling techniques. The present

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campaign was also a preliminary study for a recent effort to establish the Aquatic Global

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Passive Sampling (AQUA-GAPS) network.11

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The objectives of the present study were to (1) better understand the geographical

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distribution of freely dissolved PAH concentrations in freshwater systems of China; (2)

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examine the relationship between freely dissolved PAH concentrations and regional

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population densities to elucidate the impacts of anthropogenic activities on water quality and

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(3) diagnose the potential sources of PAHs in the freshwater systems under investigation. In

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the last decade, numerous studies have been conducted on the occurrence of organic

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contaminants in freshwater of China, which however were largely focused on East China,

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such as the Yangtze River Delta and the Pearl River Delta.12, 20, 21 To accomplish the

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objectives mentioned above, we deployed a self-developed passive sampler in a wide range

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of regions in West, East and Central China with large gradients in population densities and

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levels of economic development. The passive sampler with LDPE as the sorbent phase and a

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copper box as protecting mechanism was demonstrated to be a useful tool for quantifying

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freely dissolved organic contaminants in seawater (Hailing Bay) and in freshwater lakes of

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Antarctica.18, 19

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MATERIALS AND METHODS Passive Sampler Preparation. Materials, passive sampler preparation and

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deployment procedures, geographic information and characteristics of each sampling site are

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listed in the Supporting Information Text S1 and Tables S2-S3. Briefly, samplers were


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deployed at 42 sites, located mainly in Northeast (Songhua River Basin and Liaohe River

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Basin), Central and East (Yangtze River Basin) and Northwest (lakes and reservoirs of the

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Xinjiang Uygur Autonomous Region) China in July to November, 2013 and Southwest (lakes

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of the Tibet Plateau) China in May to September, 2015. All LDPE strips were spiked with

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the performance reference compounds (PRCs), i.e., anthracene-d10, benzo[a]anthracene-d12,

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benzo[a]pyrene-d12, PCB-29, PCB-61, PCB-155, p,p′-DDT-d8, p,p′-DDD-d8 and p,p′-DDE-d8,

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by soaking in a mixed solution (Vmethanol:Vwater = 50:50) for 30 d before deployment (placed

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on a shaking bed at 200 r min-1 in dark). The prepared LDPEs were wrapped in clean

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aluminum foil and kept in ice chests during transport to the sampling sites. At each sampling

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site, at least three passive samplers were deployed approximately one meter below the water

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surface for 15 d with 100 m or longer distance from each other depending on the sizes of the

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target lakes or reservoirs. To reduce inshore influences, the samplers were placed as far away

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as possible from the watersides. Upon retrieval, the sampling devices were disassembled,

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and the LDPE strips were retrieved and maintained in ice chests during transport to the

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laboratory. A total of 40 top surface (0‒5 cm) soil samples were collected at the same time

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when passive samplers were deployed; soil samples were not available at several sites. The

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procedures for collecting and extracting soil samples are described in Text S2.

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Extraction of Polyethylene Strips. The LDPE strips were rinsed with purified water

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and cut into small pieces (about 2 cm × 2 cm), wrapped in filter paper (sonicated with

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dichloromethane and methanol three times each and dried before use) and extracted three

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times by soaking in 200 mL of hexane for 24 h. The surrogate standards were added to each

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sample before extraction. Three extracts from each sample were combined and concentrated

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to approximately 10 mL with a Zymark Turbo Vap II (Hopkinton, MA) at 30 °C. After

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dehydration with sodium sulfate, the extract was reduced to 0.5 mL with the Zymark Turbo

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Vap II and purified on a glass column (8 mm inner diameter), packed with neutral alumina



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(0.8 g), neutral silica gel (0.8 g) and sodium sulfate (0.5 cm) from bottom to top. The eluate

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was condensed to 100 µL and spiked with internal standards, i.e., fluorene-d10, pyrene-d10,

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dibenzo[a,h]anthracene-d14, PCB-24, PCB-82 and PCB-189 prior to instrumental analysis.

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Specifically, fluorene-d10, pyrene-d10 and dibenzo[a,h]anthracene-d14 were used to quantify

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PAHs, whereas PCB-24, PCB-82 and PCB-189 were used to determine the concentrations of

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PCB or DDT compounds. Detailed instrumental analysis are described in Text S1.

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Quality Assurance and Quality Control. One field blank and one initial PRC

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concentration blank were processed at each sampling site and one laboratory blank were

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processed for every batch of 20 samples. Overall, there were 39 sampling sites with 134 field

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samples and 62 blank samples retrieved (including field, field-trip and laboratory blank

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samples). The concentrations of target PAHs in blank samples were lower than 10% of those

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in the corresponding field samples. The concentrations of PAHs in field samples were blank-

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subtracted using each specific field blanks from the corresponding site but not corrected for

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the surrogate standard recoveries. Because naphthalene was quite abundant in several LDPE

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samples, it was excluded from further analyses. The recoveries of the surrogate standards,

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i.e., naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12, PCB-67 and PCB-191,

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were 52±10%, 79±13%, 100±13%, 112±21%, 98±25% and 77±22% in all blank samples and

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47±11%, 84±10%, 104±12%, 108±20%, 98±20% and 77±19% in the field samples. The

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reporting limit (RL) was calculated from the lowest calibration level divided by the mass of

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LDPE (about 4 g for each passive sampler). It was 1.25 ng g-1 for each LDPE passive

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sampler for all target analytes except IcdP, DahA and BghiP (the abbreviations of PAH

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compounds are listed in Table S1), which had a RL of 2.5 ng g-1 for their relatively low mass

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spectral responses. The concentrations of target PAHs were all below RLs in re-extracted

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LDPE samples.


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Data Analysis. To determine dissolved PAH concentrations (Cw), the sampling rate

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(Rs) of a target analyte at each sampling site was calculated via a kinetically diffusion-

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controlled quantitation method,16, 22 i.e.,

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Cw =

Cpe   Rs t K pew 1 − exp(− ) K pew M pe  

(1)

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where Cpe is the analyte concentration in LDPE at sampling time t, Kpew is the equilibrium

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partition coefficient of the target analyte between LDPE and water, Rs is the sampling rate

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and Mpe is the LDPE mass.16 The Kpew values of PAHs (Table S1) were adopted from the

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results of Reitsma et al.23 under ambient conditions (25 oC and 0 psu), similar to the

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conditions in the present study. Rs can be estimated by the dissipation rates of pre-loaded

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PRCs using linear regression and molecular volume adjustment (Table S4). Procedures for

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calculating Cw and associated errors were detailed in our previous study.18

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Ratios of several paired PAH isomers with similar physicochemical properties have

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been employed to diagnose emission sources of PAHs derived from passive sampling

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techniques, such as Flu/(Flu+Pyr), Ant/(Ant+Phe) and BaA/(BaA+Chr).14, 15, 24-26 If the

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dissolved concentrations of individual PAH isomers were below the reporting limits, such as

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Phe, Ant and BaA at TI-1 and TI-3 sites, BaA at LH-3 and XJ-8 sites and Phe at YR-7 site,

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the corresponding paired PAH diagnostic ratios were excluded for source assessment.

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RESULTS AND DISCUSSION Spatial Trend of Freely Dissolved PAH Concentrations. Sampling rates (Rs) of

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PAHs varied at different sampling sites, and the average Rs was 6±4 L d-1 for Ant, 155±98 L

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d-1 for BaA and 1025±650 L d-1 for BaP. They increased with increasing log Kpew, which was

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similar to the results of other studies.14, 15 It should be noted that equilibrium partitioning

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between LDPE membrane and water may be reached for lighter PAH compounds with lower



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sampling rates than Ant, such as 2-mNap, 1-mNap, 2, 6-dimNap, ∑C2-Nap, BP, Acy, Ace

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and Flo at some sampling sites. On the other hand, the PAH concentrations in our sampling

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sites (most lakes and reservoirs) were assumed not to vary considerably during the 15-d

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sampling period. No floods and large point source inputs to the sampled water bodies were

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recorded during the sampling period. Thus the measured concentrations of these light PAHs

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may be taken as the water concentrations over the whole sampling period.

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The concentration data for individual PAHs, along with the sums of the 24 target PAHs

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specifically targeted in the present study (∑24PAH), 15 priority PAHs (∑15PAH) designated

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by the United States Environmental Protection Agency (USEPA) except naphthalene and 7

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carcinogenic PAHs (∑7PAH; the sum of BaA, BbF, BkF, BaP, IcdP, DahA and BghiP)

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classified by the USEPA, are presented in Tables S5-S10. The ∑24PAH, ∑15PAH and

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∑7PAH concentrations in lakes and reservoirs along Songhua River and Liaohe River located

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in the Northeast China (Figure 1) were in the ranges of 1.7−11.3 ng L-1 (mean: 7.2 ng L-1),

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1.2−5.9 ng L-1 (mean: 3.9 ng L-1) and not detected (ND)−67 pg L-1 (mean: 18.5 pg L-1),

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respectively.

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Compared to Songhua River and Liaohe River, the PAH concentrations in lakes and

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reservoirs of the Xinjiang Uygur Autonomous Region located in Northwest China (Figure 1)

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were lower, i.e., the ∑24PAH, ∑15PAH and ∑7PAH concentrations were in the ranges of

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1.3−16.4 ng L-1 (mean: 6 ng L-1), 0.7−6.7 ng L-1 (mean: 3 ng L-1) and ND−32 pg L-1 (mean:

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11 pg L-1), respectively. The PAH concentrations in the Yangtze River flowing through

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Central and East China (Figure 1) were the highest among all the regions, i.e., the ∑24PAH,

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∑15PAH and ∑7PAH concentrations were 4−538 ng L-1 (mean: 56 ng L-1), 1.4−294 ng L-1

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(mean: 29 ng L-1) and 7.4−503 pg L-1 (mean: 58 pg L-1), respectively. The greatest

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concentration among all sampling sites occurred at Southern Lake, an urban lake within

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Wuhan heavily polluted by urban wastewater derived from surrounding factories and


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residents.27 Southern Lake was therefore identified as a point source and excluded from the

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following discussions. The PAH concentrations in lakes of Tibet located in Southwest China

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(Figure 1) were the lowest among all sampling regions, with the∑24PAH, ∑15PAH and

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∑7PAH concentrations in the ranges of 0.28−0.8 ng L-1 (mean: 0.54 ng L-1), 0.01−0.05 ng L-1

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(mean: 0.03 ng L-1) and ND−0.52 pg L-1 (mean: 0.3 pg L-1), respectively.

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Anthropogenic Impacts on Levels of Freely Dissolved PAHs. Freshwater PAH

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levels (average ∑24PAH) gradually increased from west to east, i.e., 5.4±4.3, 11±11 and

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12±13 ng L-1, in Western (Tibet and Xinjiang), Central (the upper and middle reaches of the

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Yangtze River) and Eastern (the lower reaches of the Yangtze River, Liaohe River and

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Songhua River) China (Figure 1). This spatial pattern was correlated well with the

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distribution of regional population densities (Table S11), with the determination coefficients

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(r2) between the concentrations of ∑24PAH, ∑15PAH and ∑7PAH and the population densities

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at 0.95 (p < 0.0001), 0.87 (p < 0.0005) and 0.36 (p = 0.07) (Figure 3). Similarly, the

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concentrations of ∑24PAH and ∑15PAH also correlated well with the ratio of gross domestic

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product/land area (billion km-2; Table S11), with the determination coefficients (r2) at 0.97 (p

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< 0.0001) and 0.97 (p < 0.0001), respectively (Figure S1). The correlation between ∑7PAH

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concentrations and the ratio of gross domestic product/land area was not significant (r2 = 0.25

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and p = 0.25; Figure S1). The use of more target compounds appeared to yield better

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correlation, which implies that (1) dissolved PAHs in the freshwater bodies may have derived

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from multiple sources related to complicated anthropogenic activities and (2) there is an

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urgent need to identify suitable parameters for better describing anthropogenic activities.

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McDonough et al.14 also obtained a significant correlation between the concentrations of

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gaseous PAHs and population densities in the lower Great Lakes. In addition, the correlation

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between the concentrations of dissolved PAHs in surface water and PAHs in the surrounding



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soil was poor (r2 < 0.1; Figure S3), suggesting no significant contribution from nearby soil to

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the occurrence of PAHs in freshwaters.

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Besides population density, industrialization may also be an important factor. The

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population densities of Songhua River Basin and Liaohe River Basin are quite similar to each

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other (263 and 292 persons km-2, respectively),28, 29 but the ∑7PAH concentrations in

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Songhua River Basin were one to two orders of magnitude higher than those in Liaohe River

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Basin, with high levels around the city of Jilin (Figure 1). Government data30 showed that the

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amounts of industrial wastewater discharged to Songhua River Basin were much greater than

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those discharged to Liaohe River Basin over the years of 2004−2006 and 2011−2012 (Figure

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2). A great number of factories are situated along the banks of Songhua River, including

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steel, petrochemical, pulp and paper and machinery mills.30 These manufacturing plants

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discharge large amounts of insufficiently treated wastewater to Songhua River. Accidental

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spills have also been identified as input sources of organic chemicals, heavy metals, nitrogen-

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containing substances and other pollutants.31-33

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Worldwide Comparison of Freely-Dissolved PAH Levels. The concentrations of

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freely dissolved PAHs in the present study were in the middle range of those reported

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worldwide (Table 1). After excluding samples collected from the middle and lower Yangtze

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River, however, the concentrations of ∑15PAH (0.4‒10 ng L-1) in the present study were

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much lower than those reported previously in freshwaters. For example, concentrations of

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∑15PAH were 8.6‒48 ng L-1 in the Meuse-Marne Canal downstream of Paris, France,34

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9.5‒66 ng L-1 in rivers close to Johannesburg of South Africa24 and 2.8‒29 ng L-1 in the

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Danube river between Vienna and Bratislava.35 Our previous study also obtained low

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concentrations of ∑15PAH (

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