Addressing the environmental risk of persistent organic pollutants in ...

Front. Environ. Sci. Engin. 2012, 6(1): 2–16 DOI 10.1007/s11783-011-0370-y

FEATURE ARTICLE

Addressing the environmental risk of persistent organic pollutants in China Bin WANG, Jun HUANG, Shubo DENG, Xiaoling YANG, Gang YU (✉) POPs Research Center, School of Environment, Tsinghua University, Beijing 10084, China

© Higher Education Press and Springer-Verlag Berlin Heidelberg 2011

Abstract The Stockholm Convention on persistent organic pollutants (POPs) was adopted in 2001. This year is the 10th anniversary of the adoption of the Convention. Until now, 22 chemicals or chemical categories have been listed as POPs in the Stockholm Convention. The POPs Research Center was established in Tsinghua University in the same year when the Convention was adopted. In the last ten years, much work has been done by Chinese researchers to understand the environmental risk of POPs in China. This article aims to review the recent research progress of our POPs Research Center and some other Chinese researchers’ studies in addressing the environmental risk of POPs, including the priority screening and inventory study of POPs, monitoring and modeling of POPs pollution and exposure, and environmental risk assessment and modeling of POPs. Although great advances in addressing the environmental risk of POPs have been made in recent years, we are still facing quite a few problems, such as data scarcity and uncertainty in environmental risk assessment of POPs. The study on the effect of POPs mixtures is in its infancy and currently POPs are usually assessed from legal perspective by risk assessment of single chemicals. These problems should be well addressed by further efforts. Further studies should also be taken in future to study environment risk of POPs by considering aspects of coupled dynamics between climate processes and POPs. Such sound scientific, riskbased information can support decision-making aiming to effectively minimize the risk level of POPs. Keywords persistent organic pollutant (POPs), environmental risk assessment, inventory, environmental monitoring, fugacity model, emerging POPs

Received August 7, 2011; accepted August 21, 2011 E-mail: [email protected]

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Introduction

The Stockholm Convention on persistent organic pollutants (POPs), adopted in 2001 and entered into force in 2004, is a global treaty to protect human health and the environment from hazardous chemicals that can persist in the environment for a long period, accumulate in human and wildlife, and hence pose potential risk to human and ecosystem. In the Stockholm Convention adopted in 2001, 12 legacy chemicals, including pesticides, industrial chemicals and unintentionally produced chemicals, were listed as the first group of POPs. Persistent toxic compounds can be reviewed and added to the Convention if they meet certain screening criteria for POPs. The 4th conference of the parties (COP-4) held in May 2009 listed 9 new POPs into the Convention, including α-hexachlorocyclohexane (α-HCH), β-HCH, lindane (γ-HCH), commercial octabromodiphenyl ether, commercial pentabromodiphenyl ether, chlordecone, hexabromobiphenyl, pentachlorobenzene (PeCBz), perfluorooctane sulfonic acid (PFOS), its salts and perfluorooctane sulfonyl fluoride (PFOSF) [1]. Endosulfan has also been listed as a new POP in COP-5 held in April 2011, due to its persistence, bioaccumulation, toxicity and long range transportation. As the largest developing country, China plays a very important role in the implementation of the Stockholm Convention. The international community has paid much attention to the POPs pollution in China. Most of the POPs have been mass-produced and widely used in China. POPs can be released to the environment during the production and usage, as well as in the end of life phase and from the deposits. Due to their potential for long range transportation, POPs have caused mild or severe pollution all over the country, and pose potential risk to human health and the environment. To understand the environmental risk of POPs in China, Chinese researchers have conducted much work not only on the environmental risk assessment of POPs, but also on POPs inventory, environmental pollution and exposure, and modeling which can provide

Bin WANG et al. Addressing the environmental risk of POPs in China

scientific information to assess the environmental risk of POPs in China. This article mainly aims to review the recent research of our POPs Research Center, which also hosts the Stockholm Convention Regional Centre in Asia and the Pacific, as well as some other Chinese researchers’ work in addressing the environmental risk of POPs. These studies can guide future research and risk management of such POPs. It should be pointed out that this article also addresses some emerging chemicals which are not listed as POPs under the Convention, but most likely meet the POP criteria.

Robust priority screening requires a comprehensive database of property data, toxicity data, inventory data, and environmental exposure data. Estimation models, such as quantitative structure-activity relationship (QSAR) model [4,5] and fate model [6] are also very important if such data are not available. The screening for high-risk pollutants based on their hazardous properties and relative risk levels would help to decide the allocation of limited funds and resources to priority chemicals, from both research aspect and management aspect. 2.2

2 Priority screening and inventory study of POPs 2.1

Priority screening

Priority screening is to screen the priority chemicals that may pose hazardous effect or environmental risk. Priority screening involves a comprehensive evaluation of the properties, toxicities, environmental exposure, and potential environmental risks of chemicals. A dedicated article in the Stockholm Convention text encourages the parties to screen the potential POPs. According to the criteria for identifying the potential POPs listed in the Annex D of Stockholm Convention on POPs, we introduced computer-aided tools to the screening for the existing POPs in China from the “Inventory of Existing Chemical Substances in China (version 2000)”. The results show that 111 chemicals were identified as potential POPs. Further analysis of the results illustrated the applicability of computer-aided tools in primary screening for potential POPs [2]. Currently, under the support of the National High-Tech Research and Development Program (863 Program), this work is further developed by our POPs Research Centre by updating and refining the screening of priority chemicals produced or used in China which have POPs characters and may pose potential environmental risk. Sewage treatment plants (STPs) are a sink and destination of a large quantity of pollutants from industry and society and depending on the technologies applied and the management of releases are sources for environmental pollution. We also made a priority screening for some categories of hazardous chemicals, including industrial chemicals, pesticides, natural estrogens, and pharmaceuticals, in STPs of China [3]. Most of them are POPs or POP-like chemicals. Ecological risk quotients and estradiol equivalent concentrations of these hazardous chemicals were calculated and analyzed using concentrations in secondary effluents from STPs in China. Based on scoring and ranking, four priority hazardous chemicals in STPs were suggested for priority control in China, including 17α-ethynylestradiol, estrone, nonylphenol, and bisphenol A.

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Inventory study

POPs inventory investigation is a way to understand the current status of production, usage or discharge of POPs. This is also one important first step of the implementation of Stockholm Convention. Such information is useful for the evaluation of the potential exposure risk of POPs at the macroscopic level. Based on the inventory, we can screen the priority sources, priority pollutants, and hence perform environmental risk assessment and sound management of such pollutants. To date, China has conducted inventory studies on polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polychlorinated dibenzo-pdioxins and furans (PCDD/Fs), and is currently establishing the inventories of the new listed POPs, such as PFOS. 2.2.1

Inventory study of PCBs

The Stockholm Convention requires its parties to make determined efforts to identify PCB containing products and materials, as well as manage them in an environmentally sound manner. China is obligated to carry out its national PCB inventory. In China, approximately 10000 t of PCBs were produced from 1965 to 1974, including 9000 t of trichlorobiphenyl and 1000 tons of pentachlorobiphenyl [7]. Based on the international experience from United Nations Environment Programme (UNEP) and some developed countries, as well as the domestic situation, we analyzed and solved several key problems, including the identification of investigation objects, focused sectors, and investigation approaches, and then developed the China PCB inventory methodology [8]. The established inventory methodology was put into practice for demonstration study in Zhejiang Province and Liaoning Province, so as to verify the applicability of the methodology. The study has given guidance in determining the usage, storage, waste and disposal of PCB containing equipment as well as the impact on surrounding environment and finally the national PCB inventory data [9]. The general distribution of existing PCBs in China is shown in Fig. 1. 2.2.2

Inventory study of OCPs

Most of the POPs in the Stockholm Convention are OCPs

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Front. Environ. Sci. Engin. 2012, 6(1): 2–16

Fig. 1 General distribution of existing PCBs in China

[10]. Being one of the countries with the largest agricultural production, China has once been a major producer and consumer of OCPs, such as dichlorodiphenyl-trichloroethanes (DDTs), HCHs, hexachlorbenzene (HCB), chlordane, and mirex [11]. From 1950s to 1980s, the productions of HCHs and DDTs in China were 4.9 million t and 0.4 million t, accounting for 33% and 20% of the total world production, respectively [12]. Since 2009, in order to implement the Stockholm Convention, China has completely prohibited the production, usage, and circulation of DDT, chlordane, mirex, and HCB. However, endosulfan is still being widely produced and used in China. The largest emission source of OCPs is its application directly to fields, and thus, entrance to the soil, air, and aquatic environment. Emissions have been directly estimated based on crop types and land usage areas, application frequency, residual measurements, and climatic factors, which are generally available through regulatory agencies’ records. Until now, the inventories of DDT [13], HCH [14,15], chlordane [13,16], mirex [16], and endosulfan [17,18] have been established. Such inventories can be used to evaluate the general pollution and environmental risk of OCPs in China [19,20]. 2.2.3

tions should be performed for five acceptor media (air, water, land, product, and residue) for each process identified [23]. Extensive surveying of relevant industries and sources of PCDD/Fs was carried out in China. If the data collected was not sufficient to calculate an emissions factor, default or similar situation emissions factors from the UNEP toolkit or from published literature were utilized to make the China-specific inventory (Fig. 2). As a result, the annual dioxin release in China is estimated to be about 10 kg toxic equivalent (TEQ ) [24]. Open burning is the most significant source of PCDD/Fs in the national inventories of many countries. This is particularly true for developing countries. According to our study, annual emissions of PCDD/Fs from open burning of

Inventory study of PCDD/Fs

PCDD/Fs, the unintentionally produced legacy POPs, have been poorly characterized in the environmental matrices in China due to limited instrumentation and trained personnel [21]. A national inventory for dioxins was completed in China with guidance from the UNEP “Standardized Toolkit for Identification and Quantification of Dioxin and Furan Releases” [22]. In the toolkit, there are 10 main categories of emission sources. Each category includes some relevant emission sources. For each source, calcula-

Fig. 2 Flow chart diagram of China dioxin emission inventory methodology [24]


crop residues in each province of China mainland between 1997 and 2004 were estimated to be 1380–1520 g TEQ$a–1, which contributed to approximately 10%–20% of the total emissions in China [25]. Open burning of crop residues has been identified as an important emission source of PCDD/Fs. We studied the influence of pesticide contamination on the land emission of PCDD/Fs from open burning of corn straws. The concentrations released from burning of the contaminated straws were 35–270 times higher than that without additional pesticide contaminated [26]. Pesticide contamination should be considered in some hotpots where special pesticides have been sprayed. We also determined the emission factors for PCDD/Fs released from open burning of municipal solid waste through waste composition characterization study and field burning tests [27]. Emission factors determined in this study are lower than the emission factor of 300 ng TEQ$kg–1 originally proposed in the Toolkit, and have been taken into account in recent revisions. 2.2.4

Inventory study of PFOS

PFOS is a man-made chemical, which has been listed in Stockholm Convention due to its hazardous property and potential risk. Its use in a wide variety of consumer products and industrial processes make a detailed characterization of its emissions sources very challenging. These varied emissions sources all contribute to PFOS’ existence within nearly all environmental media. Currently, China is the only country documented to still be producing PFOS, though there is no China PFOS emissions inventory available. We reviewed the inventory methodologies for PFOS in some developed countries and suggested a China-specific methodology framework for a PFOS emissions inventory [28]. The suggested framework combines unknowns for PFOS-containing product penetration into the Chinese market with product lifecycle assumptions, centralizing these diverse sources into municipal STPs.

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3 Monitoring and modeling of POPs pollution and exposure 3.1

Monitoring of POPs pollution and exposure

Environmental monitoring is the direct way to understand the pollution source and environmental exposure of POPs. POPs are so diverse that various methods, including chemical analysis and bioassay methods, have been used for their environmental analysis. Great efforts have been made to monitor POPs in environment as the initial steps for environmental risk assessment. 3.1.1

Chemical analysis of POPs

Chemical analysis is the most common method for POPs analysis in the environment, organism bodies and STPs. Usually gas chromatography with electron capture detection (GC-ECD), gas chromatography/mass spectrometry (GC/MS), high-performance liquid chromatography (HPLC), high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS), or HPLC/MS/ MS are used for the chemical analysis of POPs or POP-like compounds. Environmental monitoring usually includes the monitoring of natural environment to evaluate the environmental quality and some hotspots to understand the risk sources. We have determined various POPs in some typical water bodies in China, such as polycyclic aromatic hydrocarbons (PAHs), PCBs, OCPs, PCDD/Fs, and polybrominated diphenyl ethers (PBDEs), in Tonghui River [29], Huaihe River [30], Minjiang River [31], Jinsha River [32], Haihe River, and Bohai Bay [33–36]. Our research, together with other relevant studies, can help us understand the general pollution status of POPs in China. Almost all the water bodies in China have been polluted by POPs. Here, we summarize the results of recent research on some typical POPs (DDTs and HCHs) in some water bodies in China (Fig. 3). It is shown that such POPs

Fig. 3 DDTs and HCHs in water bodies in China: (a) sediment; (b) water

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varied much in different water bodies. Even for the same water body, great variation of pollution levels was observed for different sampling sites. Figure 3 shows that relatively high sediment levels of DDTs were observed in Haihe River and its tributaries, Jiulong River, Qiantang River and Jingzhou Bay, and these water bodies, except Jiulong River, also had relatively high levels of HCHs in sediments. Haihe River and its tributaries, Bohai Bay and Daya Bay were subjected to relatively heavy water pollution of both DDTs and HCHs. China has produced some POPs for a long time. The industrial activities may cause heavy POPs pollution in the hot spots and their surrounding environment. POPs monitoring and investigation in such areas are helpful to evaluate the potential risk posed by such POPs to the human and environment. Mirex is one of the two effective OCPs used in China for termite control. We employed a HRGC/HRMS to analyze mirex in Liyang City, which once was an important mirex production base in China [19]. The detected mirex levels in soil in Liyang were 2.9–4300 pg$g–1 dw. The highest level occurred at the site near the Liyang Guanghua Chemical Factory. It implies the contribution of industrial activities to the mirex pollution in the surrounding environment. However, the factory only influenced very limited adjacent areas. Dechlorane Plus (DP) has been used as a highly chlorinated flame retardant substituting those that are now internationally regulated under the Stockholm Convention. The DP levels in Huai’an City, where the DP manufacturer is located, were determined by GC/MS in electron capture negative ionization (ECNI) mode [37]. The DP levels in soil ranged from 0.83 to 1200 ng$g–1 dw. The main DP pollution source is the commercial DP product. The above DP manufacturer is also the largest endosulfan producer. So we also determined endosulfans in the same area. The endosulfan levels in soil in Huai’an ranged from 0.28 to 45 ng$g–1 dw. The manufacturer is the point pollution source with the highest endosulfan level in its surrounding area. However, the non-point agricultural endosulfan sources are more important. Our study also showed that endosulfans posed a potentially high risk to soil organisms. 3.1.2

Bioassay of POPs

Until about ten years ago, HRGC/HRMS was the only option and the “gold standard” for dioxin analysis [38], which, however, is a time-consuming, expensive and complicated method. Moreover, HRGC/HRMS analysis only provides information about the concentrations of several target dioxin-like compounds (DLCs), such as 17 PCDD/Fs and 12 dioxin-like PCBs (dl-PCBs), but little information on the total biologic effect of the samples is available, particularly when there are complicated interactions among various DLCs and other compounds. As an alternative, the Chemically Activated LUciferase gene

eXpression (CALUX) bioassay, which is a faster and cheaper method, can provide a comprehensive measure of total aryl hydrocarbon receptor (AhR) activity and the potential hazard. CALUX bioassay, which was verified by HRGC/HRMS method, was employed to determine the total levels of DLCs, including PCDD/Fs and dl-PCBs, in extracts of sediments from the Haihe River [39]. We found that the levels of PCDD/Fs in the sediments from the Haihe River were tens of times to hundreds of times higher than those of dl-PCBs. Significant correlation was observed between the PCDD/Fs TEQs and dl-PCBs TEQs. Due to the industrial activities of pentachlorophenol in the adjacent area, high levels of DLCs were found at the sites near the influx into Bohai Bay. We also applied CALUX to characterize dioxin-like activity in the sludge of all the nine municipal sewage treatment plants from Beijing city [40], and found that anaerobic-aerobic-anoxic sewage treatment process cannot reduce dioxin-like activity effectively. Except CALUX, other bioassay methods, such as enzyme immunoassay (EIA) and ethoxyresorufin-Odeethylase (EROD) methods, have also been recently used in China for POPs analysis, especially DLC analysis [41–43]. Bioassay methods, as cost-effective tests, are useful for developing countries in monitoring programs to obtain baseline data about the scale of contamination and general environmental risk caused by POPs. It is also a useful component in the POPs monitoring capacity building. 3.1.3

Pollution of emerging POPs

More information about the POPs in China can be referred to the following reviews about OCPs [11,44], PCBs [7], PCDD/Fs [45,46], and emerging POPs [1]. Now, the emerging POPs have caused more attention. Some emerging POPs, such as PBDEs, PFOS, short chain chlorinated paraffins (SCCPs), and endosulfan are currently manufactured and used in China. Pharmaceuticals and personal care products (PPCPs) pollution has also caused our concern due to its hazardous effect, “pseudopersistence” in the environment and huge production and consumption in China [47]. Understanding the levels of emerging POPs in environmental matrices in China can help understand their environmental risks and efficiently and effectively implement the Stockholm Convention. Table 1 summarizes the situation of some emerging POPs in China, including PBDEs and PFOS which are newly listed in the Stockholm Convention, as well as DP and SCCPs, which have not been listed into the Convention [1,37,48–53]. However, few data are available to understand the long-term temporal variations of the environmental levels of such emerging POPs. More work should be done to strengthen local monitoring capacity for


emerging POPs in China to further investigate their pollution status. 3.2

Modeling of POPs pollution and exposure

Environmental monitoring based on chemical analysis or bioassay can provide important information on POPs pollution. However, in some cases, such information is rather scarce in China. To evaluate the POPs pollution status in China, comprehensive and consecutive monitoring seems to be necessary. However, it needs massive manpower, material and financial resources. Developing suitable models to estimate the pollution status of POPs in the environment and in the organisms exposed to the POPs in the environment is a feasible alternative to fill the data gap. 3.2.1

Multimedia fugacity model

Various models can be used for the simulation of the fate of POPs in the environment. Among them, multimedia fugacity model is an excellent one. Chinese researchers have attempted to develop Level III and Level IV multimedia environmental fugacity models to study Table 1

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POPs transportation and fate in the environment in China [54–56]. We developed a Level III multimedia fugacity model based on an approach of Mackay [57] and applied it to simulate the fate of POPs in China. Four bulk compartments (e. g. air, water, soil, and sediment) are included in the model. Based on the model, the fugacity fi and the general POPs concentration in each compartment i can be calculated. The developed Level III fugacity model was used to study the DDT, mirex and chlordane pollution in Chinese provinces [19,20]. Figure 4 shows an example of the estimated mirex pollution in soil in China. The results show that the highest concentration occurred in Jiangxi Province, which has the largest consumption of mirex in China. On a regional scale, the calculated concentrations of mirex in the environment are generally so low that it indicates no harm to human and organisms. Based on the model results, the total amount of mirex existing in the environment in China was estimated to be about 25 t. 3.2.2

Food web model

Aquatic ecological risk assessment (ERA) is usually

Summary of emerging POPs in China (updated from [1])

POPs

PBDEs

PFOS

DP

SCCPs a)

POP-PBDEs (PentaBDE and OctaBDE) are not produced anymore in China, but the non-listed DecaBDE still is, which can degrade to POPPBDEs.

Mass produced. The productions Until 2009, there is only one China is the largest producer in 2004–2006 were 91, 165, DP factory in Jiangsu Province. of chlorinated paraffins (CPs). and 247 t, respectively. The output is about 300 tons. But the exact information However, its production about SCCPs production capacity will be increased by is unavailable. several times.

usage

Mass used as flame retardants.

Textile treatment, metal plating, Mass used as flame retardants. semiconductor production, and fire-fighting foams are the main industries in China that utilize PFOS, with consumption amounts of 100, 25, 0.5, and 80 t, respectively.

potential source

E-waste dismantling in During the Production and Guangdong and Zhejiang etc. Usage. STPs are also During the Production and identified to be important Usage. sources.

Mainly by usage. Production During the Production and Usage. may be an unimportant source STPs are also identified to be in China. E-waste dismantling important sources. maybe a significant source.

research status

Relatively well studied in the multimedia environment, human, and organisms.

Quite a few studies have been conducted in the various environmental matrices, humans, and organisms.

Some studies have been conducted on DP pollution in China in very recent years.

In some e-waste dismantling sites in Guangdong and Zhejiang Provinces, the levels are very high. BDE-209 is usually the dominant congener.

PFOS is usually the dominant The DP levels in air in China SCCPs levels in influent of a perfluorinated chemicals are comparable to those in air STP are higher than those (PFCs) in the environment, in Great Lakes, USA. The DP reported in Japan. In China, except in the water. PFOS levels levels in soil in Huai’an were SCCPs occur widely in the in China are relatively low, due compared with the sediment natural water body, the to the lower usage in China concentrations in Lakes Ontario effluent-receiving aquatic compared to North America. and Erie. High human exposure ecosystem, and the wastewater irrigated area. levels to DP in e-waste dismantling areas were observed.

production

pollution status

Notes: a) SCCPs are candidate POPs which are currently under evaluation by the POPs Reviewing Committee

Use as additives in lubricants and cutting fluids, as well as flame retardants and plasticizers.

Several studies on the SCCPs pollution in China have been reported only in recent two years.

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Fig. 4 Model-estimated mirex pollution in soil in China (pg$g–1 dw) [19]

directly based on water concentrations of the target pollutants [30,58]. However, the tissue residue of the pollutant in the organism body is a more suitable indicator of its potential adverse effect and ecological risk to the organism [59]. The bioaccumulation of POPs in aquatic food web contributes to the adverse effects both on the aquatic organisms and on their predators. Monitoring the chemical residues in various organisms in the food web can provide necessary information for ERA. However, such information is relatively scarce in China. Although food web model can be used to fill such a data gap, it has received little attention among ecological risk assessors [60]. Fugacity-based model has been applied to quantify the bioaccumulation of POPs in the food web due to its advantage of simplicity, as compared to the conventional

concentration-based model [61]. We developed fugacitybased food web model to simulate the bioaccumulation of DDTs in the aquatic ecosystem in the Bohai Bay (Fig. 5) [62,63]. The internal exposure levels (IELs) of DDTs in various organism categories were calculated. Monte Carlo — based uncertainty analysis was performed to get the IEL distributions of DDTs in organisms. The results show that fugacities and bioaccumulation factors (BAFs) generally increased with increasing trophic level in the food web. Based on food web bioaccumulation model, the IELs of pollutants in various organisms can be calculated to help understand their potential toxicological effect to the organisms and the associated risk to ecosystem. However, because the temporal, spatial variation of environmental factors can result in a wide range of values for input parameters used in the food web model, the uncertainty analysis of the model should be performed to reflect the variability of these parameters and address the variation of IEL output. The IEL distribution derived from the uncertainty analysis can be used for internal exposure analysis in a probabilistic ERA [62].

4 Environmental risk assessment and modeling POPs exist widely in various environmental media and organisms in China. However, the potential risks of POPs to human health and ecosystems are not well studied in China. Therefore, it is urgently necessary to develop feasible health risk assessment (HRA) and ERA methodology and models to understand the environment risk of POPs in China, and thus support decision-making aiming to

Fig. 5 Food web relationship in Bohai Bay used for food web model [62,63]


effectively minimize the risk level in risk management. 4.1

Health risk assessment of POPs

The human risk can be categorized into non-cancer risk and cancer risk. For most chemicals, the potential for noncancer effects is evaluated by comparing the estimated daily intake of the chemical from dermal exposure, inhalation, drinking, and food over a specific period with the Reference Dose (RfD) for that chemical derived for a similar period of exposure. The excess risk of cancer from exposure to a chemical is described in terms of the probability that an exposed individual will develop cancer because of that exposure by age 70. To evaluate the potential health risk to local public caused by water pollution in Huaihe River, we determined various organic pollutants, including PAHs, OCPs, and some other semi-volatile organic compounds (SVOCs). Preliminary HRA was performed by calculating the probability that the concentrations of detected compounds exceeded human health criteria for consumption of water and organism (HHCWO). The probabilities of posing a risk higher than 10–6 for most potential carcinogens were greater than 0.5. Further HRA for potential carcinogens was performed based on Monte Carlo simulation. Cumulative risk probability (CRP) was introduced to characterize risk. The result showed that 3,3′-dichlorobenzidine posed the highest risk. PAHs with 4–6 rings and some OCPs, such as heptachlorepoxide, aldrin and o,p′DDT, also posed relatively high risk. This study validated the relatively high cancer incidence rate in areas along the Huaihe River [64]. Jiang et al. performed HRA of OCPs associated with fish consumption in a coastal city in China [65]. The study indicates a potentially high cancer risk due to OCP contaminants in fish, and represents an important step toward a more comprehensive understanding and evaluation of human health risks associated with OCP exposures via marine fish consumption in coastal cities in China. Yang et al. evaluated the health risk of exposure to HCHs in Tianjin using cancer risk and loss of life expectancy (LLE) method, and found a person born in 1956 has the largest cancer risk of 0.00196 and dynamic LLE of 15 days [66]. However, occupational exposure, which may cause high health risk, to POPs has been seldom studied in China. 4.2

Ecological risk assessment of POPs

ERA is relatively more complicated than HRA, so this article focuses more on the ERA of POPs. After POPs are emitted from the sources, they first enter the abiotic environment, such as air, water, and soil etc, and then the organisms in the environment will be exposed to these POPs. Whereafter, the POPs will accumulate in the organisms and arrive at the receptors and hence pose

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hazardous effect to the organisms, and affect the ecosystem (Fig. 6). Based on the exposure life cycle of POPs, we introduced a three-level ERA framework (Figs. 6 and 7). The ERA framework mainly consists of data acquisition, exposure assessment, hazard assessment, and risk characterization. A series of models are necessary in this multilevel ERA framework. POPs distribute, transport, and transform in multimedia in the environment, so multimedia model is used for environmental exposure simulation, for air, water, soil, and sediment matrices. Food web model is used to simulate the bioaccumulation of POPs in the multi trophic layer ecosystem. Exposure concentration distribution (ECD) and species sensitivity distribution (SSD) are used to characterize ecological risk.

Fig. 6 Multi-level ERA concept corresponding to the exposure life cycle of POPs

Under this framework, we conducted a series of studies on the development and improvement of SSD method, construction of a series of models and applied them to assess the ecological risk of POPs in China using multilevel methods. These studies are represented as follows. 4.2.1

Species sensitivity distribution of POPs

SSDs are increasingly used to determine the ecological hazard effects of chemicals in probabilistic ERA procedures [67–69]. Compared to traditional deterministic quotient approaches, SSDs have a greater statistical significance and ecological meaning. We developed SSDs and calculated hazardous concentration threshold for 5% of species (HC5), using both parametric and nonparametric bootstrap methods (Fig. 8) [70]. To avoid picking repetitive values in each resample when performing bootstrap and determine the influence of fluctuation of toxicity data of single species on the SSDs and HC5, modified bootstrap method was introduced, which can generate unrepetitive sampling data other than the original elements in data sets. This method can enlarge a data set without any assumption of a special distribution. Even there is intra-species variation in a certain range of toxicity data, SSDs and HC5 are not very sensitive to the local

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Fig. 7 Framework of ecological risk assessment of POPs: ① data acquisition; ② exposure assessment; ③ hazard assessment; ④ risk characterization)

Fig. 8 SSDs with 95% confidence interval derived from parametric approach and nonparametric bootstrap approach [70]: (a) SSD based on log-normal regression; (b) SSD based on modified bootstrap method

fluctuation of toxicity of single species. SSD study of 18 OCPs shows that endrin, DDTs and endosulfan have very high ecological toxicity potential, while α-HCH has the lowest ecological toxicity potential among theses OCPs. 4.2.2

Risk of POP mixture

Although organisms in the real environment are usually exposed to mixtures of various chemicals rather than single substances, most researchers only focus on the effects of

single chemicals [71,72]. The study on the effect of POPs mixtures is in its infancy and currently POPs are usually assessed from legal perspective by risk assessment of single chemicals. Exposures to multiple chemicals are often treated as individual events and the combined toxicity effects of simultaneous exposures to multiple chemicals are often not addressed. This results in a crucial underestimation of the true risk. Therefore, combined effect of chemical mixture should also be studied in ERA. For similarly acting compounds, the joint toxicity


mechanism is usually concentration addition [73–76]. Thus, total equivalent concentration of the POPs can be calculated according to the concept of concentration addition: n X

Cequ,tol ¼

Cequ,i ¼

i¼1

n X i¼1

Ci

TVref , TVi

(1)

where, Ci is the concentration of compound i, TVi and TVref are respectively the toxicity value (eg. LC50 [Half lethal concentration], EC50 [Half maximal effective concentration], NOEC [No observed effect concentration] etc) of compound i and reference compound. According to the distribution of Cequ,tol and SSD of the reference compound, the combined ecological risks of POPs can be assessed by JPC method and hazard quotient (HQ) distribution method. For different categories of similarly acting compounds (eg. DDTs, HCHs, PCBs, PCDD/Fs, PBDEs or PFOS etc), it is assumed that the joint toxicity mechanism is independent action [77]. Thus, the independent action principle of joint toxicity can be introduced to solve the ERA of dissimilar categories of chemicals: n

R ¼ 1 – ∏ð1 – Ri Þ,

(2)

i¼1

where, Ri indicates the ecological risk of a category of similarly acting compounds (eg. DDTs, HCHs, PCBs, PCDD/Fs, PBDEs or PFOS etc). 4.2.3

Level I ERA

In level I ERA based on emission inventories of POPs, the levels of some OCPs, such as DDT, mirex and chlordane was simulated for provinces in China, using multimedia fugacity model [19,20]. Then aquatic ERA was performed using HQ method and potentially affected fraction (PAF)

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method, and the similar results were acquired from both the methods (general ecological risk of DDT in Chinese provinces is shown in Fig. 9 as an example). It was concluded that the ecological risk of such OCPs in the east of China and the south of China was relatively high, while their ecological risk in the west of China and the north of China was generally low. Monte Carlo — based uncertainty analysis indicates great uncertainty and variation in regional ecological risk. 4.2.4

Level II ERA

In level II ERA based on the external environmental exposure, a tiered approach consisting of several probabilistic options was developed to refine aquatic ERA of individuals and mixture of various POPs. The tiered approach ranges from determined HQ to Joint Probability Curve (JPC) (Fig. 10) and Monte Carlo simulation based HQ-distribution (Fig. 11). The results from all tiers of ERA methods are consistent with each other. The results of ERA differ much with different ecological risk criteria. Due to the joint effect, the combined ecological risk caused by the mixture of all detected POPs is significantly higher than the risk caused by any individual POPs. A comprehensive tiered approach can help to get more credible results of risks of individuals and mixture of hazardous pollutants and screen the major risk pollutants contributing to the combined ecological risk. Some water bodies in the east of China were taken as study cases [20]. The high-risk OCPs and the high-risk regions were screened. The ecological risk of DDTs and HCHs in Haihe River, Bohai Bay, Daya Bay and Suzhou River were relatively high. The ecological risk of DDTs and HCHs in Jiaozhou Bay, Laizhou Bay, Xiamen Port and Dalian Bay was very low. In most water bodies, the risk of DDTs was higher than that of HCHs, perhaps due to the much higher ecological toxicity potential of DDTs. The

Fig. 9 General ecological risk of DDT in Chinese provinces [20]: (a) HQ; (b) PAF

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accumulation of DDTs in various trophic levels was studied. Uncertainty analysis of food web model was also performed using Monte Carlo simulation. Probabilistic ERA was performed based on IEL Distributions and internal SSDs. The ecological risks of DDTs were relatively high. The risk order was p,p′-DDT> p,p′DDE> p,p′-DDD. The results from ERA based on the internal exposure approximated those based on external exposure. The food web model is a feasible method to predict the extent of bioaccumulation and IELs of POPs in organisms as a step to evaluate their risk posed on aquatic ecosystems.

5 Fig. 10

Illustration of the Joint Probability Curve (JPC) [30]

usage of dicofol may be the major contributor to the ecological risk of DDTs [78]. A case study of Huaihe River shows that endrin, o,p′-DDT, α-endosulfan, and βendosulfan posed clear ecological risk; p,p′-DDT, p,p′DDD, aldrin, heptachlorepoxide, and methoxychlor posed potential risk; while HCHs, heptachlor, dieldrin, and HCB posed negligible risk [30]. The Haihe River is the most seriously polluted one among the seven largest rivers in China. Due to the adjacent industrial activities, the risk levels of PCBs, DDTs, and HCHs in Haihe River were relatively high. The risk order was as follows: PCBs> DDTs&HCHs> DLCs [79]. Due to their high persistence and potential source from land, the high risks of such pollutants will last a long period. 4.2.5

Level III ERA

In level III ERA based on the IEC of POPs in aquatic species, food web model was developed to estimate the IECs. Bohai Bay was taken as a study case [62]. The

Fig. 11

Challenges and future directions

Although great advances in addressing the environmental risk of POPs have been made in recent years, we are still facing quite a few problems, such as data scarcity and uncertainty in environmental risk assessment. The complex interaction between climate change and increased POPs mobilisation is another great challenge in risk assessment of POPs. 5.1

Data scarcity of POPs

So far, none of the POPs has been regularly monitored by environmental protection agencies in China. There are no consecutive and systematic monitoring data of POPs. Based on the limited data of POPs, it is difficult to evaluate the environmental risk precisely. Data share between institutes is important for researchers to access more available data. Cooperation is necessary in the study of POPs in a regional or national scale in order to acquire systematic data. Systematic and consecutive monitoring of POPs in China should be well coordinated. For ERA, the knowledge about site-special ecosystem structures, including the whole food web relationship and trophic structure, are always lacking. Toxicity data of local species are very

Illustration of (a) HQ distribution and (b) exceedance probability of HQs based on Monte Carlo simulation [30]


scarce. Food consumption databases for regions all over the China should be established to provide the necessary information for assessing the health risks associated with consumption of contaminated food. 5.2

Uncertainty in environmental risk assessment

Uncertainty in environmental risk assessment is inevitable even when high level methods are used. The uncertainty is associated with spatial and temporal variability of environmental variables, sampling procedures and measurement error, derivation of parameters from primary data, variability in ecosystem stressors, exposure data, species effect data, fate model, risk characterization model, and lack of knowledge [58,80]. The data scarcity of POPs is an important source of uncertainty. Further work should be done to get more POPs exposure data in various spatial and temporal scales. Other uncertainties should also be cautioned, such as inter-laboratory differences in measurement and extrapolation of toxicity endpoints, the lack of knowledge about the existing site-special species in real ecosystem and the importance of each species in ecological structure and function, the assumption that the limited available toxicity data can represent the comprehensive information of hazardous effects to all of the organisms in the ecosystem, the extrapolation from either simple laboratory to field environments or from single species to populations and ecosystems. Also, due to the lack of unification in the environmental risk assessment methods, the risk level might differ much if different database or risk assessment models are used. Hence, standard methods should be developed and employed to evaluate environmental risk. Despite the inherent uncertainties existing in current risk assessment, the screening for high-risk pollutants according to the relative risk levels of various pollutants would help to decide the allocation of limited funds and resources to priority risk problems. 5.3

Climate change

Recently, climate change has caused much attention. Climate change can influence the POPs source and release. POPs source is the primary factor that causes the environmental risk of POPs. Climate change can influence the direct usage and emission of some POPs, and cause the release of POPs from iceberg, forest, and frozen earth etc [81]. The mobilization of POPs from contaminated sites and landfills due to increased flooding events are considered as one of the largest threats in this respect [82,83]. Climate change can also influence environmental behaviors of POPs [84]. All the temperature–dependant physical–chemical parameters (eg. Henry’s law constant, vapor pressure, and partition coefficients) are assumed to vary with the temperature. Climate change will certainly influence such parameters and contribute to the uncertainty of environmental behaviors of POPs. Climate change may

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affect environmental risks from POPs by changing exposure to POPs, either through the alteration of pathways or through alteration of environmental concentrating mechanisms [85]. Climate change can also make a direct influence on biodiversity [86]. Global warming will harm species via increasing the sensitivity of wildlife to exposures to certain pollutants [87]. Anyway, due to the climate change, the environmental risk of POPs will be more complicated and uncertain. Further efforts should be taken in future to study environmental risk of POPs by considering aspects of coupled dynamics between climate processes and POPs. Further studies should be taken to address all the problems and challenges in environmental risk assessment of POPs. Based on the environmental risk assessment, the technical and administrative countermeasures should be taken to reduce the risk. Acknowledgements The authors thank the financial support by the Key Project of National Natural Science Foundation of China (Grant No. 50838002) and the National Key Project of Scientific and Technical Supporting Programs during the Eleventh Five-Year Plan Period (2007BAC03A09).

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Professor Gang YU received his B.S. in organic chemistry from Nanjing University in 1986, his M.S. in environmental chemistry from Nanjing University in 1989 and his Ph.D. degree in Environmental Chemistry from Research Centre for Eco-environmental Sciences, the Chinese Academy of Sciences in 1992. He is currently the dean of the School of Environment, Tsinghua University and the director of Persistent Organic Pollutants (POPs) Research Center, Tsinghua University. His research interests include environmental analysis and risk assessment of POPs, POPs wastes disposal technologies, and POPs decision supporting policy. Prof. YU has published more than 200 papers. He has served as co-chair of the UNEP Expert Group on Best Available Technology and Best Environmental Practice (BAT/BEP) relevant to Unintentional POPs, an editor in POPs section of the journal Chemosphere, the chair of the Professional Committee of Persistent Organic Pollutants in Chinese Society for Environmental Sciences, deputy director of the Expert Group of Resource & Environment for eleven-five national high technology development plan (863) in China, and vice chairmen for Commission on Environmental Chemistry in Chinese Chemical Society.