Prioritizing chemicals for environmental management in China based on screening of potential risks

Abstract

The rapid development of China’s chemical industry has created increasing pressure to improve the environmental management of chemicals. To bridge the large gap between the use and safe management of chemicals, we performed a comprehensive review of the international methods used to prioritize chemicals for environmental management. By comparing domestic and foreign methods, we confirmed the presence of this gap and identified potential solutions. Based on our literature review, we developed an appropriate screening method that accounts for the unique characteristics of chemical use within China. The proposed method is based on an evaluation using nine indices of the potential hazard posed by a chemical: three environmental hazard indices (persistence, bioaccumulation, and eco-toxicity), four health hazard indices (acute toxicity, carcinogenicity, mutagenicity, and reproductive and developmental toxicity), and two environmental exposure hazard indices (chemical amount and utilization pattern). The results of our screening agree with results of previous efforts from around the world, confirming the validity of the new system. The classification method will help decision-makers to prioritize and identify the chemicals with the highest environmental risk, thereby providing a basis for improving chemical management in China.

Graphical abstract

Keywords

chemicals / screening / risk / environmental management / priority definition

1 Introduction

Socioeconomic development and the progress of science and technology are accompanied by the creation and use of a continuously increasing number of synthetic chemicals and associated chemical species. According to the Inventory of the Existing Chemical Substances in China (MEP, 2013), more than 45,000 chemical species are currently used in China. Although synthetic and naturally occurring chemicals provide important services to support human production and life, some of these chemicals are associated with serious safety problems in terms of their potential environmental and health risks. These include persistent bioaccumulative and toxic (PBT) chemicals, carcinogens, mutagens, reproductive toxicants, and endocrine disrupters. In China, approximately 3,800 out of 45,000 chemicals have been identified as representing serious safety problems; thus necessitating the development of a strict chemical management program. Identification of the chemicals that pose the largest risks in the context of prioritized chemical management is becoming an imperative field of research. Scholars have implemented a “list type” of management (Swanson et al., 1997), where chemicals are screened based on the specific management purposes and demands for each, and are then added to control lists. Managers can use the resulting lists to prioritize the control and management of those chemicals that pose the greatest safety risks. The development of this type of management method has promoted the establishment of systematic screening of chemicals in many countries.

Since the 1970s, screening methods or technologies have been established for many chemicals and pollutants in developed countries and by international organizations, including the United States (Davis et al., 1994; Swanson et al., 1997; USEPA, 2009, 2012a, b; Singh et al., 2011), the United Kingdom (IEH, 2004), the European Union (EU Commission, 1993; Lerche et al., 2002; ECHA, 2010), Canada (Environment Canada, 1999), and Denmark (DME, 2009). Statistics compiled by organizations in the U.S., Japan, Europe, and other developed countries show that hundreds of chemical screening technologies or systems have been adopted and applied for chemical management. Even a single agency, such as the United States Environmental Protection Agency (USEPA), may implement multiple types of screening technologies or systems in their practical management of chemicals. These include: 1) in the U.S: the chemical hazard evaluation for management strategy (Davis et al., 1994; Swanson et al., 1997), the priority pollutant ranking system (USEPA, 1984), and the Agency for Toxic Substances and Disease Registry (ATSDR) screening priority management method for harmful substances (USEPA and ATSDR, 2007).; 2) in the European Union: a priority-setting method based on the comprehensive monitoring and modeling model of the European Union (Lerche et al., 2002) and the European Risk Ranking (EURAM) method (EU Commission, 1993); and 3) in Australia: the National Environment Protection Council (NEPC) material screening method (NPI Technical Advisory Panel, 1999). Table 1 summarizes the main chemical screening technologies and methods that are currently being widely used.

The American Chemical Hazard Evaluation for Management Strategies (CHEMS) and ATSDR methods and the European Union's Combined Monitoring-Based and Modelling-Based Priority Setting (COMMPS) and EURAM methods are sets of risk-based prioritization methods or technologies based on various theories of chemical toxicity hazards, environmental exposure (i.e., an assessment of the risk of exposure to a given chemical), and risk assessment. Based on these theories, various methods have been identified to evaluate the potential risks for the eco-environment or for human health. Research on screening technologies and systems has included the following screening methods: qualitative evaluation (e.g., the World Health Organization carcinogen screening; UNDP et al., 2005), quantitative calculations (e.g., the potential hazard index method; USEPA, 1979), and combined qualitative–quantitative methods (e.g., the CHEMS method). Since the late 1990s, the qualitative–quantitative method, also known as the “comprehensive scoring method”, has been the dominant chemical screening method. The methods of CHEMS and ATSDR, the grading screening system for priority pollutants in the U.S., the methods of EURAM and COMMPS in the European Union, and the Australian NEPC methods are all qualitative–quantitative methods, which are regarded as the most widely used and mature approach (Fu et al., 1990; Zhou et al., 1991). As a screening method, this approach has the advantage of being relatively simple to apply to practical management activities.

In contrast with the abovementioned screening technologies and systems, Chinese chemical screening methods have not been officially adopted or implemented. This is because China’s management capacity and technical level have not yet kept pace with the rapidly growing industrial, agricultural, and domestic use of chemicals, resulting in many difficulties in prioritizing the management of the most dangerous chemicals. In this paper, we consider the development of a framework for chemical risk assessment which could potentially result in a remedy for the current situation in China. To do so, we propose a “risk-score method,” based on the theory of risk assessment, in which researchers or managers assess the risk posed by chemicals based on the available hazard data and environmental exposure information, and transform the evaluation results into numerical values that can be easily understood. These values approximate the potential risks of a chemical.

2 Methods

2.1 Selection indices

In the selection of screening indices, there is always a series of observable attributes that are inherent to each chemical, and each attribute reflects a certain degree of hazard created by the chemical. Thus, any screening technology or system should include as many chemical parameters as possible in its indices to provide a more scientific and comprehensive evaluation of the real situation and to avoid subjective bias. However, the purpose of the screening will determine the type of screening indices that should be selected. For example, in the Australian NEPC system, the choice of indices mostly focuses on environmental exposure indicators because the purpose of the screening is to prioritize the management of chemical pollutants. In contrast, the European Union’s EURAM method is designed to prioritize the evaluation and management of chemicals. Therefore, their choice of indices focuses on indicators of ecological and human health effects.

Because there are no clear provisions for the optimal number of screening indices that would be appropriate, the selection of an index should be based on the scientific, operational, technical, and management requirements of the screening technology or system. In the selection of indices, Rausand (2011) suggested that three aspects of a chemical should be considered: 1) the human health effects that might be caused, 2) possible negative environmental effects, and 3) environmental exposure to the chemical. Figure 1 shows the relationships among nine screening indices in these three categories that are commonly used in the risk-score method of chemical screening and that we adopted in the present study.

2.2 Grading and ratings benchmark

Determination of the grading criteria for the chemical screening indices is a key link in the process. The grading criteria are used to determine if a chemical is hazardous and if so, the magnitude of the potential hazard; therefore directly reflecting the scientific results. A combination of qualitative and quantitative standards is used for different indices.

To adapt the risk-score method to accommodate the status of chemical management in China and integrate the approach with international management standards as much as possible, we decided that each screening index should use the following grading standards:

(a) For indices of persistence and bioaccumulation, we employed the regulations in China’s national standard Persistent, Bioaccumulative and Toxic Substances and High-Durability and Highly Bioaccumulative Substances Decision Method (GB/T 24789-2009).

(b) For indices of ecological toxicity, acute toxicity, carcinogenicity, mutagenicity, and reproductive and developmental toxicity, we employed the regulations in the United Nations Globally Harmonized System Grading Standard (UN, 2011).

(c) For indices of the quantity, usage, and utilization methods, we established grading standards based on a review of the literature and of China's present conditions.

We divided each of the screening indices into four or five levels. For the indices of persistence and bioaccumulation, each index was divided into four grades: Ⅰ, Ⅱ, Ⅲ, and Ⅳ, with severity scores of 4, 3, 2, and 1, respectively. For indices of ecological toxicity, acute toxicity, carcinogenicity, mutagenicity, reproductive and developmental toxicity, and usage, we divided each index into five grades: Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴ, with severity scores of 4, 3, 2, 1, and 0, respectively. For all indices, higher severity scores indicate a higher degree of potential harm. The index representing the chemical amount was also divided into five grades (Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴ), but assignment of the severity scores differed from the method used for the other indices. In summary, to make this index conform to the scores for the other indices, we transformed the chemical amount to a value between 0 and 4, with the highest grade (grade Ⅰ) given a value of 4 and the lowest grade (grade Ⅴ) given a value of 0. To assign a value to grades Ⅱ, Ⅲ, and Ⅳ, we calculated the logarithm of each chemical amount, and then used that value as the score for each grade. This both distributed the scores for grades Ⅱ, Ⅲ, and Ⅳ within the range of 0 to 4 used by the other indices and also allowed us to treat the amounts of different chemicals as a continuous range. The contributions of the index are then refined to reveal the environmental exposure risks in the future. Tables 2 to 10 summarize the criteria we used for each grade with the associated severity score.

2.3 Methods

In this paper, we propose a risk-score method for prioritizing chemical management in China. This method is based on an objective analysis of the potential risks of a chemical and transforms the risk results into a comprehensive evaluation score (CES). CES is a function of all nine screening indices for a given chemical, multiplied by their corresponding weights. Each index for a screened chemical was scored according to the grading standards in Tables 2 to 10 to provide an integrated total score for the chemical. CES has the following general form:

(1) CES=f(W_{\mathit{I}\mathit{1}}{S}_{I\mathit{1}},W_{I\mathit{2}}{S}_{I\mathit{2}},\cdots W_{In}{S}_{In}),

where I _n represents the value of screening index I for chemical n, W _{I n} is the weight of screening index I for chemical n, and S _In is the severity score for the value of screening index I for chemical n. We identified the weights of the factors by consulting experts (a total of 28 experts in the fields of environment, ecology, medicine, chemical engineering, and health and toxicology) and consolidating their judgments; this approach is commonly used in the development of screening methods.

In this conceptual model, the comprehensive chemical evaluation score is calculated by combining the hazard and the exposure potential. The resulting score represents the potential risk posed by a chemical. The risk score is calculated by:

(2) CES=SE+SH+SX.

The three parameters in this equation that are combined to create an integrated CES value equal the sum of the severity scores shown in Tables 2 to 10 for each of the following indices: 1) SE is the score for the environmental hazard, based on three indices (persistence, bioaccumulation, and eco-toxicity); 2) SH is the score for the health hazard, based on four indices (acute toxicity, carcinogenicity, mutagenicity, and reproductive and developmental toxicity); and 3) SX is the score for exposure, based on two indices (chemical quantity and usage).

2.4 Input data and case study

To test the approach, we developed a tiered process for screening the chemicals (Fig. 2). We chose a total of 296 chemicals or chemical categories from domestic and foreign lists according to the following criteria:

(a) chemicals with a large domestic production or import volume (>100 kt annually) based on Chinese statistics;

(b) chemicals with persistent bioaccumulation, high toxicity, or a potential for endocrine disruption;

(c) chemicals included in the screening lists from five or more countries;

(e) chemicals included in the management list specified by a relevant international environmental convention, and optional substances listed by related conventions;

(f) chemicals that have created a high environmental concern under China’s present conditions.

We used the following data source categories to provide values for the nine screening indices listed in Fig. 1 for the 296 chemicals:

(a) Authoritative and comprehensive chemical information databases that have been evaluated by experts or that have been officially approved.

(b) Published science and technology references about the chemicals.

(c) Quantitative structure–activity relationship simulation models. We primarily used this approach when data for a chemical was missing in other resources. The models we used were the American EPI Suite v4.11 (USEPA, 2012b), PBT Profiler v2.00 (SRC, 2012), and the European Union's Caesar (ECHA, 2009).

3 Results and discussion

We screened the 296 chemicals or chemical categories by applying the risk-score method described in Section 2.3, and calculated a comprehensive evaluation score based on the values of the nine screening indices for each chemical. The higher the severity score, the higher the risk of harm.

The results confirmed that all the selected chemicals have high environmental, health, and environmental exposure potential and therefore have a high comprehensive risk. We listed a total of 28 persistent bioaccumulative and toxic chemicals or chemical species (see Table 11); six of them (lindane, hexachlorobenzene, the perfluorooctane sulfonate class, pentabromodiphenyl ether, kepone [chlordecone], and pentachlorobenzene) are included in the Stockholm Convention on Persistent Organic Pollutants (UNEP, 2012), and the other PBT substances have been managed by developed countries, such as the US and Japan, or by groups of states such as the European Union. The 43 chemicals and chemical species that are highly hazardous to aquatic environments (Table 11) have a high degree of concern, and have therefore been prioritized for international management. Of the 39 chemicals and chemical species with a high risk of carcinogenic, mutagenic, or reproductively toxic effects (Table 11), five have been classified as human carcinogens and three as potential human carcinogens by the International Agency for Research on Cancer (IARC, 2012).

The proposed risk-score method is in line with other screening methods used around the world, such as CHEMS in America, EURAM in the European Union, and NEPC in Australia. All of these systems adopted a combination of qualitative and quantitative indicators to screen chemicals. This combination method has become the most widely used and mature chemical screening method. The risk-score method, along with other chemical screening methods, cover some aspects of chemical toxicity and exposure evaluation. However, differences exist between the risk-score method and other screening methods, especially in terms of the indices of environmental exposure. In China, data on chemical emissions and concentrations in various environmental media (e.g., atmosphere, water, soil) were difficult to obtain. Therefore, unlike the CHEMS, EURAM, and NEPC methods, our risk-score method used environmental exposure indices rather than emissions and concentrations to characterize the potential exposure. If reliable emissions and concentration data become available in the future, our method can be modified to account for this additional data.

The international experience, which is codified in the chemical environment conventions and the chemical management strategies currently in use in developed countries, suggests that the chemicals that should be prioritized for environmental management include substances that exhibit persistence, bioaccumulation, carcinogenicity, mutagenicity, reproductive and developmental toxicity, endocrine disruption, or other forms of toxicity. In this paper, we screened these chemicals using a risk-score method that accounts for the unique aspects of China's use of synthetic chemicals. The evaluation results were favorably in line with international management guidelines.

4 Conclusions

Using an approach based on risk management theory, we consulted a wide range of references and international resources to identify the chemicals that pose the greatest risk to humans and the environment. We then developed a risk-score method to rank these chemicals based on nine indices that accounted for the importance of these chemicals in the Chinese context. The resulting approach largely agreed with previous assessments in terms of the chemicals identified and their relative risks, suggesting that the proposed method provides a scientific and practical method for prioritizing the management of these chemicals in China. However, as is the case for the other screening systems, further investigation should be done to clarify the risk posed by a given chemical or group of chemicals so that our system can be updated to account for the new research results.

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