台灣土壤及地下水污染場址生態風險評估方法與關渡平原砷污染場址案例探討

Method Development and Case Study of Ecological Risk Assessment for Soil and Groundwater Contaminated Sites in Taiwan

陳士賢(Colin S. Chen) ； 沈穎(Y. Shen) ； 賴宜欣(Y. H. Lai)

《土壤及地下水污染整治》 4卷1期 (2017/01) Pp. 35-52

https://doi.org/10.6499/JSGR.2017.0401.003

摘要

生態系因受到人為活動或自然劇變，致使其生命、繁衍或棲息環境可能產生不利反應的潛勢，稱之為「生態風險」，生態風險評估（Ecological Risk Assessment）估算生態系暴露於物理性、化學性或生物性壓力下所承受的風險。依據我國土壤及地下水污染整治法規定，污染場址執行風險評估應同時關注於環境影響與人體健康兩層面，其中在人體健康方面，環保署已公告健康風險評估方法並建有線上試算系統，由於生態系統之多樣性與複雜性，生態風險評估之技術性相對較人體健康風險評估高，許多步驟與工作需要更詳細的調查與試驗，因此環保署參考具有完整污染場址評估制度的幾個國家的作法，歸納成適合我國使用之生態風險評估工具，並且具有多樣的風險分析方法。本文蒐集比較美、加、歐洲等具有較完整制度國家之生態風險評估發展成果，分析生態風險評估的關鍵工作，同時依據我國新建置的污染場址生態風險評估架構，進行案例研究，分析國內具有砷污染之關渡平原，界定其可能面臨的生態風險問題，期許能建立一個有效可行的生態風險評估工具，協助推動未來污染場址土地永續利用。

關鍵字

生態風險評估 ； 土壤及地下水污染 ； 關渡平原 ； 砷污染

並列摘要

Introduction Ecological risk assessments are conducted to transfer scientific information about the risk of human activities to the environment. Their purpose is to enable risk managers to make more informed environmental decisions. In general, ecological risk assessments evaluate the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors. An assessment may involve chemical, physical, or biological stressors, and one or many stressors may be considered. The aim of such assessments is to enable risk managers to make more informed environmental decisions. According to the Soil and Groundwater Pollution Remediation Act of Taiwan, both environmental impacts and human health need to be taken into consideration when conducting a risk assessment for contaminated sites. Health risk assessment protocols and an online assessment system have been developed by the Taiwan Environmental Protection Administration (TEPA). For countries adopting ecological risk assessment as part of the assessment tools in the site assessment system, ecological risk assessments are developed within a risk management context to evaluate human-induced changes that are considered undesirable. Indeed the processes are more complex and diverse than human health risk assessment. Additionally, various procedures and tasks may require more detailed site investigation and experiments, as well as risk analysis methods. The development of ecological risk assessment frameworks from the U.S., Canada, and Europe is described. The processes used when conducting ecological risk assessments are also analyzed. With the newly established ecological risk assessment framework for contaminated sites produced by TEPA, a case study of Guandu Plain in suburban Taipei was performed to analyze potential ecological risks. The ecological risk assessment was undertaken to analyze the Guandu Plain's stressors and resulting ecological effects, and to stimulate broader public awareness and participation in decision making for reducing ecological risks. The objectives were designed to implement a field and laboratory investigation to fill the data gaps identified during the planning stage of the ecological risk assessment.Materials and Methods The geological conditions and long-term irrigation activities in the Guandu Plain area have caused a concentration of arsenic in the soil that exceeds the related pollution control standard. In addition, Guandu Plain, located near Guandu Nature Reserve, is abundant with natural resources, and is one of the most important bird habitats in Taiwan. The site is located in north-west suburban Taipei, running for 10 km next to the Tamsui River estuary. The soil contains high concentration level of arsenic from beudantite (PbFe_3(AsO_4,SO_4)(OH)_6), and not from anthropogenic activity. These conditions thus make Guandu Plain a suitable candidate for conducting an ecological risk assessment. Since this case study only demonstrated the screening level of the assessment process, only the key steps and essential information are presented. This study intended to use the TEPA Ecological Risk Assessment paradigm to assess ecological risk. In the problem formulation process, the contaminant of concern in soil was determined to be arsenic. The concentration of arsenic in top soil ranged from 4.75 to 458 mg/kg in the TEPA investigation. A four-day biomonitoring survey was conducted in July 2014 and December 2014. The biological receptors included plants, mammals and birds at the site. Around 280 species of migrant birds and 50 species of resident birds (17%) resided in the area during the assessment. The majority of these were predatory migration birds (76.5%), such as the snipe families. In the summer this area is a breeding grounds for egrets and water-tails, while migratory birds take residence in winter. During spring and autumn, it acts as a habitat for transiting birds. The north zone serves as a habitat for terrestrial birds, while the mangrove wetland serves as a habitat of aquatic birds. Moreover, different assessment and measurement endpoints were decided according to the different classifications of biological organisms in order to establish the relationships between contaminants and receptors. Based upon different trophic levels, the valued ecosystem components of different bird species were established. Ultimately, acceptable ecological soil screening levels can be derived for different species. In the risk estimation, it was assumed there was 100% conversion of contaminants to organisms. No single species assessment was conducted. A hazard quotient of one (HQ = 1) was considered as the ecological criteria in the site.Results and Discussion The risk estimation indicated that the hazard quotients of plants, mammals, and birds were greater than one at several locations, which could have adverse effects on the species in those areas. However, the ecological survey indicated that the population of birds did not decline, with no significant changes from the numbers seen in historical observations. The uncertainty inherent in ecological risk assessments is associated with variability in ecosystem stressors, exposure data, ecological effect data, risk characterization, and lack of knowledge. Physical and biological stressors were not evaluated in this study, toxicological data were available for relatively small number of species, and the effects of minor contaminants were not characterized. Bioavailability and bioaccumulation were assumed to be 100%, and site specific parameters would be better in this context. It is thus suggested that long-term ecological monitoring or more detailed ecological risk assessments should be implemented in the future in order to reduce any uncertainties in the current work.

並列關鍵字

ecological risk assessment ； chemical of potential concerns ； arsenic ； hazard quotient