土壤重金屬污染場址暴露途徑與健康風險評估

Exposure Pathways and Health Risk Assessment for Soil Heavy Metals Contaminated Sites

鄭長和(Chang-Ho Cheng)

指導教授 ： 許正一

國立屏東科技大學/工學院/環境工程與科學系所/博士(2011年)

https://doi.org/10.6346/NPUST.2011.00059

摘要

土壤重金屬污染為世界各地常面臨的環境污染問題，國內由於有害廢棄物非法棄置造成許多污染場址，這些場址對於環境及人類健康具有潛在危害。過去，土壤污染場址係以管制標準作為整治目標，造成相當大的人力、物力及財力的耗費，因此國內外積極發展利用層次性的健康風險評估模式，建立一套有效並符合經濟的「污染場址管理策略」。1955年美國試驗材料協會(American Society for Testing and Materials, ASTM) 即提出層次性健康風險評估標準之矯正行動準則應用於石油洩漏場址（Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites, RBCA），其評估步驟的標準化，成為國內外最常被引用之評估模式。
本研究主要依據RBCA準則所提供之數學模式，來探討一土壤重金屬污染場址之層次性健康風險。在該評估中環境介質係考量土壤與地下水之污染物質，暴露情境分別考慮住宅與工商區的成人與兒童，以及七個暴露途徑。評估分析結果，第一層次致癌風險介於2.26×10-4_3.14×10-4，非致癌風險介於68.2-117；第二層次致癌風險介於5.71×10-5_1.23×10-4，非致癌風險介於6.19-7.97。第一與第二層次風險皆大於風險基準值，顯示此污染場址，對人體健康具有潛在之危害風險。第三層次風險分析採用@RISK軟體進行蒙地卡羅模擬，人體暴露參數及關切物質濃度採用常態分佈，分析結果顯示在95 %百分位之致癌風險介於1.09×10-4_1.95×10-4，非致癌風險介於10.1-65.6，顯示此污染場址之風險仍為不可接受程度。敏感性分析結果指出，影響風險主要敏感參數為受體體重、致癌平均時間、暴露時間、暴露頻率、飲用水砷濃度、飲水速率、土壤砷濃度、攝食土壤速率、皮膚吸收分率、皮膚吸附係數、暴露表面積比、污染源上方空氣混合區高度等。
層次性健康風險評估結果不但可做為訂定污染場址整治標準之依據，也是評估場址污染嚴重程度及整治急迫性的重要方法。建議國內相關單位對污染場址進行整治，應以此評估流程概念為基礎，訂定適合該場址之整治標準。

關鍵字

風險評估 ； 蒙地卡羅 ； 敏感性 ； 致癌風險 ； 非致癌風險 ； 土壤 ； 重金屬

並列摘要

Many contaminated sites were caused by illegal dumping hazardous wastes in Taiwan. These sites were potentially harmful to human health and the environment. In the past, the remediation goal of soil contaminated site was based on the control standard, which resulted in a great deal of manpower, material and financial resources consumption. Therefore, the domestic and international were actively developed a tiered approach of human health risk assessment model to establish an effective and economic "contaminated sites management strategy". A series of standard guides of RBCA have been developed by American Society for Testing and Materials (ASTM). The Risk-Based Corrective Action (RBCA) is rapidly becoming an accepted approach for the remediation of contaminated sites.
This study based on RBCA mathematical model investigated a heavy metal contaminated sites, the exposure risk assessment was conducted with a tiered approach to estimate the carcinogenic risk and the non-carcinogenic risk. Both exposure scenarios assumed the sites as the residential and the industrial areas, and both receptors of adults and children were considered with seven exposure pathways into the approach.
The results showed that the first tier of the carcinogenic risk and the non-carcinogenic risk were 2.26×10-4 – 3.14×10-4 and 68.2 - 117, respectively. The risk was clearly higher than the acceptable standard. Results of the second tier calculation showed that the carcinogenic risk and the non-carcinogenic risk ranged from 5.71×10-5 to 1.23×10-4 and from 6.19 to 7.97 respectively, which were a great threat for human health.
The third tiered risk analysis was performed by using @ RISK Palisade Monte Carlo simulation, the normal distribution was adopted for both exposure parameters and concerned pollutants. The simulation results showed that 95% percentile of the risk distribution value was between the first and second tiered risk. The carcinogenic risk and the non-carcinogenic risk ranged from 1.09×10-4 to 1.95×10-4 and 10.1 to 65.6, respectively. The risks were also demonstrated that the contaminated site was an unacceptable risk level.
However, sensitivity analysis indicated that the major parameters in adult’s carcinogenic risk were the receptor weight, the average time for carcinogenic, exposure period, exposure frequency, concentration of arsenic in groundwater, drinking water rate, concentration of arsenic in soil, soil ingestion rate, skin absorption fraction, sorption coefficient of skin, exposed surface area ratio, and height of the top sources of air mixing zone. The major sensitivity parameters in adult’s non-carcinogenic risk were the average time for non-carcinogenic, the receptor weight, exposure period, exposure frequency, event of shower frequency, concentration of chromium in soil, body surface area, fraction of the skin absorption of chromium, sorption coefficient of skin, drinking water rate, and concentration of arsenic in groundwater.
Tired approach of health risk assessment can be used not only as standards for contaminated sites remediation, but also an important way to assess the contamination degree. This study provides a streamlined process and guidelines of developing the risk-based decision-making strategy for contaminated sites in Taiwan.

並列關鍵字

Risk assessment ； Monte Carlo ； Sensitivity ； Carcinogenic risk ； Non-carcinogenic risk ； Soil ； Heavy metal

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