臺灣飲用水中多重汙染物之致癌風險評估

Abstract

乾淨且安全的飲用水對我們的日常生活至關重要，喝水、洗衣、洗澡等不同人為活動都會接觸到水中的汙染物質。因此，本研究的主要目的是評估透過口服攝入、吸入及皮膚吸收等途徑暴露到飲用水中不同污染物的累積癌症風險。另一方面，由於氣候變遷的影響，極端降雨事件更加頻繁地發生，已有研究證實颱風期間自來水中的三鹵甲烷濃度升高，藉此，本研究的第二個目的是探討在颱風期間因暴露於較高濃度的三鹵甲烷而增加的癌症風險。 本研究使用的數據來自環保署飲用水水質資料庫自2002年1月至2019年12月的水質數據以及2019年2月至2019年10月所收集的樣本分析結果。根據汙染物質的檢測率和可得的毒理資料，共計選擇八種金屬（砷、鉛、硒、鉻、鎘、鋇、銻和鎳）及七種消毒副產物（氯仿、溴二氯甲烷、二溴氯甲烷、溴仿、二氯乙酸、三氯乙酸和溴酸鹽）作為研究對象，並參照美國環境保護署的風險評估指南和臺灣人民的生活習慣，使用Crystal Ball軟體進行蒙地卡羅模擬，計算平均每日劑量、終生癌症風險及危害指數。 研究結果發現，在臺灣各地區及離島的飲用水中，這十五種污染物的累積癌症風險皆高於10-6，也就是美國環境保護署定義的可接受風險。其中，風險最高者是來自離島的飲用水，癌症風險為1.38×10-4，主要因為其總三鹵甲烷濃度較其他地區為高。而全臺灣飲用水的累積危害指數皆遠低於美國環保署訂定的可忽略危害基準。另外，颱風情境下所衍生的終生三鹵甲烷癌症風險與一般情境差異不大，主要原因為每年五天的高暴露時間與終生暴露相比沒有太大的影響。 整體言之，儘管有其他水中污染物未涵蓋在此次評估中，但累積癌症風險已高於10-6，代表值得關注飲用水中同時出現的污染物對健康效應的影響。另外，雖然颱風期間的高暴露對終生癌症風險整體影響低，但是仍應控制飲用水中的濁度和天然有機物濃度，以預防短時間高暴露可能造成的健康危害。

Safe drinking water is essential to our daily life since it is inevitable that people expose to contaminants in drinking water through multiple exposure routes every day. As a result, the main purpose of this study is to investigate the cumulative cancer risks of co-occurring contaminants in drinking water through oral ingestion, inhalation, and dermal absorption exposures in Taiwan. On the other hand, due to the effects of climate change, typhoons and extreme weather events are occurring more frequently in past decades, resulting in much higher concentrations of trihalomethanes (THMs) in the treated water during the typhoon period. Therefore, the second purpose of this study is to elucidate the lifetime cancer risk resulting from exposure to higher concentrations of THMs during typhoon seasons. The water quality data used in this study were obtained from the database of the Environmental Protection Administration of Taiwan from January 2002 to December 2019 and the analytical results of collected samples from February 2019 to October 2019. Based on the occurrence data and the available cancer potency information, eight metals (arsenic, lead, selenium, chromium, cadmium, barium, antimony, and nickel) and seven disinfection byproducts (chloroform, bromodichloromethane, dibromochloromethane, bromoform, dichloroacetic acid, trichloroacetic acid, and bromate) were chosen for investigation. Based on the United States Environmental Protection Agency (USEPA) risk assessment guidelines and the lifestyles of residents in Taiwan, the equations and the parameters for calculation of risk assessment were simulated using Monte Carlo simulations with Crystal Ball software. The results of cumulative cancer risks of these fifteen contaminants from drinking water in northern, central, southern, eastern, and offshore islands of Taiwan were all higher than 10-6, the acceptable risk level defined by USEPA. The highest cancer risk of 1.38×10-4 was in drinking water from offshore islands because the total THM concentration was higher than that in the other areas. All of the results of the hazard index in Taiwan were much lower than 1, the negligible hazard level defined by USEPA. Moreover, the increased cancer risk of exposure to THMs in the typhoon scenario was not apparent for the results of lifetime cancer risk because the five days of exposure duration per year is considerably short when compared to our lifetime. In conclusion, the cumulative cancer risks from exposure to multiple contaminants in drinking water were higher than 10-6 although there were other water contaminants not included in the assessment. These results suggested that risk assessment should concern about the cumulative health impacts of co-occurring contaminants in drinking water. Besides, it is also necessary to prevent the high exposure to THMs in typhoon seasons by controlling the turbidity and natural organic matters in drinking water, which were the precursors of THMs, during the typhoon.