游泳池環境中三鹵甲烷多暴露途徑之健康風險評估

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Title:	游泳池環境中三鹵甲烷多暴露途徑之健康風險評估
Authors:	周雯萱;Wen-Shiuan Chou
Contributors:	中國醫藥大學：環境醫學研究所
Keywords:	三鹵甲烷;游泳池;多暴露途徑;蒙地卡羅模擬;健康風險評估;THMs;swimming pool;multi-pathway exposure;Monte Carlo simulation;risk assessment
Date:	2008-07-08
Issue Date:	2009-08-11 16:56:16 (UTC+8)
Abstract:	過去公共衛生或健康風險評估對人體暴露於三鹵甲烷(trihalomethanes, THMs)的研究著重於飲用水的評估，相關的研究指出暴露於含三鹵甲烷的飲用水中三鹵甲烷的致癌風險為2.0×10-5 ~ 1.18×10-4，已超過美國環保署建議可接受的致癌風險(10-6)。游泳池的消毒方式與飲用水類似即加氯消毒，但游泳池的水是持續循環使用，使得加氯消毒所產生的消毒副產物容易累積在游泳池中。因此，相較於飲用水，游泳池水中三鹵甲烷的濃度可能較高，游泳者暴露於三鹵甲烷的風險亦可能較高。可惜針對游泳過程暴露三鹵甲烷的健康風險評估研究，目前仍相當有限，故需要針對游泳池環境中的三鹵甲烷進行檢測並進行健康風險評估。目前已有許多游泳池環境監測的研究，但針對如何進行採樣包括三鹵甲烷在時間及空間上的差異進行探討，甚至有研究只取一個樣本即代表整個游泳池水中三鹵甲烷的濃度，此作法是否可合理的反應游泳池水中三鹵甲烷的實際狀況，有待更進一步的評估。所以需要了解游泳池水中三鹵甲烷的濃度在時間及空間上是否為均質，並探討影響三鹵甲烷濃度差異的素因。本研究的研究目的：(1)分析國內游泳池環境中三鹵甲烷的濃度，以了解國人游泳過程中暴露的程度；(2)收集游泳池其他環境因子(餘氯量、總有機碳、游泳人數、溫度)，探討環境因子對水中三鹵甲烷的影響；(3)利用多暴露途徑(包括呼吸、皮膚接觸、攝食)的劑量模式，以蒙地卡羅模擬技術(Monte Carlo Simulation)，進行游泳者暴露三鹵甲烷的健康風險評估。研究結果顯示：(1)本研究檢測五座室內游泳池，水中總三鹵甲烷濃度為6.39~22.15 μg/L，優勢物種為氯仿(占總三鹵甲烷55~95.2%)，若比照飲用水的污染物容許濃度標準(總三鹵甲烷: 100 μg/L)，並未超出管制標準；以模式推估空氣中總三鹵甲烷濃度為46.37~84.26 μg/m3。(2) 每座游泳池於3~4個不同的採樣點採集水樣，結果發現12次的採樣分析中，其中有9次採樣點之間水中三鹵甲烷的濃度並無顯著的差異。另外3次有差異的部份，發現與自由餘氯、總有機碳和單位時間游泳人次有關。自由餘氯量及總有機碳為形成三鹵甲烷前趨物質，故其濃度對水中三鹵甲烷濃度分佈，呈正向的影響；另外，單位時間游泳人次與三鹵甲烷濃度改變量呈正相關，發現游泳人次愈多時，水中三鹵甲烷濃度降低量亦愈多，推測可能是游泳活動造成的擾動及紊流，促使三鹵甲烷自水中揮發。故建議進行游泳池採樣的同時，應搭配採集水中自由餘氯及計算游泳人數。(3) 依據水中三鹵甲烷濃度及模式推估的空氣濃度，結合國人相關的暴露參數進行風險評估，結果顯示，游泳過程男性所承受的風險：2.09×10-6 ~1.95×10-4，女性：1.99×10-6 ~2.04×10-4，最主要的暴露途徑為呼吸(67.23-69.83%)，其次為皮膚接觸(30.07-32.68%)。游泳池為提供健身運動的場所，本研究的結果顯示游泳池環境暴露三鹵甲烷的風險超出可接受的範圍，故游泳池的管理建議選擇其他的消毒方式，如臭氧、紫外線，可達到消毒滅菌的效果，且不會產生致癌性的消毒副產物。增加換水的頻率或在循環系統中加入適當的過濾設備，皆能有效降低三鹵甲烷的生成。如此一來，便可提供民眾安全的運動場所，確實保護人體健康。 Several studies have assessed the potential cancer risk resulted from exposure to trihalomethanes (THMs) in drinking water. These studies show that the lifetime cancer risk range from 2.0×10-5 to 1.18×10-4. These values exceed the acceptable risk (10-6) set by USEPA. In general, swimming pool water is treated in a way similar to drinking water using chlorination to keep swimmers from infections caused by microbial pathogens. Usually, swimming pool water is almost entirely recirculated. It provides the opportunity for the disinfection by-product to accumulate in pool water. Accordingly, the THMs level in swimming pool maybe higher than that of drinking water. Hence, it is necessary to monitor the level of THMs in swimming pool water and assess the risk of swimmer expose to THMs. Numerous studies have investigated the level of THMs in swimming pool water. However, most of them did not address the issue of variation of THMs level in the pool water due to spatial and temporal effect. Some of the studies even only took one sample to represent the THMs level in swimming pool. It might not reflect the actual level of THMs in the pool water. For this reason, further study is needed in order to understand the level of the variation. The objectives of this study are: (1) to determine the level of THMs in the pool water so that the level of exposure can be estimated; (2) to collect data of other environmental factors in swimming pool (free available chlorine, total organ carbon, number of swimmers, and temperature of water), and to discuss the effect of environment factor associated with the THMs level in swimming pool water; (3) to develop a multi-pathway exposure model for the swimmers, and to study the cancer risk contribution from different exposure routes (oral ingestion, inhalation and dermal absorption). The study results revealed that the THMs concentrations in five swimming pools ranged from 6.93 to 22.15 μg/L in water and from 46.37 to 84.26 μg/m3 in air. Chloroform was the dominate THMs species(55.0–95.2 %). We have conducted 12 sets of sampling schsdules, three sets showed significantly difference for the levels of THMs taken at different sampling points. The difference was attributed to the level of free available chlorine, total organic carbon (TOC), and the number of swimmers per unit time. We found that free available chlorine and TOC were positively correlated to THMs levels in swimming pool water. In addition, number of swimmers per unit time had negative correlation with the level of THMs in water. This may be due to the fact that turbulence caused by swimmers might increase the rate of volatilization of THM from water to ambient air. The lifetime cancer risk from exposure to THMs in swimming pool for males and females were in 2.09×10-6 –1.95×10-4 and 1.99×10-6 –2.04×10-4, respectively. The most important exposure pathway for swimmers was inhalation (67.23-69.83%), followed by dermal absorption (30.07-32.68%). Risk contribution from oral ingestion was insignificant in this study. In order to keep the risk of exposure to THMs at a minimum level, certain mitigation program, such as choose other disinfection agent (UV or ozone), frequent water change and circulation of pool water through an appropriate filtering system were strongly suggested.
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