污染場址附近孩童與成人暴露受重金屬污染土壤與落塵之健康風險評估

Health risk assessment of heavy metals in soil and dust for children and adults near contaminated sites

王映琳(Ying-Lin Wang)

指導教授 ： 席行正

國立臺灣大學/工學院/環境工程學研究所/博士(2021年)

https://doi.org/10.6342/NTU202104113

摘要

由於臺灣地狹人稠，住家經常坐落於污染場址附近，而孩童因體重輕且有較高頻率的手口行為，故在室外活動過程中可透過接觸含重金屬的落塵與土壤而暴露到比成人更高的風險。同時孩童因有90.5%的時間都待在室內活動，因此室內落塵中重金屬的暴露風險亦須被評估。
考量到土壤與落塵攝食率為評估孩童誤食土壤與落塵途徑風險的重要參數，本論文第三章節使用美國環保署發展的SHEDS-soil/dust模式並彙整過去建立的臺灣孩童暴露參數之分布作為輸入參數，推估3歲以下孩童的攝食率。模擬結果顯示，在活動前、間接接觸土壤與直接接觸土壤三種情境下，砂土組中24到36個月孩童的土壤與落塵攝食率分別為2.02、11.0與90.7 mg/day；而黏土組中24到36個月孩童的土壤與落塵攝食率分別為2.26、4.76與29.8 mg/day。由SHEDS-soil/dust模式區分土壤與落塵對於非飲食性攝食率的貢獻度，由高到低依序為手到口的土壤攝食率、手到口的落塵攝食率與物體到口的落塵攝食率。此外，SHEDS-soil/dust模式敏感度分析結果顯示，土壤黏附因子為主要提高臺灣孩童土壤與落塵的攝食率的重要參數，而高洗手頻率則可降低孩童的攝食率。
為了更有效地評估人體真正可吸收的重金屬含量，第四章節使用簡化生物可及性萃取法分析天然和人為污染農地土壤中鉻、鎳的食入生物可及性比例，並探討土壤性質及重金屬相態對其影響，同時評估在考量食入生物可及性比例下，孩童因誤食含高鉻、鎳土壤造成之健康風險。結果顯示，蛇紋石土壤中鉻與鎳食入生物可及性分別為10.9 ± 10.6%與7.61 ± 5.31%；電鍍廢水污染農地土壤中鉻與鎳分別為15.2 ± 11.1%與27.7 ± 9.79%，表示人為污染源較天然來源更易造成較高的食入生物可及性。相關性結果顯示，兩種來源土壤中鉻的食入生物可及性皆與總有機碳呈顯著正相關；但鎳的食入生物可及性僅在電鍍廢水污染農地土壤中觀察到此現象。此外，無論是在蛇紋石或電鍍廢水污染農地土壤中，鎳的相態都會顯著影響其食入生物可及性。風險評估結果則顯示，當考量食入生物可及性後，3歲以下孩童經由誤食土壤中高濃度鉻或鎳的健康風險皆有所下降。
評估人體健康風險時，除了食入途徑外，亦可由吸入途徑暴露到土壤中重金屬，因此第五章節中以人為汞污染土壤為例，分析使用不同體外試驗方法下食入與吸入生物可及性比例之差異，並用以評估居住在汞污染場址附近孩童及成人經食入與吸入途徑暴露到土壤汞之非致癌風險。而由於呼吸速率為影響吸入途徑暴露風險的重要暴露參數，且臺灣尚缺乏本土參數值，故此參數會透過較新穎的可攜式氣體交換分析儀(COSMED K5)，實際量測以獲得20-40歲成人之呼吸速率。由不同的體外試驗萃取方法結果顯示，汞的食入與吸入生物可及性會受到萃取液化學成分與pH值的影響。在所有污染場址中，受汞污泥非法掩埋污染之S7場址具有最高的總汞濃度(1346 mg/kg)、食入(26.2%)與吸入(30.5%)生物可及性及最高的水可溶相態(28.7%)，主要為S7場址中汞在土壤中的老化程度較低所導致。由COSMED K5實測20-40歲成人受試者之平均呼吸速率為12.3 ± 1.25 m3/day，組內相關係數分析結果(0.606–0.949)顯示，使用COSMED K5量測呼吸速率與其他代謝參數具一定可靠性。而儘管在本研究中汞之吸入暴露風險受呼吸速率影響不大，所建立之本土化呼吸速率值未來仍可被應用於其他暴露情境的風險評估，例如評估特定族群暴露於揮發性有機物或多重污染物環境下之吸入風險。本研究所提供之方法與結果，可作為相關單位擬定污染場址管制策略時評估健康風險所需的參考依據。

關鍵字

土壤 ； 重金屬 ； SHEDS-soil/dust模式 ； 土壤與落塵攝食率 ； 呼吸速率 ； 生物可及性 ； 健康風險評估

並列摘要

Because of Taiwan’s densely populated characteristics, it is not rare to find urban residences locate near contaminated sites. Children may be exposed to higher risk than adults when they play outdoors and come into contact with dust and soil containing heavy metals because of their lower body weight and higher hand-to-mouth frequency. At the same time, children spend 90.5% of their day indoors, making household dust another non-negligible exposure matrix for them.
The soil and dust ingestion rates are both important factors to estimate risks for children when they are exposed to heavy metals via the non-dietary ingestion pathway. In Chapter 3, the Stochastic Human Exposure and Dose Simulation Soil and Dust (SHEDS-S/D) model developed by the U.S. Environmental Protection Agency (EPA) was applied to estimate the soil and dust ingestion rates for Taiwanese children under 3 years old using distributions of input variables derived from the database established for Taiwanese children. The results showed that soil and dust ingestion rates in the exposure scenarios of sedentary activity, indirect contact with soil, and direct contact with soil for children aged 24 to 36 months were 2.02, 11.0, and 90.7 mg/day for the sand group, and 2.26, 4.76, and 29.8 mg/day for the clay group, respectively. Hand-to-mouth soil ingestion was identified as the main contributor to soil and dust ingestion rates, followed by hand-to-mouth dust ingestion and object-to-mouth dust ingestion. Based on the sensitivity analysis in the SHEDS-S/D model, the soil-to-skin adherence factor was the dominating factor increasing the soil and dust ingestion rate while it was noted that a higher frequency of hand washing could reduce the ingestion rates.
To accurately evaluate the absorbable fractions of metals in human body, Chapter 4 of this dissertation utilized simplified bioaccessibility extraction test (SBET) to analyze the oral bioaccessibility of Cr and Ni in serpentine and non-serpentine soils polluted by irrigation water. Soil properties and the fractionation of Cr and Ni were investigated to understand their effects on the oral bioaccessibility. Using these results, the risks based on the oral bioaccessibility were assessed for children who incidentally ingest high Cr and Ni containing soils. The results of oral bioaccessibility of Cr and Ni were 10.9 ± 10.6% and 7.61 ± 5.31% in serpentine soils and were 15.2 ± 11.1% and 27.7 ± 9.79% in non-serpentine soils contaminated by electroplating wastewater. The latter (anthropogenic sources) might cause a higher oral bioaccessibility than the former (natural sources). Results of correlation analysis showed that oral bioaccessibility of Cr was positively correlated with total organic carbon (TOC) in both the serpentine and non-serpentine soils. On the other hand, Ni was positively correlated with TOC only in non-serpentine soils. For both soil types, the fractionation of Ni significantly influenced its oral bioaccessibility. Furthermore, a lower health risks were found for children under 3 years old who are exposed to high level of Cr and Ni in soils based on the oral bioaccessibility through the soil ingestion pathway.
In addition to soil ingestion, the inhalation of heavy metals contaminated soil particles is also a critical pathway for human. In Chapter 5, the oral and inhalation bioaccessibility of Hg were investigated in anthropogenically contaminated soils using various in-vitro gastrointestinal and respiratory simulated methods. The non-carcinogenic risks of Hg through the ingestion and inhalation of soil particles for children and adults living near the contaminated sites were also assessed based on the analyzed oral and inhalation bioaccessibility. While the inhalation rate is a crucial parameter for the inhalation exposure risk, the localized inhalation rates in Taiwan are still lacking. Therefore, a portable gas exchange analyzer (COSMED K5) was applied to measure the inhalation rates for Taiwanese adults aged 20 to 40 years. It was found that chemical composition and pH of the various extractants could result in distinct oral and inhalation bioaccessible fractions of Hg. The result for the site (S7) contaminated by inappropriate dumping of Hg-containing waste sludge had the highest total Hg concentration of 1346 mg/kg, with the highest oral bioaccessibility of 26.2% and inhalation bioaccessibility of 30.5%. The results of SEP also showed that site S7 had the highest water-soluble phase (28.7%) among all sites, suggesting that the lower degree of aging of Hg-contaminated soils may enhance the Hg availability for humans. In addition, the mean inhalation rate measured by the COSMED K5 was 12.3 ± 1.25 m3/day for adults aged 20 to 40 years. The results of intraclass correlation coefficient (0.606–0.949) also showed that using the COSMED K5 to measure the inhalation rate and other metabolic variables was reliable. Notably, although not significantly affecting the results for scenarios evaluated in this study, the localized inhalation rate is still crucial for estimating the accurate inhalation risk for other scenarios, such as those who might be exposed to volatile organic compounds (VOCs) or multi-pollutants in certain environments. The results of this dissertation could not only provide a comprehensive method for the actual health risks of heavy metals exposure targeting Taiwanese people but also be applied in the management and decision making of the heavy metals contaminated sites in the future.

並列關鍵字

soil ； heavy metal ； SHEDS-S/D model ； soil and dust ingestion rate ； inhalation rate ； bioaccessibility ； health risk assessment

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