Research for Resolutions of Environmental Parameters in Risk Assessmen--A Case Study of Medical Waste Incinerators
Date Issued
2004
Date
2004
Author(s)
Huang, Tzu-Ling
DOI
zh-TW
Abstract
There are many parameters considered in risk assessment. However, it is difficult to analyze all parameters due to limited data and resources, and this causes increases in uncertainties. If more data and resources are obtained, the uncertainties may be reduced with increasing spatial resolution. In this study, a statistical method is provided to determine how much sampling is needed to reduce the uncertainty and increase the reliability of risk assessment.
This paper is divided into two parts. The first part is to evaluate the carcinogenic effects on the residents exposed to dioxins within five kilometers of medical waste incinerators in Taoyuan County and Kaohsiung County. When concentrations of dioxin from the emission of incinerators are known, dry and wet deposition and air concentration on surface can be estimated by ISCST3. Then multi-media transport and transformation model is used to evaluate the concentration and distribution of dioxin in different media. Also the results from the multi-pathway exposure model are aggregated to estimate the accumulative dioxin concentration of receptors and carcinogen risk. Finally, risk uncertainty analysis and parameter sensitivity analysis are implemented.
The second part of the paper is the study of the spatial variances involved in environmental parameters. This is to evaluate the uncertainty range and thus to reduce it in the risk assessment. By using Hydro_Gen, each point in the assessed zone is evaluated to simulate the real situations. Then number of resolutions are generated depends on how much information is obtained. There are two ways to generate different resolutions. One way is square grid method, and another one is administrative district. After comparing the cases under different resolutions and risk variability, a statistic test (t-test) is used to decide if the calculated risk could be regarded as true value in different resolution. Repeat sampling 20 times in every resolution, the risk reliability is the proportion of which could regard as real situation.
From the results, the carcinogenic risk is found to be greater than 1.00E-6, and 90% of the risk is contributed from ingestion. This indicates that the concentration of the dioxin from the emissions of the medical waste incinerators is large enough to cause an adverse effect on human health. The medical waste incinerators are therefore to be advised to reduce the concentration of dioxin to eliminate the carcinogenic risk. By using the existing risk standard of 0.5 ng-TEQ/Nm3, the risk value is evaluated to be 1.00E-6. A sensitivity analysis shows that bulk density of soil at deposition location and fraction of organic carbon in soil at deposition location are the most important parameters. Following that, spatial resolution analysis is implemented by using these two parameters to evaluate the variances and reliability of the risk assessment. However, incautious intake of soil is considered to be the most dominant source of the uncertainties.
The result from the spatial resolutions show that the risk variability decreases as the resolution increases, and the variance between difference spatial resolutions is smaller while the accumulative risk value is lower. This indicates that reducing the number of sampling may lower the accumulative risk value, and increasing the number of sampling may increase the risk reliability. If square grid method is implemented, a proposed sampling of around 100 will give a satisfactory reliability. However, if number of samples depends on the number of districts of village, the risk reliability for Taoyuan is 100% and only 30% for Kaohsiung.
Subjects
t-檢定
醫療廢棄物焚化爐
不確定性
風險評估
空間解析度
medical waste incinerator
t-test
spatial resolutions
uncertainty
risk assessment
SDGs
Type
thesis
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