A Sink Perspective for Managing Hazardous Materials- a Case Study of Pb in Taipei City

There are many environmental problems in the city, and the root of these problems are sinks where materials gather to. Urban metabolism helps us to understand the source of the problem by analyzing the flows of material. To solve the environmental problems in the city, the functions and characteristics of the sinks needs to be investigated because these characteristics would cause different environmental issues. No matter what kind of environmental issues, scientists aim to find the appropriate sinks for materials. For hazardous materials, ""the ability of anthropogenic sinks"" and ""the capacity of the environmental sinks"" should be taken into account at the same time. Material flow analysis (MFA), a systematic assessment tool, which gives rise to a holistic view of the related processes and the flows of certain materials within a city. Health risk assessment (HRA) is used to quantify the extent of health impactions caused by these flows. The MFA and HRA are integrated in this study to assess the appropriateness of harmful materials in urban anthropogenic sinks and to evaluate the environmental impact of urban metabolism. MFA is exployed to decide the appropriate treatment for harmful materials, while HRA provides the suggestion to improve material usage. Take lead materials in Taipei city as an example, the comparison and the assessment of lead materials were investigated among five different anthropogenic sinks including incinerator, bottom ash reuse, compost, wastewater treatment and sludge reuse. The result indicates that the incinerator is the most appropriate choice among these sinks because it captures most of lead and turn it into bottom ash. In contrast, the wastewater treatment is the least appropriate one because the effluent still contains lead. Although the hazard quotient is 0.15 and the cancer risk is 6.1E-08, both below the acceptable level, we only adopt these value as the reference information to manage lead in the city. In order to reduce the risk of lead from the pollution source, we design the policy scenarios based on the current situation in Taipei city. The scenario of ""reduce the plastic in the garbage but still reach the lower calorific value"" shows the most significantly reduced risk of lead. Moreover, the scenario of ""reach the 65% recovery rate and surpass Singapore, Korea and Germany"" could be a better choice, which not only decreases environmental impact but also increases the economic benefit.