Lu Li-Teh, Chang I-Cheng, Hsiao Teng-Yuan, Yu Yue-Hwa, Ma Hwong-Wen
Graduate Institute of Environmental Engineering, National Taiwan University, No. 71, Chou-Shan Road, Taipei, Taiwan.
Environ Sci Pollut Res Int. 2007 Jan;14(1):49-59. doi: 10.1065/espr2005.08.278.
Since the 1970s, at least 200 hectares (ha) of farm-land has been polluted by the heavy metal cadmium (Cd). Consequently, the Cd pollution has led to contaminate the rice production and caused acute social panic. According to the recent investigation results performed by the Taiwan Environmental Protection Administration (TEPA), it is indicated that most of the Cd pollution incidents in Taiwan resulted from the waste-water discharge of stearate Cd factories. To prevent the Cd pollution incidents from spreading, the TEPA has either forced these factories to close down or assisted them in improving their production processes since the 1980s. Unfortunately, accidental incidents of Cd pollution still emerge in an endless stream, despite the strict governmental controls placed on these questionable factories. Whether this pollution has resulted from undetected or hidden pollution sources stemming from two decades ago or comes from some new source, will be an outstanding issue. Therefore, this study attempts to identify the pollution sources of Cd in soil in Taiwan as well as to find the solution to the above-mentioned, outstanding issue by way of a methodology termed Material Flow Analysis (MFA).
The MFA has proved to be a useful tool on providing quantitative information of the flow of substances through an economic to an environmental system. Based upon the supply-and-demand theory of MFA, researchers have successfully conducted an overview of the use of materials in many industries, the construction industry being one of these. Therefore, this study tries to establish a set of analytical processes by way of MFA for identifying the pollution source of Cd in soil in Taiwan. In addition, the spirit of Life Cycle Assessment (LCA) technique was also employed to identify the materials, and products should be ignored as a crucial pollution source in this study.
According to the MFA methodology applied in this study and on the basis of related studies performed by Taiwanese governmental authorities, we arrive at the following analysis results: (1) the total amount of Cd from the economic perspective of material and product flow was approximately 441.2 tons; (2) the wastewater directly discharged into irrigation water can be concluded to be the major pollution route of Cd in farmland soil in Taiwan; (3) material plastic stabilizer (cadmium oxide, CdO), Zn-Pd compounds and Cu compounds should be the crucial pollution sources to contaminate environment through the route of wastewater in Cd flow analysis; (4) the crucial pollution sources to contaminate environment through the route of wastewater in Cd flow analysis were five factories, Coin, Jili, Taiwan Dye, Guangzheng and Mingguan, and they were all categorized as stearate Cd industries; (5) the typical source of the Cd pollution in soil in Changhua County through the pollution route of wastewater should be the metal surfacing process industries.
This study proved that MFA can be a good tool for identifying Cd flow as well as for recognizing the crux of the problem concerning incidents of Cd pollution. This study led to the conclusion that the causal relationship between farmland pollution caused by Cd and stearate Cd factories in Taiwan seemed quite close by way of MFA methodology. In addition, this study also found that the wastewater discharged from a single metal surfacing process factory will not cause remarkable farmland pollution. However, the wastewater simultaneously discharged from a group of pollution factories can result in a significant pollution incident.
This case study is only a small contribution to the understanding of the toxic material flow related to Cd in the environment. This study recommends that Taiwanese governmental authorities should not deal with problems on an ad hoc basis, but should instead deal with Cd pollution problems overall employing control measures. Finally, the more accurate information or data we can collect, the more reliable results we can identify. Therefore, the quality and quantity of related data used in this MFA model should be closely scrutinized in order to ensure the most correct and comprehensive investigation on the toxic material flow.
自20世纪70年代以来，至少200公顷农田已被重金属镉（Cd）污染。因此，镉污染导致水稻生产受到污染，并引发了严重的社会恐慌。根据台湾环境保护局（TEPA）最近的调查结果，表明台湾大多数镉污染事件是由硬脂酸镉工厂的废水排放造成的。为防止镉污染事件蔓延，自20世纪80年代以来，TEPA要么迫使这些工厂关闭，要么协助它们改进生产工艺。不幸的是，尽管政府对这些问题工厂进行了严格管控，但镉污染事故仍层出不穷。这种污染是源于二十年前未被发现或隐藏的污染源，还是来自一些新的源头，将是一个突出问题。因此，本研究试图通过一种称为物质流分析（MFA）的方法来识别台湾土壤中镉的污染源，并找到解决上述突出问题的方法。
事实证明，物质流分析是一种有用的工具，可提供物质在经济系统与环境系统中流动的定量信息。基于物质流分析的供需理论，研究人员已成功对许多行业的材料使用情况进行了概述，建筑业就是其中之一。因此，本研究试图通过物质流分析建立一套分析流程，以识别台湾土壤中镉的污染源。此外，还采用了生命周期评估（LCA）技术的理念来识别材料，并且在本研究中应将产品视为关键污染源而予以忽略。
根据本研究应用的物质流分析方法，并基于台湾政府当局进行的相关研究，我们得出以下分析结果：（１）从物质和产品流的经济角度来看，镉的总量约为441.2吨；（２）直接排放到灌溉水中的废水可被认定为台湾农田土壤中镉的主要污染途径；（３）物质塑料稳定剂（氧化镉，CdO）、锌钯化合物和铜化合物应是镉流分析中通过废水途径污染环境的关键污染源；（４）镉流分析中通过废水途径污染环境的关键污染源是五家工厂，即Coin、Jili、台湾染料、广正和明冠，它们均被归类为硬脂酸镉行业；（５）彰化县土壤中镉污染通过废水污染途径的典型来源应为金属表面处理工艺行业。
本研究证明，物质流分析可以成为识别镉流以及认识镉污染事件问题关键的良好工具。通过物质流分析方法得出结论认为，台湾镉造成的农田污染与硬脂酸镉工厂之间的因果关系似乎相当密切。此外，本研究还发现，单个金属表面处理工艺工厂排放的废水不会造成显著的农田污染。然而，一组污染工厂同时排放的废水可能导致重大污染事件。
本案例研究只是对理解环境中与镉相关的有毒物质流做出的一小点贡献。本研究建议，台湾政府当局不应临时处理问题，而应采用控制措施全面处理镉污染问题。最后，我们收集到的信息或数据越准确，我们能识别的结果就越可靠。因此，应仔细审查本物质流分析模型中使用的相关数据的质量和数量，以确保对有毒物质流进行最正确和全面的调查。
