| Summary: | 碩士 === 國立中央大學 === 環境工程研究所碩士在職專班 === 98 === Currently in Taiwan there are about 293 hectares of farmlands contaminated by heavy metals such as copper, cadmium, zinc and chromium. The main route of contamination is mostly of the improper wastewater discharge by factory plants, which leads to the pollution of irrigation water, and the water then flows through the irrigation system; Taoyuan County and Changhua County in the past were forced for land fallow and more than 100 hectares of farmland as nearby factories discharged wastewater that contained cadmium into the irrigation channels, which gave rise to the cadmium (contamination) rice event. As the contaminated agricultural land went through cleanup, the grown rice once again was found to exceed the cadmium standard for food crops and resulting in crop destruction. Thus, the original remediation purpose of the land was unsuccessful.
The approach in this study was mainly on literature review and field investigation. Related literatures were collected and summarized, where soil and plant samples of an actual pollution site were collected and analyzed. Samples were recollected after remediation, and were analyzed and compared with the original sample data. The reasons for why the agricultural land was unable to be used for farming were discussed, and finally suggestions were given for following agricultural land remediation and land use.
Results showed that Zhong-Fu area, Taoyuan was heavily polluted mainly by the heavy metal cadmium. The pollution was mostly confined between 0-30 cm of the topsoil. After applying the soil turnover dilution method, the pollutants were effectively dispersed to different depths of soil layers; however, as verification was done once again after the verification coordinates were shifted, the obtained results were different. Different sample location points shall influence the verification results. The errors of validation results will then affect the follow-up agricultural land unsuitable for farming. From the investigation of the polluted farmland at the Chunghwa section of Pate, the land after remediation was reported to once again exceed the control standard of heavy metal cadmium. The cadmium level in the farmland of Lot no. 938-1 was detected to be 1.75 mg/kg, where the cadmium level of the grown brown rice was as high as 2.28 mg/kg, exceeding the heavy metal limit, 0.4 mg/kg, in rice. The reasons for farmlands unsuitable to use after remediation are complicated, which cannot be determined by a single factor of cadmium level within the soil. The possible reasons include cadmium level within the soil, soil pH level, soil texture, redox environment, the planting crops and other different factors.
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