| 摘要: | 台灣地區目前農田約有二百九十三公頃遭受銅、鎘、鋅、鉻等重金屬污染，主要的污染途徑多為工廠的廢水不當排放造成灌溉水污染，再經灌溉系統引灌所致；過去桃園縣與彰化縣有農田因附近工廠排放含鎘廢水至灌溉渠道中所引發之鎘米事件，造成一百多公頃農田污染而休耕。受污染之農地經過整治後，在恢復耕作之後卻再次發生種出的稻米含污染物鎘超過食用作物標準之情形，導致作物銷毀，而當初整治的目的也未能達成。 本研究主要以國內外相關研究文獻進行收集歸納，再藉由現地污染場址土壤採樣與植體採樣分析，以及整治後驗證規劃採樣點的座標位移再次進行採樣，並與原採樣點數據進行分析比對，最後與蒐集之文獻相互應證，並探討農地無法農用之原因，提出後續農地整治與土地利用之建議。 經研究結果顯示桃園中福地區四筆土地，主要污染物為重金屬鎘，其污染多侷限於表土0-30公分處，經翻轉稀釋後能有效將污染物均勻分散至不同深度土層；但是驗證單位座標經位移後再次進行驗證比較，所得結果不同，不同的驗證採樣點，將會影響驗證的結果，驗證結果錯誤將影響後續農地無法農用。八德中華段污染農田調查發現，曾經整治驗證通過之地號再次檢驗出重金屬鎘超出農田土壤管制標準，938-1地號農田重金屬鎘含量檢測1.75 mg/kg，所種糙米鎘含量可達2.28 mg/kg，超出食米重金屬限量標準0.4 mg/kg。整治後農田無法農用之成因複雜，無法單由土壤含鎘濃度逕行判定，造成原因包含土壤含鎘量、土壤pH、土壤質地、氧化還原環境以及栽種作物品種等等眾多因素。 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. |
