不同抽出劑分析土壤鎘與水稻植體鎘含量之相關性分析

Abstract

國內衛生管理單位已將稻穀的鎘含量標準由現行0.45 μg g^(-1)降至0.4 μg g^(-1)，並為符合國際規範新的稻米重金屬含量之安全品質標準，研擬將稻穀的鎘含量逐步降至0.2 μg g^(-1)，對國產稻米安全品質管制將更嚴苛；另台灣農田土壤母質來源大都屬於海成堆積物質，特別在某些地區土壤鎘元素天然賦存量偏高，加以前述人類行為之影響土壤品質，多種因素糾纏一起，預測對於我國稻穀生產受新規範衝擊甚大，更多的農民的利益受到影響，未來產生的環保糾紛機率增大，本研究以數種常用土壤抽出劑的生物有效性，希望在符合衛生機關之食米重金屬限量標準之前提下，提出最適當之土壤分析方法。利用彰化縣彰化市、和美鎮及鹿港鎮選擇超過土壤污染管制標準農田8區，採集其水稻植體及根域的土壤，比較以王水消解法、0.1 M鹽酸、0.43 M硝酸、0.1 M EDTA及0.01 M氯化鈣抽出劑抽出土壤重金屬鎘與水稻植體含量之相關性，發現0.43 M硝酸、0.1 M EDTA效能相似；而0.01 M氯化鈣抽出劑抽出土壤重金屬量與水稻吸收重金屬鎘相關性最高，0.1 M鹽酸、王水消化法相關性最低。 Domestic sanitary management units are endeavoring to present an entire new norm for safety control of heavy metal content in rice to fulfill the international standard. Hence, domestic current safety control of rice production would be stricter as current norm of 0.45 μg g^(-1) may be reduced to 0.20 μg g^(-1). As parent materials of most field soil in Taiwan are derived from marine deposits that rendered considerable high indigenous Cd content in certain specific areas, and mingled with multiple factors as human activities, the new norm of rice production may bring about much impacts not only on farmers' income but also caused many rows over environmental issues. Therefore, aiming at presenting the most appropriate soil test method to fulfill the premise of an entire new norm for safety control of heavy metal content in rice stipulated by domestic sanitary management units, bioavailability of several soil extractants commonly used are tested and reviewed in detail in this study. Eight field sites distributed among Chang-hwua city, Ho-mei and Lukang township are involved in our survey, as they are considered mainly contaminated with Cu, Zn, Ni, and Cr beyond the control standard of Soil and Groundwater Pollution Remediation Act for Cropping lands. Though samplings of rice plant tissue and soils within root zone, the correlation cadmium content within rice tissue and that of soil derived from different soil extractants of aqua regia digestion, 0.1 M HCl, 0.43 M HNO_3, 0.1 M EDTA, and 0.01 M CaCl_2 are carefully determined and compared. The result indicated soil extractant of 0.43 M HNO_3 came out with similar correlation as that of 0.1 M EDTA, while best correlation was observed with use of soil extractant of 0.01 M CaCl_2. Very poor correlation was observed with use of soil extractant of both aqua regia digestion and 0.1 M HCl.