以序列萃取評估埔心溪流域農地潛在環境風險;Using sequence extraction to assess the potential environmental risk of farm land in the Puxin River Basin

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题名:	以序列萃取評估埔心溪流域農地潛在環境風險;Using sequence extraction to assess the potential environmental risk of farm land in the Puxin River Basin
作者:	陳盈秀;Chen, Ying-Hsiu
贡献者:	環境工程研究所
关键词:	土壤重金屬;總量萃取;序列萃取;生物有效性;soil heavy metals;total extraction;sequential extraction;bioavailability
日期:	2019-08-06
上传时间:	2019-09-03 17:03:38 (UTC+8)
出版者:	國立中央大學
摘要:	臺灣因工業發展需求日漸增長，政府雖然分別設立工業區以利管控事業單位之廢水處理與排放，但仍有事業單位於郊區設廠，並將未經處理之廢水直接排放至渠道，使農民直接引用廢水灌溉而污染農地。廢水中所含之重金屬由於無法被降解，具有累積性，因此除了可能造成農地土壤受重金屬長久污染而影響植作的生長與收成外，也可能間接透過植作進入食物鏈而危害人體及生態健康。這當中，以銅污染最多，其次為鋅與鎳污染。值得注意的是，我國目前所訂定的土壤管制標準皆以單位土壤質量的「金屬總濃度」來規範重金屬的污染程度，雖然重金屬對環境所造成的衝擊的確與其在環境介質中的總濃度有關，但金屬總濃度的規範已知無法明確且精準的評估其對人體健康所造成的危害程度，更關鍵的應是這些重金屬在特定環境條件下所呈現出來的生物有效性(bioavailability)，因濃度總量不代表生物可接觸與可吸收的量，亦不等同對人體所產生的毒性效應。有鑑於此，本研究選擇曾受重金屬污染的埔心溪流域周遭之農地為試驗場址，採其表土樣品後利用序列萃取的手段(但在最後殘留態的消化步驟改以鹽酸取代氫氟酸)，針對重金屬在土壤的相態分佈進行分析探討，希望藉此評估潛在的環境風險。首先，以鹽酸取代氫氟酸搭配硝酸進行消化，其結果由相對差異百分比(RPD)得知兩種不同消化液萃取相當，均落在20%以內，驗證本實驗使用微波輔助王水消化法之鹽酸搭配硝酸取代微波消化原子光譜法之氫氟酸搭配硝酸進行消化時，亦能有效進行此實驗土壤中重金屬濃度萃取。Tessier序列萃取結果得知：(1)鉻之組態分布均以殘留態存在；(2)鉛、鋅、鎳之組態分布以鐵錳氧化態及殘留態存在；(3)銅之組態分布以鐵錳氧化態、有機態、殘留態存在；(4)鎘之組態分布以可交換態及殘留態存在。針對上述部分金屬分別落在不同組態間檢視可能之原因，發現污染濃度高低為可能影響存在之組態分布比例，其中萃取濃度越高，鎘之組態分布均以可交換態存在，對生物有效性有直接影響，而銅、鋅、鎳、鉛等重金屬之組態分布大部分均依鐵錳氧化態存在，對生物有效性則有潛在影響。上述資料利用Spearman等級相關係數評估結果得知，重金屬總量濃度與鐵錳氧化態及有機態濃度分別呈現強烈至非常強烈等顯著正相關，代表重金屬總量濃度越高，鐵錳氧化態與有機態所分配的濃度亦隨之增加，其對潛在環境風險影響越大，可能透過食物鏈影響人體健康危害機率越大。;Although in Taiwan the government has set up industrial zones to control the treatment and discharge of industrial wastewater separately, there are still factories located in the suburbs and discharging untreated effluents directly into irrigation channels. Such situations have led to contamination of farmland with heavy metals. Of the metals appearing in the agricultural soil, copper is the most frequently detected one, followed by zinc and nickel. It is noted that current control standards for farmland soil in Taiwan only regulate the total metal concentration. While the impact of heavy metals on the environmental matrix is indeed related to the total concentrations, it is the bioavailability of the metals under particular environmental conditions that plays the key role in determining the potential risk exerted on the ecosystem health. In view of this, this study selected the agricultural lands in the Puxinxi River Basin that had been polluted by heavy metals as the test sites, and used the method of sequence selective extraction (but in the final step hydrofluoric acid was replaced by hydrochloric acid) to investigate the phase distribution of heavy metals in the soil, with a hope to assess the potential risks. Results showed that digestion of the residual phase with hydrochloric acid gave results comparable to hydrofluoric acid, as evidenced by the relative extraction percentage (RPD) that was < 20%. In addition, Tessier sequence extraction results showed that: (1) chromium was predominantly associated with the residual phase; (2) the distribution of lead, zinc, and nickel was mainly in the manganese or iron-oxide phases and residual phase; (3) copper mostly stayed in the manganese/iron oxides, organic and residual phases; (4) the majority of cadmium resided in the exchangeable and residual phases. Lastly, the Spearman correlation analysis showed that the total concentrations of heavy metals were significantly correlated with the concentrations of the metal in the manganese/iron oxide phase and the organic phase, respectively, suggesting that these two phases may be the key determinants of risks pertaining to heavy metal contamination.
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