銦對植物的毒性及土壤銦對食用米麥的環境風險

Abstract

銦之化合物被廣泛的使用在半導體、光電和能源等高科技產品當中，隨著使用量的增加，也增加了曝露於環境中的風險，若此污染物流布於土壤當中，則可能累積於植物體內，進入食物鏈進一步影響人體的健康。因此為評估其污染風險，有必要瞭解銦進入土壤後的生物有效性，以及食用作物對其吸收和累積。銦在土壤中主要是鐵猛氧化物結合態的形式存在，其次是氫氧化銦和磷酸銦的沈澱。銦化合物的溶解度決定了土壤中銦的有效性，在pH低時，銦的有效性較高。植物吸收的銦大部分會積累在根部，只有一小部分被運送至穀粒。銦的積累會限制植物的生長、引起氧化逆境、花青累積與植體內營養的失衡。植物根系分泌物中的檸檬酸可以作為一個潛在銦的螯合劑，降低銦的吸收。食用受銦污染的糧食作物可能是人類暴露銦污染的接觸途徑之一。為了評估食用銦污染米麥對人體健康風險造成危害程度，引用美國環保署環境風險評估公式運算銦之危害商數值。水稻和小麥分別種植在不同pH的土壤中，其中高銦濃度(1.0 mmol kg-1)的酸性土壤，被認為是現實中最壞的污染情況，因為銦在酸性條件下有最大的生物有效性。結果顯示即使在此條件下，從受銦污染的土壤中收獲的米麥，銦的最大危害商數值皆小於1，即表示不會對人類健康產生不利影響，依此，可推測銦於食用米麥的食物鏈途徑對人體的危害風險應該不高。然而，實地銦污染如何藉由食物鏈影響人體的健康仍須進一步研究，以更好地闡明種植在受銦污染土壤中的作物所帶來的環境風險。

The use of indium in semiconductor products has increased markedly in recent years. The release of indium into the ecosystem is inevitable. Under such circumstances, effective and accurate assessment of indium risk is important. However, knowledge of its environmental fate has been very limited so far. This study aims to investigate indium accumulation and its toxic effects on plants, as plants constitute the base of food chains. In soil, the predominant indium species are indium associated with iron hydroxides followed by indium hydroxide and phosphate precipitates. Their solubilities determine overall indium availability in soil, which is higher at lower pHs. Most absorbed indium accumulates at the roots, with only a tiny portion reaching the grains. Indium accumulation in plants caused stunted growth, oxidative stress, anthocyanization, and unbalanced mineral nutrition. Secreted citrate could function as a potential detoxifier to repel indium uptake. Consumption of indium-contaminated food crops is potentially a major human exposure pathway. Indium accumulation in the human body is probably carcinogenic and has various adverse effects on human health, such as heart, kidney, and liver damages. To evaluate potential risks associated with indium-contaminated consumption, rice and wheat were grown on soils with different pHs and textures, including acidic soil with a high indium concentration (1.0 mmol kg-1), which is considered the worst-case scenario because it promotes the greatest indium bioavailability. The health risks to humans, based on their grain consumption, were evaluated using the Hazard Quotient (HQ). The corresponding HQ indicated no adverse effects on human health, even in the worst-case scenario. Therefore, the consumption of rice and wheat grains harvested from indium-contaminated soils probably does not warrant concern for human health. Further field studies are necessary to better elucidate the risks associated with consuming crops grown in indium contaminated soils.