如果经常将蔬菜存放数日再食用,是非常危险的。危险来自蔬菜含有的硝酸盐。硝酸盐本身无毒,然而在储藏一段时间之后,由于酶和细菌的作用,硝酸盐被还原成亚硝酸盐,是一种有毒物质。亚硝酸在人体内与蛋白质类物质结合,可生成强致癌性的亚硝酸类物质。 蔬菜中的硝酸盐来自肥料。化肥本身没有毒,给蔬菜施肥也没有错。问题在于人们往往大量、单一地施用氮肥超过了植物的需要量, It is very dangerous if vegetables are kept for a few days and then reused. The danger comes from vegetables containing nitrates. Nitrates themselves are nontoxic, however, and after a period of storage, nitrate is reduced to nitrite as a result of enzymes and bacteria and is a toxic substance. Nitrite in the human body with protein substances, can produce strong carcinogenic nitrite substances. Nitrates in vegetables come from fertilizers. Fertilizer itself is not toxic, fertilization of vegetables is not wrong. The problem is that people tend to use large amounts of nitrogen fertilizer alone more than the plant needs,