凡是不新鲜或干瘪变质的厚皮菜、白菜以及用脏水喷洒过的蔬菜,都不同程度的带有硝酸盐。硝酸盐对人危害不大。但是由于放置不当已经发黄变质的或用小火焖煮时间过长的白菜,其中的硝酸盐会起化学变化而分解成为亚硝酸盐,这就是一种剧毒物质,人吃了这种菜半小时后,会出现 All are not fresh or shriveled the thick-skinned vegetables, cabbage and vegetables sprayed with dirty water, with varying degrees of nitrate. Nitrate is not harmful to people. However, due to improper placement has been yellowing metamorphosis or simmering for too long a small cabbage, which will change chemical decomposition of nitrite, which is a highly toxic substances, people eat this dish Half an hour later, there will be