重金属是天然存在的元素,如果污染达到一定水平,会对人们健康产生十分严重的威胁。目前最应引起人们注意的重金属污染物是铅、汞、镉。铅可以作为农药及汽油、油漆、家具、瓷器等的添加剂。燃煤也会释放出大量的铅。铅的危害主要是会引起儿童智力发育障碍。儿童处于发育阶段,机体对铅毒的易感性较高。另外,高浓度的铅尘大多距地面1m以下,这个高度恰好与儿童的呼吸带高度一致。因此,儿童通过呼吸进入体内的铅远远超过成人,加上某些儿童有吮吸手指的不洁行为,学习用具 Heavy metals are naturally occurring elements. If the pollution reaches a certain level, it will pose a very serious threat to people’s health. At present, the most should pay attention to heavy metal pollutants are lead, mercury, cadmium. Lead can be used as pesticides and gasoline, paint, furniture, porcelain and other additives. Coal burning can also release large quantities of lead. The main hazards of lead can cause mental retardation in children. Children are in the developmental stage, the body is more susceptible to lead poisoning. In addition, the high concentration of lead dust mostly below the ground 1m, this height is exactly the same height with the child’s breathing zone. As a result, the amount of lead that children breathe into the body far exceeds that of adults, together with the unclean behavior of some children who suck their fingers.