环境重金属污染物的生物有效性

The bioactivity of environment heavy metal pollutants in the vicinity of non-ferrous metal smelters

利用生态系统研究了白银有色金属冶炼矿区周围环境中重金属的分布及生物有效性。结果表明 ,工厂在冶炼过程中已造成 Pb、Cd、Cu、Zn对周围环境不同程度的污染 ,其含量与距工厂的距离呈负相关 ;重金属在各种生物体内均有不同程度的吸收和累积 ,其吸收累积量随重金属和生物种类的不同而有差异 ;土壤的污染 ,使农作物和牧草中 Pb、Cd含量超过动物的最大耐受量和中毒的临界值 ;动物研究发现 ,肾脏、骨骼和肝脏是机体内重金属蓄积的主要器官。因此 ,放牧动物可作为环境重金属污染状况的标识 。

Baiyin in Gansu Province was an important base producing non-ferrous metals in China. This region contains extensive mineral resources characterized by large quantities of ores containing copper, lead, zinc, and iron, with attendant gold, silver and a small quantity of platinoids. A number of very large industrial enterprises were formed for lead zinc, copper, and polymetallic extraction in the 1970s. During a few decades of intensive development metallurgical industries soon occupied a very wide area. There were deaths of a large number of grazing sheep and horses on farmland in the vicinity after the smelters went into operation. Accordingly, it was concluded that the disease was probably related with environmental heavy metal pollution caused by industry activities in the region. The national state of environment data for emissions and ambient environment have shown that the region is exposed to high levels of a range of pollutants, including heavy metals. The objectives of the present study were to evaluate the effect of heavy metals on biotoxicity and bioavailability in the region. In this study, the concentrations of lead, cadmium, copper and zinc in soils, water, forages, feed and blood, hair and tissues of affected sheep and horses were determined in the surroundings of the smelters in Baiyin and controls. The concentrations of these elements in soils, forages, water and feed were significantly higher than those in the control area (p<0.01). The contents of lead and cadmium were 9.3 and 690 times in forages, respectively; 10 and 35.6 times in feed. Meanwhile, the results showed a clear decrease with increasing distance to the smelters. The concentrations of lead and cadmium in blood, hair and tissues of the affected sheep and horses were significantly higher than reference values and control animals (p<0.01). Lead and cadmium intake levels, estimated according to the ingestion rates of forages, illustrates that the apported lead and cadmium through the ingestion of vegetation growing in the closest sites to the smelters were approximately 6.0mg Pb/kg body weight/day and 1.1mg Cd/kg body weight/day in horses, 21.4mg Pb/kg body weight/day and 4.0mg Cd/kg body weight/day in sheep, surpassing the fatal dosages for horses of 1.7mg Pb/kg body weight/day and for sheep of 4.4mg Pb/kg body weight/day and 1.0mg Cd/kg body weight/day. Lead and cadmium were mainly accumulated in kidney, liver and skeleton of affected sheep and horses in the region. the disease of sheep and horses in this region is caused by lead poisoning combined with cadmium, mainly due to environment heavy metal pollution by industrial activity. It is therefore suggested that as such levels of contamination in animal food and grain pose a significant potential risk to human health, these results have formed the basis for subsequent research on levels of metal contamination in human tissues from affected populations. In the present study, the concentrations of copper and zinc in soils, forages and feed were significantly higher in Baiyin region than those in control area. In general, the maximum tolerable levels for copper in sheep and horses are 25mg/kg and 800mg/kg, respectively, for zinc 300mg/kg in sheep (NRC, 1980). Whether the levels of copper and zinc in these soils and forages affect the absorption of lead and cadmium in the sheep and horses will be further investigated. The result showed that the heavy metals in the surroundings of the smelters had an effect on biotoxicity and bioavailability. Thus it can be seen that knowledge of lead and cadmium concentrations in livestock in this region is important for assessing the effects of pollutants on domestic animals themselves and contaminant intakes by humans.