BIOTRANSFER OF HEAVY METALS AS A FUNCTION OF SITE-SPECIFIC AND CROP-SPECIFIC FACTORS

摘要

A survey of the principal variables determining the uptake of heavy metals by plants is given based on recent experimental results. The biotransfer of a particular total content of heavy metals san vary widely in dependence on chemical and physical soil properties, climate conditions and plant-specific parameters. Hereby the assessment of the contents of plant-available heavy metals in the soil by chemical extraction methods is complicated. "Mild" extractions (e.g. 0,1 M CaCl_2) should be preferred,because they already reflect at a certain degree the influence of soil characteristics on solubility and mobility of heavy metals in the soil. The goal of preventing "critical" heavy metal contents in plants by establishing maximum permissible soil levels can be reached therefore by using "mild" extractions. In case of using total contents this can only be achieved in connection with other soil parameters like pH and clay content. Differences in the uptake capacity of plant roots and/or differences in the ability of the plants to translocate heavy metals from the roots can lead to quite different transfer factors. With increasing recycling of organic wastes in the agricultural area, the possibility of heavy metal accumulation in soils and plants has to be taken into account. As far as sewage sludge is concerned, long term field experiments, however, have shown that there is no danger at all, if sewage sludge application is in agreement with the legislative permissions.