Gramss Gerhard, Voigt Klaus-Dieter
Institute of Geosciences, Friedrich-Schiller-University, Burgweg 11, 07749, Jena, Germany,
Environ Geochem Health. 2014 Jun;36(3):441-52. doi: 10.1007/s10653-013-9572-5. Epub 2013 Oct 6.
Metalliferous uranium mine overburden soils integrated into arable land or stabilized by perennial rangeland plants evoke concern about the quality of crops and the exposure of grazing and thereby soil-ingesting (wildlife) herbivores to heavy metals (HM) and radionuclides. In a 2-year trial, thirteen annual and perennial forage and rangeland plants were thus potted on, or taken from, cultivated field soil of a metalliferous hot spot near Ronneburg (Germany). The content of soil and shoot tissues in 20 minerals was determined by ICP-MS to estimate HM (and uranium) toxicities to grazing animals and the plants themselves, and to calculate the long-term persistence of the metal toxicants (soil clean-up times) from the annual uptake rates of the plants. On Ronneburg soil elevated in As, Cd, Cu, Mn, Pb, U, and Zn, the shoot mineral content of all test plants remained preferentially in the range of "normal plant concentrations" but reached up to the fourfold to sixfold in Mn, Ni, and Zn, the 1.45- to 21.5-fold of the forage legislative limit in Cd, and the 10- to 180-fold of common herb concentrations in U. Shoot and the calculated root concentrations in Cd, Cu, Ni, and Zn accounted for phytotoxic effects at least to grasses and cereals. Based on WHO PTWI values for the tolerable weekly human Cd and Pb intake, the expanded Cd and Pb limits for forage, and reported rates of hay, roots, and adhering-soil ingestion, the tolerable daily intake rates of 0.65/11.6 mg in Cd/Pb by a 65 kg herbivore would be surpassed by the 11- to 27/0.7- to 4.7-fold across the year, with drastic consequences for winter-grazing and thereby high rates of roots and soil-ingesting animals. The daily intake of 5.3-31.5 mg of the alpha radiation emitter, U, may be less disastrous to short-lived herbivores. The annual phytoextraction rates of critical HM by the tested excluder crops indicate that hundreds to thousands of years are necessary to halve the HM and (long-lived) radionuclide load of Ronneburg soil, provided the herbage is harvested at all. It is concluded that the content in Cd/As, Cd, and Cu exclude herbage/Ronneburg soil from the commercial use as forage or pasture land soil for incalculable time spans. Caution is required, too, with the consumption of game.
含金属铀矿的表土若被开垦为耕地或被多年生牧场植物固定，会引发人们对作物质量以及放牧动物和食土（野生动物）食草动物接触重金属（HM）和放射性核素的担忧。在一项为期两年的试验中，将13种一年生和多年生饲料及牧场植物种植在德国罗讷堡附近一个含金属热点地区的耕地土壤上，或从该土壤中采集。通过电感耦合等离子体质谱法（ICP-MS）测定了土壤和地上部组织中20种矿物质的含量，以评估重金属（和铀）对放牧动物和植物本身的毒性，并根据植物的年吸收速率计算金属毒物的长期持久性（土壤净化时间）。在砷、镉、铜、锰、铅、铀和锌含量升高的罗讷堡土壤上，所有受试植物地上部的矿物质含量大多仍处于“正常植物浓度”范围内，但锰、镍和锌的含量高达正常浓度的四倍至六倍，镉含量是饲料法定限量的1.45至21.5倍，铀含量是常见草本植物浓度的10至180倍。地上部以及计算得出的镉、铜、镍和锌的根部浓度至少对禾本科植物和谷类作物产生了植物毒性作用。根据世界卫生组织（WHO）关于人类镉和铅每周可耐受摄入量的PTWI值、饲料中镉和铅的扩展限量以及报告的干草、根和附着土壤的摄入量，一只65千克的食草动物全年摄入的镉/铅量将超过可耐受日摄入量的11至27/0.7至4.7倍，这对冬季放牧以及食根和食土动物的高比例摄入将产生严重影响。对于寿命较短的食草动物来说，每天摄入5.3至31.5毫克的α辐射源铀可能危害较小。受试的排斥性作物对关键重金属的年植物提取率表明，要使罗讷堡土壤中的重金属和（长寿命）放射性核素负荷减半，需要数百至数千年时间，前提是所有牧草都能被收割。结论是，在无法估量的时间跨度内，镉/砷、镉和铜的含量使得罗讷堡土壤上的牧草/土壤不能用作商业饲料或牧场土地。对于野生动物的食用也需要谨慎。
