Cd, Cu, Pb and Zn content of the riparian zone of the Tisza River (Hungary) after heavy metal pollution

Abstract

At the beginning of the year 2000 two considerable waves of pollution occurred on the river Tisza. With the second wave, in a simultaneous flood, a huge amount of mud contaminated with heavy metals settled on the floodplains. As most of the contaminated areas are under agricultural use, the study of the heavy metal charge of soils and herbaceous plants of the floodplain has great importance. Along the Tisza four sampling sites were established and 300 cm deep drill cores were taken. The results of analytical examinations show that the heavy metal content of the topsoil is higher than that of the earlier formed lower layers, although contamination is also present there. This suggests that pollutions like this are not unknown in the Tisza Valley. It is greatly important to take cadmium pollution into consideration, as this element is extremely toxic and easily taken up by plants, and is likely to be a serious problem in the floodplain. The risk of contamination in the topsoil of the floodplain soils were examined in detail. The soils’ heavy metal content was the highest where the two pollution waves can be measured first at the same site. For determining the amount of heavy metals bound to other compounds sequential extractions were carried out. The proportion of the water soluble and exchangeable fraction – that is bioavailable to plants – is negligible in respect of Cu, Pb, and Zn, while it is considerable in the case of Cd, showing the risk of contamination. The gained data show that the high proportion of cadmium results in a remarkable environmental risk, while other heavy metals turn into a bioavailable form only after intensive acidification. The proportion of the heavy metal fraction bound to humus materials was expected to be low due to the exogenous origin and freshness of the topsoil.