RETROSPECTIVE EXPERIMENTAL MONITORING OF HEAVY-METALS CONTAINING IN SOILS OF THE CZECH REPUBLIC

Retrospective experimental monitoring of the changes in the heavy metal content (Cd, Co, Cr,Cu, Hg, Ni, Pb, Zn) and determination of thc state of contamination in Ap horizons of croplands (total content, content in the 2M HNO3 extract) of 23 Czech districts provided the results as folows: In the set containing 251 paired sites (502 samples) the differences among samples taken in the years 1960 to 1972 and 1987 to 1989 cannot be confirmed; only some shift of medians in Cd, Cr, Ni, Pb and Zn was found: so it is not possible to verify area trend of increasing content of heavy metals for the period of 20 to 30 years. In five soil-lithological groupings in the set of 686 samples, on the basic of distribution histogrammes and testing the distant values, background values of heavy metals and lower limits of anthropically increased values were determined: the values for medium to heavy-textured soils (without geochemical anomalies) are presented in comparison with maximum admissible values for the Czech Republic and (Germany in Tab. I. Anthropically higher contents of heavy metals were found in the whole set of 686 samples for different elements in a different way in 6 to 12 % of tested samples (Tab. II), contents exceeding maximum permitted limits given in Tab. 1, were outnumbered only sporadically. There were more than 75 % of cases where anthropically increased values appeared in the same sites yet before 20 to 30 years. The increase in the content of heavy metals in the soil is (except sites characterized by highest deposition or by waste application into soil) a very slow process. Lower limit of increased values is recommended for its regulation as a limit value restricting inputs of heavy metals in the soil. Obtaining the maximum permitted values (Tab. I) represents critical conditions for cultivation of plants with inputs into food chain.