CHANGES OF AL AND HEAVY-METAL CONCENTRATIONS IN SLOVAK SOILS DURING THE LAST 25 YEARS

The objective of this study was to investigate changes of total concen trations and various extract-defined Al and heavy metal fractions in S lovak agricultural soils during the last 25 years. We compared 7 store d soil samples collected between 1966 and 1970 with samples collected in 1994 at the same sites. Seven fractions of Al,Cd, Cr, Cu, Fe, Mn, N j, Pb, and Zn were determined with a sequential extraction procedure i n all samples. Total concentrations of Cd, Zn, Mn, Ni, and Cu were low er in the 1994 samples; those of Al, Fe, Ph, and Cr were higher. Based on the initial concentrations,the average total concentration changes were: Cd(-10,3%)<Zn(-7,2%)<Mn(-4,8%) -2,3%)<Cu(-1,4%)<Al(+2,1%)<Fe(+2 ,9%)<Cr(+7,4%<Pb(+ 8,3%). This row is consistent with the decrease in metal mobility. The differences in salt-extractable metals showed the same pattern; however, changes were more pronounced than for total con centrations. The results suggest that decreases during the last 25 yea rs are caused by higher leaching than deposition rates and increases v ice versa. The highest increase in Cr and Pb concentrations is observe d in the EDTA-extractable fraction, which mainly characterizes organic ally bound metals.