engleski

Geochemistry of potentially toxic elements in soils developed on karst in Croatia

Regional geochemical baselines in topsoils developed on karst in Croatia were determined for potentially toxic elements (PTE). The concentrations of PTE in the Croatian karst soils differ due to mineralogical composition and different types of climate which influence pedogenesis (mountain and Mediterranean). Some of the PTE (Pb, Cd, Zn, Se and Hg) correlate with the amount of annual rainfall which in mountain areas is > 3500 mm. A total of 894 sampling sites were analyzed covering 50% of Croatian karst region. Evaluation of anthropogenic impact on soils developed on karst evaluated by calculation of enrichment factors, and their mobility potential was assessed with various chemical extractions. Total concentrations and aqua regia extracts were used to evaluate the extraction capacity of aqua regia for PTE, since this method for determination of PTE in soils is defined by Croatian environmental protocols. Soils were found to be mostly impacted on a regional scale by Pb, Cd, Zn, Hg and Se and locally Cu by agricultural activities. The distributions of Cr, Ni, Co, Mn, Mo, V and As are linked substantially to pedogenic processes and content of clay minerals, Fe-Mn oxides and possible bauxite influence. Within the karst of the Dalmatian region more than 2000 deposits of bauxite were located within a belt 150km long, and were mined during the second half of the 20th century. The bauxites are enriched Cr, V, As, Cd, Ni and Pb. The results of a geochemical topsoil mapping program (Halamić, 2009), that covered the whole Croatian karst region with almost 1700 sampling sites, showed that the soils from the Dalmatian region had 30 to 50 % higher concentrations of these metals than other karst regions. As most of the underlying carbonate rocks contain low insoluble residua the chemistry of mineral dust from which the soils were formed originated from two sources during the LGM - the Po and the Neretva river floodplains which were submerged during the Holocene sea level rise. These two different provenances give the distinct geochemical patterns. The high concentrations of Al, As, Co, Cu, Fe, La, Pb, Ni, Mn, Th, V, Cr, and Zn have higher mean values in soils transported (by wind) on carbonate bedrock from the Neretva floodplain during the LGM than those from the Po plain. These signatures in both geochemical provinces are influenced by various degrees by bauxite dust derived during mining activities.

Bauxites; PTE; geochemical map; karst

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