Mobility of copper and zinc in near-surface groundwater as a function of the hypergenic zone lithology at the Kampinos National Park (Central Poland)

In the paper, we assess the mobility of copper and zinc in two sections, Granica and Kampinos, of the glacial and post-glacial sediments in the Kampinos National Park (Poland) and its buffer zone. The Granica section is practically devoid of carbonates and clay fraction, and the environment is markedly acidic. The other section, Kampinos, is characterized by a considerable content of carbonates (up to 20%) and clay fraction (up to 34%) with high sorption potential. The bonds of Zn²⁺ and Cu²⁺ cations with the solid phase occur mainly through adsorption and formation of salts, and through creation of chelated and complex connections. We found that, while sorption of Cu²⁺ within the shallow groundwater zone under typical natural environment equilibrium conditions depends mainly on the content of the sorbing solid phase (i.e. organic matter and metal oxides and hydroxides), sorption of Zn²⁺ within the shallow groundwater zone depends mainly on the fluctuating acidity and ionic strength of the groundwater, and to a lesser extent on the content and nature of the solid phase. The sorption process within the Kampinos section occurred predominantly on to three sorption media: clay fraction, organic matter and amorphous forms of Fe, Al and Mn. In the Granica section, because of the absence of clay fraction, sorption of the two metals occurred mainly with the organic matter and amorphous forms of Fe, Al and Mn. In addition, the sorption potential of the two metals in this section was low, because of the acidic pH of the environment, i.e. high availability of exchangeable hydrogen in the sorption complex. The concentrations of copper and zinc in the soil (Sₒ) were examined using both: the Lindsay and Norvell’s and aqua regia methods. The methods of variable extraction capacity yielded very similar results for copper. In addition, the study found that the amounts of extracted zinc depended on the type of solution. The highest concentrations of zinc and copper were observed using the extraction with aqua regia. The results from determining zinc and copper concentrations (Sₒ) in the soil and rocks and the results of hydrochemical modelling show that the mobility of these two elements is highly limited by sorption processes; moreover, zinc is less effectively adsorbed than copper in these sections.