Content of selected heavy metals in soil and in Virginia mallow (Sida hermaphrodita) fertilised with sewage sludge

The aim of this study has been to determine the influence of sewage sludge on the content of selected trace elements in Virginia mallow and in the soil after harvesting these plants. Sewage sludge was the source of nitrogen and phosphorus for the plants, while potassium was supplied in the form of mineral fertilisers. Virginia mallow plants grown without fertilisation served as the contnrol. The form and dose of sewage sludge did not have any larger effect on the concentrations of copper and zinc in the plants. The content of manganese and chromium increased as the the dose of either form of sewage sludge increased. In turn, the content of nickel in Virginia mallow tended to decrease as the doses of sludge rose. The biomass of Virginia mallow contained significantly more cadmium when fertilised with sewage sludge. Significantly more Mn and Pb accumulated in the soil which had been enriched with wet sewage sludge, while the soil treated with pelleted sewage sludge contained more Cd. The soil content of Zn, Mn, Pb and Cr tended to increase as the dose of sewage sludge increased. With respect to nickel and cadmium, their soil content was significantly differentiated by the applied doses of sewage sludge but the direction of these modifications was inconsistent. The forms or doses of sewage sludge applied left the content of copper in soil unaffected. Concerning the accumulation in the aerial parts of Virginia mallow plants, the heavy metals can be ordered as follows: Cd < Cu < Cr < Ni < Zn < Mn. Generally, sewage sludge applied in doses that covered the demand of Virginia mallow for nitrogen and phosphorus did not cause excessive increase in the content of heavy metals in the crop’s aerial biomass. However, an increase in the dose of sewage sludge tended to raise the content of mobile forms of heavy metals in soil after harvest of Virginia mallow.