UPTAKE OF HEAVY METALS BY VEGETABLES GROWING ON SEWAGE SLUDGE

Abstract

Concentrations of the investigated heavy metals in the representative samples of vegetable growing media differed significantly – the highest concentrations were in the root zone of pumpkin, and the lowest – in the root zone of tomato. Only cadmium exhibited higher concentrations in the root zone of pumpkin and zucchini exceeding maximum permissible limits according to LAND 20-2001. Concentrations of all other metals in the root zone of the investigated vegetables were below limit values valid for the 1st category sewage sludge. Mean concentrations of nitrogen, phosphorus and potassium in the root zone was quite different for the three selected plant species, but comparably high bioavailable concentrations of the primary plant nutrients showed potential for this sludge to be used in agriculture or forestry. Concentrations of Cr, Ni and Pb in the sewage sludge were far below the critical range, while Cd, Zn and Cu concentrations were within the range or even above critical soil concentration values suggested in the reviewed literature. While average heavy metal concentrations in different parts of the investigated vegetables (pumpkin, zucchini and tomato) were much lower than the suggested critical ones, and was within the range (Cu, Zn, Cr and Ni) or even lower (Cd and Pb) than normal HM level in plants. Concentration of all of the investigated heavy metals was significantly lower in vegetable fruits than in the roots and no metal accumulation in the vegetable biomass (roots as well as aboveground parts) was observed – all accumulation coefficients were below unity.