Availability and fractionation of Cu, Pb and Zn in an acid soil from Galicia (NW Spain) amended with municipal solid waste compost

Abstract

The potential availability and chemical fractionation of trace elements in soil after compost addition was studied in a laboratory incubation. An acid agricultural soil, developed on biotitic schists, was amended with two rates of a municipal solid waste compost (3% and 6% weight) or lime (2.5 g CaCO₃ kg^-1, calculated to raise soil pH to values close to those of the compost-amended soil), and incubated in the laboratory for five months. Compost addition increased the availability of Cu, Pb and Zn (measured in DTPA extract) with respect to the control, whereas lime reduced it. Compost amendment increased soil total Cu, Pb and Zn concentrations, and their chemical distribution, assessed by means of the BCR (Bureau Communautaire de Reference) fractionation scheme, was different for each element. Compost addition increased Pb in the reducible (iron oxide-bound) fraction, Cu in the organic and iron oxide fractions, and Zn in the soluble and reducible fractions. Lime did not change the fractionation or total concentrations of the metals analysed. The most problematic element in the compost-amended soil from an environmental point of view is Zn, because it was found in highly mobile forms, while for Cu and Pb this risk is low.