ABSTRACT
In this study the fractionation of the heavy metals in four commercial composts was assessed. The heavy metals mobility that most influenced the chemical composition of humic-like substances (HS-like) and the physicochemical, maturity and stability properties of the composts were identified. The heavy metals fractionation was performed following the modified sequential BCR (Community Bureau of Reference) extraction, which permitted to quantify the elemental concentration in the exchangeable/bioavailable, reducible, oxidisable and residual fractions. Cu, Ni, Cr and Pb were most abundant in the immobile phases, while Zn showed no dominant chemical phase. The HS-like chemical composition was influenced negatively by the residual fraction of Cu, Pb, and mainly Cr. The type or mobility of the heavy metals did not show any influence on composts maturity. However, mobile forms of Zn and Pb were correlated with high moisture content and low stability, respectively as well as with the increase of compost phytotoxicity.
