One of the alternatives to diminish the urban waste volume to be discarded is the composting process, whose final product - the compost - can be used in agriculture. However, these composts may present toxic substances for humans, i.e. heavy metals. The aim of this study was to evaluate the chemical composition of waste composts from six Brazilian capitals. Samples of cattle manure, lime, ordinary phosphate, potassium chloride, and urea were analysed to compare with the waste compost. Determinations of organic matter, C, N, P, K, Ca, Mg, Cu, Mn, Mo, Zn, Fe, Al, Ba, Cd, Co, Cr, Ni, Pb, Sr, Ti, and V were made. Nutrient contents in the compost samples were dependent on the composting processes involved. Micronutrient content was variable, some presenting values above the tolerable level of the German waste composts. The other elements analyzed, including heavy metals, were at the same reported levels for sludges in England. Considering the German tables of tolerable levels in waste compost values for Pb, Cr, Ni, and Cd, some of the samples were very high. In most of them, the total content of nutrients was smaller than in cattle manure, while that of heavy metals was higher. Considering that the content of analyzed elements is the total content, caution is advised on its use until secure results are available on the bioavailability to the plants of these elements in the composts.
Compost analysis; nutrients; heavy metals