Organic waste from the food processing industry constitutes suitable substrate for anaerobic digestion. The chemical composition of digester feedstock, the availability of nutrients for microorganisms responsible for the anaerobic decomposition of organic compounds and the substrate's toxicity for bacteria have to be controlled in plant material for biogas production. The chemical composition of biomass determines biogas yield and the quality of digestate used as fertilizer. The objective of this study was to analyze the chemical composition and toxicity of food wastes by atomic absorption spectrometry (AAS). The content of heavy and light metals was determined in selected plant wastes, including brewer's spent grain, apple pomace, strawberry pomace, carrot pomace, orange and grapefruit peel, beetroot and potato peel, potato pulp, rapeseed cake, walnut and hazelnut shells. The analyzed wastes were characterized by varied content of Pb, Cd, Cu, Zn, Cr, Ni, Na, K, Mg and Ca. The results of this study can be used to optimize the composition of feedstock for biogas plants. (c) 2014 Elsevier Ltd. All rights reserved.