Chemical and mineralogical speciation of As, Sb and other metal(loid)s determine solubility in water and stability under various pH and redox conditions. Regardless of their importance, the chemical and mineral species of hazardous metal(loid)s are not the center of parameters used to assess the risk of environmental impact on contaminated soils and sediments. The objective of the proposed Ph.D. project is to study the solid-phase speciation and mobility of As and Sb in naturally and anthropogenically contaminated soils and fluvial sediments. The study sites will include highly contaminated sites from Central Europe with bulk As and Sb concentrations in the range of hundreds to thousands of ppm. The focus will be also on contaminated sites in which the concentrations of metalloids derived from geogenic sources are generally low and often close to the background levels. To investigate the species and distribution of As and Sb in soils and sediments, different spectroscopic instruments will be used in combination with chemical fractionation and electron microscope techniques.