Effects of salinity and humic acid on the sorption of Hg on Fe and Mn hydroxides

► Adsorption of Hg2+ on Fe and Mn oxides was lower in marine than freshwater system. ► Humic acid inhibited Hg2+ adsorption on Fe and Mn hydroxides in freshwater system. ► Humic acid promoted Hg2+ adsorption on Fe and Mn hydroxides in the marine system. ► Effect of humic acid on Hg2+ adsorption was more visible for crystalline hydroxides.