BACKGROUND: Mercury is considered to be one of the most harmful metals for human health and the environment. Biomass based materials and the corresponding biochars show promising potential as Hg(II) sorbents. Sorption is an effective process to remove Hg(II) from polluted waters, and ismainly affected by water chemistry. The sorption efficiency of malt spent rootlets and their biochar was evaluated at various ionic strength levels with two different salts, NaCl and NaNO3. RESULTS: For bothmaterials, the saltswere added at concentrations of 1, 0.5, 0.1, 0.01, and 0.001 mol L-1. At pH5, Hg(II) removal was not significantly affected by the presence of NaNO3. High Hg(II) removal was obtained even at high NaNO3 concentrations; 53% at 1mol L-1 NaNO3. A significant decrease of Hg(II) sorption was observed with the increase of NaCl concentration. Hg(II) removal was 55% and 20% at 1 mmol L-1 and 1 mol L-1 NaCl, respectively. CONCLUSIONS: The differences observed in salinity effect can be related to the different counter ionspresent in the salts. LowClor NO3- concentrations did not interfere strongly withmercury sorption, but excess Cl-formed mercury species with negative charge, which demonstrated lower sorption. (C) 2017 Society of Chemical Industry