The main tendencies in the adsorption of dissolved inorganic mercury (Hg2+) and methylmercury (MeHg+) on suspended kaolin particles have been investigated in synthetic aqueous solutions. The influence of NaCl, fulvic acid (FA) and suspended particulate matter (SPM) in the system has been studied at a constant pH of 7.2. The experiments were arranged according to a full factorial design with three factors (NaCl, FA SPM) at low (-) and high (+) levels. A central point (0) was repeated four times to estimate the reproducibility of the results. The low and high levels investigated were 0-35 g l-1, 0-10 mg l-1 and 0.5-5 g l-1 for the concentrations of NaCl, FA and kaolin respectively. In order to match the linear range of the analytical technique the total concentration of mercury (as Hg2+ or MeHg+) in the synthetic suspensions was 25 ng ml-1. After chemical stabilization of each suspension, the Hg2+ or MeHg+ content in the clear filtrate was determined by an automated hyphenated technique combining the following steps: derivatization by hydride generation, preconcentration by cryogenic trapping, separation by packed column gas chromatography and detection by quartz furnace atomic absorption spectrometry. The removal of Hg2+ and MeHg+ from the solution via adsorption on particles ranged, respectively, from 12.4 to 94.9% and from 1.7 to 45.6% of the total mercury compound concentration. High concentrations of NaCl led to lower adsorption rates of both mercury species. The adsorption of MeHg+ was enhanced in the presence of FA, whereas that of Hg2+ was clearly diminished. High levels of SPM promoted the adsorption of both Hg2+ and MeHg+ on kaolin particles. Several experiments were also conducted to check the adsorption rate of Hg2+ and MeHg+ on natural particles collected in the Gironde estuary. The results confirmed the general trends observed when using reference kaolin particles. The results presented here will be helpful for groups modelling the physico-chemical behaviour of mercury in estuary conditions. Copyright © 2001 John Wiley & Sons, Ltd.