Bed sediments of the Ottawa River downstream of the Gatineau River confluence are predominantly sandy, with variable organic contents, chiefly wood chips. Mercury sorption by these sands was studied at constant temperature using a mercuric-ion specific electrode, and varying added [Hg2+] and pH. Sorption rates are highest for organic-rich sands, but variation in particle size is apparently not sufficient to reveal sorption trends related to this parameter. Sorption data were fitted to a linear form of the Langmuir equation, from which sorption maxima and mercury bonding coefficients were derived. The maxima do not vary between samples, whereas the bonding coefficient relates most closely to organic content. Mercury sorption was little affected by pH.Desorption rates are low: less than 1% Hg was leached from sediment after 70 h agitation in distilled water, and a similar amount in fulvic acid solution. The mercury–sediment bonding is evidently much stronger than that between fulvic acid and mercury, irrespective of organic content of the sediment.

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