MERCURY DISTRIBUTION IN RELATION TO IRON AND MANGANESE IN THE WATERS OF THE ST.-LAWRENCE RIVER

Waters entering the St. Lawrence River from Lake Ontario and from the Ottawa River have been sampled on a quaternary basis between March 199 5 and October 1996. Mercury, iron, manganese, organic carbon and other chemical parameters have been determined in the filtered water (< 0.5 mu m) and suspended particles (> 0.5 mu m). Average total mercury con centrations (+/-standard deviation, number of determinations) in filte red samples were 1.3 +/- 0.9 pM (39) at the mouth of Lake Ontario and 4.0 +/- 2.3 pM (54) at the outlet of the Ottawa River. The respective average concentrations in suspended particles were 1.1 +/- 0.4 (39) an d 0.6 +/- 0.2 (55) nmol g(-1). Partial correlation analyses reveal tha t in the fraction < 0.5 mu m - which seems to consist of a significant fraction of colloids - mercury was significantly linked to iron, whil e in the particulate phase, mercury was related to manganese. Mercury was not correlated with organic carbon. A sorption model on iron and m anganese hydroxides is proposed to explain these observations. (C) 199 8 Published by Elsevier Science B.V.