Complexation capacity of freshwater from Saguenay river, Canada

SUMMARY The Saguenay River is a major affluent of the St. Lawrence River, Quebec, Canada. The Saguenay River which drains a heavily industrialized region can be subdivided into two sections : the upper section is rather shallow and contains freshwater as the lower one is a deep fjord characterized by a thermohalocline at about 25 m. This work aimed at identifying the possible modifications brought up by anthropogenic sources upon the complexation capacity of the freshwater of this River. Five different stations were sampled for surface water the same day on the upper section of the River. The samples were filtered on 0,4 UJII membrane (pre-cleaned with HN03). A portion was analyzed and other ones were fractionnated as a function of the nominal molecular mass (NMM) of dissoived ligands by using in series four gel permeation chromatographic (GPC) columns filled with Sephadex G-10, G-15, G-25 and G-50 respectively, the elution being done by purified 18Mii water. The complexation capacity (CC) and critical stability constant (CSC) of the different fractions hâve been characterized using a method based on free Cu2+ back-titration by Differentiel Pulsed Anodic Stripptng Voltammetry (DPASV) and a 1:1 complexation scheme. Because copper was giving two unresolved peaks on the taillng of the oxygen peak, ail polarograms bave been deconvolved by a PASCAL computer program based on a least-sqares nonlinear fit using the Taylor different!al correction technique. AH results compiled were from the peak centered at - 60 mV against an Ag/AgCI reference. By manipulating the usual equations to determine CC and CSC with the free Cu2* back-titration, we were able to calculate CC by three different routes and CSC by two different routes ; when enough reliable data were available for each route, ail values obtained were concordant. So we observed that, going downstream, the CC decreased from 0,32 to 0,14 u,M for whote samples. At this point, we cannot identify the cause of this decrease wether it is due to