Etude par D.PA.S.V. de l'aptitude de la matdere organique colloidale a fixer et a transporter les metaux: Exemples de bassins versants en zone tropicale

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Abstract
Rock weathering under humid tropical climates is considered to be a fast process. The role of detritic organic carbon is often postulated to explain this efficiency. The contribution of organic collo?ds seems to be important for metal mobility in the aquatic environment. For this purpose natural waters from Paranã river basin have been sampled and submitted to physical fractionation using sequential ultrafiltration. A system of mass balance equations is proposed to control the conservation of total dissolved organic carbon (D.O.C.) during the whole process. The copper complexing capacity (CL) has been determined by D.P.A.S.V. measurements for each collected fraction. The CL/DOC ratio, defined as the quantity of available complexation sites, is the main parameter retained to compare the different samples. The observed distribution ratio is discussed considering: the size and geometry (sphero or linear collo?ds), pH and ionic strength, electrochemical conditions (deposit potential and electrode response). For all sampled areas the sites density is maximum in the range 20 000D ‐ 100 000D. For larger collo?ds (100 000D ‐ 0,45 μm) active sites might be masked to analysis (spheric conformation). This tendency is confirmed by pH and ionic strength effects: acidic medium or high ionic strength favors spherocollo?ds. Electrochemical measurements allow, in some cases, differenciation between usual organometallic interactions in solution (complexes) and adsorption of metal on submicroparticles.

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