DPASV ANALYSIS (DIFFERENTIAL-PULSE ANODIC -STRIPPING VOLTAMMETRY) OF THE SUITABILITY OF ORGANIC COLLOIDS FOR BINDING AND MOBILIZATION OF METALS - CASE OF CATCHMENT BASINS IN TROPICAL REGIONS

Rock weathering under humid tropical climates is considered to be a fa st process, The role of detritic organic carbon is often postulated to explain this efficiency. The contribution of organic colloids seems t o be important for metal mobility in the aquatic environment. For this purpose natural waters from Parana river basin have been sampled and submitted to physical fractionation using sequential ultrafiltration. A system of mass balance equations is proposed to control the conserva tion of total dissolved organic carbon (D.O.C.) during the whole proce ss. The copper complexing capacity (CL) has been determined by D.P.A.S .V. measurements for each collected fraction. The CL/DOC ratio, define d as the quantity of available complexation sites, is the main paramet er retained to compare the different samples. The observed distributio n ratio is discussed considering: the size and geometry (sphero or lin ear colloids), pH and ionic strength, electrochemical conditions (depo sit potential and electrode response). For all sampled areas the sites density is maximum in the range 20 000D - 100 000D. For larger colloi ds (100 000D - 0,45 mum) active sites might be masked to analysis (sph eric conformation). This tendency is confirmed by pH and ionic strengt h effects: acidic medium or high ionic strength favors spherocolloids. Electrochemical measurements allow, in some cases, differenciation be tween usual organometallic interactions in solution (complexes) and ad sorption of metal on submicroparticles.