The removal of colloidal lead during estuarine mixing: seasonal variations and importance of iron oxides and humic substances

Abstract : In the present study, seven colloidal fractions of lead (Pb) were analysed along the mixing zone of the Penzé estuary over the Year 2009, with the aim to provide some insight into the mechanism that removes the metal from the <0.45-µm fraction. According to our results, Pb was generally found as large colloids (>300 kDa) and was removed in the salinity range 0-10 from all of the size fractions where it was significantly found. Because the colloidal fractionation of Pb was strongly linked to that of iron (Fe) and humic substances (HS), the removal of Pb in the mixing area must occur under flocculation of organomineral complexes. A key period corresponding to the first strong autumnal precipitations was also revealed in the present work. At this time of the year, the mobilisation of Pb (and Fe) from catchment soils is enhanced by the mobilisation of HS and the metal is associated with smaller colloids (30-300 kDa).