Migration and speciation of lead in a river system heavily polluted from a smelter

Abstract

Anodic stripping voltammetry was used for the study of the migration and speciation of lead in surface waters affected by atmospheric deposits around a smelter, by ore mining and urban runoff. Three physiocochemical forms of lead were distinguished: dissolved-labile (Pb 2+, PbOH + and PbCO 3), dissolved-bound (colloids or strong complexes) and particulate (retained by 0.40 μm membrane filter). Labile forms represented a very significant part of lead input from the washout of the atmospheric deposits, whereas most of lead from urban runoff and ore mining was in particulate or bound forms. Rather large stability of high concentrations of the labile forms of lead in the waters was found. It has been concluded that the precipitation of sparingly soluble lead compounds is not a primary factor controlling the concentration of dissolved lead in stream waters. The migration and speciation of lead was strongly affected by water flow rate. With increasing water flow rate, the concentration of particulate and labile lead increased whereas the concentration of bound forms decreased. Most of the lead was carried downstream in a small river during high water flow rate, but sedimented in a larger river. Rapid removal of lead by sedimentation occurred during low streamflow conditions.