KINETICS OF DISSOLUTION OF LEAD AND ZINC FROM RURAL ATMOSPHERIC AEROSOLS IN FRESH-WATER AND SYNTHETIC SOLUTIONS

The time-dependent release of lead and zinc from rural aerosol samples has been studied in four natural lake waters and various synthetic solutions spanning a pH range of 2.99-8.02. Automatic direct measurement of the released metals in the experimental vessel was performed at 1 min intervals using square wave anodic stripping voltammetry. Substantial initial release occurred within minutes. Further release was sometimes complete within 15 min but could be still continuing after 60 min depending on the nature of the aerosol and the pH of the solution. A maximum concentration of metal in solution observed after a few minutes for some aerosols was attributed to initial release followed by readsorption to the aerosol occurring as a result of a temporary pH minimum induced by the dissolution process. High concentrations (1.8 meg 1(-1)) of calcium in solution stimulated release of lead and zinc, consistent with a surface exchange mechanism. The pH dependence of the percentage of zinc released was the same for synthetic and natural waters. Complete dissolution required more acid conditions than would be expected if release was entirely controlled by a simple, reversible exchange of ions at the particle surface. The pH dependence of lead release is more dependent on solution conditions.