GEOCHEMICAL BEHAVIOR OF LEAD IN AN ALFISOL AND AN ULTISOL AT HIGH-LEVELS OF CONTAMINATION

The behavior of Pb in the A and B horizons of an Alfisol from Michigan and an Ultisol from Virginia was studied to determine the effects of ''shock'' loading. Combined sequential extraction-sorption isotherm an alysis (CSSA), a relatively new and little tested method, was used in the study. After spiking to simulate severe contamination (similar to 3000 to 60,000 mg/kg), CSSA revealed unexpectedly high levels of excha ngeable Pb in the A horizon of the Alfisol and in both horizons of the Ultisol, and showed that the sorption capacities of the phases common ly responsible for fixation of Pb at low to moderate levels of contami nation were exceeded. Carbonate sorbed the bulk of the Pb in the Alfis ol B horizon and has a high sorption capacity in both soils, despite t he presence of other phases with a strong affinity for Pb. Thus, when shock loading occurs (e.g., at a shooting range or dump sites), the hi ghly contaminated A horizons of both soils are expected to pose a seri ous toxic hazard to humans, and groundwater contamination is possible in association with the Ultisol. CSSA proved useful for determining th e sorption capacities of the individual phases while together in a nat ural soil system and therefore is a valuable method for predicting the attenuation capabilities of soils.