Sorption, desorption and leaching transport of heavy metals in soils common to New England

Abstract

Heavy metals are recognized as human health and environmental contaminants of concern. Non-industrial human exposures typically involve metals dissolved in water, sorbed in the soil, or contained in foods. Leaching of heavy metals to groundwater supplies is of particular concern. Heavy metals bioaccumulate in biota, and bioconcentrate in animals at higher trophic levels in the food chain. Animal exposures typically include ingestion of water, plant material and contact with soil. Risk characterization is a formal part of the process for remediation of properties contaminated with hazardous materials. The risk posed by heavy metals in the environment is a function of toxicity, physical parameters, and the mobility of the metal in the soil. To date, there is limited quantitative data regarding the sorption, leaching, and transport of metals in the vadose zone. This paper presents the results of bench scale experiments to evaluate these phenomena. Sixteen study soil columns were prepared using soils common to New England. Soils contained varying amounts of plastic and non-plastic fines, and included outwash sands, clay and till deposits. Physical parameters of each column were determined, including cation exchange capacity, particle size parameters and plasticity. Each column was filled with one liter of solution contain ing known concentrations of cadmium, chromium, copper, nickel and zinc. After a four-day contact period, columns were gravity drained for two days, and the volume of effluent solution and associated metals concentrations determined. Columns were then leached by application of 20 tap water rinses of approximately one pore volume each, and the concentration of each metal in the rinse lixiviant determined. Data were used to investigate the following questions: the capacity of soils to sorb metals, whether soil physical parameters are predictive of sorption, the ability of tap water to leach the metals, and the kinetics of the leaching process. © 2005 Springer Science + Business Media, Inc.