Assessment of gross accumulation and leaching characteristics of heavy metals in a contaminated urban soil

The city of East St. Louis, IL has a history of abundant industrial activities including smelters of ferrous and non-ferrous metals, a coal-fired power plant, companies that produced organic and inorganic chemicals, and petroleum refineries. The East St. Louis Action Research Program (ESLARP) was initiated to revitalize a once prosperous community. Included in the ESLARP agenda was the assessment of the extent of industrial contamination in community soils. To this end, a protocol for soil analysis was developed to produce sufficient information on the extent of heavy metal contamination in East St. Louis.; Soil cores representing every borough of East St. Louis were analyzed using neutron activation analysis and x-ray fluorescence spectrometry. The top three inches of topsoil contained heavy metal concentrations as high as 10,360 ppm zinc, 40.2 ppm antimony, 12.5 ppm cadmium, 1,860 ppm lead, 14,400 ppm copper, 1,130 ppm tin, and ppm quantities of mercury. Based on the topsoil data, specific soils were analyzed as a function of depth to determine the migration depth of contaminants. In sandy soil from a vacated rail depot near the bank of the Mississippi River, the metals were fairly evenly distributed down to 15 inches in depth. Clay soils from near a zinc smelter contained a systematic drop in heavy metal concentration.; Leaching tests were performed on specific soils to elucidate heavy metal associated mineral fractions and general leachability. The Toxicity Characteristic Leaching Procedure was performed on three different soils and all metal leachates were well below regulatory limits. Sequential extraction revealed that the leached residual fractions were low for the heavy metals. Also, the importance of the reductive and oxidative fractions was identified. Cadmium was the only metal recovered in quantity using mild extractants targeting exchangeable and carbonate species.; Next, garden soil was leached in a column experiment to elucidate the leaching characteristics of the soil under natural conditions. The leachate concentrations were low for all heavy metals. The results were modeled and the importance of instantaneous dissolution was evident from the model. By incorporating desorption/adsorption terms into the source term, the model was adapted very well to the time dependent heavy metal leachate concentrations. The results demonstrate the utility of a simple model to describe heavy metal leaching from contaminated soils.; The soils of East St. Louis contained many regions of elevated heavy metal concentrations although extreme heterogeneity was evident. In general, the western end of the city contained the most sites with anomalous levels of metals. However, the leaching experiments, although limited in scope, suggested that similar soils would not leach heavy metals appreciably. Moreover, remediation efforts should be directed towards increasing vegetation coverage on the bare soils that characterize many areas of the western end of the city. This would reduce resuspended emissions that have been shown to be an important factor in airborne emissions and would also help control the oxidation and pH conditions of the soils.