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Lead speciation, bioaccessibility and source attribution in Missouri’s Big River Watershed (Cincinnati)
Citation:
Noerpel, Matthew, M. Pribil, D. Rutherford, P. Law, K. Bradham, C. Nelson, Rob Weber, G. Gunn, AND K. Scheckel. Lead speciation, bioaccessibility and source attribution in Missouri’s Big River Watershed (Cincinnati). To be Presented at Geological Society of America - Joint North Central and Southeastern section annual meeting 2022, Cincinnati, OH, April 07 - 08, 2022.
Impact/Purpose:
The Southeast Missouri lead district is historically among the most productive lead deposits in the world. It is composed of three major sub-districts, the Old Lead Belt, Mine La Motte-Fredericktown, and the Viburnum Trend as well as several smaller sub-districts. The study area for this investigation is the Old Lead Belt which lies to the east of the Viburnum Trend and the northwest of Mine La Motte-Fredericktown. The Old Lead Belt was first mined in the 1700’s, though this was limited to small scale operations going no more than 10 feet deep. Larger scale operations in the region of interest for this study started in 1864 and ran until 1972. In addition to mining operations, a lead smelter also operated in Herculaneum from 1891 until 2013 approximately 30 miles to the northeast of the Old Lead Belt on the Mississippi River. The suspected source of the lead pollution are the tailings piles left behind after lead ore processing. There are six major piles in the study area, all of which have been addressed by joint or unilateral administrative orders by the United States Environmental Protection Agency (USEPA) in the last two decades. Another pile, Doe Run, is located south of the sampling area in the St. Francois River watershed rather than the Big River watershed. This pile has not yet been addressed by the USEPA. The tailing piles consist mainly of the parent material, in this case dolomite, with some residual ore material that was not removed in the beneficiation process. There are two main objectives in this study. The first is to determine the source of the downstream lead contamination using lead isotope ratio analysis. The second is to inform exposure risk from lead contamination in the study area through x-ray spectroscopy to determine lead speciation and in-vitro bioaccessibility (IVBA) data to measure the physiological solubility of lead in contaminated soils and sediments.
Description:
The Southeast Missouri Lead District is among the most productive lead deposits exploited in modern times. Intensive mining conducted prior to regulations resulted in a legacy of lead contaminated soil, large piles of mine tailings and elevated childhood blood lead levels. This study sought to identify the source of the lead contamination in the Big River and inform risk to the public. Isotopic analysis indicated the mine tailing piles at the head of the Big River are the primary source of the lead contamination. The isotopic signature of the lead in these mine tailings matched the lead in the stream bed and in the lood plain for over 100 km downstream. All of the other potential lead sources investigated had different isotopic signatures. Lead concentrations in soils and sediments decrease with distance downstream of the mine tailings piles. Additionally, the speciation of the lead changes from predominantly mineralized forms, such as galena, to adsorbed lead. This is reflected in the in-vitro bioaccessibility assay (IVBA) analysis which shows higher bioaccessibility further downstream, demonstrating the importance of speciation and bioaccessibility in risk evaluation.