Environmental impact of the historical slag pile at Davenport, Iowa, United States: Trace metal contamination in soils and terrestrial vegetation

Metal processing has played a key role in the history of the upper Midwest. In addition to economic prosperity, the legacy of large metal refining operations includes soil and water pollution that is often not immediately apparent. One example is the disposal of iron (Fe) slag on the east bank of Carp Lake, a former sand quarry located adjacent to the Mississippi River in Davenport, Iowa, United States. Iron foundry slag is known to contain high concentrations of Fe as well as trace metals that can include cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn), among others. Despite efforts to place soil and revegetate the pile, more than eight decades of erosion have exposed raw slag. To understand the composition of this slag pile and relationships with surrounding environment, samples of slag, soil, and vegetation were collected from sites on the slag pile and along the bank of Carp Lake. Iron was the predominant metal found in slag pile and Carp Lake bank (CLB) soils. Both Pb and Fe concentrations exceeded the US Environmental Protection Agency (USEPA) standards as well as reference site concentrations. Metal concentrations were found to vary across sample sites. This is indicative of the heterogeneous nature of the slag pile. In terrestrial vegetation samples, only Cd was found at actionable levels in the leaves of Amur honeysuckle (Lonicera maackii) and dogwood (Cornus sericea). Metals in the CLB soils were within USEPA recommended ranges. However, the trace metal concentrations in CLB soils were higher than the reference site. Further, the elevated Pb concentration in the bank soil located closest to the slag pile supports the suspicion that the slag pile is a source of metal contamination. We hope the results of this study will provide reference for environmental quality assessments and will help decision-makers to manage this and similar locations.