ATTENUATION OF LEAD AND ANTIMONY IN SHOOTING RANGE SOILS BY IRON AMENDMENTS

Lead (Pb) and antimony (Sb) contamination pose a major environmental threat to training land sustainability for areas used by the U.S. Department of Defense (DoD). This is a result of firing excercises that use soil berms as backstops. Fragments of bullets are susceptible to weathering processes in soil environments, leading to the release of metal(loid) species into solution. Pb and Sb are contaminants of interest because they primarily constitute small arms rounds. Pb and Sb are both toxic, and Sb is also a suspected carcinogen. The geochemistry of Pb in soils has been the subject of numerous studies, while less is known about the environmental behavior of Sb. Understanding both Pb and Sb speciation and mobility is essential for identifying the potential toxicity of a range soil and for remediating a given site.

As a result, stabilization of metal contaminants is of interest, particularly, what types of substrates have potential to promote the retention of Pb and Sb from migrating off-site. Treating soils with both cationic (Pb) and oxyanionic (Sb) components can be difficult due to enhanced mobility of Sb at circumneutral/high pHs and enhanced mobility of Pb at low pHs. Traditional treatments, such as phosphate or carbonate would not be approprite, however, iron (Fe) has been shown to be a potentially effective sorbent.

In the present study, we fired identical bullets in a controlled event into newly constructed berms made from four well charaterized soils. Over the past 4 years, we have been continuously monitoring both the berm soil and porewater. In addition, we designed and monitored parallel laboratory soil columns to study Pb and Sb behavior in a more controlled environment. In the past year, we added Fe(II) chloride and nanoscale zero-valent iron (NZVI), in a dispersion, to the four types of soil in both the laboratory columns and the shooting range berms in order to study the effects Fe has on metal attentuation. The field berms remain open to the environment and the columns were flushed with simulated rainwater and monitored. We found significant attentuation of Sb by Fe in certain systems, whereas Pb initially became more mobilized. The results from this study are essential for understanding the potential for off-site migration, as well as determining the ultimate bioavailability and toxicity of Pb and Sb in shooting ranges.