The interactions between soils and human health are complex. In particular the interaction with soil minerals upon inhalation or ingestion is poorly understood. There is a considerable body of biomedical literature on exposures to quartz, asbestos or coal that provides a basis for understanding the interaction of soils with the human body. A common theme is that minerals may lead to cellular disregulation through the formation of Reactive Oxygen Species (ROS), such as super oxide, hydrogen peroxide and OH radical. The cellular disregulation may lead to oxidative stress. Iron is thought to play a pivotal role in the ability of minerals to form radicals. Ferrous iron can react with dissolved oxygen through a sequence of reactions referred to as the Haber-Weiss cycle to form ROS. Our multidisciplinary team, consisting of geoscientists and biochemists, has developed a strategy and protocols to determine the ability of minerals to form ROS (in particular hydrogen peroxide and radicals) in aqueous slurries as well as within cells. In addition, we have developed protocols to determine the rate of RNA and adenine decomposition in mineral slurries. Finally, we have adopted standard biochemical assays to determine cell survival and the release of cytokines in cultures of human epithelium cells exposed to earth materials. Taken together these protocols provide a strategy to rapidly assess the potential for soil minerals to form ROS. The challenge is, however, to extend these protocols so that soils and not just soil minerals can be evaluated. The complexity of soils —the presence of microorganisms and the presence of organic matter— presents significant challenges. The presence of soil microorganisms limits the use of RNA as a model target molecule. In this assay, yeast RNA is added to a slurry and the concentration of RNA is determined as a function of time using a molecular probe. The probe, Ribogreen™ (Molecular Probes), binds to intact RNA and fluoresces. Exposure to radicals causes strand scissions and the RNA strands become too short to induce the fluorescence. Hence, in essence, the Ribogreen™ provides a measure of “intact” RNA. Microbes will readily degrade RNA, which masks the loss due to radical degradation. We are currently exploring the use of microwave radiation to sterilize the soil before using the RNA assay. Another possibility is to use Adenine, a base. Adenine is not readily metabolized by microorganisms, but it is readily decomposed by OH radicals. The presence of soil organic matter complicates the interpretation of results. Some types of organics are expected to act as radical scavengers, while other components may become a source of organo-radicals. We are currently investigating this complexity by studying mineral-organic mixtures. The use of any of the cellular assays requires that we sterilize the soil before it is used. Although there is still much work to be done on the development of tools, we have begun to apply these tools to soil-related problems. In collaboration with the US Geological Survey, we are studying the formation of ROS by archived soil samples form Northern California. Soils in this area are naturally rich in nickel and chromium. There is a possible link between the metal content in these soils and the prevalence of certain types of cancer in the area. A second project involves flood sediment deposited by Hurricane Katrina in New Orleans and surrounding Parishes. Some of these sediments contain pyrite, which has been shown to produce ROS and readily degrade RNA and DNA[1, 2]. Acknowledgements-- Studies related to the Katrina sediments has been funded by NSF-EAR. Drs. Geoff Plumlee and Marty Goldhaber at the USGS are thanked for providing samples and the necessary geological framework for both soil-related studies.

1 C.A. Cohn, M.J. Borda and M.A. Schoonen, RNA decomposition by pyrite-induced radicals and possible role of lipids during the emergence of life, Earth and Planetary Science Letters 225(3-4), 271-278, 2004. 2 C.A. Cohn, A. Pak, M.A.A. Schoonen and D.R. Strongin, Quantifying hydrogen peroxide in iron-containing solutions using leuco crystal violet, Geochemical Transactions 6(3), 47–52, 2005.