MINERAL-INDUCED RADICAL FORMATION: THE GOOD AND THE BAD

Over the last decade research has been conducted on the formation of radicals by minerals. Most of the work has been conducted in acellular studies focused on the ability of minerals in slurries to generate hydroxyl radicals. These studies have shown that a variety of rocks, minerals, and soils can spontaneously generate hydroxyl radical. Many of our studies have focused on pyrite, which generates significant amounts of radicals as it forms hydrogen peroxide as a result of incomplete oxidation of dissolved oxygen. Hydrogen peroxide and ferrous iron leads to the formation of hydroxyl radical. Various assays have been developed so that we can determine the formation of hydroxyl radical and hydrogen peroxide in mineral slurries.

The formation of hydroxyl radical is detrimental to biological systems. We have shown that the exposure of epithelial lung cells to pyrite induces cell death, while reactive oxygen species (ROS, including OH radical) is upregulated in the surviving cells. Exposure to ROS can also induce mutagenesis as RNA and DNA have been shown to be damaged by exposure to several minerals. Grinding of mineral tends to increase the production of ROS, presumably due to the formation of surface radicals.

The production of radicals is desired if the objective is to kill bacteria or decompose persistent organic pollutants. Preliminary studies in our group have shown that pyrite and other minerals are capable of killing E. coli bacteria, which are responsible for many deaths among children in developing countries as a result of drinking water contaminated with sewage. Decomposition of persistent organic pollutants can be facilitated by pyrite and other minerals capable of producing hydroxyl radicals. Others have shown that trichloroethylene dissolved in water is dehalogenated by pyrite through the formation of OH radicals.

While progress has been made over the last decade in the study of mineral-driven radical formation, much remains to be done. However, it is clear that it is important to understand these processes better because of the implications to human health as well as the possible application to remediation of persistent organics and disinfection of drinking water.