Investigating the Quantity and Form of Heavy Metal Contaminants for Improved Risk Analysis and Mitigation

Abstract

Trace contaminants like chromium, lead, or uranium are sometimes found in groundwater, drinking water, or soils, either as a result of geologic processes or human activity. While the presence of heavy metal contamination is a cause for concern, the toxicity, bioavailability, and health risk associated with such contamination depend greatly on the specific chemical form of the potentially hazardous substance. One famous example is that of chromium (Cr), which is toxic and carcinogenic in its hexavalent form, Cr(VI). In contrast, trivalent chromium, or Cr(III), is a trace nutrient important in digestion. Lead (Pb) is a health hazard commonly associated with lead-based paint, lead pipes, and in some cases geologic sources, but chemical and geologic factors can potentially mitigate the health hazards in both water and soils. Similarly, hexavalent uranium or U(VI) can be highly toxic and mobile in groundwater and is sometimes found in drinking water supplies (particularly in well water, as the source of the uranium is typically geologic). However, the mobility of uranium in groundwater is heavily influenced by its form, and by the surrounding mineralogy. Geochemistry can even be exploited to mitigate uranium hazards, by altering its chemical form. In order to analyze and mitigate the risks posed by heavy metal contamination, one must consider not only the quantity of the contaminant, but also its form. A variety of techniques exist for examining both the quantity and form of heavy metal contaminants, and this chapter discusses some of those techniques, with a focus on applications of X-ray spectroscopic approaches such as X-ray fluorescence (XRF) spectrometry, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS).