METAL SPECIATION AND ITS ROLE IN BIOACCESSIBILITY AND BIOAVAILABILITY

Abstract

Metals play important but varied roles in human health. Some metals are required for normal metabolic function, with optimal amounts for maximum benefit. Others are only known to cause toxic effects. Most of our knowledge of the function of metals in human health has been acquired in the last 100 years. However, evidence of adverse health effects attributed to metal exposures dates back to early civilizations. For example, it has been deduced that extensive mining and smelting of lead and its widespread use in the Roman Empire caused significant incidence of lead poisoning (Nriagu 1983; Hong et al. 1994). The source of metals in the environment ultimately can be traced back to their occurrence primarily in rocks, with their release to soil, water, and air facilitated by weathering processes. Consequently, the natural occurrences of metals in soils and waters are strongly correlated to the varied distribution of rock types and the compositions of the constituent minerals. More than 2000 years ago the Greek physician Hippocrates recognized relationships between disease and location, illustrating that environmental factors influenced human health. Today there are many known geographic patterns of disease that have been correlated with properties of soils or waters, or even aerosol particles. It has been difficult to demonstrate cause-effect relationships for many correlations, and efforts to relate total concentration of a metal contaminant to toxic impact have proven difficult (Davies et al. 2005). This point illustrates the essential concept that the total amount of an element in an environmental setting