ABSTRACT
Risk is defined as the probability or chance of injury, loss, or damage. This is a very general definition of risk that includes situations such as financial losses, storm damage, and human or animal health effects from exposure to pollutants. This chapter summarizes the basic concepts used in risk assessment and illustrates how the risk assessment process is used in writing environmental regulations or determining cleanup levels for contaminated sites with an emphasis on soils and waters. There are two major reasons we would be concerned with risk assessment for soil contaminants. First, if the concentration of a substance in soil is deliberately increased, will any organism experience an unacceptable increase in risk? Second, what increased risks are realized by organisms because of soil contamination that has already occurred? Recall from Figure 1.2 that there are both direct and indirect ways for organisms to be exposed to substances in soils that can cause harm. Therefore, an increase in risk can be realized from the ingestion of soil itself (e.g., by children or grazing livestock) or indirectly from the consumption of groundwater or surface water contaminated by a substance present in soil, or from the consumption of crops grown in, or livestock exposed to, the contaminated soil.
