Before we can discuss risk assessment, we must have a definition of risk. At its simplest, risk is the probability that harm will occur from a specific act. This definition covers a lot of ground. One can imagine just about anything having a risk associated with it even if it is slight.

The process of living exposes all organisms to various risks. For humans some of these risks are self-imposed such as smoking tobacco, which increases the risk of developing lung cancer. However, the risks that are important to trade differ somewhat from the examples mentioned above. Sanitary and phytosanitary (SPS) procedures have been established by many countries to protect their agricultural economy and natural environment (Gray et al., 1998). The goal of these procedures is to limit the entry of foreign pests and diseases in their respective countries.

Risks associated with SPS measures are broken down into three categories:

1. Direct food risks—additives, contaminants, toxins, or disease-causing organisms in food. Some examples are hormones and antibiotics in beef, pesticide residues in crops, aflatoxin in grains, Escherichia coli, Salmonella, Listeria, and botulism toxin in various foods, and food additives (colorings, flavor agents, etc.).

2. Introduction of exotic organisms—plant-or animal-carried diseases, pests, diseases, or disease-causing organisms. Some examples are various insect pests that are introduced in produce such as the Mediterranean fruit fly, species that are introduced in something other than a commodity such as the Asian longhorn beetle, infectious agents such as prions that cause mad cow disease, and weed pests like purple loose strife.

3. Damage caused by exotic organisms—by entry, establishment, or spread of pests. Here the concern is the actual damage that may be inflicted on agricultural industries.

The National Academy of Sciences defines risk assessment as "the determination of the probability that an adverse effect will result from a defined exposure" (NRC, 1983). Contrary to popular belief, risk assessment is not a science but rather a combination of science and expert judgment. Scientific data are used to develop an assessment of risk, but the risk assessor does not often have extensive data and has to make a judgment call. Furthermore, the type of data available are not uniform for each risk assessment. For some chemicals, for example, a complete toxicological profile will be available whereas for others the data may be much more limited.