Assessing Risk
How much risk is associated with a particular source depends on the characteristics of the source, the availability of pathways for it to reach the receptor, and the characteristics of the receptors. No single piece of information alone is sufficient, and incomplete information can be highly misleading. Among the key questions that must be asked in determining risk are the following:
  1. What are the hazardous properties of the substance? What effects can it have on living things or on the environment? (To answer this question, it is often necessary to consider the state of research on the substance, and how much is really known about it.)
  2. How much of the substance exists at the source, and in what concentration? A higher quantity or concentration of a toxic substance is more dangerous. However, the risk posed by a highly concentrated toxic substance entering the environment depends on the pathways available to it, and to what extent the concentration is reduced by the time it reaches receptors.
  3. In what form is the substance? Whether the substance is in large blocks or tiny particles, or whether it is a liquid or a vapor, will be important in determining not only how it might travel, but also how it could contact and enter the body.
  4. What are the chemical and physical characteristics of the substance? These characteristics determine in what environmental pathways it is likely to move and how rapidly. They include, for example, whether the substance can easily dissolve in water.
  5. How is the substance contained? If the chemical is in old, rusting containers that can leak, the danger is clearly greater than if the container is solid and appropriate to the substance.
  6. What pathways of exposure exist? When scientists study the risk in any particular situation, they look at all the ways a contaminant could reach the population at risk and make measurements to see how much of it is moving through each identified path. For example, if the source were near a stream, water samples would be taken at several places to see what level of contamination exists at different distances from the source.
A possible exposure pathway involving the food chain: toxic fumes and particles from a waste dump are carried through the air to a cornfield; corn grown in this field is fed to an animal, which is later processed for human consumption.
  1. Where is the population located in relation to the source? Distance is a critical factor. For example, if you are far downstream from a place where toxic waste is entering a waterway, you may have little risk because the substance is so diluted. Closer to the source there might be a high enough concentration to pose a real problem.
  2. What are the characteristics of people who are at risk? The susceptibility of any individual to a toxic substance varies depending on age, weight, sex, and individual sensitivity.
  3. How long does the exposure to the chemical last? Its duration is another key factor in determining risk. Are receptors exposed for only a few hours at a high level (such as when a contaminated air plume passes over a home), or at a low level over a number of years (such as when groundwater supplying a well becomes contaminated)?
The analysis of a situation to determine the level of risk inherent in that situation is called risk assessment. A risk assessment is conducted by scientists from many different disciplines and uses data about a chemical’s effects combined with research into the particular situation to get a clear picture of the risk posed. A decision will then be made as to what action, if any, is needed to remedy the situation. This is called risk management.