What is risk?

A common definition of risk is the "possibility of loss or injury: peril." (Webster Dictionary, 1999) This general definition can apply to any type of risk, including sources of potential risk to human health or the environment.

What is environmental risk?

Environmental risk generally refers to the increased chance that biological or ecological damage could occur as a result of exposure to hazardous substances present in the environment. Any living organism can be affected.

What is human health risk?

Human health risk, or the increased chance that an individual's health may be affected by a hazardous substance, exists only when an individual is exposed to that substance. A person can be directly exposed and thus be at risk. Or a person can be indirectly exposed by breathing contaminated air, eating contaminated food, drinking contaminated water, or absorbing a substance through the skin. If there is no chance that a person will be exposed to a source of contamination, risk does not exist.

Does risk assessment identify only present risks, or can it be used to estimate past or future risks?

The risk assessment process can be used to estimate past, present or future risks. For example, the U.S. Environmental Protection Agency uses risk assessment to predict present and future risks at a contaminated site if it is not cleaned up. The estimated risks are compared with criteria established for clean-up actions to protect human health and the environment. The U.S. Department of Energy is estimating the present and future risks posed by the existing contamination at the Rocky Flats site to determine requirements for environmental restoration.

Risk assessment also can be used to evaluate past contaminant releases and risk as in the State of Colorado's Historical Public Exposures Studies on Rocky Flats. In these studies, the researchers identified routine and accidental contaminant releases from Rocky Flats that occurred from 1952 through 1989. After analyzing how people in nearby locations might have been exposed during this period, the study team then estimated the potential human health risks due to past Rocky Flats operations.

Are all risks assessed the same way?

No. Some risks, such as the average risk of dying in an automobile accident, can be determined by counting numbers of deaths due to those accidents and relating it to miles driven (a measure of exposure). In contrast, health risks related to exposure to chemicals or other contaminants must be estimated for several reasons: actual data on the occurrence of health effects are not always available, the relationship between cause and effect may be unclear, and diseases such as cancer often take a long time to develop (called a latency period). Individual scientists often use different assumptions to calculate risks to populations, resulting in different estimates of risk for the same source of contamination.

How is population risk different from individual risk?

Not every individual's risk is the same as the overall risk to a population group. For example, one computes the average risk from dying in an automobile accident after counting the actual number of deaths from such accidents in the specified population. An individual's risk of dying in an automobile accident, however, depends on a number of factors. These include the type and condition of the vehicle, how the person drives, and use of alcohol or drugs, among other factors. Likewise, risk to an individual living near an industrial facility that has released contaminants varies according to a number of factors such as age, lifestyle, personal health condition and the length of time the person lived in that location. Partly because individual risks vary considerably, risk estimates usually are expressed not as single numbers, but as ranges of possible risks. An individual's health risk is likely to fall somewhere within the range of estimated risks. See the technical topics paper entitled, "Uncertainty in Analyzing Health Risks" for additional discussion of this issue.

How do scientists estimate risk?

The National Academy of Sciences adopted a four-step risk assessment process that is the generally accepted scientific method used by regulatory agencies to assess potential human health risks. The process combines analysis and mathematical calculations to:

1. Identify the types of hazardous materials and estimate the quantities released. (What contaminants might hurt a person?)
2. Analyze the potential exposure pathways, or ways in which substances could be transported through air, water or soil to locations where humans could be exposed. (How much might a person breathe in, eat, drink or absorb through his or her skin?)
3. Assess the toxicity, or possible harmful effects, resulting from human exposure to the estimated concentration of each substance. (How much does it take to cause harm to a person)
4.  Using the exposures estimated in step 1 and the toxicity data from step 3, assess the risks for each material identified in step 1.

How much risk is acceptable?

As individuals, we make judgments about how much risk is acceptable from various sources. Individuals' perceptions of risk often are influenced by personal experience and other factors, such as fairness, morality and control. We are surrounded by sources of risk. Some we can control, others we cannot. Research indicates that risks taken voluntarily are more acceptable than risks caused by activities outside of our control. Some people may feel that no level of health risk is acceptable, if it comes from a source outside their control. However, it is seldom possible (technically or economically), to eliminate all risk. In many cases, it is impossible.

Comparisons of risk from different sources sometimes are used to provide a frame of reference to help us understand the degree of risk. The most appropriate comparisons are those between similar types of risk, such as driving a car versus taking a commercial airplane flight. Most people agree that is not appropriate to compare a voluntary risk, such as smoking a cigarette, with an involuntary risk, such as air pollution from an industrial plant. In some cases, estimates of health risk from man-made contamination are compared with "background" risks from naturally occurring sources, such as solar radiation or minerals in the soil and water. It is not the purpose of such comparisons to prove that a source of risk is or is not acceptable, but to provide information so that people can form their own conclusions.

How can government manage and reduce risk?

Government agencies work to regulate, manage and reduce risks from both voluntary and involuntary sources that threaten public health and safety. In some cases, a combination of individual action and state laws have worked to reduce traffic deaths; an example is the use of seatbelts in vehicles. We rely on government regulation to manage sources of risk that are outside of individual control. However, decisions about risk reduction are most effective when input is considered from all affected or interested parties.

Based on studies of toxic effects, environmental agencies set limits on the concentrations of hazardous substances in drinking water, air and soil that are thought to be strict enough to protect human health and the environment. Municipal drinking water must be tested for a number of substances. If these concentrations are found to be above acceptable limits, the water must undergo treatment. At hazardous waste sites, clean-up options are based on reducing risk from contaminants to provide an extra margin of safety and protection for human health and the environment.

Have the Historical Public Exposures Studies on Rocky Flats been helpful in current activities?

This study's findings about historical emissions from the plant are available to the public, government officials and interested scientists and engineers. Valuable lessons can be learned from reviewing past practices used at the plant, and can be applied to future management and cleanup of contamination. The process used in developing estimates of risk from previous operations at Rocky Flats is useful in helping the public understand current and future risks.