Dangers Identified by Risk Assessment

CHEMICALS ARE USED THROUGHOUT our society and have resulted in many obvious benefits. The use of herbicides and pesticides, for example, has increased crop yields so that millions of people can eat better and live longer. Indeed, life expectancy in the United States has increased steadily since the early 1900's, as has the general quality of life for most Americans.

Matt Schlenker of DEQ's Radiation Lab
examines computer data as part of a
health risk assessment.
Click "here" for full size photo.

However, along with the benefits of scientific advancements, society has found itself exposed to more and greater quantities of chemicals than at any time in history. Exposure can come from many sources, not the least of which can be pollution. It is estimated that 400,000 new chemical compounds are created worldwide each year, with approximately 1,000 of them being used commercially. Materials known to be hazardous to human health, such as benzene, a compound found in gasoline, are regularly released into the environment.

With all of these chemicals being put into our environment, how do we know we are safe? There is a process called a human health risk assessment, used by

"A health risk assessment tries to find out what possible health effects or risks persons may encounter if they are exposed to certain amounts and kinds of chemicals."

regulatory agencies to try and determine how much risk exists when we are exposed to dangerous chemicals.

A health risk assessment tries to find out what possible health effects or risks persons may encounter if they are exposed to certain amounts and kinds of chemicals. This process can be used to help determine the need for cleanup and the extent of cleanup required at locations that have been contaminated with dangerous chemicals. It is important to be able to determine how much of a chemical must be cleaned up in order to protect public health adequately. Risk assessments can also be used to compare the effectiveness and desirability of alternative cleanup methods or to determine which of the problem areas should be cleaned up first.

There are four parts to a human health risk assessment:

1. data collection and evaluation,
2. exposure assessment,
3. toxicity assessment, and
4. risk characterization.

Data collection and evaluation can be described simply; we must know what chemicals there are, how much of each chemical exists, and where each chemical is at a site. At most locations that have been contaminated, the chemical being studied is found in many places, and the amount of the chemical varies from location to location on the site. Because of this, the first thing that must be done is to take samples of the air, water, and soil so the levels of the chemical can be determined around the site. It is very important that the data collected is good. In order to make certain of this, rigorous quality assurance and quality control measures are taken. Samples must be taken correctly, and custody of these samples must be assured from the time the sample is collected to the time it arrives at the laboratory. The laboratory that analyzes the samples must have similar quality assurance/quality control procedures in place.

After you know how much of what chemicals you have and where they are, you can proceed to the next step.

The objective of the exposure assessment is to determine how the chemicals that were found during collection and evaluation could possibly come in contact with people. In other words, how can people become exposed to the chemicals on the site.

The exposure assessment process basically involves three steps. First, the physical nature of the site is determined. Factors such as climate, topography, geology, groundwater hydrology (depth, direction, and type of flow of underground water), and the location of surface waters are examined. These factors can help determine how chemicals might move in the environment and how fast they might move.

The location, proximity, and number of people who live around the site, as well as who they are (children, elderly, sickly, etc.), are identified. This is coupled with the type of building and its use, such as residence, health-care facility, school, or nursing home. This type of data is collected so that the risk assessment can evaluate what the effects of the chemical will be on the most susceptible portion of the population.

Step two of the exposure assessment is the consideration of exposure pathways by which the identified populations may come in contact with contaminants. People can be exposed in several different ways. Breathing vapors that come from the site, ingesting (eating) soil contaminated by the chemical, or drinking water from the site that is contaminated are some exposure routes. These and many other exposure routes are evaluated.

Once the exposure pathways have been determined, the potential exposures are then quantified in step three. Exposures are generally estimated for an extended period of time; for example, it is assumed that two liters of contaminated water will be drunk every day by the same person for 70 years. This is done for each type of exposure pathway that has been determined to exist at the site. Many times, computerized mathematical models are used to estimate the amount of a chemical that would be present where a person might be exposed. This indicates what chemical and how much of it a person can be exposed to.

The toxicity assessment is generally accomplished in two steps. The first step, hazard identification, is the evaluation of available health-effect evidence for the chemicals of concern. Here, it is determined which chemicals cause particular adverse health effects in exposed individuals. The second step, dose-response evaluation, is a determination of how the amount of chemical to which individuals are exposed (the dose) relates to the type and severity of any effects (the response). This indicates what the amount of chemicals a person is exposed to will do to the health of that person.

In most cases there are no human studies available for reference, so animal study data is used. Generally, animal testing has been done with specific chemicals. Such tests have tried to determine the effects of these chemicals on the health of the animals. It is generally assumed that the impact of the chemicals on the animals will be the same on humans. For example, if chemical "A" has been found to damage the liver in mice at a given dose - measured by mass/weight (mg) of chemical to the mass/weight of the mouse (kg), written as mg/kg body weight - then we expect essentially the same effect on humans. This study is called toxicology.

Many different types of medical impacts can be measured, and many different measurements are taken. Both cancer and noncancer diseases can result. The term "No Observable Effects Level," or NOEL, describes a level of contamination where no effects were found in the laboratory tests. If cancer is found to occur from a chemical - making it a carcinogen - this NOEL level is set at zero, which means that any amount of the chemical is considered dangerous.

The final step of the health risk assessment process is risk characterization. This combines the exposure data and the assumed health-effects data for the dose in question. Cancer risks are considered, as are all of the health effects found through health studies done on animals and humans. Presently, one out of three Americans develops cancer in his or her lifetime from all cancer sources. However, it is thought that less than 2 percent of all human cancers are caused by environmental pollution. Because the causes of cancer are not known for certain, the 2 percent estimate may not be accurate.

"Presently, one out of three Americans develops cancer in his or her lifetime from all cancer sources."

The U.S. Environmental Protection Agency considers a 70 in 1,000,000 increase in the risk of developing cancer due to carcinogenic chemical exposure as protective of human health. That is, the statistics say that 333,333 out of every 1,000,000 people (one-third of the population) have a chance to contract cancer. The risk (not the certainty, just the risk) that an additional 70 cancers might occur out of that same million people (an increase from 333,333 to 333,403 cancers) as a result of chemical exposure is considered an acceptable risk. This risk is generated from the calculated dose of a cancer-causing chemical that these 1,000,000 people would receive.

To put this in perspective, the annual risk of death associated with motorcycling accidents is 2 percent (20,000 deaths/1,000,000 persons at risk) and with motor vehicle accidents is .024 percent (240 deaths/1,000,000 persons at risk). Not all cancers are fatal, and not all accidents are fatal. Many more people have accidents on motorcycles or vehicles, and the injury rate for these activities is much higher than the death percentages.

It is also important to note that the risks attributed to motorcycling and motor vehicles are actual risks obtained from counting fatalities. On the other hand, cancer risk is an estimated, not actual, risk.

In summary, human health risk assessment provides a process through which careful observation, data collection, testing, and professional judgment are used to strengthen the confidence for making health-based decisions and environmental policies.

While elimination of environmental risk - or any risk, for that matter - is impossible, the basic framework provided by this process establishes realistic goals for ensuring the protection of human health and the environment.

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