When contamination in the environment is suspected, scientists try to determine the amount and type of contamination, how it is moving in the environment, and if the contamination poses a risk to human health. In order to do so, scientists use the information available from agencies and local residents.
Scientists approach the study of environmental health by looking for contaminants in the environment first, not by measuring contaminants in people's bodies. This is because scientists need to know what people may be exposed to. Scientists also want to know if contaminants present in the environment are found at high enough levels that they might be detected in people exposed to the contaminants. Also, different chemicals behave in different ways in the human body. Some are present in the body for a short amount of time, and some are there longer. Looking for chemicals in people's bodies is known as biological monitoring (also called biomonitoring); it is important to note that this approach cannot determine where exactly people were exposed to the contaminants. Biological monitoring can only show what chemicals were in their bodies at the time they were tested.
Scientists use strategies such as site characterization, evaluation of modeled data, exposure assessment, and risk assessment. These strategies are described more fully below. Not all strategies are used for every situation - each scenario is different, and scientists make choices depending on the type of contamination and resources available.
A visit to the area helps scientists identify sources of contaminants such as an industrial facility or a hazardous waste site. The scientist can observe conditions, broken fences where children can go onto a hazardous waste site and physical hazards that could lead to injury. Scientist can also see how close residents are to the sources of the contamination.
Speaking with local residents is important to understand how people may come in contact with the contamination. For example, residents may take walks in certain areas that scientists assumed no one accessed, or people may report eating fish from watersheds affected by contamination.
Local agencies and their staff also provide very helpful information. For example, agencies may have old sampling data and records of complaints that could help scientists evaluate potential exposure pathways. Local agency staff are also more familiar with the community's culture and habits. For example, they could describe the spots where people fish and the types of fish they typically catch. This information could be used when studying levels of contaminants in fish in the area.
Specifically, investigators want to determine what parts of the environment (air, water, and soil) contain contamination, and what specific contaminants are at the site. Site characterization includes the collection and analysis of environmental data from the site to determine the characteristics of the site. The information from the site characterization can help determine what future cleanup actions are necessary for the site.
Exposure assessments may use measured data or model estimates. A critical component of an exposure assessment involves estimating the level of contact of the exposed population with the chemical. The level of contact involves two factors: 1) the location of the people and 2) the daily human activities that influence how often people come in contact with the chemical. In addition, the frequency of use of the chemical, duration of exposure to the chemical, and conditions of use of the chemical are all important factors. Estimates of exposure may come from published studies or be based on site-specific information.
A risk assessment combines the exposure assessment (site-specific) with hazard assessment (compound-specific). A hazard assessment provides an understanding of the potential for the compound to cause adverse effects to humans, as well as plant and animal life. There are very few studies evaluating health effects caused by contamination to communities from sources such as nearby hazardous waste sites. Therefore, most hazard assessments are based on studies of people exposed in workplace settings, where they are usually exposed to higher levels of contamination. Other studies used for hazard assessments are from industrial accidents, poisonings, or on information from animal studies. Because there is often some uncertainty as to how these other studies relate to more general population exposures, hazard assessments often incorporate "uncertainty" or "safety" factors.
A risk assessment may help to determine if a health study would be useful. The results of a risk assessment may indicate the need for an exposure to be reduced or eliminated. Risk assessments may also be used to set regulations to protect the public from hazards in the air, water, food or other aspects of the environment. It may also be used to determine how much clean-up is necessary when contamination already exists.