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.

Gather Background Information
In order to evaluate the contaminants and how people may come into contact them, scientists often take the following steps: visit the area, speak with local residents, and visit local agencies that may have information related to the sources of the chemicals. Local knowledge is important because scientists can become aware of ways people interact with the contaminants that they would not have otherwise known about.

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.

Understand Conditions at the Site
Site characterization is the investigation of a site that is known or suspected to contain environmental contamination. The purpose of the investigation is to determine the extent of contamination. The information from site characterization can be used to make an initial assessment of potential health effects and impact on the environment due to site contamination.

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.

Model Contaminant Flow
When sampling data is not enough to evaluate all the ways people could be exposed to contaminants at a site, scientists sometimes use modeled data to estimate exposure. The limited information that is known is used as input into the model. Computer software and statistical tools are used to create a model estimating how the contamination spread into the environment. Modeling can help scientists figure out how contamination spread in the past, or how it might spread in the future.
Modeling can be conducted for contamination in the air, groundwater, surface water, and soil. These are the types of questions that modeling can help answer:
Find Out if Exposure is Occurring
Exposure occurs through contact with a chemical. Contact can occur by inhaling air, drinking water, eating food, or touching things that contain the chemical. The concentration of the chemical and the extent of the contact are important components of exposure assessment.
An exposure assessment attempts to answer the following questions for a particular substance or chemical:

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.

Evaluate Risk to Human Health
A risk assessment is the process of assessing the likelihood that a given hazardous material may contribute to a particular disease or ill health. The process is based on published research findings available at the time of the risk assessment and may change over time, as more information becomes available.

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.