Human Exposures to
Exposure to chemicals can be hard to quantify, yet it is a critical piece of the toxics puzzle. It is also a particularly difficult piece, because there are so many points along the path from chemical production to a target tissue where relevant information may be gathered, and each point along the path provides only a limited snapshot of information.
The Environmental Protection Agency defines exposure as contact between the outer boundary of the human body (e.g., skin, nose, throat) and a pollutant or pollutant mixture. 1 It is difficult to measure a person's total daily exposure to a chemical at the point of entry into the body, and even harder to measure the total exposure to the complex mixtures that people encounter every day. Despite the technical difficulties and expense, some studies have attempted this type of exposure assessment for some known or suspected reproductive toxicants. There are also ways of estimating human exposure using surrogates, such as chemical production, use, and release. These data are poor estimates of potential human exposure, but sometimes they are the only available information on a particular chemical.
In order to result in exposure, a chemical must be in indoor or outdoor air; in water that is used for drinking, swimming, or fishing; or in food or dust—all sources that can be sampled and measured. Once people have been exposed, some chemicals can be measured in blood, urine, fat, or breast milk. This biomonitoring information lets us know that human exposure has occurred but often gives little information about the route of exposure or the original source. Figure 7.1 outlines