Relative Source Contribution

What is this project and why are we doing it?

When MDH develops a drinking water guidance value for a chemical, we must consider that water is not the only source of exposure. Chemicals can get into your body from several different sources:

picture of lotion bottles
  • Drinking water;
  • Food and medications;
  • Products that are applied to the skin, such as sunscreen and lotion; and
  • The air you breathe, which may include aerosols from showering or gases released from products in the home.

  • It can be difficult to estimate how much of a chemical gets into your body from each of these sources. When exposure data are not available, the U.S. Environmental Protection Agency approach is to limit the estimated exposure from drinking water to 20 percent of the total exposure that is considered safe. This allows for the possibility that as much as 80 percent of exposure may be from sources other than drinking water. MDH does not know if this is the best approach for other kinds of chemicals, especially those that are used in consumer products or pharmaceuticals. To answer this question, MDH hired a contractor to research how computer models could be used to estimate exposure from many different sources. This project sought to:

  • Review and evaluate existing exposure models;
  • Determine the skill set required to use the models; and
  • Evaluate how useful these models are in estimating exposure to CECs in Minnesota (including exposures that can occur in the home).

What are some key outcomes?

In the first phase of the project, the contractor evaluated 28 different computer models and reported on their capabilities, ease of use, and data requirements. Ten “preferred” models were identified. The contractor also listed which models were the best choices for various types of exposures. The second phase of the project is currently in progress.

How will MDH use this information?

MDH may use this information to develop new methods of estimating exposure to chemicals. This would help MDH determine whether the estimate of 20 percent for drinking water is appropriate for some contaminants.  


Updated Thursday, November 14, 2013 at 07:51AM