Relative Source Contribution Project - Phase I
One of the main challenges MDH faces is explaining to the public how they can be affected by the chemicals that fill our environment. Our use of computer models adds to our understanding of chemical exposure and helps us determine how to reduce exposure to harmful substances. Since this project was completed, we have used the models in a limited way to compare experimental exposure data to modeled results. The process of applying the models to real-world problems highlighted the importance of using good judgment in selecting model inputs, and interpreting the results. The models are still being incorporated into our process for evaluating CECs. While more testing on the models with different types of CECs needs to be done, these models may allow us to better understand chemical exposures in cases where real-world data are not available.
When the Minnesota Department of Health (MDH) develops a drinking water guidance value for a contaminant, we must consider that water is not the only source of exposure. Contaminants can get into your body from several different sources, such as:
- drinking water,
- food and medications,
- contaminated dust and soil,
- products that are applied to the skin, such as sunscreen and lotion, and
- the air you breathe.
Standard practice for developing health-protective guidance includes incorporating a relative source contribution (RSC) factor to account for multiple exposure sources (food, water, air, consumer products) or routes of exposure (ingestion, inhalation, or dermal absorption). The RSC is used to decide how much of exposure is from drinking water so that total exposure does not exceed a safe level.
Using a Relative Source Contribution (RSC) of 20 percent, based on recommendations from the U.S. Environmental Protection Agency, was created to assess traditional contaminants. We are now trying to assess newer, non-traditional contaminants known as contaminants of emerging concern (CECs). CECs often come to the attention of MDH because of new exposure information, including types of exposure never considered in the past. Because of this, it is possible that our historic approach for estimating exposure may not work well for them. We wanted to see if CEC exposures could be estimated using computer-based models, providing MDH with additional tools to estimate relative source contributions for CECs.
In the first phase of this project, we hired a contractor to review all available exposure models and determine which models would work best to estimate RSCs for CECs in Minnesota. At the end of this phase, the contractor identified ten models out of a total of 33 that seemed to work best for evaluating relative source contributions from CECs.
$445,000 the first year and $890,000 the second year are for addressing public health concerns related to contaminants found in Minnesota drinking water for which no health-based drinking water standard exists. The commissioner shall characterize and issue health-based guidance for three or more additional unregulated drinking water contaminants in fiscal year 2010, and seven or more additional unregulated drinking water contaminants in fiscal year 2011.
Review, identification, and evaluation of existing exposure models.
Review, identification, and evaluation of existing exposure models.