Scorecard's screening-level cancer and noncancer risk assessments utilize the following conventional assumptions regarding human exposure to pollutants:
1) The average person has a body weight of 70 kilograms and a breathing rate of 20 cubic meters per day. This default assumption may underestimate risks to children and more highly sensitive individuals.
2) Risk estimates assume that people spend their lifetime (70 years) exposed to the annual average outdoor hazardous air pollutant concentrations estimated for their area. This assumption could lead to overestimation of potential health risks if pollution levels decline over time. It could lead to underestimation if people live in "hotspots" where pollutant concentrations are higher than area averages.
3) Risk values do not incorporate chemical-specific uptake factors for each pollutant, but rather assume 100% of the inhaled dose is absorbed into the body. This could be a source of overestimation of risks.
4) Exposures to hazardous air pollutants through other media, such as food and drinking water, are not taken into account. Omission of these exposures may underestimate potential human health risks.
5) The lack of comprehensive cancer and noncancer toxicity data for each hazardous air pollutant means that the cumulative risk estimates for cancer and noncancer health effects may be underestimated.
These default assumptions are based on science policy decisions to address uncertainties in the risk assessment process. Therefore, cancer and noncancer risk estimates are best utilized for comparative purposes and should not be interpreted as an accurate prediction of observed health outcomes. These types of risk estimates provide a way to screen for those pollutants that are of public health significance in order to prioritize research and regulatory intervention efforts.