WHAT COUNTS AS EXPOSURE DATA?
In assessing the availability of exposure data, Scorecard tracks all chemicals covered by existing national monitoring or exposure estimation programs in seven different media: ambient air, indoor air, surface waters, drinking water, biota, food or human tissue. Scorecard considers any chemical with publicly accessible data that characterizes concentrations of the chemical in a specific environmental medium as one for which exposure data are available.
For ambient air, Scorecard assumes a chemical has exposure data if it is included in ongoing ambient air monitoring by national or state programs. Scorecard also credits exposure estimates that have been generated by three U.S. EPA projects: the Cumulative Exposure Project estimated ambient concentrations of 140 hazardous air pollutants in 1990 for all census tracts in the lower 48 states; the National-Scale Air Toxics Assessment estimated ambient concentrations of 41 hazardous air pollutants in 1996 for all census tracts in the lower 48 states; and the Risk-Screening Environmental Indicators project, which provides exposure estimates for communities around industrial facilities covered by the Toxics Release Inventory.
For water, Scorecard assumes a chemical has exposure data if that chemical is subject to a national monitoring program, such as those mandated by the Clean Water Act or the Safe Drinking Water Act. This is a generous assumption about the availability of local monitoring data: the fact that a chemical has been included in a national monitoring program does not mean there is any information about exposures to that chemical in a specific region.
IMPORTANT CAVEAT - IGNORANCE MAY BE UNDERSTATED
Note that several of Scorecard's sources of national exposure data are based on regulatory compliance and enforcement efforts. Scorecard assumes that monitoring is taking place for any chemical with an enforceable regulatory standard in place, even if such monitoring is not carried out in all areas of the U.S. Note also that Scorecard considers monitoring data as "available" even if a specific monitoring program has ceased collecting exposure data, as several have. These assumptions result in an overstatement of the availability of current exposure data in many areas, and thus an understatement of the degree of ignorance about exposures to the chemical in question.
WHAT ABOUT STATE EXPOSURE MONITORING DATA?
The national EPA exposure projects identified above provide estimates of ambient concentrations of hazardous air pollutants for all census tracts in the lower 48 states, so the activities of limited state monitoring programs do not significantly affect Scorecard's assessment of the availability of exposure data. Scorecard does provide access to state ambient air monitoring data in its Hazardous Air Pollutants section, whenever states have made these data available in digital form.
In assessing the availability of water exposure data, state programs are generally not credited. In most states the results of such monitoring are not publicly accessible.
WHAT ABOUT EXPOSURE MODELING OR ESTIMATION?
In tracking whether the exposure information required for safety assessment is available, Scorecard does not consider whether exposure could be estimated using environmental fate and exposure assessment models. Modeling can provide information about exposure in many situations where actual monitoring is not taking place and where no enforceable standard is in effect. Scorecard credits exposure modeling data only when it has been made publicly available and covers a significant proportion of the U.S. population (such as the EPA ambient air estimation projects identified above).
For other environmental media (indoor air, surface waters, drinking water,
biota, food or human tissue), there are no publicly available data sets that estimate potential exposures to toxic chemicals for substantial portions of the U.S. While exposure estimates are sometimes generated by various regulatory programs (e.g., drinking water contamination from hazardous waste sites, pesticide residue exposures from the food supply), these estimates are virtually impossible for the public to obtain and evaluate.