1.4 Reviewing Background Data
Introduction and Uses
Background data describe natural levels of chemicals in the environment
(such as metals in soil). Also, levels of chemicals in the environment
introduced through human activity (such as pesticides from mosquito control
spraying) may be considered background data. Site environmental data are
compared with background data. The comparison may indicate the chemical
levels associated with the site.
What if no site-related chemicals are found in a community, but unsafe
levels of chemicals from another source are found?
The health assessor must alert people to the presence of any chemical
they may contact at levels that may harm them. If the source of the chemical
is not the site under investigation, the health assessor is required to
clearly state that.
There is no single reference that documents background concentrations for all contaminants in all media. For a more complete discussion of the topic, see "Exposure Evaluation: Evaluating Environmental Contamination" in ATSDR's Public Health Assessment Guidance Manual (Revised January, 2005). The following documents, however, might include reasonable estimates of background concentrations for your site: (also consider accessing similar state sources)
- ATSDR's Toxicological Profiles (http://www.atsdr.cdc.gov/toxpro2.html) : In each profile, the chapter titled "Potential for Human Exposure" contains a section named "Levels Monitored or Estimated in the Environment." This is a useful reference for concentrations of contaminants that have been reported in the literature. When accessing these references, note that the chapter often times cites both levels of environmental contamination measured near sources of significant releases and levels that are believed to represent background.
- For soils, the U.S. Geological Survey (http://www.usgs.gov/), the U.S. Department of Agriculture Natural Resources Conservation Service (http://soils.usda.gov), U.S. Department of Energy's Office of Environmental Management (http://rais.ornl.gov/homepage/back_com.shtml) and the State Geological Surveys are all potential sources of county, state, and national soil data. The USDA and the NRCS, in union with the new soil geochemistry program, have developed a soil geochemistry database at http://soils.usda.gov/survey/geochemistry/ . The database includes major and trace elements with associated characterization data and features a geospatial display of data. In the absence of other more recent or geographically similar information, a 1984 technical paper, released by USGS, provides national background concentrations for metals in soil (Shacklette and Boerngen 1984).
- For sediments, the U.S. Army Corps of Engineers and EPA have worked together to assess the nature and quality of sediments in Federal Navigation Channels, and the sediment sampling data are available from most EPA regional offices. EPA's Council on Regulatory Environmental Modeling (CREM) has a Web site that has sediment data archived for many watersheds. (http://www.epa.gov/osp/crem)
- For surface water and groundwater, background levels will vary from one watershed to the next and from one aquifer to the next, respectively. Health assessors should access background data that applies specifically to the watershed or aquifer of interest. Such data might be documented in site reports or might be accessible from literature searches. EPA and the U.S. Geological Survey often report background data for specific watersheds and aquifers.
- For air, background concentrations can vary widely depending on when they were measured and where. A good reference for levels of organic contaminants commonly measured in air is EPA's Urban Air Toxics Monitoring Program (UATMP). Summary reports from this program are available at: http://www.epa.gov/ttn/amtic/cpreldoc.html. Be sure, however, to understand how, where, and when the air concentrations were measured before using any UATMP data in your public health assessments.