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Ambient air monitoring data and ambient air sampling data are measurements of the levels of air contamination that people might actually breathe. These are critical elements of this PHA, because they are direct measures of exposure point concentrations and do not involve the inherent uncertainties of modeling studies. ATSDR invested considerable effort in obtaining all ambient air monitoring data and ambient air sampling data that might be relevant to air quality issues associated with the TSCA Incinerator.

The main difference between ambient air monitoring and ambient air sampling is that “ambient air monitoring” typically implies periodic measurement of air contamination levels, such as measurements being made once per week; “ambient air sampling,” on the other hand, generally refers to air quality measurements of discrete events, such as a TRV opening. Therefore, monitoring data are most useful for characterizing routine releases from a source, while sampling data are most useful for evaluating non-routine or episodic releases.

This appendix presents ATSDR's review of all relevant ambient air sampling studies identified for the TSCA Incinerator. The reviews present key information on the studies, such as number and locations of sampling stations, sampling frequencies, number of samples collected, pollutants measured, and comparisons of measured concentrations to health-based comparison values. Sections III.D and III.E of this PHA indicate how ATSDR interpreted the ambient air monitoring and ambient air sampling data when reaching conclusions for this site.

Note: Throughout this appendix, the units of measurement shown are the same as those reported in the original studies. In the main body of this PHA, ATSDR converts readings for the same parameters into a single set of units to allow better comparison across studies.

C.1. DOE Data (DOE 1991–2002)

For several decades, DOE has operated a routine environmental surveillance program at ORR. This program has been fully functional the entire time that the TSCA Incinerator has processed wastes. DOE's ambient air monitoring and ambient air sampling follow general procedures specified in the ORR site-wide environmental monitoring plan (DOE 2003c), which outlines extensive quality assurance and quality control procedures. Much of DOE's sampling activities are conducted under TDEC oversight (see Appendix C.3).

The scope of DOE's monitoring efforts has changed over the years. For instance, many changes occurred in 1992, when DOE conducted a systematic review of the monitoring locations, siting requirements, quality assurance measures, and standard operating procedures. Deficiencies identified during this review were promptly corrected. While some contaminants have been removed from the monitoring program over the years (typically after multiple years of data demonstrate that contamination levels are safely below levels of public health concern), other contaminants have been added to the program.

ATSDR's review of DOE's routine monitoring and sampling results follow, organized by groups of contaminants. Refer to Section III.D.2 for a summary of DOE's air quality measurements made during TRV events.

Particulate matter

From 1991 to 2000, DOE routinely monitored ambient air concentrations of two size fractions of particulate matter: PM10 and TSP. All measurements were made using EPA reference method devices that have been shown to measure particulate matter concentrations both accurately and precisely. With few exceptions, the monitoring involved collection of 24-hour integrated samples every 6 days. Such a schedule, which ensures that sampling results will be available for all 7 days of the week, is widely used for particulate matter monitoring applications. Data trends for both sets of measurements follow.

From 1991 to 1995, DOE measured TSP concentrations at seven different monitoring stations. Figure C-1 shows the locations of these stations, and Table C-1 reviews the monitoring results. As the figure indicates, monitoring occurred at locations surrounding the incinerator, including at locations where modeling results predicted elevated ground-level impacts would occur. Over this 5-year time frame, DOE collected more than 1,200 valid TSP samples. The data summary in Table C-1 shows that none of the measurements, individually or averaged over a year, exceeded EPA's health-based standards for TSP.

Starting in 1991, DOE included PM10 monitoring as part of its routine environmental surveillance network. Figure C-2 shows where DOE installed three PM10 monitoring stations between 1991 and 2000, and Table C-1 summarizes the measurement results. To date, DOE has collected more than 775 samples from these three stations, not one of which has exceeded EPA's health-based air quality standard. Further, the annual average concentrations of PM10 have all been below EPA's corresponding annual average standard.

Overall, more than 2,000 particulate matter samples have been collected at or near ETTP since the TSCA Incinerator began operating, and every measured concentration has been well below corresponding health-based air quality standards. Further, the particulate matter levels detected at these stations are little different from the nationwide average levels that EPA has recently reported (EPA 2003). With 10 years of monitoring data showing particulate matter levels below levels of health concern, DOE stopped conducting these measurements at the end of calendar year 2000.

DOE's TSP Monitoring Locations
Figure C-1. DOE's TSP Monitoring Locations

Table C-1. DOE's Monitoring Data for Particulate Matter (1991–2000)


Years of Operation

Number of Samples

Highest Annual Average Concentration (µg/m3)

EPA’s Annual NAAQS

Highest 24-Hour Average Concentration

EPA’s 24-Hour NAAQS

Monitoring results for TSP





75 µg/m3


260 µg/m3































Monitoring results for PM10





50 µg/m3


150 µg/m3











Notes: Source of data: DOE 1991–2002.
The numbers of samples for every station were taken from DOE's annual site environmental reports. However, the 1993 report did not specify the numbers of samples that were collected that year. Therefore, the exact number of samples for stations that operated during 1993 is not known.
The table presents EPA's former health-based standards for TSP. The annual TSP standard was actually based on an annual geometric mean concentration, not an annual average (or arithmetic mean). This distinction has no bearing on the conclusion, given the substantial difference between the measured concentrations and the standard.

DOE's PM10 Monitoring Locations
Figure C-2. DOE's PM10 Monitoring Locations


Since 1991, DOE has measured ambient air concentrations of metals at 14 different locations within and near ETTP (see Figure C-3). The monitoring locations were chosen for various reasons: to characterize maximum impacts from the TSCA Incinerator; to assess upwind-downwind differences in air quality; and to evaluate air contamination at locations where winds blow off ORR property. Between 1991 and 2001, DOE measured ambient air concentrations of seven different metals, including four known human carcinogens.

DOE sent PM10 and TSP filters to an analytical laboratory to determine the composition of the collected airborne particles. The laboratory created composite monthly samples for every monitoring station from the individual filters that DOE collected on the 6-day rotating schedule. Filter analyses were performed using inductively coupled plasma/mass spectrometry, which is consistent with analytical methodologies EPA has published for such chemical speciation work.

Table C-2 summarizes DOE's metals monitoring data. The highest annual average air concentrations of four of the metals — beryllium, lead, nickel, and uranium — did not exceed their corresponding health-based comparison values. In fact, the measured concentrations were considerably lower than these screening numbers. For instance, the highest annual average concentration for uranium (0.001373 µg/m3) was more than 200 times lower than uranium's comparison value (0.3 µg/m3). On the other hand, measured levels for arsenic, cadmium, and chromium all exceeded their corresponding Cancer Risk Evaluation Guides (CREGs). Accordingly, ATSDR selected these three metals as contaminants of concern and used more detailed evaluations to understand the public health implications of inhaling them (see Section IV).

DOE's Metals Monitoring Locations
Figure C-3. DOE's Metals Monitoring Locations

Table C-2. DOE's Monitoring Data for Metals (1991–2001)


Time Frame of Monitoring

Highest Annual Average Concentration

Health-Based Comparison Value

Type of Comparison Value
















Chromium (total)




CREG (see notes)















(see notes)

Notes: Source of data: DOE 1991–2002.
The highest annual average concentration is the highest average value reported for any of the monitoring stations for any of the years on record. This highest value was selected as the first step in the screening process. In cases where a metal was not detected in every sample, DOE used the detection limit to compute arithmetic means and reported the annual average as being “less than” the computed value.
DOE measured ambient air concentrations of total chromium. The comparison value is for hexavalent chromium, which is a subset of total chromium. Refer to Section IV.B for ATSDR's detailed evaluation of chromium exposures.
The comparison value for uranium is ATSDR's EMEG for chronic exposure to highly soluble uranium salts. This comparison value is suitable for evaluating the chemical toxicity of uranium. Refer to Tables C-3 and C-4 for ATSDR's evaluation of exposures to radioactivity associated with uranium.

Radiation and radionuclides

For several years before the TSCA Incinerator first operated, DOE's environmental surveillance network at ORR included external gamma radiation monitoring. This monitoring helps determine whether releases from ORR facilities are causing increases in external gamma radiation above background levels. The measurements are collected using external gross gamma radiation monitors that are equipped with dual-range, high-pressure ion chamber sensors and digital electronic count-rate meters. The external gamma readings are recorded weekly, including at station PAM-42, which is in close proximity to ETTP (see Figure C-4). Between 1991 and 2002, the average external gamma radiation levels at this location were 5.9 µR/hr. These levels not only were consistent with measurements at designated background monitoring stations (i.e., Fort Loudon Dam, Norris Dam), but also fell within the range of gamma radiation levels in urban and suburban locations around the country (DOE 1991–2002).

DOE's Radionuclide Monitoring Locations
Figure C-4. DOE's Radionuclide Monitoring Locations

To supplement the gamma radiation measurements, DOE also measures concentrations of radionuclides around the perimeter of the main ORR facilities. ATSDR reviewed the history of sampling results for stations PAM35 and PAM42, as documented in the annual site environmental reports (DOE 1991–2002). At both of these stations, two sampling devices operate. The first device continuously collects particulate matter on filters, which are removed biweekly and analyzed as quarterly composites.8 The second device collects water vapor to measure concentrations of tritium. An analytical laboratory then conducts all isotopic analyses of the sampling media. TDEC's state radiochemistry laboratory has performed much of the filter analyses for the radionuclide samples.

Table C-3 summarizes DOE's monitoring data for radionuclides and compares the highest annual average concentration measured to DOE's Derived Concentration Guides (DCGs) for inhalation exposure (see Appendix D). As the table shows, all of the radionuclides documented in DOE's annual site environmental reports were found at concentrations at least 100 times lower than their corresponding DCGs.

Table C-3. DOE's Monitoring Data for Radionuclides (1991–2001)


Highest Annual Concentration Measured (µCi/mL)

DOE’s Derived Concentration Guide (µCi/mL)

Margin of Safety (See Notes)


1.6 x 10-13

4.0 x 10-8



1.6 x 10-16

4.0 x 10-10



1.5 x 10-16

4.0 x 10-10



3.8 x 10-15

9.0 x 10-10



7.0 x 10-18

4.0 x 10-14



3.8 x 10-16

4.0 x 10-14



8.3 x 10-18

7.0 x 10-15



1.1 x 10-11

1.0 x 10-7



7.2 x 10-17

9.0 x 10-14



1.1 x 10-17

1.0 x 10-13



4.6 x 10-17

1.0 x 10-13


Notes: Source of data: DOE 1991–2002.
Concentrations for radionuclides are the highest annual averages reported in DOE's annual site environmental reports for the two perimeter monitoring stations at ETTP. The table lists those radionuclides for which measurement data were reported in at least three annual site environmental reports.
DOE's Derived Concentration Guides (DCGs) represent exposure levels that would deliver annual effective dose equivalents of 100 mrem/year to an individual who is continuously exposed to the measured amounts, 24 hours per day, 365 days per year.
Margin of safety in this table is calculated as the quotient of the DCG and the highest activity measured. Margins of safety greater than 1 imply that measured levels are safely below the relevant DCGs.

In summary, DOE's environmental surveillance network offers extensive insights into the air contamination levels of particulate matter, metals, and radionuclides. These data are particularly useful due to their extensive temporal and spatial coverage: monitoring for most contaminants has occurred the entire time the TSCA Incinerator has operated, and monitoring stations are located in and near the areas expected to have the greatest air quality impacts from the incinerator's emissions. The monitoring data suggest that ambient air concentrations of many pollutants do not reach levels of potential health concern; however, ambient air concentrations of arsenic, cadmium, and chromium require additional evaluation (see Section IV). Section III.D.1 of this PHA reviews DOE's monitoring data in light of air quality measurements made by other parties; that section also lists several recommendations for improving the reporting of the monitoring results. Section III.D.2 summarizes ambient air concentrations DOE measured during TRV events.

C.2. EPA Data (EPA 1996–2003)

In 1973, EPA established the Environmental Radiation Ambient Monitoring System (ERAMS) to identify nationwide trends in radionuclide levels in multiple environmental media. One station EPA installed (see Figure 10) is located immediately downwind from the TSCA Incinerator, where the agency has continuously collected airborne particulates on sampling filters since July 1996. Twice weekly, TDEC employees remove the filters, which are then surveyed in the field for gross beta activity and sent to an EPA laboratory for a more accurate and precise measurement of gross beta activity. Composites of the semi-weekly sampling filters are then analyzed, either quarterly or annually, for activity levels of selected uranium and plutonium isotopes. The sampling and analytical procedures at all monitoring stations are consistent with specifications in the ERAMS Quality Assurance Project Plan. EPA publishes the sampling results in quarterly reports (EPA 1996–2003) and has posted them on a project Web site (EPA 2004e). According to EPA, all ERAMS data posted on the Web site have undergone thorough quality assurance and quality control checks.

Table C-4 summarizes data trends for three ERAMS stations: the K-25 station, which is located immediately downwind from the TSCA Incinerator, and stations in Knoxville and Nashville, which are included for comparison purposes. The table presents average activity levels for gross beta, two plutonium isotopes, and three uranium isotopes. These summary statistics indicate that the annual average levels of the two plutonium isotopes at K-25 are lower than the levels observed in Knoxville and Nashville, while the opposite trend exists for the three uranium isotopes. More importantly, the activity levels for all five isotopes shown in Table C-4 are safely below health-protective comparison values developed by EPA.

Table C-4. EPA's ERAMS Data (1996–2000)


Monitoring Station

Highest Annual Average Air Activity

Health-Based Comparison Value or Screening Value (See Notes)

Gross Beta


0.012 pCi/m3

1 pCi/m3


0.018 pCi/m3


0.015 pCi/m3



0.46 aCi/m3

140 aCi/m3


0.83 aCi/m3


0.64 aCi/m3



0.37 aCi/m3

140 aCi/m3


18.3 aCi/m3


0.21 aCi/m3



59.1 aCi/m3

420 aCi/m3


31.8 aCi/m3


20.7 aCi/m3



4.23 aCi/m3

470 aCi/m3


3.63 aCi/m3


2.58 aCi/m3



69.7 aCi/m3

510 aCi/m3


29.8 aCi/m3


19.6 aCi/m3

Notes: Data source: EPA 1996–2003.
Health-based comparison values for plutonium and uranium isotopes are taken from EPA's ERAMS Web site (EPA 2004e). Specifically, the values selected represent exposure levels that would present theoretical cancer risks of less than 1 in 1,000,000 for the majority of the exposed population.
A screening value of 1 pCi/m3 is used to evaluate gross beta radiation. When levels exceeded this amount, EPA performed a gamma analysis of the sampling filters. The data for gross beta are average activities from 1996 to 2003, not the highest annual average.
Data from monitoring stations in Knoxville and Nashville are presented for comparison purposes.
1 aCi = 10-18 Ci = 10-6 pCi

C.3. TDEC Data (TDEC 1996–2002)

To assist ATSDR with the public health assessment process, TDEC provided copies of its annual Environmental Monitoring Reports from calendar years 1996 to 2002 (TDEC 1996–2002). ATSDR thoroughly reviewed these documents, which present environmental sampling data for multiple media throughout ORR. The following paragraphs describe TDEC's ambient air sampling efforts, as those relate most directly to the issues evaluated in this PHA.

Ambient radiation monitoring using environmental dosimetry

Since 1995, TDEC has operated an extensive network of thermoluminescent dosimeters (TLDs) to continuously measure gamma radiation levels at numerous locations throughout ORR. Currently, TDEC's network includes nearly 65 monitoring locations, though the number and placement of TLDs has changed over the years. The overwhelming majority of these monitoring locations are in on-site areas that the public cannot access. Both aluminum oxide TLDs and lithium fluoride TLDs are used in this network. TDEC collects the TLDs quarterly and returns them to the manufacturer (Landauer, Inc.) for analysis.

When evaluating the gamma radiation data, ATSDR considered the monitoring locations nearest ETTP where the public might have routine access. Based on these criteria, ATSDR focused its evaluation on gamma radiation levels measured at the “K-25 Visitor Center,” which is located along the Oak Ridge Turnpike (Route 58), just south of the main entrance to ETTP. According to measurements documented in TDEC's annual monitoring reports, annual average radiation doses at this location have ranged from 8.9 to 22.5 mrem/year (above background), with an 8-year average of 15.7 mrem/year (above background). These levels are considerably lower than 100 mrem/year, which is both ATSDR's MRL for ionizing radiation and TDEC's primary dose limit for protecting members of the public.

Monitoring for metals

From 1997 to the present, TDEC conducted ambient air monitoring for metals at multiple locations around ETTP, but primarily at stations where DOE also monitors metals. These measurements occur at stations K2, PAM35, and PAM42 (see Figure C-3). A stated purpose of the TDEC monitoring is “to provide an independent verification of monitoring results as reported by the DOE” (TDEC 1996–2002). The program has focused on a core group of metals: arsenic, beryllium, cadmium, chromium, lead, nickel, and uranium. In the first years this monitoring was conducted, TDEC operated a single particulate sampling device at a fixed location for a set time frame (roughly 1 month), after which the device would be moved to another location for a set time frame, and so on. The program changed in 2002, with TDEC operating three separate sampling devices at three different locations.

Table C-5 summarizes TDEC's monitoring data for metals. Of the analytes considered, only arsenic and chromium had at least one measured concentration greater than their health-based comparison values. This finding is somewhat consistent with trends among DOE's monitoring data for metals from the same time frame. According to TDEC's monitoring data, ambient air concentrations of the remaining metals (beryllium, cadmium, lead, nickel, and uranium) did not exceed health-based comparison values. Based on trends among both DOE's and TDEC's monitoring data, ATSDR selected arsenic, cadmium, and chromium as contaminants warranting further evaluation, as documented in Section IV of this PHA. As noted elsewhere in this PHA, the detection of the metals in ambient air near ETTP does not mean the metals originate from the TSCA Incinerator. Rather, multiple air emissions sources — some not associated with ORR operations (e.g., mobile sources) — contribute to the airborne levels of metals summarized below.

Table C-5. TDEC's Monitoring Data for Metals (1997–2002)


Time Frame of Monitoring

Highest Average Concentration (µg/m3)

Health-Based Comparison Value (µg/m3)

Type of Comparison Value
















Chromium (total)




CREG (see notes)















(see notes)

Notes: Source of data: TDEC 1996–2002.
The highest average concentrations are the highest values in TDEC's annual reports that did not have a “<” before the concentration. In the case of uranium, every measurement was either reported as “not detected” or as “<0.01.” The averaging period for the concentrations shown in this table varies, because TDEC moved its sampling equipment from location to location during the first several years this program operated.
TDEC measured ambient air concentrations of total chromium. The comparison value is for hexavalent chromium, which is a subset of total chromium. Refer to Section IV.B for ATSDR's detailed evaluation of chromium exposures.
The comparison value for uranium is ATSDR's EMEG for chronic exposure to highly soluble uranium salts. This comparison value is suitable for evaluating the chemical toxicity of uranium. Refer to Tables C-3 and C-4 for ATSDR's evaluation of exposures to radioactivity associated with uranium.

Additional monitoring and sampling activities

ATSDR acknowledges that TDEC conducts numerous additional activities related to environmental surveillance. For instance, TDEC takes the lead in providing oversight of DOE's emissions and ambient air sampling programs. The oversight activities involve observing sampling efforts, reviewing equipment operation, evaluating sampling results, conducting independent sampling events, and analyzing some samples collected by DOE. For instance, TDEC's state radiochemistry laboratory analyzes particulate filters collected at DOE's perimeter monitoring stations (see Appendix C.1). Finally, TDEC conducts many other monitoring and surveillance activities aimed at characterizing releases and exposure levels within ETTP property, where the public cannot access. These activities include monitoring fugitive radiological emissions, real-time ambient monitoring for gamma radiation, and various special studies that focus on specific issues.

Section III.D.1 describes how TDEC's monitoring results factored into ATSDR's analysis and recommends how TDEC can improve its documentation of monitoring data in future annual reports.

C.4. TVA Data (EPA 2004d)

Early in the Oak Ridge TSCA Incinerator public health assessment process, a community member recommended that ATSDR consult with TVA to determine whether that agency collected any ambient air monitoring data from locations near the TSCA Incinerator. ATSDR contacted TVA and received a listing of that agency's ambient air monitoring stations, only one of which is located within 5 miles of this site. As Figure 10 depicts, that TVA station is located approximately 3 miles south of the site along a bend in the Clinch River, where TVA continuously measured ambient air concentrations of nitrogen dioxide, ozone, and sulfur dioxide for nearly 2 years, between 1999 and 2000. Measurements were made with EPA-approved monitoring methodologies and were validated before submission to a centralized database of monitoring results maintained by EPA. Table C-6 summarizes TVA's monitoring data from this station, which are reviewed below for the three main contaminants:

Nitrogen dioxide

TVA collected 10,940 1-hour average observations of ambient air concentrations of nitrogen dioxide. The annual average concentrations computed from these measurements were safely below EPA's health-based air quality standards.


Between 1999 and 2000, TVA's monitoring station south of the TSCA Incinerator collected valid ozone data on approximately 380 days. A single 1-hour average measurement (0.131 ppm) exceeded EPA's previous health-based standard for ozone. During this same time, 8-hour average ozone concentrations exceeded EPA's current health-based standard for ozone on 22 days, or roughly 6% of the days on which ozone monitoring occurred. As multiple sections of this PHA describe, the elevated ozone levels observed in the Knoxville metropolitan area should be viewed as a regional air quality issue caused by an extremely wide range of emissions, both local and distant. Air emissions from the TSCA Incinerator likely have an insignificant effect on the ozone concentrations previously measured by TVA.

Sulfur dioxide

TVA collected 12,206 1-hour average observations of ambient air concentrations of sulfur dioxide. Every 3-hour average, 24-hour average, and annual average concentration computed from these values was safely below EPA's corresponding health-based air quality standards.

Trends from the TVA monitoring data provide very limited insights into the TSCA Incinerator's potential air quality impacts, given the pollutants that were measured. Nonetheless, other sections of this PHA refer to the TVA monitoring data when considering general air quality issues for the Knoxville metropolitan area.

Table C-6. TVA's Monitoring Data for Criteria Pollutants (1999–2000)


Averaging Time

Highest Concentration Measured

Comparison Value (See Notes)

Nitrogen dioxide

Annual average

0.0084 ppm

0.053 ppm


1-hour average

0.131 ppm

0.12 ppm

8-hour average

0.108 ppm

0.08 ppm

Sulfur dioxide

Annual average

0.0031 ppm

0.03 ppm

24-hour average

0.014 ppm

0.14 ppm

3-hour average

0.049 ppm

0.5 ppm

Notes: Data source: EPA 2004d.
The comparison values are all EPA National Ambient Air Quality Standards (NAAQS). For nitrogen dioxide, ozone, and the annual average and 24-hour average concentrations of sulfur dioxide, the comparison values are health-based. For the 3-hour average concentration of sulfur dioxide, the comparison value is a secondary standard, which is designed to protect things people value, other than their health (e.g., visibility, vegetation, building surfaces).


Following are definitions of the various health-based comparison values that ATSDR used in this PHA to put the measured and modeled levels of environmental contamination into perspective:


Cancer Risk Evaluation Guide, a highly conservative and theoretical value that is believed to cause no more than one excess cancer in a million persons exposed over time.


Derived Concentration Guide, radionuclide exposure level reported by DOE that would deliver (for inhalation pathways) an annual effective dose equivalent of 100 millirem/year to an individual who is continuously exposed 24 hours per day, 365 days per year. DOE has also calculated DCGs for ingestion exposures.


Environmental Media Evaluation Guide, a media-specific comparison value that is used to select contaminants of concern. Levels below the EMEG are not expected to cause adverse noncarcinogenic health effects. These have been developed for acute exposure scenarios, intermediate exposure scenarios, and chronic exposure scenarios.


Minimal Risk Level, an estimate of daily human exposure to a dose of a chemical that is likely to be without an appreciable risk of adverse non-cancerous effects over a specified duration of exposure.


National Ambient Air Quality Standard, an ambient air concentration that EPA has established to characterize air quality. The standards are health-based and were designed to be protective of many sensitive populations, such as people with asthma and children. The standards have been developed only for a small subset of pollutants, and their averaging times and statistical interpretations vary among the regulated pollutants.


Risk-Based Concentration, a contaminant concentration that is not expected to cause adverse health effects over long-term exposure. These have been developed for both cancer outcomes (RBC-C) and non-cancer outcomes (RBC-N).


Reference Concentration, an ambient air concentration developed by EPA that people, including sensitive subpopulations, likely can be exposed to continuously over a lifetime without developing adverse non-cancer health effects. RfCs typically have uncertainty factors built into them to account for any perceived limitations in the data on which they are based.


The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public health agency with headquarters in Atlanta, Georgia, and 10 regional offices in the United States. ATSDR's mission is to serve the public by using the best science, taking responsive public health actions, and providing trusted health information to prevent harmful exposures and diseases related to toxic substances. ATSDR is not a regulatory agency, unlike the U.S. Environmental Protection Agency (EPA), which is the federal agency that develops and enforces environmental laws to protect the environment and human health.

This glossary defines words used by ATSDR in this PHA. It is not a complete dictionary of environmental health terms. If you have questions or comments, call ATSDR's toll-free telephone number, 1-888-42-ATSDR (1-888-422-8737).


Occurring over a short time [compare with chronic].

Acute exposure

Contact with a substance that occurs once or for only a short time (up to 14 days) [compare with intermediate-duration exposure and chronic exposure].

Adverse health effect

A change in body function or cell structure that might lead to disease or health problems.


Surrounding (for example, ambient air).

Background level

An average or expected amount of a substance or radioactive material in a specific environment, or typical amounts of substances that occur naturally in an environment.

Background radiation

The amount of radiation to which a member of the general population is exposed from natural sources, such as terrestrial radiation from naturally occurring radionuclides in the soil, cosmic radiation originating from outer space, and naturally occurring radionuclides deposited in the human body.


Plants and animals in an environment. Some of these plants and animals might be sources of food, clothing, or medicines for people.


Any one of a group of diseases that occurs when cells in the body become abnormal and grow or multiply out of control.

Cancer risk

A theoretical risk of for getting cancer if exposed to a substance every day for 70 years (a lifetime exposure). The true risk might be lower.


A substance that causes cancer.

Case-control study

A study that compares exposures of people who have a disease or condition (cases) with people who do not have the disease or condition (controls). Exposures that are more common among the cases may be considered as possible risk factors for the disease.


[See Comprehensive Environmental Response, Compensation, and Liability Act of 1980.]


Occurring over a long time (more than 1 year) [compare with acute].

Chronic exposure

Contact with a substance that occurs over a long time (more than 1 year) [compare with acute exposure and intermediate-duration exposure].

Committed Effective Dose Equivalent (CEDE)

The sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent to the organs or tissues. The committed effective dose equivalent is used in radiation safety because it implicitly includes the relative carcinogenic sensitivity of the various tissues. The unit of dose for the CEDE is the rem (or, in SI units, the sievert — 1 sievert equals 100 rem.)

Comparison value (CV)

Calculated concentration of a substance in air, water, food, or soil that is unlikely to cause harmful (adverse) health effects in exposed people. The CV is used as a screening level during the public health assessment process. Substances found in amounts greater than their CVs might be selected for further evaluation in the public health assessment process.

Completed exposure pathway

[See exposure pathway.]

Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA)

CERCLA, also known as Superfund, is the federal law that concerns the removal or cleanup of hazardous substances in the environment and at hazardous waste sites. ATSDR, which was created by CERCLA, is responsible for assessing health issues and supporting public health activities related to hazardous waste sites or other environmental releases of hazardous substances.


The amount of a substance present in a certain amount of soil, water, air, food, blood, hair, urine, breath, or any other medium.


A substance that is either present in an environment where it does not belong or is present at levels that might cause harmful (adverse) health effects.

Curie (Ci)

A unit of radioactivity. One curie equals that quantity of radioactive material in which there are 3.7 x 1010 nuclear transformations per second. The activity of 1 gram of radium is approximately 1 Ci; the activity of 1.46 million grams of natural uranium is approximately 1 Ci.


Referring to the skin. For example, dermal absorption means passing through the skin.

Dermal contact

Contact with (touching) the skin [see route of exposure].

Detection limit

The lowest concentration of a chemical that can reliably be distinguished from a zero concentration.

Disease registry

A system of ongoing registration of all cases of a particular disease or health condition in a defined population.

Dose (for chemicals that are not radioactive)

The amount of a substance to which a person is exposed over some time period. Dose is a measurement of exposure. Dose is often expressed as milligrams (a measure of quantity) per kilogram (a measure of body weight) per day (a measure of time) when people eat or drink contaminated water, food, or soil. In general, the greater the dose, the greater the likelihood of an effect. An “exposure dose” is how much of a substance is encountered in the environment. An “absorbed dose” is the amount of a substance that actually gets into the body through the eyes, skin, stomach, intestines, or lungs.

Dose (for radioactive chemicals)

The radiation dose is the amount of energy from radiation that is actually absorbed by the body. This is not the same as measurements of the amount of radiation in the environment.

Environmental media

Soil, water, air, biota (plants and animals), or any other parts of the environment that can contain contaminants.

Environmental media and transport mechanism

Environmental media include water, air, soil, and biota (plants and animals). Transport mechanisms move contaminants from the source to points where human exposure can occur. The environmental media and transport mechanism is the second part of an exposure pathway.


The study of the distribution and determinants of disease or health status in a population; the study of the occurrence and causes of health effects in humans.


Contact with a substance by swallowing, breathing, or touching the skin or eyes. Exposure can be short-term [see acute exposure], of intermediate duration [see intermediate-duration exposure], or long-term [see chronic exposure].

Exposure assessment

The process of finding out how people come into contact with a hazardous substance, how often and for how long they are in contact with the substance, and how much of the substance they are in contact with.

Exposure pathway

The route a substance takes from its source (where it began) to its end point (where it ends), and how people can come into contact with (or get exposed to) it. An exposure pathway has five parts: a source of contamination (such as an abandoned business); an environmental media and transport mechanism (such as movement through groundwater); a point of exposure (such as a private well); a route of exposure (eating, drinking, breathing, or touching), and a receptor population (people potentially or actually exposed). When all five parts are present, the exposure pathway is termed a completed exposure pathway.


Water beneath the earth’s surface in the spaces between soil particles and between rock surfaces [compare with surface water].


A source of potential harm from past, current, or future exposures.

Hazardous waste

Potentially harmful substances that have been released or discarded into the environment.

Health consultation

A review of available information or collection of new data to respond to a specific health question or request for information about a potential environmental hazard. Health consultations are focused on a specific exposure issue. They are therefore more limited than public health assessments, which review the exposure potential of each pathway and chemical [compare with public health assessment].

Health education

Programs designed with a community to help it know about health risks and how to reduce these risks.

Health investigation

The collection and evaluation of information about the health of community residents. This information is used to describe or count the occurrence of a disease, symptom, or clinical measure and to estimate the possible association between the occurrence and exposure to hazardous substances.

Health statistics review

The analysis of existing health information (i.e., from death certificates, birth defects registries, and cancer registries) to determine if there is excess disease in a specific population, geographic area, and time period. A health statistics review is a descriptive epidemiologic study.

Indeterminate public health hazard

The category used in ATSDR’s public health assessment documents when a professional judgment about the level of health hazard cannot be made because information critical to such a decision is lacking.


The number of new cases of disease in a defined population over a specific time period [contrast with prevalence].


The act of swallowing something through eating, drinking, or mouthing objects. A hazardous substance can enter the body this way [see route of exposure].


The act of breathing. A hazardous substance can enter the body this way [see route of exposure].

Intermediate-duration exposure

Contact with a substance that occurs for more than 14 days and less than a year [compare with acute exposure and chronic exposure].


Nuclides having the same number of protons in their nuclei, and hence the same atomic number, but differing in the number of neutrons, and therefore in the mass number. Identical chemical properties exist in isotopes of a particular element. The term should not be used as a synonym for “nuclide,” because “isotopes” refers specifically to different nuclei of the same element.


Moving from one location to another.

National Priorities List for Uncontrolled Hazardous Waste Sites (National Priorities List or NPL)

EPA’s list of the most serious uncontrolled or abandoned hazardous waste sites in the United States. The NPL is updated on a regular basis.

No apparent public health hazard

A category used in ATSDR’s public health assessments for sites where human exposure to contaminated media might be occurring, might have occurred in the past, or might occur in the future, but is not expected to cause any harmful health effects.

No public health hazard

A category used in ATSDR’s public health assessment documents for sites where people have never and will never come into contact with harmful amounts of site-related substances.


[See National Priorities List for Uncontrolled Hazardous Waste Sites.]


A volume of a substance that moves from its source to places farther away from the source. Plumes can be described by the volume of air or water they occupy and the direction in which they move. For example, a plume can be a column of smoke from a chimney or a substance moving with groundwater.

Point of exposure

The place where someone can come into contact with a substance present in the environment [see exposure pathway].


A group or number of people living within a specified area or sharing similar characteristics (such as occupation or age).


The number of existing disease cases in a defined population during a specific time period [contrast with incidence].


Actions that reduce exposure or other risks, keep people from getting sick, or keep disease from getting worse.

Public comment period

An opportunity for the public to comment on agency findings or proposed activities contained in draft reports or documents. The public comment period is a limited time period during which comments will be accepted.

Public health action plan

A list of steps to protect public health.

Public health advisory

A statement made by ATSDR to EPA or a state regulatory agency that a release of hazardous substances poses an immediate threat to human health. The advisory includes recommended measures to reduce exposure and reduce the threat to human health.

Public health assessment (PHA)

An ATSDR document that examines hazardous substances, health outcomes, and community concerns at a hazardous waste site to determine whether people could be harmed by coming into contact with those substances. The PHA also lists actions that need to be taken to protect public health [compare with health consultation].

Public health hazard

A category used in ATSDR’s public health assessments for sites that pose a public health hazard because of long-term exposures (greater than 1 year) to sufficiently high levels of hazardous substances or radionuclides that could result in harmful health effects.

Public health hazard categories

Statements about whether people could be harmed by conditions present at the site in the past, present, or future. One or more hazard categories might be appropriate for each site. The five public health hazard categories are no public health hazard, no apparent public health hazard, indeterminate public health hazard, public health hazard, and urgent public health hazard.


The emission and propagation of energy through space or through a material medium in the form of waves (e.g., the emission and propagation of electromagnetic waves, or of sound and elastic waves). The term “radiation” (or “radiant energy”), when unqualified, usually refers to electromagnetic radiation. Such radiation commonly is classified according to frequency, as microwaves, infrared, visible (light), ultraviolet, and x and gamma rays and, by extension, corpuscular emission, such as alpha and beta radiation, neutrons, or rays of mixed or unknown type, such as cosmic radiation.

Radioactive material

Material containing radioactive atoms.


Spontaneous nuclear transformations that result in the formation of new elements. These transformations are accomplished by emission of alpha or beta particles from the nucleus or by the capture of an orbital electron. Each of these reactions may or may not be accompanied by a gamma photon.


An unstable or radioactive isotope (form) of an element that can change into another element by giving off radiation.


Any radioactive isotope (form) of any element.


[See Resource Conservation and Recovery Act (1976, 1984).]

Receptor population

People who could come into contact with hazardous substances [see exposure pathway].


A unit of dose equivalent that is used in the regulatory, administrative, and engineering design aspects of radiation safety practice. The dose equivalent in rem is numerically equal to the absorbed dose in rad multiplied by the quality factor (1 rem is equal to 0.01 sievert).

Resource Conservation and Recovery Act (1976, 1984) (RCRA)

This act regulates management and disposal of hazardous wastes currently generated, treated, stored, disposed of, or distributed.


The probability that something will cause injury or harm.

Route of exposure

The way people come into contact with a hazardous substance. Three routes of exposure are breathing [inhalation], eating or drinking [ingestion], and contact with the skin [dermal contact].


A portion or piece of a whole; a selected subset of a population or subset of whatever is being studied. For example, in a study of people the sample is a number of people chosen from a larger population [see population]. An environmental sample (for example, a small amount of soil or water) might be collected to measure contamination in the environment at a specific location.


A liquid capable of dissolving or dispersing another substance (for example, acetone or mineral spirits).

Source of contamination

The place where a hazardous substance comes from, such as a landfill, waste pond, incinerator, storage tank, or drum. A source of contamination is the first part of an exposure pathway.

Special populations

People who might be more sensitive or susceptible to exposure to hazardous substances because of factors such as age, occupation, sex, or behaviors (for example, cigarette smoking). Children, pregnant women, and older people are often considered special populations.


A person, group, or community who has an interest in activities at a hazardous waste site.


A chemical.

Surface water

Water on the surface of the earth, such as in lakes, rivers, streams, ponds, and springs [compare with groundwater].


[see epidemiologic surveillance]


A systematic collection of information or data. A survey can be conducted to collect information from a group of people or from the environment. Surveys of a group of people can be conducted by telephone, by mail, or in person. Some surveys are done by interviewing a group of people.

Toxicological profile

An ATSDR document that examines, summarizes, and interprets information about a hazardous substance to determine harmful levels of exposure and associated health effects. A toxicological profile also identifies significant gaps in knowledge on the substance and describes areas where further research is needed.


The study of the harmful effects of substances on humans or animals.

Uncertainty factor

A mathematical adjustment for reasons of safety when knowledge is incomplete — for example, a factor used in the calculation of doses that are not harmful (adverse) to people. These factors are applied to the lowest-observed-adverse-effect-level (LOAEL) or the no-observed-adverse-effect-level (NOAEL) to derive a minimal risk level (MRL). Uncertainty factors are used to account for variations in people’s sensitivity, for differences between animals and humans, and for differences between a LOAEL and a NOAEL. Scientists use uncertainty factors when they have some, but not all, the information from animal or human studies to decide whether an exposure will cause harm to people.

Units, radiological



Becquerel* (Bq)

1 disintegration per second = 2.7 x 10-11 Ci

Curie (Ci)

3.7 x 1010 disintegrations per second = 3.7 × 1010 Bq

Gray* (Gy)

1 J/kg = 100 rad

Rad (rad)

100 erg/g = 0.01 Gy

Rem (rem)

0.01 sievert

Sievert* (Sv)

100 rem

*International Units, designated (SI)

Urgent public health hazard

A category used in ATSDR's public health assessments for sites where short-term exposures (less than 1 year) to hazardous substances or conditions could result in harmful health effects that require rapid intervention.

Other Glossaries and Dictionaries

Environmental Protection Agency

National Center for Environmental Health (CDC)

National Library of Medicine


Throughout this document, ATSDR reported observations in many different units of measurement. While ATSDR can appreciate a desire to use consistent units when measuring a given phenomenon (e.g., an air concentration), the reality is that many different types of units are widely used by scientists, often due to conventions that have been followed for many years. Some of these reporting conventions vary from one type of pollutant to the next.

This appendix defines the different units of measurement used throughout this PHA and presents unit conversion information, where appropriate. This appendix should not be viewed as an exhaustive account of units of measurement. Rather, it provides perspective on the units presented throughout this PHA.

Units used when reporting concentrations of radioactive contaminants

aCi/m3 = attocuries per cubic meter

pCi/m3 = picocuries per cubic meter

µCi/ml = microcurie per milliliter

Note: The following information may be useful for appreciating the terminology used in these units of measurements and for converting between the units:

1,000,000 µCi = 1 Ci

1,000,000 pCi = 1 µCi

1,000,000 aCi = 1 pCi

1,000,000 ml = 1 m3

Units used when reporting concentrations of non-radioactive contaminants

µg/m3 = micrograms per cubic meter

ppm = parts per million

Notes: Scientists typically report ambient air concentrations of particulate matter and metals in units of micrograms per cubic meter.

There is no widely used convention for reporting ambient air concentrations of organics and inorganic compounds. Some scientists use mass concentrations (e.g., micrograms per cubic meter and variations upon this unit); other scientists use volume concentrations (e.g., parts per million and variations upon this unit).

Units used when reporting stack gas concentrations

grains/dscf = grains per dry standard cubic foot

ng/dscm = nanograms per dry standard cubic meter

µg/dscm = micrograms per dry standard cubic meter

Notes: Grains are a mass measurement commonly used when reporting stack gas concentrations of particulate matter. There are 7,000 grains in a pound.

“Nanograms” and “micrograms” are commonly used when reporting stack gas concentrations of trace gases, such as PCBs and dioxins. There are 1,000,000 micrograms in a gram, and there are 1,000,000,000 nanograms in a gram.

Units used when reporting mass emission rates

lb/hour = pounds per hour

lb/day = pounds per day

µg/second = micrograms per second

ng/second = nanograms per second

Note: The most appropriate unit of measurement for mass emission rates is often based on reporting convention and regulatory requirements. Some regulations, for instance, require facility operators to report maximum hourly emission rates; in such cases, pounds per hour might be an acceptable unit of measurement. The pollutants also determine what units are most appropriate. Pollutants present in very trace amounts (e.g., dioxins) often are reported in terms of micrograms or nanograms.

8 Note that the averaging time and compositing frequency for this and other sampling efforts have changed over the years.

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