PUBLIC HEALTH ASSESSMENT
TUCSON INTERNATIONAL AIRPORT AREA
TUCSON, PIMA COUNTY, ARIZONA
Figure 1: Location map of the Tucson International Airport Superfund Site
Figure 2: Location of Larger Plume A and Smaller Plume B
Figure 3: Close-up Map of Plume B
Figure 4: Results of 1994 and 1998 Private Well Studies Conducted by Pima County
Department of Environmental Quality
Listed below are some of the comparison values used by ADHS to select chemicals which merit detailed site specific evaluation. In addition, other non-ADHS values are listed which are sometimes used to provide a meaningful frame of reference for environmental chemical data. For convenience, the list also includes some of the common abbreviations used for common units of measure. Following the list is a brief description of each value.
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CREG = Cancer Risk Evaluation Guide MRL = Minimal Risk Level EMEG = Environmental Media Evaluation Guide RMEG = Reference Dose Media Evaluation Guide RfD = Reference Dose RfC = Reference Dose Concentration RBC = Risk Based Concentration DWEL = Drinking Water Equivalent Level LTHA = Lifetime Health Advisory MCL = Maximum Contaminant Level HBGL = Human Health Based Guidance Level PRG = Permissible Remediation Goal (Action Level) PEL = Permissible Exposure Limit TLV = Threshold Limit Value ppm = parts per million ppb = parts per billion kg = kilogram (1000 grams) mg = milligram (0.001 grams) ug = microgram (0.000001 grams) L = liter m3 = cubic meter (referring to 1000 liters of air) |
Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrations expected to cause no more than one excess cancer in one million persons exposed over a lifetime. CREGs are calculated from USEPA's cancer slope factors or cancer potency factors using standard assumptions for exposure rates. These cancer estimates are commonly used because low-dose chemical exposure lab studies typically are not in the scientific literature and the true risk is unknown (and may be as low as zero).
Minimal Risk Levels (MRLs) are estimates of daily human exposure to a chemical (usually in terms of milligrams chemical per kilogram of body weight per day) that are unlikely to be associated with any appreciable risk of adverse noncancer effects over a specified duration of exposure. MRLs are calculated using data from human and animal studies and are usually reported for one of three time frames: acute (up to 14 days exposure), intermediate (15 - 364 days exposure), and chronic (1 year or more of exposure). MRLs are developed by the federal Agency for Toxic Substances and Disease Registry (ATSDR) and are published in ATSDR's Toxicological Profiles.
Environmental Media Evaluation Guides (EMEGs) are media-specific concentrations of chemicals calculated from ATSDR minimal risk levels using standard body weight and ingestion assumptions. EMEGs may be developed for specific timeframes of exposure duration such as acute, intermediate, or chronic (see MRLs). Chemical amounts below an EMEG are considered to be harmless to public health while amounts above an EMEG require detailed site-specific evaluation.
Reference Dose Media Evaluation Guide (RMEG) is the concentration of a contaminant in air, water, or soil that corresponds to USEPA's RfD for that contaminant when standard assumptions of body weight and intake rates are taken into account.
Reference Dose (RfD) is USEPA's estimate of the daily exposure to a contaminant unlikely to cause noncarcinogenic adverse health effects. Like the ATSDR MRL, the RfD is a dose expressed in mg/kg/day.
Reference Concentration (RfC) is a concentration of a substance in air which USEPA considers unlikely to cause non-cancer adverse health effects over a lifetime of exposure.
Risk-Based Concentrations (RBCs) are media-specific concentrations calculated from RfDs, RfCs, or USEPA's Cancer Slope Factors. They represent concentrations of a contaminant that are considered unlikely to cause adverse health effects over a lifetime of chronic exposure.
Drinking Water Equivalent Levels (DWELs) are based on USEPA's oral RfD and represent corresponding concentrations of a substance in drinking water that are estimated to have negligible deleterious effects in humans at an intake rate of 2 liters per day for life, assuming that drinking water is the sole source of exposure.
Lifetime Health Advisories (LTHA) are calculated from the DWEL and represent the concentration of a substance in drinking water estimated to have a negligible deleterious effect in humans over a lifetime of 70 years, assuming 2 liters per day consumption for a 70 kilogram adult, and taking into account other probable sources of exposure. In the absence of chemical specific data, the assumed fraction of total intake from drinking water is 20%. Lifetime health advisories are not derived for compounds considered potentially carcinogenic for humans.
Maximum Contaminant Levels (MCLs) are legally enforcible contaminant concentrations in drinking water that USEPA deems protective of public health (considering the availability and economics of water treatment technology) over a 70 year lifetime at an exposure rate of 2 liters of water per day.
Health Based Guidance Levels (HBGLs) are calculated by ADHS to limit excess lifetime cancer risk to one-in-one million (10-6) for known human carcinogens and to one-in-one-hundred-thousand (10-5) for possible and probable human carcinogens. HBGLs are considered individually protective of human health, including sensitive groups, over a lifetime. Chemical concentrations that exceed the applicable HBGL may not necessarily represent a health hazard. Rather, when contaminant concentrations exceed the HBGL, further evaluation may be necessary to determine whether a contaminant poses an unacceptable health hazard to humans.
Permissible Remediation Goals (PRGs), or Action Levels, are chemical- and media- specific levels of contamination which, when exceeded, automatically trigger a regulatory response or remedial action of some kind.
Permissible Exposure Limit (PEL) is an 8-hour time-weighted average concentration of a substance in workplace air designed by the Occupational Safety and Health Administration (OSHA) to provide that, to the extent feasible, chemical exposures in the workplace do not impair the health or functional capacity of workers throughout their working life. The PEL may be exceeded for brief periods, but the sum of the exposure levels averaged over 8 hours is not to exceed to PEL.
Threshold Limit Value (TLV), developed by the American Conference of Governmental Industrial Hygienists (ACGIH), is "the time-weighted average concentrations for a normal 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect." Many of ACGIH's TLVs were adopted by OSHA for use as PELs. Note that TLVs and PELs, which were designed to protect healthy workers, are usually much higher than the public health based values of ATSDR and USEPA, which were designed to protect the health of the general population, including subgroups such as the very young and the elderly.
Glossary
LIST OF ACRONYMS AND ABBREVIATIONS
| ADHS | Arizona Department of Health Services |
| ADEQ | Arizona Department of Environmental Quality |
| AMC | American Cancer Society |
| ATSDR | Agency for Toxic Substances and Disease Registry |
| COC | chemical of concern |
| HBGL | Health-based Guidance Levels |
| MCL | maximum contaminant level |
| MRL | minimum risk level |
| NA | not applicable |
| ND | non-detect |
| NS | not sampled |
| PCDEQ | Pima County Department of Environmental Quality |
| ppm | parts per million |
| SLE | Systemic Lupus Erythematosus |
| TCE | trichloroethylene |
| TIAA | Tucson International Airport Area |
| USEPA | United States Environmental Protection Agency |
| VOCs | volatile organic compounds |
| µg/L | micrograms per liter |
Agency for Toxic Substances and Disease Registry
Division of Health Assessment and Consultation
Attn: Chief, Program Evaluation, Records, and Information Services Branch E-56
1600 Clifton Road NE, Atlanta, Georgia 30333
