PUBLIC HEALTH ASSESSMENT
LANGLEY AIR FORCE BASE
and
NASA LANGLEY RESEARCH CENTER
HAMPTON, YORK COUNTY, VIRGINIA
TABLE 3. EXPOSURE PATHWAYS
| Pathway Name | Exposure Pathway Elements | Comments | |||||
| Source of Contamination | Environmental Medium | Point of Exposure | Route of Exposure | Time of Exposure | Exposed Population | ||
| POTENTIAL EXPOSURE PATHWAYS | |||||||
| Fish or shellfish from Tabbs Creek | Polychlorinated biphenyls (PCBs) and polychlorinated terphenyls (PCTs) from hydraulic systems, electrical equipment, compressors, and casting operations at NASA LaRC | Fish and shellfish | Human ingestion of fish and shellfish from Tabbs Creek | Ingestion | Past Present, and Future: Contaminants exist in fish and shellfish in Tabbs Creek. | Residents of Langley AFB and the surrounding communities who eat fish or shellfish from Tabbs Creek. | Occasional ingestion of fish or shellfish from Tabbs Creek is not expected to result in adverse health effects. |
| Fish or shellfish from the Back River | PCBs and PCTs from hydraulic systems, electrical equipment, compressors, and casting operations at NASA LaRC and Langley AFB, and silver from photographic operations at Langley AFB | Fish and shellfish | Human ingestion of fish and shellfish from the Back River | Ingestion | Past Present, and Future: Unknown. Sampling from the Back River is incomplete. | Residents of Langley AFB and the surrounding communities who eat fish or shellfish from the Back River. | ATSDR is waiting for the results of fish and shellfish studies from the Back River. |
| Soil | Various industrial and aviation activities at Langley AFB and NASA LaRC | Soil | Various sites throughout Langley AFB and NASA LaRC | Ingestion Dermal |
Past, Present, and Future: Contaminants exist in surface soil at some sites. | Employees of Langley AFB and NASA LaRC and potential trespassers. | Based on industrial use of the contaminated sites, contaminants are not detected at levels that are likely to pose a health hazard. |
Figure 1: Location Map: Langley AFB and NASA LaRC
Figure 2: Topographic Map: Langley AFB and NASA LaRC
Figure 3: Demographics of Population Residing Within a 1-Mile Radius
Figure 4: ATSDR's Exposure Evaluation Process
Figure 5: IRP Site Map: Langley AFB and NASA LaRC
Figure 5 was not available in electronic format for conversion to HTML at the time of preparation of this document. To obtain a hard copy of the document, please contact:
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
APPENDIX B: Comparison Values
The conclusion that a contaminant exceeds the comparison value does not mean that it will cause adverse health effects. Comparison values represent media-specific contaminant concentrations that are used to select contaminants for further evaluation to determine the possibility of adverse public health effects.
Cancer Risk Evaluation Guides (CREGs)
CREGs are estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million (10-6) persons exposed over lifetime. ATSDR's CREGs are calculated from EPA's cancer potency factors.
Environmental Media Evaluation Guides (EMEGs)
EMEGs are based on ATSDR minimal risk levels (MRLs) and factors in body weight and ingestion rates. An EMEG is an estimate of daily human exposure to a chemical that is likely to be without noncarcinogenic health effects over a specified duration of exposure.
Maximum Contaminant Level (MCL)
The MCL is the drinking water standard established by EPA. It is the maximum permissible level of a contaminant in water that is delivered to the free-flowing outlet. MCLs are considered protective of public health over a lifetime (70 years) for people consuming 2 liters of water per day.
Reference Media Evaluation Guides (RMEGs)
ATSDR derives RMEGs from EPA's oral reference doses. The RMEG represents the
concentration in water or soil at which daily human exposure is unlikely to result in adverse
noncarcinogenic effects.
APPENDIX C: Evaluation of Estimated Exposure Doses and Health Effects for Ingestion of Fish and Shellfish from Tabbs Creek and Soil Contact at Langley AFB Sites OT-06, OT-25, and FT-41
Deriving Exposure Doses
The Agency for Toxic Substances and Disease Registry (ATSDR) estimated the human exposure doses for residents of Langley Air Force Base (Langley AFB) and nearby communities from ingestion of fish and shellfish from Tabbs Creek, for children playing at the former playground at Langley AFB Site OT-06, and for trespassers at Langley AFB sites OT-25 and FT-41. Deriving exposure doses requires evaluating the concentrations of contaminants to which people may have been exposed and how often and for how long exposure to those contaminants occurred. Health effects are also related to individual characteristics such as age, gender, and nutritional status that influence how a chemical might be absorbed, metabolized, and eliminated by the body. Together, these factors help influence the individual's physiological response to chemical contaminant exposure and potential noncancer or cancer outcomes. In the absence of exposure-specific information, ATSDR applied several conservative exposure assumptions to define site-specific exposures as accurately as possible for residents near Tabbs Creek and children at the former playground at OT-06.
Evaluating Potential Health Hazards
The estimated exposure doses are used to evaluate potential noncancer and cancer effects associated with chemicals of concern. When evaluating noncancer effects, ATSDR uses standard health guidelines, including ATSDR's minimal risk levels (MRLs) and the U.S. Environmental Protection Agency's (EPA's) reference doses (RfDs), to evaluate whether adverse effects may occur. The chronic MRLs and RfDs are estimates of daily human exposure to a substance that are unlikely to result in adverse noncancer effects over a specified duration. ATSDR compared estimated exposure doses associated with fish ingestion and soil exposure scenarios to conservative health guidelines such as MRLs or RfDs for each contaminant. If the exposure dose is greater than the MRL or RfD, then a possibility exists that noncancer effects will occur. Because comparison values do not represent thresholds of toxicity, however, exposure to chemical concentrations above comparison values does not necessarily produce health effects.
To evaluate cancer effects, ATSDR uses cancer potency factors (CPFs) that define the relationship between oral exposure doses and the increased likelihood of developing cancer over a lifetime. The CPFs are developed using data from animal or human studies and often require extrapolation from high exposure doses administered in animal studies to the lower exposure levels typical of human exposure to environmental contaminants. The CPF represents the upper-bound estimate of the probability of developing cancer at a defined level of exposure; therefore, they tend to be very conservative (i.e., overestimate the actual risk) in order to account for a number of uncertainties in the data used in the extrapolation.
ATSDR estimated the potential for cancer to occur using the following equation. The estimated exposure doses and CPF values for the contaminants of concern are incorporated into the equation:
Although no risk of cancer is considered acceptable, it is impossible to achieve a zero cancer risk.
Consequently, ATSDR often uses a range of 10-4 to 10-6 estimated lifetime cancer risk (or 1 new
case in 10,000 to 1,000,000 exposed persons), based on conservative assumptions about
exposure, to determine whether a concern regarding cancer effects is valid. This range is
consistent with values adopted by EPA for evaluating the need for cleanup at hazardous waste
sites. Several of the chemicals of concern detected in the fish and shellfish from Tabbs Creek and
soil at Langley AFB Sites OT-06, OT-25, and FT-41 are considered to be human carcinogens or
probable human carcinogens. More detailed information about specific chemicals can be found in the ATSDR Toxicological Profiles.
Tabbs Creek: Fish and Shellfish
Ingestion of Fish and Shellfish from Tabbs Creek
ATSDR used the following equation to estimate human exposure doses for ingestion of fish and
shellfish from Tabbs Creek:
| Estimated Exposure Dose = |
Conc. × IR × FI × EF × ED
|
|
BW × AT
|
where:
| Conc. | = | Maximum contaminant concentration in fish/shellfish samples (mg/kg) (see Table C-1) |
| IR | = | Ingestion Rate (kg/day): 0.0065 kg/day daily intake averaged over a year (EPA, 1989) [slightly less than 1 8-ounce meal per month] |
| FI | = | Fraction ingested from Tabbs Creek (assumed to be 100 percent) |
| EF | = | Exposure frequency, or number of exposure events: 365 days/year |
| ED | = | Exposure duration, or the duration over which exposure occurs: adult: 30 years; child: 6 years |
| BW | = | Body weight (kg): adult: 70 kg; child: 10 kg (0 to 6 years old) |
| AT | = | Averaging time, or the time period over which cumulative exposures are averaged (ED × 365 days/year for noncancer effects; 70 years × 365 days/year for cancer effects) |
Assumptions for Estimating Human Exposure Dose:
Table C-1 lists the minimum and maximum detected concentrations, the frequency
of detection, the frequency of risk-based concentration (RBC) exceedence, and
the RBC noncancer and cancer values for each contaminant.
Table C-1. Maximum Contaminant Concentrations Above EPA Region
III Risk-Based Concentrations (RBC) in Fish Fillet and Shellfish Samples From
Tabbs Creek
| Contaminant | Contaminant Concentration | RBC (ppm) | ||||
| Minimum (ppm) |
Maximum (ppm) | Frequency Detection/Total Samples | Frequency of RBC Exceedence | Noncancer | Cancer | |
|
Fish Fillet | ||||||
| 4,4'-DDD | 0.015 | 0.015 | 1/7 | 1 | no value | 0.013 |
| 4,4'-DDE | 0.0026 | 0.033 | 6/7 | 2 | no value | 0.0093 |
| Aroclor 1248 | 0.084 | 0.084 | 1/7 | 1 | no value | 0.00161 |
| Aroclor 1260 | 0.0073 | 0.049 | 4/7 | 4 | no value | 0.00161 |
| bis(2-ethylhexyl)-phthalate | 5 | 13 | 4/7 | 4 | no value | 0.23 |
| arsenic | 1.9 | 1.9 | 1/1 | 1 | 0.41 | 0.0021 |
|
Oyster | ||||||
| 4,4'-DDD | 0.012 | 0.038 | 3/4 | 2 | no value | 0.013 |
| 4,4'-DDE | 0.008 | 0.053 | 4/4 | 3 | no value | 0.0093 |
| 4,4'-DDT | 0.011 | 0.011 | 1/4 | 1 | no value | 0.0093 |
| Aroclor 5432 | 0.269 | 0.945 | 3/4 | 3 | no value | 0.00072 |
| bis(2-ethylhexyl)-phthalate | 0.4 | 16 | 4/4 | 4 | no value | 0.23 |
| arsenic | 1.7 | 1.7 | 1/1 | 1 | 0.41 | 0.0021 |
| zinc | 630 | 630 | 1/1 | 1 | 410 | no value |
| 2,3,7,8-TCDF | 0.000003 | 0.000003 | 1/1 | 1 | no value | 0.0000000213 |
| OCDD | 0.00004 | 0.00004 | 1/1 | 1 | no value | 0.0000000213 |
| Total TCDF | 0.00002 | 0.00002 | 1/1 | 1 | no value | 0.0000000213 |
|
Crab | ||||||
| 4,4'-DDD | 0.023 | 0.39 | 14/14 | 14 | no value | 0.013 |
| 4,4'-DDE | 0.041 | 0.22 | 13/14 | 13 | no value | 0.0093 |
| Aroclor 5432 | 0.7 | 2.42 | 3/14 | 3 | no value | 0.00072 |
| dieldrin | 0.0022 | 0.076 | 6/14 | 6 | no value | 0.0002 |
| bis(2-ethylhexyl)-phthalate | 0.26 | 12 | 3/14 | 3 | no value | 0.23 |
| arsenic | 1.3 | 2 | 8/8 | 8 | 0.41 | 0.0021 |
| 2,3,7,8-TCDF | 0.000003 | 0.000003 | 1/1 | 1 | no value | 0.0000000213 |
| OCDD | 0.00003 | 0.00003 | 1/1 | 1 | no value | 0.0000000213 |
| Total TCDF | 0.000003 | 0.000003 | 1/1 | 1 | no value | 0.0000000213 |
| Total PeCDF | 0.00002 | 0.00002 | 1/1 | 1 | no value | 0.0000000213 |
1 RBC for polychlorinated biphenyls
2 RBC for polychlorinated terphenyls
3
RBC for 2,3,7,8-TCDD
Likelihood of Health Effects From Incidental Ingestion of Fish and Shellfish from Tabbs Creek
During the remedial investigation for Tabbs Creek, mummichog (whole fish analysis), Atlantic croaker (fish fillet analysis), eastern oyster, blue crab, grass shrimp, ribbed mussel, and snapping turtle samples were collected. ATSDR evaluated the results of all the sampling data but presented only the analysis of fish fillet, oyster, and crab samples as representatives of edible seafood caught in Tabbs Creek. The results for shrimp, mussel, and turtle analysis were similar. Samples were taken at five stations, four along Tabbs Creek and one at its mouth to the Back River as a background sample. With the exception of crabs, fewer than ten samples for each species were analyzed.
Adult
Noncancer Effects: The estimated doses for an adult ingesting the maximum concentrations of contaminants in fish fillets were all lower than health guideline values. They do not pose a health hazard. For oyster ingestion, the estimated doses for an adult exposed to the highest concentrations of Aroclor 5432, OCDD, and Total TCDF were very slightly elevated compared to the health guideline values. For crab ingestion, the estimated doses for an adult exposed to the highest concentrations of Aroclor 5432, OCDD, and Total PeCDF were very slightly elevated compared to the health guideline values. The estimated doses for exposure to the maximum concentrations of all other contaminants in oysters and crabs were lower than health guideline values and therefore do not pose a public health hazard.
Cancer Effects: No increased likelihood of developing cancer was associated with exposures to the highest concentrations of any contaminants in fish fillets, oysters, or crabs for adults consuming almost one fish meal from Tabbs Creek per month for 30 years. The estimated exposure dose for Aroclor 5432 in oysters was at the high end of the range.
Child
Noncancer Effects: For ingestion of fish fillets, the estimated doses for a child exposed to the highest detected concentrations of arsenic, Aroclor 1248, and Aroclor 1260 were very slightly elevated compared to the health guideline values; the estimated doses for the maximum concentrations of all other contaminants in fish fillets were lower than health guideline values and therefore do not pose a public health hazard. For ingestion of oysters, the estimated doses for a child exposed to the highest detected concentrations of arsenic, zinc, Aroclor 5432, 2,3,7,8-TCDF, OCDD, and Total TCDF were slightly elevated compared to the health guideline values; for 4,4'-DDD, 4,4'-DDE, and 4,4'-DDT in oysters, they were below health guidelines and therefore do not pose a public health hazard. For ingestion of crabs, the estimated doses for a child exposed to the highest detected concentrations of arsenic, Aroclor 5432, 2,3,7,8-TCDF, OCDD, Total TCDF, and Total PeCDF were slightly elevated compared to the health guideline values; for pesticides, they were below health guidelines and therefore do not pose a public health hazard.
Discussion of Health Risk
Estimated exposure doses for contaminants in all fish and shellfish samples were very slightly elevated when compared with MRLs or RfDs for both adults and children. Because MRLs and RfDs do not represent thresholds of toxicity, elevated exposure doses that exceed them, especially only slightly, do not necessarily imply a health hazard. Cancer risk estimates were also only very slightly elevated for children.
The estimated exposure doses for Aroclor 5432 in crabs were slightly elevated. This contaminant was detected in only 3 of 14 crab samples; furthermore, two of those detections came from sample duplicates with no corresponding detection in the primary samples. It is highly unlikely that a person would be exposed to the highest concentration of Aroclor 5432 in crab every time the person ingested crab from Tabbs Creek. Most of the detected concentrations of Aroclor 5432 in crabs would result in exposure dose estimates below health guidelines and would therefore not be associated with a health hazard.
The estimated doses for non-2,3,7,8-TCDD dioxins and furans (OCDD, 2,3,7,8-TCDF, Total TCDF, and Total PeCDF) were compared to the chronic MRL for 2,3,7,8-TCDD. Because 2,3,7,8-TCDD is considered the most toxic of the dioxins and furans, this comparison most likely overestimates risks for the other dioxins and furans. It should be noted that dioxins and furans were only analyzed in one sample of each species of fish or shellfish; these samples may or may not be representative.
Former Playground at Langley AFB Site OT-06: Soil
Benzo(a)pyrene Toxic Equivalents
When estimating exposure doses for carcinogenic effects of polycyclic aromatic hydrocarbons (PAHs), ATSDR uses a Toxic Equivalency Factor (TEF) approach to account for the fact that toxicity values are not available for all the PAHs detected in soil at the site (EPA, 1993). The benzo(a)pyrene toxic equivalent is a weighted concentration of carcinogenicity of PAHs in a mixture that compensates for the differences in toxicity among the different PAHs. A TEF has been assigned to 17 individual PAH compounds based on laboratory evidence of carcinogenicity and on their prevalence at hazardous waste sites. Although the TEF approach assumes that the carcinogenic activity of PAH mixtures depends primarily on the carcinogenic PAHs, noncarcinogenic PAHs are included because they may increase the potency of the carcinogenic PAHs (Nisbet and LaGoy, 1992).
The relative weight is 1 for benzo(a)pyrene; 5 for dibenzo(a,h)anthracene; 0.1 for benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, and indeno(1,2,3-cd)pyrene; 0.001 for anthracene, benzo(g,h,i)perylene, and chrysene; and 0.0001 for acenaphthene, acenaphthylene, fluoranthene, fluorene, 2-methylnaphthalene, naphthalene, phenanthrene, and pyrene. ATSDR used the benzo(a)pyrene equivalent to evaluate the likelihood for cancer effects to occur from contact with or incidental ingestion of soil at the former playground at OT-06.
Because the TEF approach, and therefore the benzo(a)pyrene equivalent, is relevant for cancer effects of PAHs only, ATSDR used the maximum PAH values for samples collected on site to estimate exposure doses for noncancer effects. The PAH value is the sum of the concentrations of the individual PAHs used to estimate the benzo(a)pyrene equivalent.
Incidental Ingestion of Soil at the Former Playground at OT-06
ATSDR used the following equation to estimate human exposure doses from incidental
ingestion of soil in order to evaluate possible exposures for children playing
at the former playground at OT-06:
|
Estimated Exposure Dose = |
Conc. × IR × CF × EF × ED BW × AT |
where:
| Conc. | = | Maximum contaminant concentration in on-site surface soil (mg/kg) (see Table C-2) |
| IR | = | Ingestion Rate (mg/day): 200 mg/day for a child, 5,000 mg/day for a pica child (child with an abnormally high soil ingestion rate) |
| CF | = | Conversion factor: 10-6 kg/mg |
| EF | = | Exposure frequency, or number of exposure events
per year of exposure: child: 5 days per week for 52 weeks per year = 260 days per year |
| ED | = | Exposure duration, or the duration over which exposure occurs: child: 6 years |
| BW | = | Body weight (kg): child: 10 kg (0 to 6 years old) |
| AT | = | Averaging time, or the time period over which cumulative exposures are averaged (ED × 365 days/year for noncancer effects; 70 years × 365 days/year for cancer effects) |
Assumptions for Estimating Human Exposure Dose:
Table C-2 lists the minimum and maximum detected concentrations, the frequency
of detection, the frequency of comparison value (CV) exceedence, and the CV
for each contaminant.
Table C-2. Maximum Contaminant Concentrations Above Comparison
Values in On-Site Surface Soil at OT-06
| Contaminant | Contaminant Concentration | Comparison Value (CV) | ||||
| Minimum (ppm) |
Maximum (ppm) | Frequency Detection/ Total Samples | Frequency
of CV Exceedence pica/child/adult |
Concentration (ppm) pica/child/adult | Ref. | |
| PAHs benzo(a)pyrene equiv |
0.01 N/A |
125.67 44.16 |
N/A | N/A | no value | N/A |
| benzo(a)pyrene1 | 0.01 | 20 | 81/121 | 26 | 0.1 | CREG |
| delta-BHC | 0.001 | 0.128 | 56/121 | 1/0/0 0/0/0 |
0.08/2/30 0.6/20/200 |
I-EMEG2 RMEG2 |
| gamma-BHC | 0 | 0.161 | 61/121 | 1/0/0 0/0/0 |
0.08/2/30 0.6/20/200 |
I-EMEG RMEG |
| alpha-chlordane | 0 | 9.66 | 70/121 | 4 13/1/0 2/0/0 |
0.5 0.1/3/40 1/30/400 |
CREG3 RMEG3 C-EMEG3 |
| gamma-chlordane | 0 | 10.1 | 75/121 | 4 14/1/0 1/0/0 |
0.5 0.1/3/40 1/30/400 |
CREG3 RMEG3 C-EMEG3 |
| 4,4'-DDE | 0.001 | 3.54 | 111/121 | 1 2/0/0 |
2 1/30/400 |
CREG4 I-EMEG4 |
| 4,4'-DDT | 0 | 1.94 | 105/121 | 0 2/0/0 |
2 1/30/400 |
CREG I-EMEG |
| dieldrin | 0 | 23.4 | 121/121 | 66 55/3/0 |
0.04 0.1/3/40 |
CREG C-EMEG |
| heptachlor epoxide | 0 | 0.15 | 42/121 | 2 7/0/0 |
0.08 0.03/0.7/9 |
CREG RMEG |
| antimony | 0.025 | 1.44 | 109/121 | 3/0/0 | 0.8/20/300 | RMEG |
| arsenic | 0.047 | 35.8 | 121/121 | 120 119/1/0 |
0.5 0.6/20/200 |
CREG C-EMEG |
| barium | 7.27 | 345 | 121/121 | 2/0/0 | 100/4,000/50,000 | RMEG |
| beryllium | 0.095 | 1.22 | 121/121 | 115 0/0/0 |
0.2 10/300/4,000 |
CREG RMEG |
| chromium | 3.46 | 47.6 | 121/121 | 100/0/0 | 10/300/4,000 | RMEG5 |
| iron | 2150 | 49,100 | 121/121 | 13 | 23,000 | EPA6 |
| manganese | 9.75 | 453 | 121/121 | 120/1/0 | 10/300/4,000 | RMEG |
| mercury | 0.002 | 7.95 | 120/121 | 4/0/0 | 4/100/1,000 | I-EMEG7 |
| silver | 0.131 | 28.6 | 101/121 | 5/0/0 | 10/300/4,000 | RMEG |
| vanadium | 5.06 | 58.1 | 121/121 | 119/0/0 | 6/200/2,000 | RMEG |
C-EMEG: chronic environmental media evaluation guide
CREG: cancer risk evaluation guide
EPA: EPA Region III RBCs
I-EMEG: intermediate environmental media evaluation guide
RMEG: reference dose media evaluation guide
EMEG
and RMEG values are for pica children/children/adults.
1 Because it is the most toxic of the PAHs, benzo(a)pyrene
is reported as an example.
2 CVs for gamma-BHC.
3 CVs for chlordane.
4 CVs for DDT.
5 CV for hexavalent chromium.
6 EPA Region III Risk-Based Concentration.
7
CV for inorganic mercury.
Likelihood of Health Effects From Incidental Ingestion of On-Site Soil at OT-06
Child
Noncancer Effects: The estimated dose for a child exposed to the highest detected concentrations of alpha-chlordane, gamma-chlordane, dieldrin, and arsenic were slightly elevated compared to health guideline values. The estimated exposure doses for the maximum concentrations of all other contaminants were lower than health guideline values and therefore do not pose a public health hazard.
Cancer Effects: Based on the highest detected concentrations, the cancer risk estimates for the benzo(a)pyrene equivalent and dieldrin were slightly elevated. No increased likelihood of developing cancer was associated with incidental exposures to any other soil contaminants at OT-06, even using conservative assumptions.
Pica Child
Noncancer Effects: The estimated dose for a pica child exposed to the highest detected concentrations of alpha-chlordane, gamma-chlordane, DDE, dieldrin, arsenic, barium, chromium, silver, and vanadium were slightly elevated. The estimated exposure doses for the maximum concentrations of other contaminants were very slightly elevated.
Cancer Effects: Based on the highest detected concentrations, the cancer risk estimates for the benzo(a)pyrene equivalent, alpha-chlordane, gamma-chlordane, dieldrin, arsenic, and beryllium were slightly elevated for a pica child. No increased likelihood of developing cancer was associated with incidental exposure to any other soil contaminants at OT-06, even using conservative assumptions.
Discussion of Health Risk
With the exception of a couple of estimated exposure doses for pica children, most of the estimated exposure doses were only slightly elevated in comparison to the MRLs or RfDs. Because the assumptions that ATSDR used were conservative and probably tended to overestimate exposure, noncancer and cancer health effects are unlikely to occur from exposure to soil contaminants at the former playground at OT-06, for several reasons.
ATSDR used the highest concentrations of contaminants detected at the site to estimate exposure doses. A child at the playground is unlikely to come into contact with the highest concentrations of contaminants detected at the site on every visit. For PAHs, for instance, most of the 121 samples taken contained PAHs below comparison values (CVs), which would not be expected to be associated with adverse health effects. Furthermore, ATSDR used the detected concentrations in the one sample that had substantially higher levels of PAHs than any other sample. In that sample, for instance, 20 ppm of benzo(a)pyrene was detected (see Table C-2); the next highest concentration of benzo(a)pyrene detected was 2.16 ppm, one tenth of the value ATSDR used. For alpha-chlordane, gamma-chlordane, DDE, heptachlor epoxide, barium, and silver, detections above CVs were infrequent (see Table C-2); therefore, exposure to the highest concentrations of any of these contaminants would also be infrequent and not likely to be associated with adverse health effects.
Chromium and vanadium were detected slightly above the CV for pica children and were associated with potential adverse health effects for pica children only. Adverse health effects from beryllium were also associated with pica child behavior only. In order for adverse health effects to possibly occur from these contaminants, a pica child would have to go to the playground 5 days a week, disturb soil, and actually ingest 5,000 mg of dirt each time they were at the playground. Because these assumptions are extremely conservative, the actual exposure is expected to be much lower.
Dieldrin and arsenic were detected above the CV for a pica child as well as above the CREG in several samples, but rarely above the CV for a child (see Table C-2). Like the pica child CV, the CREG is an extremely conservative CV and is based on cancer risk. Cancer risks are based on lifetime exposures (70 years). Because exposures at a playground are not expected to occur over an entire lifetime, cancer health effects are unlikely to occur from exposures to contaminants at detected levels at OT-06. Furthermore, dieldrin was detected above the CV in only about half the samples, thereby reducing actual exposures at the playground.
Abandoned Entomology Building (Langley AFB Site OT-25) and Fire Training Area (Langley AFB Site FT-41): Soil
Incidental Ingestion of Soil at the Abandoned Entomology Building at OT-25 or the Fire Training Area at FT-41
ATSDR used the following equation to estimate human exposure doses from incidental ingestion
of soil in order to evaluate possible past exposures for children and youths trespassing at the
abandoned entomology building at OT-25 or the fire training area at FT-41:
|
Estimated Exposure Dose = |
Conc. × IR × CF × EF
× ED BW × AT |
where:
| Conc. | = | Maximum contaminant concentration in on-site surface soil (mg/kg) (see Table C-3) |
| IR | = | Ingestion Rate (mg/day): 200 mg/day for a child, 100 mg/day for a youth |
| CF | = | Conversion factor: 10-6 kg/mg |
| EF | = | Exposure frequency, or number of exposure events per year
of exposure: child or youth: 2 days per week for 52 weeks per year = 104 days per year |
| ED | = | Exposure duration, or the duration over which exposure occurs:
child: 6 years; youth: 10 years |
| BW | = | Body weight (kg): child: 10 kg (0 to 6 years old); youth: 50 kg (8 to 18 years old) |
| AT | = | Averaging time, or the time period over which cumulative exposures are averaged (ED × 365 days/year for noncancer effects; 70 years × 365 days/year for cancer effects) |
Assumptions for Estimating Human Exposure Dose:
Table C-3 lists the minimum and maximum detected concentration, the frequency of detection, the frequency of CV exceedence, and the CV for each contaminant at Sites OT-25 and FT-41.
Table C-3. Maximum Contaminant Concentrations Above Comparison Values in On-Site Surface Soil at OT-25 and FT-41
| Contaminant | Contaminant Concentration | Comparison Value (CV) | ||||
| Minimum (ppm) |
Maximum (ppm) |
Frequency
Detection/ Total Samples |
Frequency
of CV Exceedence child/adult |
Concentration
(ppm) child/adult |
Reference | |
| Abandoned Entomology Building: OT-25 | ||||||
| chlordane | 0.788 | 0.788 | 1/9 | 1 0/0 |
0.5 3/40 |
CREG RMEG |
| dieldrin | 0.044 | 0.044 | 1/9 | 1 0/0 |
0.04 3/40 |
CREG C-EMEG, RMEG |
| Fire Training Area: FT-41 | ||||||
| dieldrin | 0.00583 | 0.158 | 4/5 | 1 0/0 |
0.04 3/40 |
CREG C-EMEG, RMEG |
| beryllium | 0.275 | 0.596 | 4/5 | 4 0/0 |
0.2 300/4,000 |
CREG RMEG |
| iron | 9,380 | 1,070,000 | 5/5 | 2 | 23,000 | EPA |
| manganese | 117 | 1,070 | 5/5 | 2 | 300/4,000 | RMEG |
| thallium | 2.29 | 11.5 | 4/5 | 2 | 4/40 | RMEG1 |
| vanadium | 19.8 | 534 | 5/5 | 1 | 200/2,000 | I-EMEG |
| arsenic | 2.37 | 40.2 | 5/5 | 5 2/0 |
0.5 20/200 |
CREG C-EMEG; RMEG |
C-EMEG: chronic environmental media evaluation guide
CREG: cancer risk evaluation guide
EPA: EPA Region III RBCs
I-EMEG: intermediate environmental media evaluation guide
RMEG: reference dose media evaluation guide
EMEG
and RMEG values are for children/adults.
1CV for thallium carbonate.
Likelihood of Health Effects From Incidental Ingestion of On-Site Soil at OT-25 and FT-41
Child
Noncancer Effects: The estimated doses for the maximum concentrations of contaminants at the abandoned entomology building at OT-25 and the fire training area at FT-41 were lower than health guideline values and therefore do not pose a public health hazard.
Cancer Effects: Based on the highest detected concentrations, no increased likelihood of developing cancer was associated with incidental exposures to any soil contaminants at either OT-25 or FT-41, even using conservative assumptions.
Youth:
Noncancer Effects: The estimated doses for the maximum concentrations of contaminants at the abandoned entomology building at OT-25 and the fire training area at FT-41 were lower than health guideline values and therefore do not pose a public health hazard.
Cancer Effects: Based on the highest detected concentrations, no increased likelihood of developing cancer was associated with incidental exposures to any soil contaminants at either OT-25 or FT-41, even using conservative assumptions.
REFERENCES
EPA. 1989. U.S. Environmental Protection Agency. Risk Assessment Guidance for Superfund, Volume I, Human Health Evaluation Manual (Part A). Office of Emergency and Remedial Response. December, 1989. EPA/540/1089/002.
Nisbet, I.C. and P.K. LaGoy. 1992. Toxic equivalency factors (TEFs) for polycyclic aromatic
hydrocarbons (PAHs) Regul. Toxicol. Pharm. 16:290-300
The Langley Air Force Base (Langley AFB) and National Aeronautics and Space Administration Langley Research Center (NASA LaRC) public health assessment was available for public review and comment from September 14, 1998, through November 1, 1998. Copies of the public health assessment were made available for review at the Hampton Public Library and the office of the Chief of Environmental Restoration at Langley AFB. The public health assessment was also sent to state and federal agencies and interested members of the general public.
The Agency for Toxic Substances and Disease Registry (ATSDR) received the following comments/questions for the Langley AFB and NASA LaRC public health assessment. The specific comments that were received either identified new information; questioned specific sentences or paragraphs in the text or tables; or suggested additions or corrections to improve the clarity, completeness, or accuracy of a specific sentence or paragraph. Those specific comments that were not repeated by other respondents are listed separately. This list of specific comments does not include editorial comments concerning word spelling, sentence syntax, format, etc. If the accuracy of a statement was questioned, the statement was verified and corrected. Comments which requested that information be added to the document without providing document sources of that information were not addressed here.
Response: The text was changed accordingly.
For the Storm Sewer System: West Area under the column entitled "Site Description/Waste Disposal History," in the second sentence which begins "Sources for the contamination include...," Building 1247 should be changed to Building 1247D. Also, under the column entitled "Corrective Activities and/or Current Status" the third sentence should be revised to read "The storm system was remediated to a cleanup goal of no detectable PCBs and the Federal Facility Compliance Agreement has been closed."
Response: The text was changed accordingly.
Response: The text was changed accordingly.
Response: The text was changed accordingly.
Response: ATSDR addresses issues of public health, including physical hazards. The ATSDR Public Health Assessment Guidance Manual includes the presence of physical hazards as "some of the important factors that must be weighed in the analysis." Therefore, the physical hazards associated with the fire training area were included in the PHA.
Response: A preliminary assessment/site investigation is being performed on the Back River. This study includes sediment sampling but not biota sampling. A separate study, which includes fish and shellfish sampling, is being performed through the Department of Natural Resources at Langley AFB. Results of both of these studies are expected in early 1999. The text was changed accordingly.
Response: The text was changed accordingly.
Response: The text was changed accordingly.
Response: The text was changed accordingly.
Response: The text was changed accordingly.
Response: The text was changed accordingly.
Response: The units provided in Appendix B were incorrect. The EMEG represents the concentration in ppm or ppb that is likely to be without noncarcinogenic health effects over a specified duration of exposure. The text in Appendix B was changed accordingly.
Response: No conversion factor was used when estimating exposure doses for fish ingestion. The text describing the equation has been corrected to reflect this.
Response: Because there is no noncancer toxicity value for Aroclor 5432, ATSDR used the chronic oral MRL for Aroclor 1254 (0.00002 mg/kg/day). The cancer risk estimate for an adult ingesting the highest concentration of Aroclor 5432 in crabs for 30 years was 7.5 × 10-5, which is within the range of 10-4 to 10-6. The cancer risk estimate for an adult ingesting the highest concentration of Aroclor 5432 in oysters for 30 years was 1.9 × 10-4, which is at the upper end of the range. Text was added to reflect this.
Response: The text was changed accordingly.
