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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.



FIGURES


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


Figure 6: Map of Tabbs Creek



APPENDIX A: Glossary

Analyte
A chemical component of a sample to be determined or measured. For example, if the analyte is mercury, the laboratory test will determine the amount of mercury in the sample.


Background level
A typical or average level of a chemical in the environment. Background often refers to naturally occurring or uncontaminated levels.


Carcinogen
Any substance that may produce cancer.


CERCLA
The Comprehensive Environmental Response, Compensation, and Liability Act of 1980, also known as Superfund. This is the legislation that created ATSDR.


Comparison Values
Estimated contaminant concentrations in specific media that are not likely to cause adverse health effects, given a standard daily ingestion rate and standard body weight. The comparison values are calculated from the scientific literature available on exposure and health effects.


Concentration
The amount of one substance dissolved or contained in a given amount of another. For example, sea water contains a higher concentration of salt than fresh water.


Contaminant
Any substance or material that enters a system (the environment, human body, food, etc.) where it is not normally found.


Dermal
Referring to the skin. Dermal absorption means absorption through the skin.


Dose
The amount of substance to which a person is exposed. Dose often takes body weight into account.


Environmental contamination
The presence of hazardous substances in the environment. From the public health perspective, environmental contamination is addressed when it potentially affects the health and quality of life of people living and working near the contamination.


Exposure
Contact with a chemical by swallowing, by breathing, or by direct contact (such as through the skin or eyes). Exposure may be short-term (acute) or long-term (chronic).


Hazard
A source of risk that does not necessarily imply potential for occurrence. A hazard produces risk only if an exposure pathway exists and if exposures create the possibility of adverse consequences.


Ingestion
Swallowing (such as eating or drinking). Chemicals can get into or on food, drink, utensils, cigarettes, or hands where they can be ingested. After ingestion, chemicals can be absorbed into the blood and distributed throughout the body.


Media
Soil, water, air, plants, animals, or any other parts of the environment that can contain contaminants.


Minimal Risk Level (MRL)
An MRL is defined as an estimate of daily human exposure to a substance that is likely to be without an appreciable risk of adverse effects (noncancer) over a specified duration of exposure. MRLs are derived when reliable and sufficient data exist to identify the target organ(s) of effect or the most sensitive health effects(s) for a specific duration via a given route of exposure. MRLs are based on noncancer health effects only. MRLs can be derived for acute, intermediate, and chronic exposures by the inhalation and oral routes.


National Priorities List (NPL)
The Environmental Protection Agency (EPA) list of sites that have undergone preliminary assessment and site inspection to determine which locations pose immediate threat to persons living or working near the release. These sites are most in need of cleanup.


No Apparent Public Health Hazard
Sites where human exposure to contaminated media is occurring or has occurred in the past, but the exposure is below a level of health hazard.


Plume
An area of chemicals in a particular medium, such as air or groundwater, moving away from its source in a long band or column. A plume can be a column of smoke from a chimney or chemicals moving with groundwater.


Polychlorinated Biphenyls (PCBs) and Polychlorinated Terphenyls (PCTs)
PCBs and PCTs are very stable, non-flammable liquids used as heat insulation fluids in transformers. Because PCBs and PCTs are very stable chemicals, they tend to persist in the environment. Several types of PCB and PCT mixtures exist; some commercial mixtures are known by their industrial trade name, Aroclor.


Polycyclic Aromatic Hydrocarbons (PAHs)
PAHs comprise one category of base/neutral and acid extractable compounds and are a group of chemicals that are formed during the burning of coal, oil, gas, wood, or other organic substance. Some PAHs are contained in asphalt used for paving roads or runways. There are more than 100 different PAH compounds and they are found throughout the environment in air, water, and soil. Most PAHs do not appear alone in the environment but, rather, in complex mixtures of many individual PAHs, which may be carcinogenic or noncarcinogenic.


Potentially Exposed
The condition under which valid information, usually analytical environmental data, indicates the presence of contaminant(s) of a public health concern in one or more environmental media contacting humans (i.e., air, drinking water, soil, food chain, surface water), and there is evidence that some of those persons may have an identified route(s) of exposure (i.e., drinking contaminated water, breathing contaminated air, having contact with contaminated soil, or eating contaminated food).


Public Health Assessment
The evaluation of data and information on the release of hazardous substances into the environment in order to assess any current or future impact on public health, develop health advisories or other recommendations, and identify studies or action needed to evaluate and mitigate or prevent human health effects; also the document resulting from that evaluation.


Public Health Hazard
Sites that pose a public health hazard as the result of long-term exposures to hazardous substances.


Route of Exposure
The way in which a person may contact a chemical substance. For example, drinking (ingestion) and bathing (skin contact) are two different routes of exposure to contaminants that may be found in water.


Semivolatile Organic Compounds (SVOCs)
Compounds amenable to analysis by extraction of the sample with an organic solvent. Polycyclic aromatic hydrocarbons, such as naphthalene, phenanthrene, benzo(a)pyrene, and chrysene, comprise one category of SVOCs. The term SVOCs is used synonymously with base/neutral and acid extractable compounds (BNAs).


Superfund
Another name for the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), which created ATSDR.


Superfund Amendments and Reauthorization Act (SARA)
The 1986 legislation that broadened ATSDR's responsibilities in the areas of public health assessments, establishment and maintenance of toxicologic databases, information dissemination, and medical education.


Volatile Organic Compounds (VOCs)
Substances containing carbon and different proportions of other elements such as hydrogen, oxygen, fluorine, chlorine, bromine, sulfur, or nitrogen; these substances easily become vapors or gases. A significant number of the VOCs are commonly used as solvents (paint thinners, lacquer thinner, degreasers, and dry-cleaning fluids).



APPENDIX B: Comparison Values

The conclusion that a contaminant exceeds the comparison value does not mean that it will causeadverse health effects. Comparison values represent media-specific contaminant concentrationsthat are used to select contaminants for further evaluation to determine the possibility of adversepublic health effects.

Cancer Risk Evaluation Guides (CREGs)

CREGs are estimated contaminant concentrations that would be expected to cause no more thanone excess cancer in a million (10-6) persons exposed over lifetime. ATSDR's CREGs arecalculated 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 andingestion rates. An EMEG is an estimate of daily human exposure to a chemical that is likely to bewithout 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 levelof a contaminant in water that is delivered to the free-flowing outlet. MCLs are consideredprotective of public health over a lifetime (70 years) for people consuming 2 liters of water perday.

Reference Media Evaluation Guides (RMEGs)

ATSDR derives RMEGs from EPA's oral reference doses. The RMEG represents theconcentration in water or soil at which daily human exposure is unlikely to result in adversenoncarcinogenic effects.


APPENDIX C: Evaluation of Estimated Exposure Doses and Health Effects for Ingestion ofFish 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 exposuredoses for residents of Langley Air Force Base (Langley AFB) and nearby communities fromingestion of fish and shellfish from Tabbs Creek, for children playing at the former playground atLangley AFB Site OT-06, and for trespassers at Langley AFB sites OT-25 and FT-41. Derivingexposure doses requires evaluating the concentrations of contaminants to which people may havebeen exposed and how often and for how long exposure to those contaminants occurred. Healtheffects are also related to individual characteristics such as age, gender, and nutritional status thatinfluence how a chemical might be absorbed, metabolized, and eliminated by the body. Together,these factors help influence the individual's physiological response to chemical contaminantexposure and potential noncancer or cancer outcomes. In the absence of exposure-specificinformation, ATSDR applied several conservative exposure assumptions to define site-specificexposures as accurately as possible for residents near Tabbs Creek and children at the formerplayground at OT-06.

Evaluating Potential Health Hazards

The estimated exposure doses are used to evaluate potential noncancer and cancer effectsassociated with chemicals of concern. When evaluating noncancer effects, ATSDR uses standardhealth guidelines, including ATSDR's minimal risk levels (MRLs) and the U.S. EnvironmentalProtection Agency's (EPA's) reference doses (RfDs), to evaluate whether adverse effects mayoccur. The chronic MRLs and RfDs are estimates of daily human exposure to a substance that areunlikely to result in adverse noncancer effects over a specified duration. ATSDR comparedestimated exposure doses associated with fish ingestion and soil exposure scenarios toconservative health guidelines such as MRLs or RfDs for each contaminant. If the exposure doseis 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 tochemical concentrations above comparison values does not necessarily produce health effects.

To evaluate cancer effects, ATSDR uses cancer potency factors (CPFs) that define therelationship between oral exposure doses and the increased likelihood of developing cancer over alifetime. The CPFs are developed using data from animal or human studies and often requireextrapolation from high exposure doses administered in animal studies to the lower exposurelevels 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 anumber of uncertainties in the data used in the extrapolation.

ATSDR estimated the potential for cancer to occur using the following equation. The estimatedexposure doses and CPF values for the contaminants of concern are incorporated into theequation:

    Lifetime Cancer Risk = Estimated exposure dose (mg/kg/day) CPF (mg/kg/day)-1

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 newcase in 10,000 to 1,000,000 exposed persons), based on conservative assumptions aboutexposure, to determine whether a concern regarding cancer effects is valid. This range isconsistent with values adopted by EPA for evaluating the need for cleanup at hazardous wastesites. Several of the chemicals of concern detected in the fish and shellfish from Tabbs Creek andsoil at Langley AFB Sites OT-06, OT-25, and FT-41 are considered to be human carcinogens orprobable 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 andshellfish 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:

  • Estimated daily intakes are heavily dependent on assumed ingestion rates (IR) ofrecreationally caught fish. The fish ingestion rates that ATSDR used are for approximately1 8-ounce fish meal from Tabbs Creek (EPA, 1989). This assumption implies that a personwho lives near Tabbs Creek might catch and eat fish or shellfish from the creek once amonth. Fishing is currently prohibited in the creek (due to bacterial contamination);therefore, this assumption is overly conservative and will overestimate fish ingestion.
  • The fraction ingested (FI) was conservatively assumed to be 100 percent, meaning that allfish meals considered in the analysis were caught in Tabbs Creek.
  • The duration of exposure (ED) was assumed to have occurred over 30 years for an adultand six years for a child.
  • The averaging time (AT) for noncancer effects was assumed to be 30 years for 365 daysper year for an adult (10,950 days) and 6 years for 365 days per year for a child (2,190days). For cancer effects, the AT was assumed to be 70 years for 365 days per year (or 25,550 days).

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'-DDD0.0150.0151/71no value0.013
4,4'-DDE0.00260.0336/72no value0.0093
Aroclor 12480.0840.0841/71no value0.00161
Aroclor 12600.00730.0494/74no value0.00161
bis(2-ethylhexyl)-phthalate5134/74no value0.23
arsenic1.91.91/110.410.0021

Oyster

4,4'-DDD0.0120.0383/42no value0.013
4,4'-DDE0.0080.0534/43no value0.0093
4,4'-DDT0.0110.0111/41no value0.0093
Aroclor 54320.2690.9453/43no value0.00072
bis(2-ethylhexyl)-phthalate0.4164/44no value0.23
arsenic1.71.71/110.410.0021
zinc6306301/11410no value
2,3,7,8-TCDF0.0000030.0000031/11no value0.0000000213
OCDD0.000040.000041/11no value0.0000000213
Total TCDF0.000020.000021/11no value0.0000000213
Crab
4,4'-DDD0.0230.3914/1414no value0.013
4,4'-DDE0.0410.2213/1413no value0.0093
Aroclor 54320.72.423/143no value0.00072
dieldrin0.00220.0766/146no value0.0002
bis(2-ethylhexyl)-phthalate0.26123/143no value0.23
arsenic1.328/880.410.0021
2,3,7,8-TCDF0.0000030.0000031/11no value0.0000000213
OCDD0.000030.000031/11no value0.0000000213
Total TCDF0.0000030.0000031/11no value0.0000000213
Total PeCDF0.000020.000021/11no value0.0000000213

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), Atlanticcroaker (fish fillet analysis), eastern oyster, blue crab, grass shrimp, ribbed mussel, and snappingturtle samples were collected. ATSDR evaluated the results of all the sampling data but presentedonly the analysis of fish fillet, oyster, and crab samples as representatives of edible seafood caughtin Tabbs Creek. The results for shrimp, mussel, and turtle analysis were similar. Samples weretaken at five stations, four along Tabbs Creek and one at its mouth to the Back River as abackground sample. With the exception of crabs, fewer than ten samples for each species wereanalyzed.

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 slightlyelevated when compared with MRLs or RfDs for both adults and children. Because MRLs andRfDs do not represent thresholds of toxicity, elevated exposure doses that exceed them, especiallyonly slightly, do not necessarily imply a health hazard. Cancer risk estimates were also only veryslightly elevated for children.

The estimated exposure doses for Aroclor 5432 in crabs were slightly elevated. This contaminantwas detected in only 3 of 14 crab samples; furthermore, two of those detections came fromsample duplicates with no corresponding detection in the primary samples. It is highly unlikelythat a person would be exposed to the highest concentration of Aroclor 5432 in crab every timethe person ingested crab from Tabbs Creek. Most of the detected concentrations of Aroclor 5432in crabs would result in exposure dose estimates below health guidelines and would therefore notbe associated with a health hazard.

The estimated doses for non-2,3,7,8-TCDD dioxins and furans (OCDD, 2,3,7,8-TCDF, TotalTCDF, and Total PeCDF) were compared to the chronic MRL for 2,3,7,8-TCDD. Because2,3,7,8-TCDD is considered the most toxic of the dioxins and furans, this comparison most likelyoverestimates risks for the other dioxins and furans. It should be noted that dioxins and furanswere only analyzed in one sample of each species of fish or shellfish; these samples may or maynot 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 thattoxicity values are not available for all the PAHs detected in soil at the site (EPA, 1993). Thebenzo(a)pyrene toxic equivalent is a weighted concentration of carcinogenicity of PAHs in amixture that compensates for the differences in toxicity among the different PAHs. A TEF hasbeen assigned to 17 individual PAH compounds based on laboratory evidence of carcinogenicityand on their prevalence at hazardous waste sites. Although the TEF approach assumes that thecarcinogenic activity of PAH mixtures depends primarily on the carcinogenic PAHs,noncarcinogenic PAHs are included because they may increase the potency of the carcinogenicPAHs (Nisbet and LaGoy, 1992).

The relative weight is 1 for benzo(a)pyrene; 5 for dibenzo(a,h)anthracene; 0.1 forbenzo(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, andpyrene. ATSDR used the benzo(a)pyrene equivalent to evaluate the likelihood for cancer effectsto 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 cancereffects of PAHs only, ATSDR used the maximum PAH values for samples collected on site toestimate exposure doses for noncancer effects. The PAH value is the sum of the concentrations ofthe 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:

  • A soil ingestion rate (IR) of 200 mg/day for a child and 5,000 mg/day for a pica child (achild with an abnormally high soil ingestion rate) was based on an assumption that soil onthe hands is incidentally ingested while eating or playing, and that soil adheres to the palmsof the hands. A more typical value for ingestion over an entire day is probably less than 50mg/day. The soil ingestion rate also assumes that the contaminant in soil is bioavailable asthe pure chemical, whereas the actual bioavailability may be substantially less.
  • The exposure frequency (EF), or number of exposure events per year, was assumed to be260 days per year for children. This assumes that a child might have spent 5 days a week atthe playground for every week of the year. ATSDR believes that the assumption that achild spends almost every day at the playground more than adequately accounts forpossible exposure.
  • The duration of exposure (ED) was assumed to have occurred over 6 years for a child.Since the average stay for military personnel at one base is usually about 3 years, thisassumption probably overestimates exposure.
  • The averaging time (AT) was assumed to be 6 years for 365 days per year (2,190 days) fornoncancer effects and 70 years for 365 days per year (or 25,550 days) for cancer effects.

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/AN/Ano valueN/A
benzo(a)pyrene10.012081/121260.1CREG
delta-BHC0.0010.12856/121 1/0/0
0/0/0
0.08/2/30
0.6/20/200
I-EMEG2
RMEG2
gamma-BHC00.16161/121 1/0/0
0/0/0
0.08/2/30
0.6/20/200
I-EMEG
RMEG
alpha-chlordane09.6670/121 4
13/1/0
2/0/0
0.5
0.1/3/40
1/30/400
CREG3
RMEG3
C-EMEG3
gamma-chlordane010.175/121 4
14/1/0
1/0/0
0.5
0.1/3/40
1/30/400
CREG3
RMEG3
C-EMEG3
4,4'-DDE0.0013.54111/121 1
2/0/0
2
1/30/400
CREG4
I-EMEG4
4,4'-DDT01.94105/121 0
2/0/0
2
1/30/400
CREG
I-EMEG
dieldrin023.4121/121 66
55/3/0
0.04
0.1/3/40
CREG
C-EMEG
heptachlor epoxide00.1542/121 2
7/0/0
0.08
0.03/0.7/9
CREG
RMEG
antimony0.0251.44109/1213/0/00.8/20/300RMEG
arsenic0.04735.8121/121 120
119/1/0
0.5
0.6/20/200
CREG
C-EMEG
barium7.27345121/1212/0/0100/4,000/50,000RMEG
beryllium0.0951.22121/121 115
0/0/0
0.2
10/300/4,000
CREG
RMEG
chromium3.4647.6121/121100/0/010/300/4,000RMEG5
iron215049,100121/1211323,000EPA6
manganese9.75453121/121120/1/010/300/4,000RMEG
mercury0.0027.95120/1214/0/04/100/1,000I-EMEG7
silver0.13128.6101/1215/0/010/300/4,000RMEG
vanadium5.0658.1121/121119/0/06/200/2,000RMEG

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 theestimated exposure doses were only slightly elevated in comparison to the MRLs or RfDs.Because the assumptions that ATSDR used were conservative and probably tended tooverestimate exposure, noncancer and cancer health effects are unlikely to occur from exposureto 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 exposuredoses. A child at the playground is unlikely to come into contact with the highest concentrationsof contaminants detected at the site on every visit. For PAHs, for instance, most of the 121samples taken contained PAHs below comparison values (CVs), which would not be expected tobe associated with adverse health effects. Furthermore, ATSDR used the detected concentrationsin the one sample that had substantially higher levels of PAHs than any other sample. In thatsample, for instance, 20 ppm of benzo(a)pyrene was detected (see Table C-2); the next highestconcentration of benzo(a)pyrene detected was 2.16 ppm, one tenth of the value ATSDR used. Foralpha-chlordane, gamma-chlordane, DDE, heptachlor epoxide, barium, and silver, detectionsabove CVs were infrequent (see Table C-2); therefore, exposure to the highest concentrations ofany of these contaminants would also be infrequent and not likely to be associated with adversehealth effects.

Chromium and vanadium were detected slightly above the CV for pica children and wereassociated with potential adverse health effects for pica children only. Adverse health effects fromberyllium were also associated with pica child behavior only. In order for adverse health effects topossibly occur from these contaminants, a pica child would have to go to the playground 5 days aweek, 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 bemuch lower.

Dieldrin and arsenic were detected above the CV for a pica child as well as above the CREG inseveral samples, but rarely above the CV for a child (see Table C-2). Like the pica child CV, theCREG is an extremely conservative CV and is based on cancer risk. Cancer risks are based onlifetime exposures (70 years). Because exposures at a playground are not expected to occur overan entire lifetime, cancer health effects are unlikely to occur from exposures to contaminants atdetected levels at OT-06. Furthermore, dieldrin was detected above the CV in only about half thesamples, 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 FireTraining Area at FT-41

ATSDR used the following equation to estimate human exposure doses from incidental ingestionof soil in order to evaluate possible past exposures for children and youths trespassing at theabandoned 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:

  • A soil ingestion rate (IR) of 200 mg/day for a child and 100 mg/day for a youth trespasserwas based on an assumption that soil on the hands is incidentally ingested while eating orplaying, and that soil adheres to the palms of the hands. A more typical value for ingestionover an entire day is probably less than 50 mg/day. The soil ingestion rate also assumes thatthe contaminant in soil is bioavailable as the pure chemical, whereas the actualbioavailability may be substantially less.
  • The exposure frequency (EF), or number of exposure events per year, was assumed to be104 days per year for either child or youth trespassers. This assumes that a trespasser mighthave spent 2 days a week at the site for every week of the year. ATSDR believes that theassumption that a child or a youth trespassed either the abandoned entomology building orthe fire training area twice a week, every week more than adequately accounts for possibleexposure.
  • The duration of exposure (ED) was assumed to have occurred over 6 years for a child and10 years for a youth trespasser. Since the average stay for military personnel at one base isusually about 3 years, this assumption probably overestimates exposure.
  • The averaging time (AT) for noncancer effects was assumed to be 6 years for 365 days peryear (2,190 days) for a child trespasser and 10 years for 365 days per year (3,650 days) fora youth trespasser. For cancer effects, the AT was assumed to be 70 years for 365 days peryear (or 25,550 days).

Table C-3 lists the minimum and maximum detected concentration, the frequency of detection, thefrequency 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/
TotalSamples
Frequency of CV Exceedence
child/adult
Concentration (ppm)
child/adult
Reference
Abandoned Entomology Building: OT-25
chlordane0.7880.7881/9 1
0/0
0.5
3/40
CREG
RMEG
dieldrin0.0440.0441/9 1
0/0
0.04
3/40
CREG
C-EMEG, RMEG
Fire Training Area: FT-41
dieldrin0.005830.1584/5 1
0/0
0.04
3/40
CREG
C-EMEG, RMEG
beryllium0.2750.5964/5 4
0/0
0.2
300/4,000
CREG
RMEG
iron9,3801,070,0005/5223,000EPA
manganese1171,0705/52300/4,000RMEG
thallium2.2911.54/524/40RMEG1
vanadium19.85345/51200/2,000I-EMEG
arsenic2.3740.25/5 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 RemedialResponse. December, 1989. EPA/540/1089/002.

Nisbet, I.C. and P.K. LaGoy. 1992. Toxic equivalency factors (TEFs) for polycyclic aromatichydrocarbons (PAHs) Regul. Toxicol. Pharm. 16:290-300


APPENDIX D: Public Comments

The Langley Air Force Base (Langley AFB) and National Aeronautics and Space AdministrationLangley Research Center (NASA LaRC) public health assessment was available for public reviewand comment from September 14, 1998, through November 1, 1998. Copies of the public healthassessment were made available for review at the Hampton Public Library and the office of theChief of Environmental Restoration at Langley AFB. The public health assessment was also sentto state and federal agencies and interested members of the general public.

The Agency for Toxic Substances and Disease Registry (ATSDR) received the followingcomments/questions for the Langley AFB and NASA LaRC public health assessment. The specificcomments that were received either identified new information; questioned specific sentences orparagraphs 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 werenot repeated by other respondents are listed separately. This list of specific comments does notinclude editorial comments concerning word spelling, sentence syntax, format, etc. If the accuracyof a statement was questioned, the statement was verified and corrected. Comments whichrequested that information be added to the document without providing document sources of thatinformation were not addressed here.

  1. Comment: Page 4, last paragraph (continues on page 5): All potable water used at theNASA Langley Research Center is provided by the City of Newport News Waterworks.The Center remains connected to the Big Bethel Reservoir as a backup.

    Response: The text was changed accordingly.

  2. Comment: Page 59, Table 2: For the Storm Sewer System: East Area under the columnentitled "Site Description/Waste Disposal History," add a final sentence reading "TheFederal Facility Compliance Agreement has been closed."

    For the Storm Sewer System: West Area under the column entitled "SiteDescription/Waste Disposal History," in the second sentence which begins "Sources for thecontamination include...," Building 1247 should be changed to Building 1247D. Also,under the column entitled "Corrective Activities and/or Current Status" the third sentenceshould be revised to read "The storm system was remediated to a cleanup goal of nodetectable PCBs and the Federal Facility Compliance Agreement has been closed."

    Response: The text was changed accordingly.

  3. Comment: Page 61, Table 2: For Tabbs Creek under the column entitled "CorrectiveActivities and/or Current Status," the third sentence should be replaced with the followingsentence: "A Record of Decision was signed in September 1998 by EPA and NASA LaRCwhich calls for dredging and off-site disposal."

    Response: The text was changed accordingly.

  4. Comment: Page vi: Under abbreviations, RAB: "Regional Advisory Board" should read,"Restoration Advisory Board."

    Response: The text was changed accordingly.

  5. Comment: Why are physical hazards addressed in this document?

    Response: ATSDR addresses issues of public health, including physical hazards. TheATSDR Public Health Assessment Guidance Manual includes the presence of physicalhazards 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 thePHA.

  6. Comment: Page 18: The second bullet under "Ongoing Actions/Actions Planned"indicates that the investigation of the Back River includes sampling of fish and shellfish.Please note that the current investigation does not include fish and shellfish sampling.

    Response: A preliminary assessment/site investigation is being performed on the BackRiver. This study includes sediment sampling but not biota sampling. A separate study,which includes fish and shellfish sampling, is being performed through the Department ofNatural Resources at Langley AFB. Results of both of these studies are expected in early1999. The text was changed accordingly.

  7. Comment: Table 1, Page 28: The table indicates that soil has been remediated at OT-6.There has been no soil remediation at OT-6 based on human health risk. The site is stillbeing investigated for potential ecological impacts.

    Response: The text was changed accordingly.

  8. Comment: Table 1, Page 30: The table indicates that the groundwater is under long termmonitoring. Note that the decision to perform long term monitoring has not been made yet,although the option is being considered.

    Response: The text was changed accordingly.

  9. Comment: Table 1, Page 43: "ST-38" should be "OT-38." The meaning of the term"limited remedial investigation" is not clear. Note that the remedial investigation for thissite has been completed. The Proposed Plan recommends no further action.

    Response: The text was changed accordingly.

  10. Comment: Table 1, Page 51: Since AOC-02 is being investigated under LF-17 and theremedial investigation has not been completed, it is premature to state that no furtheractivity is expected.

    Response: The text was changed accordingly.

  11. Comment: Table 2, Page 61: The cleanup goal for Tabbs Creek is 5 ppm (not a range of5-15 ppm). The Record of Decision has been signed. The remedial action will be dredgingand off-site disposal.

    Response: The text was changed accordingly.

  12. Comment: Page B-1: In Appendix B, an Environmental Media Evaluation Guide (EMEG)is defined as an estimate of human exposure in mg/kg/day. On Tables C-2 and C-3 the unitsfor the EMEGs are in ppm. The definition should be clarified.

    Response: The units provided in Appendix B were incorrect. The EMEG represents theconcentration in ppm or ppb that is likely to be without noncarcinogenic health effects overa specified duration of exposure. The text in Appendix B was changed accordingly.

  13. Comment: Page C-2: It is not clear why the conversion factor has been included in theequation for exposure to fish and shellfish from Tabbs Creek.

    Response: No conversion factor was used when estimating exposure doses for fishingestion. The text describing the equation has been corrected to reflect this.

  14. Comment: Page C-6:
    a. What was the noncancer toxicity value used to evaluate Aroclor 5432?
    b. The second paragraph states that there is no increased likelihood of developing cancerassociated with exposures to the highest concentrations of contaminants in fish fillets,oysters, or crabs for adults. Page C-2 indicates that ATSDR often uses a range of 10-4 to10-6 to determine whether there is a concern for cancer effects. It appears that the cancerrisk estimates are greater than 10-4 for oysters and crabs. The criteria for making thedetermination should be clarified.

    Response: Because there is no noncancer toxicity value for Aroclor 5432, ATSDR usedthe chronic oral MRL for Aroclor 1254 (0.00002 mg/kg/day). The cancer risk estimate foran 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 adultingesting 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.

  15. Comment: The report cover and Figure 3 on Page 66 refer to Hampton County. Note thatthere is no Hampton County in Virginia.

    Response: The text was changed accordingly.



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