PUBLIC HEALTH ASSESSMENT
BARSTOW MARINE CORPS LOGISTICS BASE
(a/k/a MARINE CORPS LOGISTICS BASE BARSTOW)
BARSTOW, SAN BERNARDINO COUNTY, CALIFORNIA
- Administrative Record:
- Documents, reports, letters, and other material produced or used by the Installation Restoration Program to evaluate contamination and cleanup the base.
- In geology, attenuation is the process where a chemical in groundwater adsorbs and desorbs from soil at rate that makes it move slower than the groundwater it is dissolved in.
- Background Level:
- A typical or average level of a chemical in the environment. Background often refers to naturally occurring or uncontaminated levels.
- 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.
- 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.
- Any substance or material that enters a system where it is not normally found, or that is found in greater concentrations than background levels.
- Environmental Contamination:
- The presence of hazardous substances in the environment. From the public health perspective, environmental contamination is addressed when it potentially effects the health and quality of life of people living and working near the contamination.
- 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).
- Fate and Transport Modeling:
- The mathematical calculations used to predict the movement and resulting fate of a chemical in water, air, or soil.
- 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.
- A probe driven into the ground with pressure to sample groundwater, soil, or soil gas.
- Soil, water, air, plants, animals, or any other parts of the environment that can contain contaminants.
- Minimum 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 effect(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 duration exposures by inhalation and oral routes.
- National Priorities List (NPL):
- EPA's listing of sites that have undergone preliminary assessment and site inspection to determine which locations pose an immediate threat to persons living or working near the release. These sites are most in need of cleanup.
- No Apparent Public Health Hazard:
- The designation given to 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.
- A groundwater well used for measuring pressure water elevation and water pressure.
- Potentially Exposed:
- The condition where 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 (e.g., air, drinking water, soil, food chain, surface water). There is evidence that some of those persons may have an identified route(s) of exposure (e.g., 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 actions needed to evaluate and mitigate or prevent human health effects; also, the document resulting from the evaluation.
- Route of Exposure:
- The path 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.
- Semi-Volatile 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).
- Volatile Organic Compounds:
- Substance 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 VOCs are commonly used as solvents (e.g., paint thinners, lacquer thinners, degreasers, and dry cleaning fluids).
- The movement of a chemical from water to the atmosphere.
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)
Estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million (10-6) persons exposed over a 70-year life span. 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 (mg/kg/day) 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 exposure is unlikely to result in adverse noncarcinogenic effects.
ATSDR typically evaluates the public health implications of exposure by considering the contaminant's chemical class, concentrations of the contaminants to which people may have been exposed, and how often and how long exposure to these 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 response to chemical contaminant exposure and potential noncarcinogenic and carcinogenic outcomes.
ATSDR used the following equation to estimate an exposure dose for ingestion of water:
|Concentration=||Maximum Concentration in water (ppm).|
|IR=||Ingestion rate: 4 liters per day (adult); 3 liter per day (child) - to account for inhalation during cooking and showering.|
|EF=||Exposure frequency or number of exposure events per year of exposure.|
|ED=||Exposure duration or the duration over which exposure occurs.|
|BW=||Body weight: 70 kg (adult); 10 kg (child).|
|AT=||Averaging time or the period over which cumulative exposures are averaged.|
When evaluating noncancer effects, ATSDR compares the estimated exposure dose to standard toxicity values, including ATSDR's minimal risk levels (MRLs) and EPA's reference doses (RfDs), to determine whether adverse effects will occur. The chronic MRLs and RfDs are estimates of daily exposure to a substance that are likely to be without appreciable risk of adverse noncancer effects over a specified duration. The chronic MRLs and RfDs are conservative values, based on the levels of exposure reported in the literature that represent no-observed-adverse-effects levels (NOAEL) or lowest-adverse-effects-levels (LOAEL) for the most sensitive outcome for a given route of exposure (e.g., dermal contact, ingestion). In addition, uncertainty (safety) factors are applied to NOAELs or LOAELs to account for variation in the human population and uncertainty involved in extrapolating human health effects from animal studies.
When evaluating the potential for cancer to occur, ATSDR uses cancer potency factors (CPF) that define the relationship between exposure doses and the likelihood of an increased risk 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 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., overestimates the actual risk) in order to account for a number of uncertainties in the data used in extrapolation.
ATSDR estimated the potential for cancer to occur using the following equation. The estimated exposure doses and CPF values for contaminants of concern are incorporated into the equation:
Lifetime Cancer Risk = Estimated exposure dose (mg/kg/day) x CPF (mg/kg/day)-1
Although no risk of cancer is considered acceptable, because a zero cancer risk is not possible to achieve, 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 there is a concern for cancer effects.
Estimated Exposure Dose for Consumption of Trichloroethylene in a Private Well Adjacent to the Nebo Main Base
TCE was present in a private well adjacent to the Nebo Main Base at levels above both ATSDR's CREG of 3 ppb and EPA's enforceable MCL of 5 ppb. To determine the potential for adverse health effects from exposure to TCE in the private well, ATSDR estimated an oral/inhalation exposure dose using very conservative assumptions for residents (including adults and children) using the well. ATSDR assumed that a 70 kg resident drinks (or otherwise consumes) 4 liters of water and a 10 kg child drinks (or otherwise consumes) 3 liters of water at a frequency of 365 days a year for 30 years for adults and for 6 years for children. ATSDR assumed that the water contains the maximum TCE concentration detected (11 ppb) in the well.
In the ATSDR Toxicological Profiles, MRLs are developed for acute, intermediate, and chronic exposure intervals. A MRL for TCE is only available for acute (14 days or less) exposures and was used to evaluate potential noncancer effects associated with drinking water exposures. The resulting estimated exposure doses of 0.00063 mg/kg/day for adults and 0.0033 mg/kg/day for children do not exceed ATSDR's MRL of 0.2 mg/kg/day for acute oral exposure. A chronic oral exposure MRL or chronic RfD are not available for TCE. ATSDR reviewed the available studies using intermediate and chronic exposures for animals and found that the conservative exposure dose estimates for MCLB were 67 times less than the lowest LOAEL in the literature. ATSDR does not expect the use of the drinking water to cause noncarcinogenic health effects for residents (adults and children).
Although TCE has been shown to produce cancer in experimental animals when administered in large doses, the link between TCE in drinking water and human cancer cases is not well established (ATSDR, 1997). EPA, in an effort to determine cancer classification for TCE, is currently reviewing the scientific literature pertaining to carcinogenicity of TCE. For screening purposes, ATSDR used a previously derived CPF for TCE of 0.011 (mg/kg/day)-1. This approach provides a conservative evaluation of the likelihood of exposures to TCE in the private well adjacent to the Nebo Main Base. ATSDR derived a lifetime cancer estimate from drinking water from the private well of 6.9 x 10-6 (or 7 new cases in 1,000,000 exposed individuals). As the estimate falls within the range of 10-4 to 10-6, ATSDR does not consider an increased risk of cancer from TCE to be a concern for residents consuming the water from the private well adjacent to Nebo Main Base.
Estimated Exposure Dose for Consumption of Trichloroethylene in On-Site Drinking Water at the Yermo Annex
TCE was present in an on-site base production well at the Yermo Annex for a period of approximately one month before the well was decommissioned and a carbon-activated adsorption water treatment system was installed to remove the organic contaminants at levels above both ATSDR's CREG of 3 ppb and EPA's enforceable MCL of 5 ppb. To determine the potential for adverse health effects from exposure to TCE in the on-site production well, ATSDR used the same conservative assumptions for adults as those used for the private well adjacent to Nebo Main Base except the exposure period of three years. ATSDR assumed that the water contains the maximum TCE concentration detected (25 ppb) in the well. The resulting estimated exposure doses of 0.0014 mg/kg/day for adults do not exceed ATSDR's MRL of 0.2 mg/kg/day for acute oral exposure. A chronic oral exposure MRL or chronic RfD are not available for TCE. ATSDR reviewed the available studies using intermediate and chronic exposures for animals and found that the conservative exposure dose estimates for MCLB were 27 times less than the lowest LOAEL in the literature. ATSDR does not expect the use of the drinking water to cause noncarcinogenic health effects for workers.
ATSDR derived a lifetime cancer estimate from drinking water from the private well of 6.5 x 10-7 (or 6.5 new cases in 10,000,000 exposed individuals). As the resulting estimate is smaller than the range of 10-4 to 10-6, ATSDR does not consider an increased risk of cancer from TCE to be a concern for workers consuming from the water from production well at the Yermo Annex.
|A. Urgent public health hazard||This category is used for sites that pose an urgent public health hazard as the result of short-term exposures to hazardous substances.||
|B. Public health hazard||This category is used for sites that pose a public health hazard as the result of long-term exposures to hazardous substances.||
|C. Potential (indeterminate) public health hazard||This category is used for sites with incomplete information.||
|D. No apparent public health hazard||This category is used for 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.||
|E. No public health hazard||This category is used for sites that do not pose a public health hazard.||