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Regional Location of NCBC Davisville, Rhode Island
Figure 1. Regional Location of NCBC Davisville, Rhode Island

NCBC Davisville Area Map
Figure 2. NCBC Davisville Area Map

Installation Restoration Sites at NCBC Davisville
Figure 3. Installation Restoration Sites at NCBC Davisville

Installation Restoration Program Study Area at NCBC Davisville
Figure 4. Installation Restoration Program Study Area at NCBC Davisville

Demographic Statistics
Figure 5. Demographic Statistics

ATSDR's Exposure Evaluation Process
Figure 6. ATSDR's Exposure Evaluation Process


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 Potency Factor (CPF)
Usually derived from dose-response models and expressed in mg/kg/day, CPFs describe the inherent potency of carcinogens and estimate an upper limit on the likelihood that lifetime exposure to a particular chemical could lead to excess cancer deaths.

Cancer Risk Evaluation Guide (CREG)
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.

EPA Region III Risk-Based Concentration
EPA combines reference doses and carcinogenic potency slopes with "standard" exposure scenarios to calculate risk-based concentrations, which are chemical concentrations corresponding to fixed levels of risk (i.e., a hazard quotient of 1, or lifetime cancer risk of 10-6, whichever occurs at a lower concentration) in water, air, fish tissue, and soil.

Maximum Contaminant Level (MCL)
The MCL is the drinking water stand established by EPA and enforced by the states. It is the maximum permissible level of a contaminant in water that is delivered to the free-flowing outlet. MCLs are considered protective of human health over a lifetime (70 years) for individuals consuming 2 liters of water per day.

Minimal Risk Levels (MRL)
MRLs are estimates of daily human exposure to a chemical (i.e., doses expressed in mg/kg/day) that are unlikely to be associated with any appreciable risk of deleterious non-cancer effects over a specified duration of exposure. MRLs are calculated using data from human and animal studies and are reported for acute (< 14 days), intermediate (15-364 days), and chronic (> 365 days) exposures. MRLs are published in ATSDR Toxicological Profiles for specific chemicals.


How a chemical enters a person's blood after the chemical has been swallowed, has come into contact with the skin, or has been breathed in.

Adverse Health Effect:
A change in body function or the structures of cells that can lead to disease or health problems.

The Agency for Toxic Substances and Disease Registry. ATSDR is a federal health agency in Atlanta, Georgia that deals with hazardous substance and waste site issues. ATSDR gives people information about harmful chemicals in their environment and tells people how to protect themselves from coming into contact with chemicals.

Background Level:
An average or expected amount of a chemical in a specific environment. Or, amounts of chemicals that occur naturally in a specific environment.

Used in public health, things that humans would eat - including animals, fish and plants.

A group of diseases which occur when cells in the body become abnormal and grow, or multiply, out of control

Any substance shown to cause tumors or cancer in experimental studies.

See Comprehensive Environmental Response, Compensation, and Liability Act.

Completed Exposure Pathway:
See Exposure Pathway.

Comparison Value:
Concentrations or the amount of substances in air, water, food, and soil that are unlikely, upon exposure, to cause adverse health effects. Comparison values are used by health assessors to select which substances and environmental media (air, water, food and soil) need additional evaluation while health concerns or effects are investigated.

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA):
CERCLA was put into place in 1980. It is also known as Superfund. This act concerns releases of hazardous substances into the environment, and the cleanup of these substances and hazardous waste sites. ATSDR was created by this act and is responsible for looking into the health issues related to hazardous waste sites.

A belief or worry that chemicals in the environment might cause harm to people.

How much or the amount of a substance present in a certain amount of soil, water, air, or food.

See Environmental Contaminant.

Dermal Contact:
A chemical getting onto your skin. (see Route of Exposure).

The amount of a substance to which a person may be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day".

The amount of time (days, months, years) that a person is exposed to a chemical.

Environmental Contaminant:
A substance (chemical) that gets into a system (person, animal, or the environment) in amounts higher than that found in Background Level, or what would be expected.

Environmental Media:
Usually refers to the air, water, and soil in which chemical of interest are found. Sometimes refers to the plants and animals that are eaten by humans. Environmental Media is the second part of an Exposure Pathway.

U.S. Environmental Protection Agency (EPA):
The federal agency that develops and enforces environmental laws to protect the environment and the public's health.

Coming into contact with a chemical substance.(For the three ways people can come in contact with substances, see Route of Exposure.)

Exposure Assessment:
The process of finding the ways people come in contact with chemicals, how often and how long they come in contact with chemicals, and the amounts of chemicals with which they come in contact.

Exposure Pathway:
A description of the way that a chemical moves from its source (where it began) to where and how people can come into contact with (or get exposed to) the chemical.

ATSDR defines an exposure pathway as having 5 parts:
  1. Source of Contamination,

  2. Environmental Media and Transport Mechanism,

  3. Point of Exposure,

  4. Route of Exposure; and,

  5. Receptor Population.

When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these 5 terms is defined in this Glossary.

How often a person is exposed to a chemical over time; for example, every day, once a week, twice a month.

Hazardous Waste:
Substances that have been released or thrown away into the environment and, under certain conditions, could be harmful to people who come into contact with them.

Health Effect:
ATSDR deals only with Adverse Health Effects (see definition in this Glossary).

Indeterminate Public Health Hazard:
The category is used in Public Health Assessment documents for sites where important information is lacking (missing or has not yet been gathered) about site-related chemical exposures.

Swallowing something, as in eating or drinking. It is a way a chemical can enter your body (See Route of Exposure).

Breathing. It is a way a chemical can enter your body (See Route of Exposure).

The National Priorities List. (Which is part of Superfund.) A list kept by the U.S. Environmental Protection Agency (EPA) of the most serious, uncontrolled or abandoned hazardous waste sites in the country. An NPL site needs to be cleaned up or is being looked at to see if people can be exposed to chemicals from the site.

No Apparent Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where exposure to site-related chemicals may have occurred in the past or is still occurring but the exposures are not at levels expected to cause adverse health effects.

No Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where there is evidence of an absence of exposure to site-related chemicals.

Public Health Assessment. A report or document that looks at chemicals at a hazardous waste site and tells if people could be harmed from coming into contact with those chemicals. The PHA also tells if possible further public health actions are needed.

A line or column of air or water containing chemicals moving from the source to areas further away. A plume can be a column or clouds of smoke from a chimney or contaminated underground water sources or contaminated surface water (such as lakes, ponds and streams).

Point of Exposure:
The place where someone can come into contact with a contaminated environmental medium (air, water, food or soil). For examples:
the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, the location where fruits or vegetables are grown in contaminated soil, or the backyard area where someone might breathe contaminated air.

A group of people living in a certain area; or the number of people in a certain area.

Public Health Assessment(s):
See PHA.

Public Health Hazard:
The category is used in PHAs for sites that have certain physical features or evidence of chronic, site-related chemical exposure that could result in adverse health effects.

Public Health Hazard Criteria:
PHA categories given to a site which tell whether people could be harmed by conditions present at the site. Each are defined in the Glossary. The categories are:
  1. Urgent Public Health Hazard

  2. Public Health Hazard

  3. Indeterminate Public Health Hazard

  4. No Apparent Public Health Hazard

  5. No Public Health Hazard

Receptor Population:
People who live or work in the path of one or more chemicals, and who could come into contact with them (See Exposure Pathway).

Route of Exposure:
The way a chemical can get into a person's body. There are three exposure routes:
- breathing (also called inhalation),
- eating or drinking (also called ingestion), and
- or getting something on the skin (also called dermal contact).

The Superfund Amendments and Reauthorization Act in 1986 amended CERCLA and expanded the health-related responsibilities of ATSDR. CERCLA and SARA direct ATSDR to look into the health effects from chemical exposures at hazardous waste sites.

Source (of Contamination):
The place where a chemical comes from, such as a landfill, pond, creek, incinerator, tank, or drum. Contaminant source is the first part of an Exposure Pathway.

Superfund Site:
See NPL.

Harmful. Any substance or chemical can be toxic at a certain dose (amount). The dose is what determines the potential harm of a chemical and whether it would cause someone to get sick.

Volatile organic compound (VOC):
Substance containing carbon and different proportions of other elementssuch as hydrogen, oxygen, fluorine, chlorine, bromine, sulfur, or nitrogen;these substances easily become vapors or gases. A significant number of theVOCs are commonly used as solvents (e.g., paint thinners, lacquer thinner,degreasers, dry cleaning fluids).


Estimates of Human Exposure Doses and Determination of Health Effects

Deriving Exposures Doses

ATSDR estimated the human exposure doses from ingestion of shellfish from Allen Harbor, wheremetals, PCBs, pesticides, and PAHs were detected in the shellfish at levels above comparisonvalues. Deriving exposure doses requires evaluating contaminant concentrations to which peoplemay have been exposed and how often and how long exposure to those contaminants occurred.Together, these factors help influence the individual's physiological response to chemicalcontaminant exposure and potential outcomes. In the absence of complete exposure-specificinformation, ATSDR applied several conservative exposure assumptions to define site-specificexposures as accurately as possible.

Evaluating Potential Health Hazards

The estimated exposure doses are used to evaluate potential non-cancer and cancer effectsassociated with chemicals of concern. When evaluating non-cancer effects, ATSDR uses standardtoxicity 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 ofdaily human exposure to a substance that are unlikely to result in adverse non-cancer effects over aspecified duration. To be very protective of human health, MRLs and RfDs have built in"uncertainty" or "safety" factors that make them much lower than levels at which health effectshave been observed. Therefore, if an exposure dose is much higher than the MRL or RfD, it doesnot necessarily follow that adverse health effects will occur.

When evaluating cancer effects, ATSDR sometimes uses cancer potency factors (CPFs) that definethe relationship between oral exposure doses and the increased likelihood of developing cancerover a lifetime. 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 exposure levelstypical of human exposure to environmental contaminants. CPFs represent the upper-boundestimate of the probability of developing cancer at a defined level of exposure; therefore, they tendto be very conservative (i.e., overestimate the actual risk) in order to account for a number ofuncertainties 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) x 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 new case in 10,000 to 1,000,000 exposed persons), based on conservative assumptions about exposure,to determine the likelihood of excess cancer resulting from this exposure.

In addition to estimating the likelihood of non-cancer and cancer effects, ATSDR reviewed thetoxicologic literature to evaluate possible health effects associated with exposure at thedoses/concentrations estimated for the pathways described below.

Estimated Exposure Doses for Ingestion of Shellfish

ATSDR concludes that shellfish from Allen Harbor are not safe to eat.

ATSDR used the following equation to estimate exposure doses for ingestion of Allen Harbor shellfish:

mathematical equation


Conc = Maximum concentration in shellfish (mg/kg)
IR = Ingestion rate: 0.0065 kg/day (approximately one 8-ounce meal per month), average consumption of fish and shellfish from estuarine and freshwater by the general U.S. population (EPA 1989). Because a child likely eats smaller fish meals, ATSDR assumed that a child eats one 4-ounce meal per month.
FI = Fraction ingested from contaminant source (assumed 100%)
EF = Exposure frequency, or number of exposure events: 365 days per year
ED = Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years
BW = Body weight (kg): adult = 70 kg (154 pounds); child = 10 kg (22 pound)
AT = Averaging time, or the time period over which cumulative exposures are averaged 30 years x 365 days/year or 6 years x 365 days/year) for non-cancer effects; 70 years x 365 days/year for cancer effects )

Determination of Human Health Effects

Non-cancer Effects

Using maximum detected concentrations and other conservative assumptions about exposure, thedoses estimated for ingestion of fish containing either arsenic, cadmium, zinc, and PCBs (Aroclor-1254 and Aroclor-1260) are lower or just slightly greater than their corresponding MRL or RfD(see Table C-1). Because of the conservative assumptions used in estimating the exposure doses,slightly higher values (within an order of magnitude) do not indicate a health concern.

No MRL or RfD exists for copper, iron, or lead. In the absence of health-based guidelines forcopper and lead, ATSDR reviewed toxicologic literature and found that the estimated values aremany orders of magnitude lower than the lowest levels at which adverse health effects have beenreported in animal studies" (ATSDR 1990, 1997). Iron is not generally known to be toxic to humans.

The doses for adult and child exposures to mercury exceed the corresponding ATSDR MRL (formethylmercury) by one to two orders of magnitude, suggesting that exposure could result inharmful effects. Exposure to high levels of mercury in fish has been associated with an increaserisk of developing mercury-related adverse health effects such as neurological problems. Childrenare particularly sensitive to the effects of mercury because it can cause damage to the developingnervous system. For these reasons, ATSDR concludes that people can best protect themselves fromthe harmful effects of mercury by adhering to the shellfish ban issued at Allen Harbor.

Cancer Effects

ATSDR derived lifetime cancer risk estimates (Table C-2) for arsenic, aldrin, DDE,benzo(a)pyrene, and Aroclors 1242, 1254, and 1260, contaminants EPA has classified as known orsuspected human contaminants. All cancer risk estimates fall within the range (10- 4 to 10-6 excesscancer cases) considered "acceptable" by ATSDR and EPA. Therefore, consumption of shellfishfrom the harbor is not likely to lead to an increased likelihood of developing cancer.


Agency for Toxic Substances and Disease Registry (ATSDR). 1990. Toxicological Profile forCopper. December 1990.

ATSDR. 1997. Toxicological Profile for Lead (Update). September 1997.

Environmental Protection Agency (EPA). 1989. Risk assessment guidance for Superfund. Volume1. Human health evaluation manual (part A). U.S. Environmental Protection Agency. EPA/540/1-89-001. December 1989.

Food and Drug Administration (FDA). 1993. Guidance document for arsenic in shellfish. January 1993.

Table C-1. Estimated Exposure Doses--Non-cancer Effects Ingestion of Shellfish From Allen Harbor

Contaminant Maximum Detected Contaminant Concentration (mg/kg)** Estimated Exposure Dose (mg/kg/day) Health Guideline Chronic Oral
Basis for Health Guideline
Adult Child
Arsenic 0.286* 0.000003 0.000009 0.0003 MRL/RfD
Cadmium 0.239 0.00002 0.00008 0.0002 MRL
Copper 12.6 0.001 0.004 no value  
Iron 80.0 0.007 0.003 no value  
Lead 0.149 0.00001 0.000005 no value  
Mercury 4.91 0.0005 0.002 0.0003 MRL
Zinc 473.0 0.04 0.15 0.3 MRL/RfD
Aldrin 0.000046 0.000000004 0.00000002 0.00003 MRL/RfD
Benzo(a)pyrene 0.00124 0.0000001 0.0000004 no value  
Aroclor-1242 0.00331 0.0000004 0.000002 0.00002 MRL/RfD for 1254
Aroclor-1254 0.00124 0.000004 0.00001 0.00002 MRL/RfD
Aroclor-1260 0.0229 0.000002 0.000007 0.00002 MRL/RfD for 1254

Doses are based on average consumption of shellfish.

*10% of the maximum arsenic concentration was used for analysis (FDA 1993)
**10% of the maximum concentrations of contaminants was used as a conversion factor to change dry weight to wet weight concentrations (EPA 2000b).
Key: ppm=parts per million; mg/kg/day=milligrams contaminant per kilogram body weight per day; MRL=minimal risk level; RfD=reference dose.

C-2. Estimated Exposure Doses--Cancer Effects Ingestion of Allen Harbor Shellfish

Contaminant Maximum Detected Contaminant Concentration
Estimated Exposure Dose - Cancer
CPF Lifetime Cancer Risk 1
Arsenic 0.2.86 0.000001 1.5 2 x 10-6
Aldrin 0.000046 0.000000002 17 3 x 10-8
DDE 0.239 0.0000001 0.34 5 x 10-8
Aroclor-1242 0.00468 0.0000002 2 5 x 10-8
Aroclor-1254 0.039 0.000002 2 4 x 10-7
Aroclor-1260 0.0229 0.0000009 2 3 x 10-6
Benzo(a)pyrene 0.00124 0.000005 7.3 2 x 10-6

1 Lifetime Cancer Risk = estimated dose (cancer) x CPF.

Key: CPF = cancer potency factor; ppb=parts per billion; mg/kg/day=milligrams contaminant per kilogram body weight per day.

1. Site 9 shallow groundwater contamination may discharge into the harbor and result in potential future exposure if people were to swim in Allen Harbor. Site 07 shallow groundwater may also discharge into local surface water. Site 07 shallow groundwater contained maximum detected total chlorinated volatile organic contaminants up to: 23 ppb at MW07-01S; 1 ppb at MW07-02S; 1,481 ppb at MW07-21S; 5,950 ppb at MW07-21S; and 1,483 ppb at MW07-26S. These contaminants may discharge into the surface water channel between Allen Harbor and Narragansett Bay.
2. Comparison value taken from trans-1,2-dichloroethene.

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

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