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Select PCB Exposure Pathways




APP Agana Power Plant
ATSDR Agency for Toxic Substances and Disease Registry
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
EMEG Environmental Media Evaluation Guide
FDA United States Food and Drug Administration
GEPA Guam Environmental Protection Agency
GPA Guam Power Authority
I-TEQ International Toxic Equivalency
LOAEL Lowest Observed Adverse Effect Level
MAFF Ministry of Agriculture, Fisheries, and Food
mg/kg milligrams per kilograms
mg/kg/day milligrams per kilograms per day
MRL Minimal Risk Level
NAS Naval Air Station
PAH Polycyclic Aromatic Hydrocarbons
PCBs Polychlorinated Biphenyls
PHA Public Health Assessment
POI Point of Interest
RAB Restoration Advisory Board
RCRA Resource Conservation and Recovery Act
RfD Reference Dose
RMEG Reference Dose Media Guide
TCDD Tetrachlorodibenzo-p-dioxin
TCRA Time-Critical Removal Action
TDI Total Daily Intake
TDS Total Diet Study
TEF Toxic Equivalency Factor
TEQ Toxic Equivalency
UOG University of Guam
USCOE United States Army Corps of Engineers
USEPA United States Environmental Protection Agency
USFWS United States Fish and Wildlife Service
USGS United States Geological Society
UXO Unexploded Ordnance
WERI Water and Environmental Research Institute of the Western Pacific
WHO World Health Organization
WHO-TEQ World Health Organization Total Equivalency


The Agency for Toxic Substances and Disease Registry. ATSDR is a federal public 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 exposure to harmful 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.

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.

Completed Exposure Pathway:
See Exposure Pathway.

Comparison Values:
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.

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

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

See Environmental Contaminant.

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

Dose / Response:
The relationship between the amount of exposure (dose) and the change in body function or health that results.

The amount of time (days, months, years) 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 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.

Environmental Media:
Usually refers to the air, water, and soil in which chemicals 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.

The study of the different factors that determine how often, in how many people, and in which people disease will occur.

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 a chemical moves from its source (where it began) to where and how people can come into contact with (or become exposed to) the chemical.

ATSDR defines an exposure pathway as having 5 parts:

  • Source of Contamination
  • Environmental Media and Transport Mechanism
  • Point of Exposure
  • Route of Exposure
  • Receptor Population

When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. If any part is missing, people can not be exposed.

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

Hazardous Waste or Substance:
Substances that have been released or disposed 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).

Kilogram (kg):
One thousand grams.

Lowest Observed Adverse Effect Level. The lowest dose of a chemical in a study, or group of studies, that has caused health effects in people or animals.

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

Milligram (mg):
One thousandth of a gram.

Minimal Risk Level (MRL):
An estimate of daily human exposure–by a specified route and length of time–to a dose of a chemical that is likely to be without a measurable risk of adverse, noncancerous effects. An MRL should not be used as a predictor of adverse health effects.

No Apparent Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where exposure to site-related chemicals might 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.

Point of Exposure:
The place where someone can come into contact with a contaminated environmental medium (air, water, food or soil). Examples include 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.

Potentially Exposed:
The condition where valid information, usually analytical environmental data, indicates the presence of contaminant(s) of public health concern in one or more environmental media. These contaminants must have a way of contacting people (i.e., air, drinking water, soil, food chain, surface water), and there must be evidence that some people have been exposed through 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 (PHA):
A report or document that looks at chemicals at a hazardous waste site and determines whether people could be harmed from coming into contact with those chemicals. The PHA also determines whether possible further public health actions are needed.

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

Public Health Hazard Criteria:
PHA categories given to a site which determine whether people could be harmed by conditions present at the site. Each are defined in the Glossary. The categories are:
  • Urgent Public Health Hazard
  • Public Health Hazard
  • Indeterminate Public Health Hazard
  • No Apparent Public Health Hazard
  • 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).

Reference Dose (RfD):
An estimate, with safety factors (see safety factor) built in, of the daily, lifetime exposure of human populations to a possible hazard not likely to cause harm to the person.

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).

Safety Factor:
Also called Uncertainty Factor. When scientists do not have enough information to decide if an exposure will cause harm to people, they use "safety factors" and formulas in place of the information that is not known. These factors and formulas can help determine the amount of a chemical that is not likely to cause harm to people.

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.

Special Populations:
People who might be more sensitive to chemical exposures because of certain factors such as age, a disease they already have, occupation, sex, or certain behaviors (like cigarette smoking). Children, pregnant women, and the elderly are often considered special populations.

A method to collect information or data from a group of people (population) by asking questions and recording answers and observations. Surveys can be done by phone, mail, or in person. ATSDR cannot do surveys of more than nine persons without approval from the U.S. Department of Health and Human Services.

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.

Toxicology :
The study of the harmful effects of exposure to chemicals in humans or animals.

Abnormal growth of tissue or cells that have formed a lump or mass.

United States Environmental Protection Agency (USEPA):
The federal agency that develops regulations and enforces laws to protect the environment and the public health.

Urgent Public Health Hazard:
This category is used in ATSDR's Public Health Assessment documents for sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects and require quick intervention to stop people from being exposed.


Table I-1:

Exposure Situation and Hazard Summary Table - Mongmong Community and Agana Power Plant, Guam
Exposure Situation Contaminant(s) Source Media Point of Exposure Route of Exposure Exposed Populations Time Comments
Contaminants in fish, eels, and snails harvested in the Agana Swamp and River PCBs
Runoff from Agana Power Plant


Fish, eels,and snails Ingestion Completed exposure to people who eat fish, eels, and snails from the Agana Swamp and River: 270 adults; 140 children 1950s to present Levels of PCBs and other chemicals in fish, eels, and snails are very low and do not pose a public health hazard. There could be, however, hazards from bacteria, viruses, parasites, and other infectious agents. People should thoroughly cook all foods to kill any biologic contaminants and avoid touching raw fish with open cuts or wounds. The government of Guam should conduct a baseline survey of biologic contaminants as funding becomes available.
viruses, parasites, and other infectious agents
Septic tanks and sewage systems; snails
Contaminants in fruits and vegetables grown in Agana Swamp and in the soil runoff areas near APP PCBs
Runoff from Agana Power Plant Biota Fruits and vegetables Ingestion Potential exposure to people who eat fruits and vegetables from the Agana Swamp and River: 270 adults; 140 children 1950s to present Levels of PCBs and other chemicals in fruits and vegetables are either not detectable or very low and do not pose a public health hazard.
Playing in the Dirt, Runoff Ditches near the APP and Gardening in runoff areas near APP PCBs Runoff from Agana Power Plant Surface soil Ditches and runoff areas, including residential properties Skin absorption,


Completed exposure to people come in contact with soil Agana Swamp and River: 220 adults; 150 children 1950s to present The levels of PCBs in the soils from and around the runoff ditches and in residential areas do not pose a public health hazard.
Swimming or wading (contacting water) in the Agana Swamp PCBs

Bacteria, parasites, viruses, and other infectious agents

Runoff from Agana Power Plant, Septic tanks and sewage systems Surface water Agana Swamp and River Skin absorption; Ingestion Completed exposure to people who swim and wade in the Agana Swamp and River: 220 adults; 150 children 1950s to present Swimming and wading in the Agana Swamp poses no public health hazard from PCB contamination because the levels in the sediment are low. Also, PCBs do not dissolve easily in water, and would have diluted in the large volume of water. Still, the Swamp is possibly contaminated with bacteria, viruses, parasites, and other infectious agents and could pose a public health hazard. People with open cuts or wounds should not wade or swim and should avoid swallowing the water.

* Potential pathway


Click here to view Appendix J in PDF format (PDF, 58KB)


The Agency for Toxic Substances and Disease Registry released the Agana Power Plant Mongmong,Guam Public Health Assessment (PHA) for public review and comment on September 10, 2002. Thepublic comment period, which ended on November 7, 2002, was announced in a press release onSeptember 27, 2002. The health assessment was made available for public comment at the followingrepositories on Guam: Nieves M. Flores Memorial Library, Robert F. Kennedy Memorial Library,and the Micronesia Area Research Center at the University of Guam. The PHA was also sent toGuame and federal agencies and interested members of the general public. For comments thatquestioned the validity of statements made in the PHA, ATSDR verified or corrected the statements.The following list of comments received during the public comment period does not include editorialcomments such as word spelling or sentence syntax. Comments were combined when possible.

Comment: One reviewer suggested mapping the sampling sites of the data used in the APP PHA.

Response: Navy documents with maps showing sampling locations are available at Nieves Flores Memorial Library, 254 Martyr Street, Hagatna, GU 96910.

ATSDR has obtained a number of maps of the area around the power plant—including soil,elevation (topographic), wetland, and geologic maps—from groups and agencies such as theUniversity of Guam, U.S. Fish and Wildlife Service and U.S. Geological Survey. Becauseeach of these maps uses different grid systems or projections, ATSDR has been unable to plotNavy sampling coordinates on these maps. ATSDR is continuing to request assistance fromother groups and agencies so that the sampling points may be accurately plotted on thedifferent map projections. If the issues relative to sampling coordinates, grid systems, andprojections are resolved, maps will be included in ATSDR's second PHA addressing air andgroundwater issues and public concerns.

Comment: One sample of tilapia was collected during the Navy's sampling. A reviewersuggested that more samples of tilapia should be collected to ensure that the tilapia will notexceed FDA's 2.0 mg/kg limit.

Response: ATSDR agrees that additional tilapia samples would have been preferred. However, ATSDR based its overall conclusions on a variety of information. When combined with other sampling data for fish, sediment and soil, ATSDR believes that PCB levels are below levels of health concern for non-subsistence fishing. In addition, the number of fish available in the Agana Swamp and River, including tilapia, appears to be lower than needed to support a subsistence fishing population. Also, ATSDR has not identified a population of subsistence fish eaters who exclusively consume tilapia. Therefore, for subsistence fish-eating individuals and families, exposure should be below the levels found in the tilapia sample. The Navy sampling plan was designed to find if PCB from Agana Power Plant had reached Agana Swamp and River. It is uncertain if the PCBs found in the sample of tilapia are from Agana Power Plant, or another location such as PCB-contaminated soil near Agana Springs, unregulated waste, or septic tank and sewage releases. ATSDR believes that low levels of PCBs are widespread in the Agana Swamp and other hot spots of PCB may be found in the future.

However, based on sampling from soils, sediment, and other fish—including eel andcatfish—ATSDR believes that the levels of PCBs in tilapia will be consistent with PCBlevels in fish already sampled.

Comment: Although the exposure doses calculated from fish, eels, and snails do not exceedthe World Health Organization (WHO) tolerable daily intake for dioxins, many of thesamples exceeded the EPA's risk-based concentration (RBC) for total dioxins.

Response: ATSDR used EPA's RBC as part of our screening process. The RBC is a very conservative concentration. It overestimates risk for individuals and families who do not regularly eat the amount of fish used by ATSDR to calculate the risk based screening numbers. ATSDR reviewed the literature for information about total dioxins in the food supply of the U.S. and other countries. Table 6 presents the levels of dioxin residues detected in common foods. The average levels of total dioxins in the majority of sampled Mongmong fish, eels, and snails are almost identical to or below many common foods eaten daily in the United States and other countries. In addition, ATSDR did not identify individuals whose only source of fish was from the Agana River and Swamp.

Comment: The one sample of a taro root exceeds the USEPA's RBC for dioxins in fish. Onereviewer commented that there is no comparison value in the document for this value. A reviewer also suggested that more taro, eel and tilapia samples should be collected andanalyzed for dioxin.

Response: ATSDR reviewed the literature for information about total dioxins in the food supply of the U.S. and other countries. Table 6 presents levels of dioxin residues detected in common foods. Known incidents of high dioxin levels in humans have resulted from accidental exposure, not dietary exposures. Despite a large body of research and data collection, there are numerous questions and uncertainties regarding scientific data on and analysis of dioxin risk. This fact is acknowledged by the EPA's Science Advisory Board, which nonetheless also acknowledged that these uncertainties are unlikely to be resolved in the near future.

Taro is rich in protein, carotene, fibre, potassium and phosphorus. Taro (root and leaf) iseaten cooked because it is poisonous (calcium oxalate crystals) when eaten raw—the skinalso contains an oil that is an irritant. If additional sampling occurs, it would be useful ifcooked and non-cooked taro were both sampled. Local recipes and cooking methods (skin onor off, broiled, steamed, fermented) should probably be considered during development ofsampling and analysis plans.

Dioxin levels in Agana Power Plant soil where PCBs leaked on the ground are extremelylow. One taro root sampled had dioxins but no PCBs at detection levels. It is unclear if thedioxins were in soil attached to the taro root, in surface cuts on the root, or in the skin of thetaro root. It appears that the dioxins may have come from manmade sources of incompletecombustion that might have also included trash burning, or septic tank and sewage releases,or natural processes, such as brush and swamp fires. The term "natural background" fordioxins refers to the dioxins that are in the environment because of these natural processes.We do not know what the natural background level of dioxins is. The term "currentbackground" refers to the level of dioxin in the environment today. Current background is primarily made up of dioxins from manmade (anthropogenic) sources.

If a regulatory agency or a potentially responsible party determines that additional sampling isneeded to determine natural, manmade (anthropogenic) or current background levels ofdioxin in and around Mongmong, Agana River and Agana Swamp, ATSDR will reconsider itevaluation if levels in the local food are higher than found in the common food supply.

Comment: This PHA discusses three activities related to APP and identifies five other issuesnot directly related to the APP that will be addressed in a future document. One reviewersuggests that the APP PHA implies the presence of unknown contamination everywhere andthat this raises doubts as to the safety of the five activities not associated with APP withoutproviding references regarding these issues or a rationale for the presence of the unknowncontamination. The reviewer believes that the report adds fear of the unknown without beingspecific about the contamination and how these five activities could be linked to the APPPHA.

Response: The issues are community concerns that are related to APP but are not limited to APP. The community concern about swamp fires is an example of this. The community concerns included the concern that PCB came from the power plant and washed into the swamp and would then be in the smoke from the swamp fires. ATSDR's response is to the overall community concern about smoke and all PCBs in the swamp fires and not just PCBs from Agana Power Plant in the swamp fires.

Comment: The table on page 12 lists sites on the northeast side of the Agana River aspossible sources of environmental pollution in the Agana Swamp and River. A reviewersuggests that references for these sources be provided. The reviewer also believes that thisinformation adds apprehension about the unknown since the report does not offer any detailson the type of contamination or the activities of each site that could have produced thecontamination.

Response: In the Agana Power Plant health consultation released in 2000, ATSDR provided a historical map showing the locations of areas used by military and non-military groups during 1945 and a map showing an unnamed military reservation. In that document and this PHA ATSDR stated that these were possible source areas and identified a few of the items such as chemical warfare materiel identification sets that have now been removed from local property.

ATSDR emphasizes that the goal of its PHA is to help put environmental data intomeaningful public health perspective for the community. That is, ATSDR tries to answer thequestion of whether environmental exposure occurred and whether any such exposure mightbe harmful. One of the challenges we face is to evaluate potential health hazards given thelack of historical records, environmental monitoring data from source areas, and points ofhuman exposure. Without additional data and information, ATSDR can only say that theseare possible sources of contamination based on the fact that similar sites have hadcontamination associated with them.

Comment: One reviewer suggests an appendix including information about health conditionsreported by Mongmong residents might add to apprehension of the unknown by indirectlyimplying that the conditions reported by Mongmong residents may be associated with PCBexposure. Instead, the reviewer suggests that ATSDR include information that concentrateson the health effects of PCB exposure, its toxicity, how it can enter the body, types of cancerfound in animal and human studies of PCBs, and other health conditions pertaining to PCBexposure.

Response: Villagers were concerned that family illnesses and deaths were associated with PCB exposure from APP. ATSDR does not believe that these health problems are related to PCBs. ATSDR has added an appendix with information on health effects of PCBs.

During conversations with ATSDR some family members asked what could be causing thehealth problems if PCBs were not responsible. To respond to the request for informationabout these health problems, ATSDR included information about the causes of the healthproblems to help families and individuals make informed health care choices. ATSDR hasalso suggested that individuals and families discuss their health concerns with their physicianor health care provider and have routine physicals.

Comment: A few reviewers suggested that information about dioxin be added to an appendix and wanted to know ATSDR recommendations for diet and breast feeding.

Response: Questions and Answers About Dioxins were prepared by the Interagency Working Group on Dioxin (January 2003). On the world wide web they may be found at . The Interagency Working Group is made up of the following:

- Executive Office of the President
- U. S. Department of Health and Human Services
- U. S. Department of Agriculture
- U. S. Department of Veterans Affairs
- U. S. Environmental Protection Agency
- U. S. Department of Defense
- U. S. Department of State

The questions and answers are presented in four sections:

  • General information about dioxins
  • Overview of the EPA dioxin report
  • Food safety questions and answers
  • Risk assessment questions and answers

Some key points on food safety issues, breastfeeding, and dioxin include:

  • The U.S. food supply is among the safest and most nutritious in the world. While the federal food and environmental agencies are concerned about dioxin, the EPA draft dioxin reassessment report does not change the government's view of the overall safety of the food supply in this country. Maintaining the safety of the food supply is a top U.S. government priority.

  • Known incidents of high dioxin levels in humans have resulted from accidental exposure, not typical dietary exposures. Despite a large body of research and data collection, there are numerous questions and uncertainties regarding scientific data on and analysis of dioxin risk. This fact is acknowledged by the EPA's Science Advisory Board, which nonetheless also acknowledged that these uncertainties are unlikely to be resolved in the near future. The levels of dioxin were higher in the past than they are today.

  • In the long-term, efforts to reduce dioxin in the environment should also reduce dioxin levels in the food supply. Federal agencies have been monitoring the levels in foods and conducting an investigation whenever a particular food has dioxin levels detected over the background levels in that food.

  • For most people, adjusting their diet to fall within the Federal Dietary Guidelines will result in multiple health benefits, including reduced dioxin exposure. The dietary guidelines provide the best scientifically based advice on what constitutes a healthy diet and provide guidance on how to plan a varied diet by choosing individual foods from a number of food groups.

  • Some people consume more foods high in saturated fats (meat and dairy) than is recommended in the Dietary Guidelines. For these people, there are well-known and significant health benefits of reducing saturated fat intake that go beyond the potential risks of dioxin. The Dietary Guidelines, however, do not recommend that people avoid all fats, as fats are an important part of balanced nutrition.

  • There are overwhelming benefits of breastfeeding both for the mother and her infant. The American Academy of Pediatrics and many other professional organizations have concluded that the benefits of breastfeeding far outweigh the potential effects of dioxin in breast milk. Breast milk is known to be the most complete form of nutrition for infants, with benefits for infant health, growth, immunity, and development. The benefits of breastfeeding for children include fewer cases and less severity of diarrhea, respiratory infections, ear infections, and meningitis, among others. Breastfeeding may also reduce the risk of sudden infant death syndrome and may lower rates of childhood cancer.

  • In addition to the benefits for children, breastfeeding also has benefits for mothers. Breastfeeding has been shown to reduce postpartum bleeding, promote earlier return to pre-pregnancy weight, and reduce the risk of breast cancer.

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
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