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Varied Sampling and Laboratory Techniques

According to documentation reviewed by ATSDR, annual sampling did not always follow the same general sampling plan. Different laboratories and techniques were used, so the data quality, number of samples, and location of measurements vary. Nevertheless, the available monitoring results are in good agreement and they can be used to assess public health concerns and to assist in clean-up decisions.

Estimates of Plutonium Isotopes

Weapons-grade plutonium contains various amounts of plutonium isotopes, including plutonium 239, plutonium 240, and americium 241. The Air Force calculated plutonium concentrations based on the concentration of americium 241 detected, as determined mostly by gamma spectrometry. ATSDR identified data quality issues that need to be addressed because gamma spectrometry has two important sources of error.

  • The ratio of plutonium 239 to americium 241. The likely ratio is 5.4:1. One must consider several things (having to do with inclusion of plutonium 240 and sample preparation) to apply this ratio correctly. Typical laboratory procedures cannot separate plutonium 239 from plutonium 240, because their radiation decay energies are essentially identical. Reported ratios for the data sets reviewed are 5.9, 2.8, and 3.83. Nonetheless, the magnitude of the possible error maintains the concentrations within a factor of two.

  • Small-scale distribution of debris. According to the initial observations of the accident and early reports generated after the accident, the debris was initially distributed as particles, which are largely insoluble. This insolubility insures little migration of the contaminants except by physical movement. One result of this is that the material remains heterogeneously distributed as particulate matter in the environment. This heterogeneity is very important in the detection, fate, and transport analysis of contamination in the environment.
  • Gamma radiation spectrometry assumes that the gamma emissions originate homogeneously throughout the volume of soil being analyzed. If, despite extensive laboratory sample preparation, the samples are not homogeneous--the plutonium and americium are not uniformly distributed throughout the soil--large errors can be introduced into the analysis, especially for detection of americium 241. Americium 241 has a very weak gamma ray energy that can be easily absorbed, reducing its detection efficiency. Therefore, heterogeneous distribution of particles of nuclear material in the soil would make the uncertainty of a single sample high. The error from the heterogeneity can be compensated for if multiple samples from the same source are analyzed, as is generally the case for the BOMARC site.


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.

Acute Exposure:
Contact with a chemical that happens once or only for a limited period of time. ATSDR defines acute exposures as those that might last up to 14 days.

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.

Chronic Exposure:
A contact with a substance or chemical that happens over a long period of time. ATSDR considers exposures of more than one year to be chronic.

Completed Exposure Pathway:
See Exposure Pathway.

Comparison Value (CVs):
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.

Delayed Health Effect:
A disease or injury that happens as a result of exposures that may have occurred far in the past.

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".

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

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 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.

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

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

  • Source of Contamination,
  • Environmental Media and Transport Mechanism,
  • Point of Exposure,
  • Route of Exposure, and
  • 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).

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).

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

See Cancer.

Minimal Risk Level. An estimate of daily human exposure - by a specified route and length of time -- to a dose of 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.

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 Observed Adverse Effect Level. The highest dose of a chemical in a study, or group of studies, that did not cause harmful health effects in people or animals.

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:
  • 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, life-time exposure of human populations to a possible hazard that is 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 don't 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.

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.

Special Populations:
People who may 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 older people are often considered special populations.

Superfund Site:
See NPL.

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

Synergistic effect:
A health effect from an exposure to more than one chemical, where one of the chemicals worsens the effect of another chemical. The combined effect of the chemicals acting together are greater than the effects of the chemicals acting by themselves.

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.

The study of the harmful effects of chemicals on humans or animals.

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

Uncertainty Factor:
See Safety Factor.


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. The conclusion that a contaminant exceeds the comparison value does not mean that it will cause adverse health effects.

Cancer Risk Evaluation Guides (CREGs)

CREGs are estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million (10-6) persons exposed over their lifetime. ATSDR's CREGs are calculated from EPA's cancer potency factors.

Environmental Media Evaluation Guides (EMEGs)

EMEGs are based on ATSDR minimal risk levels (MRLs). An EMEG is an estimate of daily human exposure to a chemical (in 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 human exposure is unlikely to result in adverse noncarcinogenic effects.


What is radioactivity?

"Radioactive" is the word used to describe an unstable atomic nucleus that spontaneously emits radiation. Atoms are the smallest units of an element that have the same properties as the element. All matter is made up of atoms, and atoms are made up of protons and neutrons (found in the nucleus of the atom) and electrons. The number of protons in an atom of a particular element is always the same, but the number of neutrons may vary. Whether an atom is unstable is determined by the ratio of neutrons to protons. Isotopes are forms of the same element with different numbers of neutrons. The number of protons and neutrons in the atom are added to name the isotope. For example, an atom of cobalt that has 27 protons and 33 neutrons is called cobalt-60. Cobalt-60 is radioactive and is therefore called a radioisotope or a radionuclide.

What causes radioactivity?

All elements heavier than lead (which contains 83 protons) are naturally radioactive. Atoms can also become radioactive through natural processes in the environment. (Carbon 14 is an example of this.) Everyone is exposed to naturally occurring radiation from space and from radioactive materials in the ground. Humans can also create radioactive atoms of most elements. (For example, humans create radioactive atoms to use as tracers to help measure the flow of materials in the environment.) Radioactive material can travel through the air as particles or gases and can also enter soil, water, plants, and animals. Most radiation that people are exposed to is radon, an alpha emitter that results from decaying uranium 238, which is found in all air.

What is radiation?

Radiation is the emission of waves or particles from an unstable atom undergoing a transformation to stabilize the number of protons compared to the number of neutrons in its nucleus. This transformation changes the radioactive atom into a stable atom of a different element. For example, a proton in a cobalt-60 atom may change into a neutron and emit radiation, leading the atom to become a nickel-60 atom.

What are alpha particles, beta particles, and gamma radiation?

Alpha particles can be emitted by atoms that are more massive than lead, such as radium. Alpha particles are composed of two protons and two neutrons and have a large charge, which can pull electrons off neighboring atoms (or cause them to ionize). Alpha particles cannot penetrate the skin, but can be taken into the body by inhaling particles or ingesting foods contaminated with alpha particles. If they enter the human body, alpha particles can be absorbed in the blood, incorporated into molecules in the body, and deposited in living tissue. Plutonium is an alpha emitter.

Beta particles are high-energy electrons that result from a neutron changing into a proton or a proton changing into a neutron. Some beta particles have very little energy and cannot pass through the dead outer layer of a person's skin, but most can do so and expose the living tissue underneath the outer layer of skin to radiation. Beta particles cannot penetrate through the human body, however. Exposure to beta radiation can also result from internal exposure, such as through inhaling air or ingesting food or liquids containing beta particles.

Gamma rays result from the release of excess energy when an atom gives off an alpha or beta particle. Gamma rays consist of moving energy and have no mass or charge. They can travel long distances and move through the air, body tissue, or other materials. A gamma ray that passes through a body might hit nothing inside it, but it might hit atoms in its path. Gamma rays are the primary type of radiation that can harm people when they are exposed to a source outside the body (external gamma radiation). Americium emits gamma rays.

Source: Agency for Toxic Substances and Disease Registry. 1999. Toxicological profile for ionizing radiation. September 1999.


The Agency for Toxic Substances and Disease Registry (ATSDR) received the following comments/questions during the public comment period (June 10 to July 25, 2002) for the BOMARC Public Health Assessment (PHA). Comments were received from a total of three respondents from the U.S. Air Force and the Army. Most of the comments provided new or updated information, which ATSDR has incorporated into the PHA. ATSDR documents our reply to two comments below.

Comment: A commenter noted that ATSDR references the International Commission on Radiological Protection (ICRP) Publication 60 for guidance on radiological hazards. The commenter questioned whether the ICRP Publication 60 was relevant in the context of this PHA and U.S. Federal Radiation protection guidelines and suggested that ATSDR use ICRP Publication 26.

Response: ATSDR is keeping the text and references to ICRP 60 in the PHA as written. It is important to note that the ICRP 26 provides guidance on assessing worker exposures, while the ICRP 60 provides guidance for both worker and public exposures. As described in the PHA, some of the responders to the accident were civilian firefighting force. These responders would not have been considered radiation workers, but members of the public. ATSDR, therefore, uses the guidance for members of the public as provided in ICRP 60 publication to accurately assess exposure for these responders.

Comment: A commenter noted that the 2,000 millirem (mrem) (or 20 millisievert [mSv]) average for one year's exposure cited in the PHA has not been accepted in the United States.

Response: ATSDR acknowledges that the 2,000 mrem has not been accepted in the United States. As a non-regulatory agency, ATSDR is not restricted to any established evaluation criteria. Rather, ATSDR made decisions about public health based upon the best available information and guidance provided by reputable national or international organizations.

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