Skip directly to search Skip directly to A to Z list Skip directly to site content




In evaluating these data, ATSDR used comparison values (CVs) to determine which chemicals to examine more closely. CVs are health-based thresholds below which no known or anticipated adverse human health effects occur. CVs can be based on cancer or non-cancer health effects. Non-cancer levels are based on the lowest (i.e., most toxic) value from a valid toxicologic study for a chemical and the assumption that a small child (22 pounds) is exposed every day. Cancer levels are the media concentrations at which there would be a one in a million excess cancer risk for an adult eating or drinking contaminated soil or water every day for 70 years. For chemicals for which both cancer and non-cancer numbers exist, the more toxic (i.e., lower) level is used. A description of the CVs used in this evaluation can be found in Appendix B. Exceeding a CV does not mean that health effects will occur, but rather that more evaluation is needed.

Further evaluation focuses on identifying which chemicals and exposure situations are likely to be a health hazard. The first step is the calculation of child and adult exposure doses, as described in Appendix C. These are then compared with an appropriate health guideline for a chemical. An exposure dose is the amount of chemical ingested daily per unit of body weight. Health guidelines are the amount of chemical per unit of body weight where health effects very likely do not occur, based on investigations of human exposures to the chemical, or, if human data don't exist or are not valid, of animal experiments. Most health guidelines are based on animal data. Any exposure situation resulting in an exposure dose lower than the appropriate health guideline is eliminated from further evaluation.

The next step in the evaluation process is determining if the worst case exposure situations used in earlier calculations need to be revised to better fit the actual situation. For example, if soils are covered with snow for four months out of the year, average exposure doses should be reduced accordingly.

The last evaluation step is the comparison of these revised exposure doses with known toxicological values for the chemical of concern. This would include the no observed and lowest observed adverse effect levels (NOAEL and LOAEL) identified in ATSDR Toxicological Profiles. If the chemical of concern is a carcinogen, the cancer risk is recalculated using the revised exposure dose. These comparisons are the basis for stating whether the exposure might be a health hazard.


Health Comparison Values (CVs) are the contaminant concentrations found in a specific media (air, soil, or water) and used to select contaminants for further evaluation. The CVs used in this document are listed below.

Environmental Media Evaluation Guides (EMEGs) are estimated contaminant concentrations in a media where no chance exists for non-carcinogenic health effects to occur. The EMEG is derived from U.S. Agency for Toxic Substances and Disease Registry's (ATSDR's) minimal risk level (MRL).

Remedial Media Evaluation Guides (RMEGs) are estimated contaminant concentrations in a media where no chance exists for non-carcinogenic health effects to occur. The RMEG is derived from U.S. Environmental Protection Agency's (EPA's) reference dose (RfD).

Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrations that would be expected to cause no more than one additional excess cancer in a million persons exposed over a lifetime. CREGs are calculated from EPA's cancer slope factors (CSFs).

Risk-Based Concentrations (RBCs) are the estimated contaminant concentrations in which no chance exists for carcinogenic or noncarcinogenic health effects. The RBCs used in this public health assessment were derived using provisional reference doses or cancer slope factors calculated by toxicologists of EPA's Region 3.

EPA Action Levels (ALs) are the estimated contaminant concentrations in water of which additional evaluation is needed to determine whether action is required to eliminate or reduce exposure. Action levels can be based on mathematical models.

EPA Soil Screening Levels (SSLs) are estimated contaminant concentrations in soil at which additional evaluation is needed to determine if action is required to eliminate or reduce exposure.


Comparison of Exposure Dose to Health Guidelines

Groundwater Ingestion

Exposure doses for groundwater ingestion are calculated in the following manner. The maximum concentration for a groundwater contaminant, in milligrams per liter (mg/L), is multiplied by the groundwater ingestion rate for adults, 2 liters/day, or children, 1 liter/day. The multiplication product is divided by the average weight for an adult, 70 kg (154 pounds), or for a child, 10 kg (22 pounds). The result is the exposure dose, in units of mg/kg/day, which is compared to accepted health guidelines. These calculations assume that there has been daily exposure, via ingestion, to groundwater contaminated at the pertinent maximum concentration shown for well water in contamination data tables. If exposure is less frequent, then an appropriate exposure factor is used to decrease the calculated dose.

Surface Water Ingestion

Calculations very similar to those described above for groundwater were used to determine exposure doses for surface water ingestion.

To determine exposure doses for incidental ingestion of surface water, the drinking water ingestion rate is decreased by a factor of 100. The average concentration of the data is used to estimate exposure. Exposure is assumed to occur 40 days out of the year.

Soil or Mine Tailings Ingestion

Chronic exposure doses for soil or mine waste ingestion are calculated by multiplying the average concentration for soil or mine tailings, in mg/kg (or ppm), by the soil ingestion rate for adults, 0.00005 kg/day, or children, 0.0002 kg/day. The multiplication product is divided by the average weight for an adult, 70 kg (154 pounds) or a child, 10 kg (22 pounds). The result is the exposure dose, in units of mg/kg/day. These calculations assume that there has been daily exposure to the concentration shown for soil or tailings in contamination data tables. If exposure is less frequent, then an appropriate exposure factor is used to decrease the calculated dose.

Acute exposure to soils is calculated by multiplying the maximum concentration measured in children's play areas, in mg/kg (or ppm), by the soil ingestion rate for children exhibiting pica behavior (eating of non-food items), 0.005 kg/day. The multiplication product is divided by the average weight for a child, 10 kg (22 pounds). The result is the exposure dose, in units of mg/kg/day. All the soil ingestion is assumed to take place on the same day. We did not consider repeated pica exposures.

Road Dust Inhalation

Instead of estimating inhalation exposure doses, ATSDR compares the chemical's concentration in air with the chemical's concentration used in animal and human studies. Typical exposure doses are not calculated because the nasal passages of rodents, the most common animal used to obtain toxicity data, have a significantly different structure compared to human nasal passages. Therefore, ATSDR believes that a direct comparison of air concentrations more accurately reflects the ability of a chemical to cause harmful effects.

The average of the data on road fill material, in mg/kg, was multiplied by a dust loading factor of 8×10-6 kg/m3 to obtain the concentration in air in mg/m3. These concentrations were then multiplied by factors to correct for intermittent exposures.

Calculation of Risk of Carcinogenic Effects

Groundwater or Surface Water Ingestion

Carcinogenic risk from groundwater or surface water ingestion is calculated by multiplying the adult exposure doses for ingestion of the water (calculated as described previously) by EPA's Cancer Slope Factor for the contaminants of concern. The results represent the maximum risk for excess cancer after 70 years of exposure to the maximum concentration of the contaminant.

Soil or Tailings Ingestion

Carcinogenic risk from ingestion of soil or tailings is calculated by multiplying the adult exposure doses for soil or tailings ingestion (calculated as described previously) by EPA's Cancer Slope Factor for the contaminants of concern. The results represent the maximum risk for excess cancer after 70 years of exposure to the maximum concentration of the contaminant.

Road Dust Inhalation

Carcinogenic risks from the inhalation of contaminated road dust were calculated through the following process. The corrected air concentration (calculated as described previously) was multiplied by EPA's Cancer Slope Factor for inhalation of the contaminants of concern. The results represent the maximum risk for excess cancer after 70 years of exposure to the maximum concentration of the contaminant.

Uncertainties in Calculating Cancer Risk

The actual risk of cancer is probably lower than the calculated number. The method used to calculate EPA's Cancer Slope Factor assumes that high dose animal data can be used to estimate the risk for low dose exposures in humans.(1) The method also assumes that there is no safe level for exposure.(1) There is little experimental evidence to confirm or refute these two assumptions. The method computes the 95 percent upper bound for the risk, rather than the average risk, suggesting that the cancer risk is actually lower, perhaps by several orders of magnitude.(1)


The Upper Tenmile Creek Mining Area Public Health Assessment was released April 24, 2001 and was available for public review and comment until June 30, 2001. This appendix lists the comments received and ATSDR's responses to those comments.

Comments from two private citizens (Rimini residents)

  1. In the demographic section on page 3, snowmobiles, ATV's, dirt bikes, and other off road vehicle (ORV) use, as well as mountain biking was not mentioned. Rimini is a popular area for these types of activities. Woodcutting/gathering is also an activity that was not mentioned but that is popular in the watershed for Rimini as well as Helena residents.
  2. ATSDR Response: The document has been changed to include these activities.

  3. On page 16, pica was defined but the term was first used on page 15.
  4. ATSDR Response: Thank you for pointing this out. The document has been changed. The definition of pica behavior (eating of non-food items such as dirt) now appears when the term is first used on page 15.

  5. Page 23, we found the section on road dust of interest. Enclosed is a copy of MDEQ's results from the June 1997 sampling of road fill material at various locations along Rimini Road. The results of this study concerned us since we have two small children and our house is located by the 3440-S sample location. John Arrigo, at MDEQ, personally came to our house to assure us that the road dust/contaminated road fill material was not a health concern, even though MDEQ'S recommendations suggested paving or dust suppression, and to further characterize the road fill material through additional sampling. After the sampling results were brought to our attention, and we later determined that the MDEQ and County were not going to follow up on either recommendation, we had magnesium chloride sprayed on the road in front of our house in 1998 and 1999. Since 1999, the EPA has had magnesium chloride sprayed on Rimini Road for the CERCLA mine removal activities in the upper watershed.
  6. Based on a recent telephone conversation with Mike Bishop, at EPA, in June 2001, the EPA plans to cover the mine tailings on Rimini Road with dirt. Covering the tailings with dirt does not appear to follow the ATSDR recommendations for the contaminated road fill as stated on page 28, which recommends removal and remedial actions for the contaminated road fill, or a plan for permanent control of road dust. The County routinely grades the road through Rimini at least a couple of times a year, and with the results of the June 1997 sampling showing the majority of the heavy metal contamination to be in the upper 6 inches of the road fill, the potential to re-expose this material in the near future is highly probable. We recommend a more permanent solution to the road dust/contaminated road fill problem than suggested by the EPA, preferably paving or removing and replacing the road fill material.

    ATSDR Response: Based on a recent conversation with EPA's contractor, the remedial alternative you described was one of the alternatives considered in the feasibility study process. However, at this time the preferred alternative will likely be to remove the top 18 inches of road cover and replace it with clean fill. Another alternative being considered is paving the road.

    Our recommendation was that action be taken to reduce exposures from contaminants in road dust. Although we have not formally reviewed the proposed actions for their impact on public health, we feel that either removal as described in the preceding paragraph or paving would be protective. ATSDR is willing to perform a formal review and comment on all potential remedial alternatives at the request of EPA or the community.

  7. On page 24, the results of the road material did not show the presence of lead. Was the road fill material analyzed for lead, since that was one of the metals detected in high levels during the June 1997 sampling?
  8. ATSDR Response: The road fill was analyzed for 13 compounds, including lead. Lead did not appear in Table 10 because lead was addressed in the discussion of other pathways and because there was no comparison value available for lead for the inhalation pathway. Although high lead levels are of concern, arsenic levels will likely drive the cleanup efforts. Lead levels are expected to be reduced by addressing high arsenic levels.

  9. Page 27, the section on Community Health Concerns does not reflect our opinion. We were offended by the comments that the community voiced no concerns regarding human health, and that community members were only concerned about the quantity of water in Tenmile Creek and the state of the fishery. As full time residents of Rimini our foremost concern is our health, not the fishery or stream flow quantities. Being professional biologists, we would like to see water in the stream for the fishery, but that does not take precedence over our health. We feel the viewpoint regarding the concerns for water quantity and the fishery are not representative of full time residents of the community, but rather those of the seasonal property owners in attendance at the meeting. The seasonal or part time residents may own property in the watershed, but they do not live here everyday, and therefore, they have a different perspective regarding health issues and concerns than someone who permanently resides in the area.
  10. We have spent thousands of dollars to insure our water is safe, long before EPA said there was a problem in the area. Also, we have spent hundreds of dollars on road dust suppression after learning of the heavy metal contamination, even though MDEQ told us that it was not a health concern.

    We are both 40-hour OSHA hazardous waste trained; and have worked on hazardous waste sites in the past. Based on this training and work experience, we feel we have taken many precautions to make living in Rimini safe for our children and ourselves. We knew the past history of Rimini when we purchased our home, but we feel we have created a safe place to reside by suppressing the road dust, purchasing a water treatment system, maintaining a lush vegetated yard, and monitoring our children's activities.

    ATSDR Response: We realize that the views expressed at the May 2000 Watershed Planning Meeting may not have fully represented views of all community members. We have updated the section on Community Health Concerns to reflect your opinion, as well as the opinions expressed by community members at the June 2001 meeting we attended.

    We support and applaud the proactive and common sense measures taken by you and other Rimini community members to protect your health. Our conclusions and recommendations are meant to enhance the current efforts to permanently clean up the site, so that future residents can be more assured of their health and safety.

  11. Page 28, we agree with recommendations 3 and 5, and urge the EPA to conduct these activities in the immediate future. Under recommendation number 2, based on our experience it would seem that heavy metal contamination in the surface water would fluctuate based on seasonal high water flows resulting from snow runoff and rain events.
  12. ATSDR Response: Based on a conversation with EPA's contractor, the proposed plan for the site will be out shortly. EPA's intent is for remediation of yards and the road through Rimini to take place in the 2002 field season. Your comment about surface water is correct. The limited available data from the Tenmile intake did not indicate high metals levels; however, based on data from other intakes and anecdotal accounts of flood events, high heavy metals are possible at times in surface water. This observation has been added to the Surface Water section of the document.

  13. On page 31, reference number 16, URL should be URS.
  14. ATSDR Response: Thank you for pointing this out. The document has been corrected.

Comments received during a meeting on June 21, 2001 between Jill Dyken and John Crellin, ATSDR; Mike Bishop, EPA; Mike Spence, MDPHHS; and Joan Bowser, Lewis & Clark City-County Health Department

  1. Recommendation 4, add pregnant women residing in houses built on tailings to group for which we recommend blood lead testing.

  2. Add mention of water treatment systems to discussion of drinking water.

  3. Conclusion 4, change "tailings" to "tailings and waste rock".

  4. Include mention of ingestion pathway in discussion of road dust.

  5. Add mention of risk from flooding to discussion and conclusions about surface water.
  6. ATSDR Response: The document has been changed to address the above suggestions.

Comments from Jim LaVelle, CDM Federal (EPA's contractor)

  1. [Comment on differences in how analyses are presented in the ATSDR public health assessment (PHA) and the EPA Human Health Risk Assessment (HHRA)]. "... As a specific example, the health assessment says little potential exists for significant lead impacts from exposure to soils. The RA says significant potential for health impacts exists, but only if the highest concentrations are found in yards, and are representative of average concentrations in these yards. I am a little concerned that the public might see these as different conclusions (I think they are not)."
  2. ATSDR Response: The differences mentioned result from the different purposes of the documents. ATSDR's PHAs are meant to give the public an indication of the actual chance for health effects, while the EPA HHRA performs more theoretical calculations of risk in order to formulate risk management decisions about the cleanup of the site. We have attempted to convey, through our interactions with the public, the apparent differences in the procedures ATSDR and EPA use to come to conclusions. Based on the comments received, the public is comfortable with the way the analyses are presented in our document.

  3. The analysis of surface water impacts (as drinking water source) might also be perceived to be different between ATSDR and EPA documents. The health assessment only addresses one surface water sampling location in the site (I think). The RA looks at all surface water data. The RA, therefore, reaches the conclusion that IF surface water in many stream reaches was used, impacts could be significant. This conclusion is followed with appropriate caveats about current and possible use of this resource. Again, will the public think we are on different pages?
  4. ATSDR Response: Because we focus on actual exposures, we only evaluated data from the intake where people were actually withdrawing water. We admit that this limited data may not give an accurate picture of contaminant levels in the surface water. In response to comments from site officials and community members, we have added some qualitative discussion of the potential for higher, more dangerous levels of metals during flooding and other events.

  5. The analysis of cadmium in wells suggests that serious health effects could occur if exposure occurred over "several months". The EPA reference dose for cadmium assumes accumulation of cadmium in the kidney over many years. Is ATSDR's approach different and if so should this difference be pointed out? Also, later in the cadmium discussion, the statement is made that no cancer slope factor exists for cadmium. This is true for oral exposure, but not for inhalation, based on EPA evaluations.
  6. ATSDR Response: ATSDR's definition of chronic is any exposure duration greater than 1 year. The NOAELs and LOAELs referenced are for chronic exposures. However, some calculated child doses significantly exceeded the chronic LOAEL and approached LOAELs found for animals in some intermediate (15 - 365 days) toxicological studies. Therefore, it is possible that some effects could be seen over an exposure duration of several months.

    The discussion of cancer risk from cadmium in well water has been clarified to indicate that no oral cancer slope factor exists for cadmium. Later, in the section on road dust inhalation, we did use the inhalation cancer slope factor for cadmium in calculating inhalation cancer risk.

  7. On page 21 (at least on my copy) you mention that "some houses are being built directly on tailings". Do we have direct evidence?
  8. ATSDR Response: Our statement was based on discussions with Mike Bishop, the remedial project manager for the site. We do not have direct evidence.

  9. The health assessment does not address some exposure media (adit discharge, groundwater seeps, fish) that are addressed in the RA. None of these appears to be of great concern, but, again, will the public perceive something missing from the health assessment?
  10. ATSDR Response: We focus our evaluation on completed exposure pathways, while the HHRA must look at theoretical potential risk. Fish were considered a potential (incomplete) exposure pathway because of the depressed fishery in the area (although we note that fish samples taken in 1998 showed contaminant levels too low to lead to health effects). The adit discharges and seeps were also considered incomplete because no people in the area are known to be directly contacting them. A section on adit discharges and groundwater seeps has been added to the section on completed exposure pathways.

Comments on returned reader evaluation forms (anonymous)

  1. I never received the results of soil tests from my property.
  2. ATSDR Response: EPA is responsible for conveying soil testing results to homeowners. The data used in the public comment version of this document was "hot off the press," and individual results of soil testing had not been prepared yet. Property owners should contact EPA to learn more about soil testing results.

  3. The report did not separate adit discharges from surface water. Several adit discharges are unique in that they should be evaluated as a category of sources/ pathways.
  4. ATSDR Response: We focused our evaluation on completed exposure pathways. Adit discharges and groundwater seeps were considered incomplete exposure pathways because no people in the area are known to be directly drinking this water. A section on adit discharges and groundwater seeps has been added to the section on completed exposure pathways.

  5. It would be more informative if sample location maps and results were presented so the residents could locate the contaminated areas and avoid exposure.
  6. ATSDR Response: Due to legal and property value concerns, it is ATSDR's policy to remove information which could be used to identify specific contaminated properties or individuals who may be excessively exposed. People were informed of soil testing results of their yards, allowing them to take appropriate measures to avoid exposure there. In addition, people can minimize other exposures by avoiding mine tailings and waste rock and by not drinking untreated surface water.

  7. My relatives mined in the area in the early 1800s. An uncle of mine died of lung cancer from mining in the area.
  8. ATSDR Response: It is impossible at this time and without more information to comment on potential causes of your uncle's cancer. However, inhaling compounds such as arsenic, cadmium, and lead are known to increase risk of lung cancer. Occupational activities such as mining would have greatly increased exposures compared to residential or recreational exposures.

  9. I have breathing problems, but the mountain area and my cabin situated a mile high - and the pristine water and air - certainly agree with me.
  10. ATSDR Response: As you imply, risk from contaminants is just one factor in the health of people in the area. We support the cleanup of the site as a step towards our goal of improving public health.

  11. [Concern expressed for] children in the Tenmile area that have always played in the stream before the EPA assessment.
  12. ATSDR Response: Based on our calculations discussed in the surface water recreational pathway and stream sediments pathway sections of the document, the contaminants in the stream water and sediments are not likely to lead to health effects in children or adults.

  13. EPA has certainly put a lot of effort into cleanup of the area. It will be so much better for the community.
  14. ATSDR Response: We agree that the proactive and efficient cleanup of the site will improve the quality of life in the area.

  15. I would like to see more site specific data and biomonitoring done and then evaluation of that information.
  16. ATSDR Response: This public health assessment is based on the data available at this time. We are willing to review and comment on public health significance of new data as it comes available, upon request of the community, EPA, or local health officials. Please contact the authors of this report if you wish to make a request.

  17. The report is not specific enough.
  18. ATSDR Response: Because we attempt to determine the overall public health impact of releases of hazardous materials, our public health assessments are generally written in a qualitative manner. We are willing, upon request, to answer specific questions in a public health consultation.


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.

Additive Effect:
A response to a chemical mixture, or combination of substances, that might be expected if the known effects of individual chemicals, seen at specific doses, were added together.

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

Antagonistic Effect:
A response to a mixture of chemicals or combination of substances that is less than might be expected if the known effects of individual chemicals, seen at specific doses, were added together.

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.

See Relative Bioavailability

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

See Community Assistance Panel.

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.

Community Assistance Panel (CAP):
A group of people from the community and health and environmental agencies who work together on issues and problems at hazardous waste sites.

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. This act created ATSDR and gave it the responsiblity to look into 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 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.

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:
  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).

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). Some exampes include: the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, 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 Responsible Party. A company, government or person that is responsible for causing the pollution at a hazardous waste site. PRP's are expected to help pay for the clean up of a site.

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.

Relative Bioavailability:
The amount of a compound that can be absorbed from a particular medium (such as soil) compared to the amount absorbed from a reference material (such as water). Expressed in percentage form.

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 resulting from chemical exposures at hazardous waste sites.

Sample Size:
The number of people that are needed for a health study.

A small number of people chosen from a larger population (See Population).

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.

A branch of the math process of collecting, looking at, and summarizing data or information.

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.

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.

1. U.S. Environmental Protection Agency (EPA), Office of Emergency and Remedial Response. Risk Assessment Guidance for Superfund, Volume 1, Human Health Evaluation Manual. December 1989.

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

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #