PUBLIC HEALTH ASSESSMENT
BASIN MINING AREA
BASIN, JEFFERSON COUNTY, MONTANA
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) 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 contaminated soil 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, just 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 whether 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 4 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 the 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 the US 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 1 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 III.
EPA Action Levels (ALs) are the estimated contaminant concentrations in water at 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.
Exposure doses for soil ingestion were calculated in the following manner. The 95th percentile concentration for soil and mine tailings, in mg/kg (or ppm), was multiplied by the soil ingestion rate for adults, 0.0002 kg/day, or children, 0.0001 kg/day. The multiplication product was 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 daily exposure to soil contaminated at the 95th percentile concentration shown for soil in contamination data tables. If exposure to tailings is less frequent, then an appropriate exposure factor is used to decrease the calculated dose.
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.
Exposure doses for groundwater ingestion were calculated in the following manner. The maximum concentration for a groundwater contaminant, in milligrams per liter (mg/L), was multiplied by the groundwater ingestion rate for adults, 2 liters/day, or children, 1 liter/day. The multiplication product was 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 was compared to accepted health guidelines. Those calculations assume 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.
For incidental ingestion of surface water, the drinking water ingestion rate was decreased by a factor of 100. Exposure was assumed to occur 40 days out of the year.
Carcinogenic risk from ingestion of tailings was calculated through the following procedure. The adult exposure doses for soil ingestion (calculated as described previously) were multiplied by EPA's Cancer Slope Factor for ingestion 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.
Carcinogenic risks from the inhalation of contaminated air were calculated through the following process. The mean air concentration 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.
Carcinogenic risk from groundwater ingestion was calculated through the following procedure. The adult exposure doses for ingestion of groundwater (calculated as described previously) were multiplied 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.
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.(2) The method also assumes that there is no safe level for exposure.(2) There is little experimental evidence to confirm or refute those two assumptions. Lastly, 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.(2)
- 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. 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 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:
- Source of Contamination,
- Environmental Media and Transport Mechanism,
- Point of Exposure,
- Route of Exposure; and,
- Receptor Population.
- 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 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 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
- 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.
- 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.
2. 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.