PUBLIC HEALTH ASSESSMENT
CALLAHAN MINING CORPORATION
BROOKSVILLE (CAPE ROSIER), HANCOCK COUNTY, MAINE
APPENDIX A: EXPLANATION OF EVALUATION PROCESS
In evaluating these data, ATSDR used comparison values (CVs) to determine which chemicals to examine more closely. CVs are the contaminant concentrations found in a specific media (air, soil, or water) and are used to select contaminants for further evaluation. CVs incorporate assumptions of daily exposure to the chemical and a standard amount of air, water, and soil that someone might inhale or ingest each day.
As health-based thresholds, CVs are set at a concentration below which no known or anticipated adverse human health effects are expected to occur. Different CVs are developed for cancer and noncancer health effects. Noncancer levels are based on valid toxicologic studies for a chemical, with appropriate safety factors included, and the assumption that small children (22 pounds) and adults are exposed every day. Cancer levels are based on a one-in-a -million excess cancer risk for an adult eating contaminated soil or drinking contaminated water every day for 70 years. For chemicals for which both cancer and noncancer levels exist, we use the lower level to be protective. Exceeding a CV does not mean that health effects will occur, just that more evaluation is needed.
CVs used in this document are listed below:
Environmental Media Evaluation Guides (EMEGs) are estimated contaminant concentrations in a media where noncarcinogenic health effects are unlikely. EMEGs are derived from the Agency for Toxic Substances and Disease Registry's (ATSDR) minimal risk level (MRL).
Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrations that would be expected to cause no more than one additional excess cancer in one million persons exposed over a lifetime. CREGs are calculated from the U.S. Environmental Protection Agency's (EPA) cancer slope factors (CSFs).
Reference Media Evaluation Guides (RMEGs) are estimated contaminant concentrations in a media where noncarcinogenic health effects are unlikely. RMEGs are derived from EPA's reference dose (RfD).
Preliminary Remediation Goals (PRGs) are the estimated contaminant concentrations in a media where carcinogenic or noncarcinogenic health effects are unlikely. The PRGs used in this public health assessment were derived using provisional reference doses or CSFs calculated by EPA's Region 9 toxicologists.
Risk-Based Concentrations (RBCs) are the estimated contaminant concentrations at which carcinogenic and noncarcinogenic health effects are not expected to occur as a result of exposure. The RBCs used in this public health assessment were derived using provisional reference doses or CSFs calculated by EPA's Region 3 toxicologists.
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.
Determination of Exposure Pathways
ATSDR identifies human exposure pathways by examining environmental and human components that might lead to contact with COCs. A pathway analysis considers five principal elements: a source of contamination, transport through an environmental medium, a point of exposure, a route of human exposure, and an exposed population. Completed exposure pathways are those for which the five elements are evident, and indicate that exposure to a contaminant has occurred in the past, is now occurring, or will occur in the future. Potential exposure pathways are those for which exposure seems possible, but one or more of the elements is not clearly defined. Potential pathways indicate that exposure to a contaminant could have occurred in the past, could be occurring now, or could occur in the future. It should be noted that the identification of an exposure pathway does not imply that health effects will occur. Exposures might be, or might not be, substantive. Therefore, even if exposure has occurred, is now occurring, or is likely to occur in the future, human health effects might not result.
ATSDR reviewed site history, information on site activities, and the available sampling data. On the basis of this review, ATSDR identified numerous exposure pathways that warranted consideration. Additional information regarding the completed and potential exposure pathways identified for the Callahan Mining Corporation site is provided in Appendix B of this public health assessment. Summaries of these pathways are discussed below.
Evaluation of Public Health Implications
The next step is to take those contaminants present at levels above the CVs and further identify which chemicals and exposure situations are likely to be a health hazard. Child and adult exposure doses are calculated for the site-specific exposure scenario, using our assumptions of who goes on the site and how often they contact the site contaminants. The exposure dose is the amount of a contaminant that gets into a person's body. Following is a brief explanation of how we calculated the estimated exposure doses for the site.
Soil, Tailings, and Waste Rock Contaminant Ingestion
Exposure doses for ingestion of contaminants present in soil from the source areas were calculated using the average concentration measured in the source areas, in milligrams per kilogram (mg/kg), or parts per million (ppm), multiplied by the soil ingestion rate for adults (100 mg/day) or children (200 mg/day).
The multiplication product was divided by the average weight for an adult, 70 kg (154 pounds) or a 10-year old child, 36.3 kg (80 pounds). The resulting dose was then multiplied by a factor of 104/365, because the exposure was assumed to occur on average of twice per week throughout the year.
Soil, Tailings, and Waste Rock Contaminant Inhalation of Fugitive Dust
For exposure to contaminants in source soil via inhalation of fugitive dust from source area soil, the average detected soil concentrations was multiplied by an inhalation rate and an exposure time of 2 hours per day. An inhalation rate of 2.3 cubic meters per hour (m3/hour) for adults and 1.74 m3/hour for children was assumed, based on moderate activity. The multiplication product was divided by the average weight for an adult, 70 kg (154 pounds) or a 10-year old child, 36.3 kg (80 pounds). The resulting dose was then multiplied by a factor of 104/365, because the exposure was assumed to occur on average of twice per week throughout the year, as in the soil ingestion calculation.
Exposure doses for surface water ingestion were calculated using the average concentration for a surface water contaminant, in milligrams per liter (mg/L), multiplied by an incidental surface water ingestion rate of 0.02 liter/day for adults or 0.01 liter/day for children. These ingestion rates are 1/100th of the EPA default drinking water rates. The multiplication product was divided by the average weight for an adult (70 kg or 154 pounds), or for a 1-year old child (10 kg or 22 pounds). The resulting dose was then multiplied by a factor of 60/365, because the exposure was assumed to occur 5 days per week during 3 summer months of the year.
Exposure doses for ingestion of contaminants from the sediment were calculated using the average concentration measured in the sediment, in mg/kg or ppm, multiplied by 1/10th of the soil ingestion rate, 10 mg/day for adults or 20 mg/day for children. The multiplication product was divided by the average weight for an adult (70 kg or 154 pounds) or a 10-year-old child (36.3 kg or 80 pounds). The resulting dose was then multiplied by a factor of 60/365, because the exposure was assumed to occur 5 days per week during 3 summer months of the year.
In this public health assessment, we evaluated dermal exposure to source area soil, surface water, and sediment. Dermal absorption depends on numerous factors including the area of exposed skin, anatomic location of exposed skin, length of contact, concentration of chemical on skin, chemical-specific permeability, soil adherence, medium in which the chemical is applied, and skin condition and integrity. Because chemicals differ greatly in their potential to be absorbed through the skin, each chemical needs to be evaluated separately and is discussed as needed in the main body of the public health assessment. The assumed receptor body weights, exposure frequency, and exposure duration are the same as described in the above calculations of the ingestion route. The skin surface area and soil-to-skin adherence factors used in this public health assessment were taken from EPA's Exposure Factor Handbook.1 Absorption factors and other chemical-specific factors were taken from the ATSDR Toxicological Profile for each specific chemical.
Ingestion of Biota (Mussels) from Goose Cove
Exposure doses for ingestion of mussels from Goose Cove were calculated using the maximum detected concentration measured in mussel samples, in mg/kg or ppm, multiplied by average ingestion rates of 11.0 grams per day (g/day) and 5.6 g/day for adults and children, respectively. The calculated value was also multiplied by a conversion factor of 0.001 kilograms per gram. The multiplication product was divided by the average weight for an adult (70 kg or 154 pounds) or a child less than two years of age (16 kg or 35 pounds).
The calculated exposure doses are then compared to an appropriate health guideline for that chemical. Health guideline values are considered safe doses; that is, health effects are unlikely below this level. The health guideline value is based on valid toxicological studies for a chemical, with appropriate safety factors built-in to account for human variation, animal-to-human differences, and/or the use of the lowest adverse effect level. For noncancer health effects, the following health guideline values are used.
Minimal Risk Level (MRLs) - Developed by ATSDR
An MRL is 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. A list of MRLs can be found at http://www.atsdr.cdc.gov/mrls.html.
Reference Dose (RfD) - Developed by EPA
An RfD is an estimate, with safety factors built in, of the daily, life-time
exposure of human populations to a possible hazard that is not likely to cause
noncancerous health effects. RfDs can be found at http://www.epa.gov/iris 
.
If the estimated exposure dose for a chemical is less than the health guideline value, then the exposure is unlikely to cause a noncarcinogenic health effect in that specific situation. If the exposure dose for a chemical is greater than the health guideline, then the exposure dose is compared to known toxicologic values for that chemical and is discussed in more detail in the public health assessment (see Discussion section). These toxicologic values are doses derived from human and animal studies that are summarized in the ATSDR Toxicological Profiles. A direct comparison of site-specific exposure and doses to study-derived exposures and doses that cause adverse health effects is the basis for deciding whether health effects are likely or not.
Calculation of Risk of Carcinogenic Effects
The estimated risk of developing cancer resulting from exposure to the contaminants
was calculated by multiplying the site-specific adult exposure dose by EPA's
corresponding CSF (which can be found at http://www.epa.gov/iris
). The results estimate the
maximum increase in risk of developing cancer after 70 years of exposure to
the contaminant.
The actual risk of cancer is probably lower than the calculated number, which gives a worst-case excess cancer risk. The method used to calculate EPA's CSF assumes that high-dose animal data can be used to estimate the risk for low dose exposures in humans. The method also assumes that no safe level exists for exposure. Little experimental evidence exists to confirm or refute those two assumptions. Lastly, the method computes the 95% 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
Because of uncertainties involved in estimating carcinogenic risk, ATSDR employs a weight-of-evidence approach in evaluating all relevant data.3 Therefore, the carcinogenic risk is described in words (qualitatively) rather than giving a numerical risk estimate only. The numerical risk estimate must be considered in the context of the variables and assumptions involved in their derivation and in the broader context of biomedical opinion, host factors, and actual exposure conditions. The actual parameters of environmental exposures must be given careful consideration in evaluating the assumptions and variables relating to both toxicity and exposure.
APPENDIX B: EXPOSURE PATHWAYS FOR CALLAHAN MINING CORPORATION SITE
| PATHWAY NAME | ENVIRONMENTAL MEDIA & TRANSPORT MECHANISMS | POINT OF EXPOSURE | ROUTE OF EXPOSURE | EXPOSURE POPULATION | TIME | NOTES | COMPLETE? |
| Soil | Erosion of waste to surface soils; redeposition of fugitive dust | Site soils, residences nearby | Incidental ingestion, inhalation, dermal exposure | Nearby residents, fishers and shellfish collectors, trespassing teenagers and adults | Past, present, future | Population might include children 10 years and older. | Y |
| Waste rock and tailings | Waste rock and tailings piles on site; erosion dispersed | Waste piles on site | Incidental ingestion, inhalation, dermal exposure | Site workers, trespassing teenagers and adults | Past, present, future | Population might include children 10 years and older. | Y |
| Surface water | Surface water runoff over wastes to bay; dissolution from underwater mine pit | Water in Goose Pond and Goose Cove | Incidental ingestion, inhalation, dermal exposure | Fishers and shellfish collectors, recreational users of bay (children and adults) | Past, present, future | Population might include young children. | Y |
| Sediments | Deposition from surface water runoff into bay; underwater tailings | Along shoreline in Goose Pond | Incidental ingestion, dermal exposure | Fishers and shellfish collectors, recreational users of bay (children and adults) | Past, present, future | Population might include young children. | Y |
| Biota | Bioaccumulation of contaminants from surface water and sediments into shellfish and fish | Meal prepared using fish or shellfish from site | Ingestion | Fishers and shellfish collectors and their families; purchasers of local seafood | Past, present, future | Population might include young children | Y |
| Well water | Infiltration to groundwater | Groundwater wells supplying drinking water taps | Ingestion, inhalation, dermal exposure | Residents and workers near the site | Past, present, future | Population might include young children | N |
| Air | Volatilization of contaminants; fugitive dust | Groundwater wells supplying drinking water taps | Inhalation, dermal exposure | Residents and workers near the site | Past, present, future | Population might include young children | N |
APPENDIX C: ATSDR PLAIN LANGUAGE GLOSSARY OF ENVIRONMENTAL HEALTH TERMS
ATSDR defines an exposure pathway as having 5 parts:
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.
