PUBLIC HEALTH ASSESSMENT
WEST SITE/HOWS CORNER ENVIRONMENTAL A. Contamination
PLYMOUTH, PENOBSCOT COUNTY, MAINE
Introduction
In order to determine what environmental contaminants may be a concern, ATSDR has evaluated all of the environmental data for the Hows Corner site made available to it. Environmental data was taken from references 3 - 7. ATSDR selects and discusses contaminants using the following information:
ATSDR uses screening values -- contaminant concentrations in specific media that are
considered protective of public health -- to select contaminants for further evaluation. ATSDR
and other agencies have developed the screening values to provide guidelines for estimating
contaminant concentrations in media at which adverse health effects are not expected to occur A standard daily ingestion rate and body weight are assumed in deriving these values. The
following screening values may be used in this section:
| Action Level | Action Levels are derived by the EPA for use in evaluating drinking
water. These levels are concentrations in water at or below which daily
human exposure is unlikely to result in adverse noncancerous effects. |
| CREG | Cancer Risk Evaluation Guide: Derived by ATSDR from the EPA
cancer slope factor. It represents a concentration in water, soil, or air at
or below which excess cancer risk is not likely to exceed one case of
cancer in a million persons exposed over a lifetime. |
| EMEG | Environmental Media Evaluation Guide: Derived by ATSDR from
ATSDR's minimal risk level (MRL). It is the concentration in water,
soil, or air at or below which daily human exposure is unlikely to result
in adverse noncancerous effects |
| RMEG | Environmental Reference Dose Evaluation Guide: Derived by ATSDR
from the EPA oral reference dose. It is the concentration in water or
soil at or below which daily human exposure is unlikely to result in
adverse noncancerous effects. |
| LTHA | Lifetime Health Advisory: Derived by EPA. It is a drinking water
concentration at or below which adverse, noncancerous adverse health
effects would not be expected. |
| CLHA | Child Longer-Term Health Advisory: Derived by EPA. It is a drinking
water concentration at or below which adverse, noncancerous adverse
health effects would not be expected in children after exposure up to 7
years in duration. |
| MCL | Maximum Contaminant Level: Enforceable drinking water regulation
established by EPA that is protective of human health to the "extent
feasible" over a lifetime. MCLs take into account technological and
economic feasibility. |
| MCLG | Maximum Contaminant Level Goal: Non-enforceable drinking water health goal recommended by EPA and set at a level at or below which no known or anticipated adverse human health effects are expected. |
EMEGs and CREGs are the first choice for screening value. In addition, any contaminants will be contaminants of concern if they have no CREG, but have been designated as carcinogens or potential carcinogens by 1) the National Toxicology Program in the Department of Health and Human Services, 2) the US EPA, or 3) the International Agency for Research on Cancer. If a contaminant is not a carcinogen, and has no EMEG, then the following values (in order of preference) will be chosen for the screening value if available: the RMEG, the LTHA or CLHA (whichever is lower), the MCLG, the MCL, or the Action Level.
In the data tables that follow under both On-Site and Off-Site Contamination, the presence of a listed contaminant does not necessarily indicate that it will cause adverse health effects. Instead, the list indicates contaminants that will be evaluated further in this public health assessment.
Surface Soils
There have been three limited studies made on surface soils on the site. The first two studies were made for the Maine Department of Environmental Protection (DEP) by its contractor, Weston Geophysical Corporation. These studies were made in May and November, 1988 (3-4). The third study (7) was done in June, 1990 for the U.S. Environmental Protection Agency (EPA).
Surface soils on the Hows Corner site have generally been contaminated with chlorinated hydrocarbons and PCBs. The maximum concentration for those contaminants which are of concern is listed in Table 1. These contaminants are from the waste oils and solvents which were spilled onto the ground. They may have become contaminated as early as 1960, when the waste oil storage and transfer facility began operating. In 1991, the contaminated soils on the site were removed and remediated to cleanup levels. Soils which were left at the site could be contaminated by as much as 10 parts per million (ppm), the clean-up level, of PCBs, tetrachloroethylene, or total chlorobenzenes(2). One area in particular was contaminated with PCBs. This area was distinguished by a stand of dead cedar trees. Surface soils were removed by the EPA in 1990 and 1991.
ATSDR defines surface soils as the top three inches of soil. It is not clear from the previously mentioned studies, the depth of the soil sampling which was reported to be surface soil. However, ATSDR will assume that these samples are representative of the top three inches of soil.
| Table 1: Contaminants of Concern in Surface Soils | |||
| Contaminant | Maximum
Concentration (mg/kg) |
Date | Screening Value (mg/kg) |
| PCBs | 890 | 11/88 (4) |
0.09(CREG) |
| Tetrachloroethene | 65 | 6/90 [EPA, 1990] | 10 (CREG) |
| Trichlorobenzenes | 540 | 5/88 (3) |
500 (RMEG for 1,2,4-trichlorobenzene) |
| Tetrachlorobenzenes | 345 | 5/88 (3) |
10 (RMEG for 1,2,4,5-tetrachlorobenzene) |
| Pentachlorobenzene | 58.6 | 5/88 (3) |
40 (RMEG) |
Groundwater
On-site groundwater was studied by installing several monitoring wells(3) in the area. Water from
these wells was periodically sampled and analyzed for the Maine DEP beginning in August,
1988. Results from these analyses are summarized in Table 2. They indicate that the on-site groundwater is contaminated with several substances, including hydrocarbons, chlorinated hydrocarbons, lead, and PCBs. These substances were in the waste oils and solvents which were spilled onto the ground, and then moved through the soil and into the groundwater. PCBs are not very soluble or mobile in groundwater, and so it is unusual to find groundwater contaminated with PCBs. The PCBs which were seen in groundwater at this site were found in only one well cluster in the area most heavily contaminated by PCBs.
| Table 2: Contaminants of Concern in Groundwater from On-Site Monitoring Wells | |||
| Contaminant | Maximum Concentration (µg/L) |
Date |
Screening Value (µg/L) |
| n-Butyl benzene | 1.7 | 11/93 (7) | none |
| 1,4-Dichlorobenzene | 5 | 11/93 (7) | carcinogen |
| 1,1-Dichloroethane | 65 | 11/93 (7) | carcinogen |
| 1,1-Dichloroethene | 92 | 6/90 (7) | 0.06 (CREG) |
| cis 1,3-Dichloropropene | 2.8 | 11/93 (7) | none |
| Isopropyl benzene | 1.4 | 11/93 (7) | none |
| Lead | 90 | 8/89 (4) | 15 (Action Level) |
| PCB (Aroclor-1260) | 840 | 8/89 (4) | 0.005 (CREG) |
| n-Propyl benzene | 3.0 | 11/93 (7) | none |
| p-iso-Propyl toluene | 1 | 11/93 (7) | none |
| Tetrachloroethene | 42,000 | 8/89 (4) | 0.7 (CREG) |
| 1,2,3-Trichlorobenzene | 142 | 11/93 (7) | 40 (LTHA) |
| 1,2,4-Trichlorobenzene | 390 | 8/89 (4) | 100 (RMEG) |
| 1,1,1-Trichloroethane | 4,500 | 8/89 (4) | 200 (LTHA) |
| Trichloroethene | 190 | 11/93 (7) | 0.3 (CREG) |
| 1,2,4-Trimethyl benzene | 15.4 | 11/93 (7) | none |
| 1,3,5-Trimethyl benzene | 6 | 11/93 (7) | none |
Groundwater
Monitoring Wells
Off-site groundwater has been contaminated by many of the contaminants found in on-site
groundwater. Monitoring wells were installed in several locations surrounding the Hows Corner
site, and periodically sampled and analyzed beginning in August, 1988. Analyses of the water
from these wells indicate that the groundwater contamination extends to the northeast, southwest, and east of the site. This pattern may have occurred because of the presence of residential wells in these directions, which could have pulled the contaminated groundwater toward them as they pumped water. Table 3 summarizes maximum concentrations of the contaminants of concern found in the off-site monitoring wells. These contaminants include chlorinated hydrocarbons. In addition, they incude arsenic and chromium, which were not contaminants of concern in on-site groundwater.
| Table 3: Contaminants of Concern in Groundwater from Off-Site Monitoring Wells | |||
| Contaminant | Maximum
Concentration (µg/L) |
Date of Maximum Concentration | Screening Value (µg/L) |
| Arsenic | 30 | 8/89 | 0.02 (CREG) |
| Chromium | 150 | 8/89 | 100 (LTHA) |
| 1,4-Dichlorobenzene | 2 | 10/92 | carcinogen |
| 1,1-Dichloroethane | 1.65 | 10/92 | carcinogen |
| 1,1-Dichloroethene | 29 | 11/92 | 0.06 (CREG) |
| Tetrachloroethene | 3,300 | 11/92 | 0.7 (CREG) |
| 1,1,1-Trichloroethane | 480 | 11/92 | 200 (LTHA) |
| Trichloroethene | 63 | 11/92 | 0.3 (CREG) |
Several residential wells have become affected by contamination from the Hows Corner site.
Nine wells were initially identified in 1987 and 1988 as being contaminated. Contaminants in
these wells included several chlorinated hydrocarbons. Contamination of a tenth well containing petroleum hydrocarbons was considered to be from a separate source.
Table 4 summarizes the range of contaminant concentrations to which residents were exposed until the Maine DEP supplied them with bottled water and placed their wells on a filtration system.
| Table 4: Contaminants of Concern in Groundwater from Contaminated Residential Wells Prior to the Placement of a Filtration System(4). | ||
| Contaminant | Concentration Range (µg/L) | Screening Value (µg/L) |
| 1,1-Dichloroethene | 6 - 11 | 0.06 (CREG) |
| 1,2-Dichloroethene | 5.1 - 66 | 30 (CLHA) |
| Tetrachloroethene | ND - 2,500 | 0.7 (CREG) |
| 1,1,1-Trichloroethane | 9.5 - 280 | 200 (LTHA) |
| Trichloroethene | 6 - 36 | 3 (CREG) |
Data Gaps
In a telephone conversation with Terry Connelly 8, a U.S. EPA Remedial Project Manager, ATSDR was made aware that recent groundwater sampling events indicate that contaminated groundwater is migrating further off of the site. ATSDR has requested to review recent sampling data and any other data which may be appropriate to make a more thorough evaluation of the Hows Corner site's public health impact.
B. Exposure
Introduction
In this section of the document, the possible environmental exposure pathways are evaluated to help determine whether individuals have been, are being, or will be exposed to site-related contaminants. The pathways analysis consists of five elements:
An environmental exposure pathway is considered complete when there is good evidence that all five elements exists9. The presence of a completed pathway indicates that human exposure to contaminants has occurred in the past, is occurring, or will occur in the future. When one or more of the five elements are missing, that pathway is considered potential. The presence of a potential pathway indicates that human exposure to contaminants could have occurred, could be occurring, or could occur in the future. An exposure pathway can be eliminated from consideration if at lease one of the five elements is missing and will never be present. If there is uncertainty about the site-relatedness of the contaminants of concern in an exposure pathway, the pathway will be evaluated as if the contaminants are site-related. The discussion that follows incorporates only those pathways that are important and relevant to the site.
The major contaminants at this site are chlorinated hydrocarbons and polychlorinated biphenyls (PCBs). These contaminants came from the waste oils and solvents which were stored on-site. They have been found in both soils and groundwater.
Exposures Which Are Known to Have Occurred
Surface Soil
During the period from 1960 until the site ended operations in 1980, the site was used by workers. During the entire period from 1960 until the soils were removed in 1991, the site was accessible to the community. Workers and others who may have come onto the site were exposed to these contaminated soils by either inhaling and then ingesting wind-borne soils and dusts(5), or by getting the soil on their hands, and then eating, drinking or smoking. Workers were also likely exposed via inhalation during material handling, from volatilization of spilled material, as well as inhaling and then ingesting soil and dust. The number of people who may have been exposed to the contaminated surface soils is not known, although it is not expected to be large. An estimate is that fewer than 90 people may have been exposed to contaminated on-site soils; 30 people or fewer who may have worked at the site, and 60 people or fewer who may have ventured onto the site for other reasons.
Groundwater
The groundwater contamination extends to the northeast, southwest, and east of the site (figure 2). This pattern may have occurred because of the presence of residential wells in these directions, which could pull the contaminated groundwater toward them as they pumped water.
Several residential wells have become contaminated from the Hows Corner site. Nine wells were initially identified in 1987 and 1988 as being contaminated. Contaminants in these wells
included several chlorinated hydrocarbons. Contamination of a tenth well containing petroleum
hydrocarbons was considered to be from a separate source. Residents who used water from these
nine affected wells became exposed to contaminants in the water by drinking it, bathing in it, and using it for other household needs. The contaminants could have entered their bodies through ingestion (drinking the contaminated water), by being absorbed through the skin, and by being inhaled either in air-borne water droplets or as an evaporated gas. It is not known how long these residents may have been exposed to contaminated groundwater, but a conservative estimate is that exposure began in 1970(6), and ended in 1988 when the Maine DEP provided these residents with bottled drinking water and maintained carbon filtration systems for their wells. The filtration systems were maintained by the Maine DEP, and removed virtually all of the contamination that was found in the water. In 1988, approximately 50 people were affected by
contaminated residential wells(7).
Figure 2: Approximate area of affected groundwater at West Site/Hows Corner.
Exposures Which Are Potential
Surface Water
Several ponds are to the north and downhill of the site, including Plymouth Pond. These ponds are fed in part by springs flowing from the hillside below the site. Some of these springs may contain contaminants from the contaminated groundwater. However, the majority of the groundwater contaminants are volatile substances which evaporate fairly quickly upon exposure to the air. For this reason, most of the contaminants in the groundwater should not affect the ponds. These ponds have not been sampled for contamination.
A few of the contaminants which were found in the contaminated groundwater at this site are not volatile, and so could possibly affect the ponds. These substances include PCBs and a few metals. However, these substances are not expected to pose a problem in the ponds, since the PCBs were found in groundwater in only one on-site area which has subsequently been cleaned-up, and since the metals were found in only a few of the groundwater samples.
Air
The chlorinated hydrocarbons which are present in the contaminated groundwater can readily
volatilize, or evaporate into the air. This can even occur under the ground, so that soil gases may be generated which are contaminated. These soil gases can then slowly mix with the ambient air and contaminate it. The air may also be affected by contaminants evaporating from springs. The concentrations of the contaminants in the air resulting from these processes should be relatively small.
C. Quality
In preparing this Health Assessment, ATSDR relies on the information provided in the
referenced documents. The Agency assumes that adequate quality assurance and quality control
measures were followed with regard to chain-of-custody, laboratory procedures, and data
reporting. The validity of the analysis and conclusions drawn for this health assessment is
determined by the reliability of the referenced information.
D. Physical
Physical hazards were not apparent at the site.
E. Toxic
The EPA maintains the Toxic Release Inventory (TRI), a database of over 320 different toxic
substances released from facilities into the environment. TRI was searched for information about releases that may have occurred from other facilities in the area surrounding the Hows Corner site. No other releases were listed.
PUBLIC A. Toxicological
Introduction
The contaminants of concern released into the environment at the West Site/Hows Corner site have the potential to cause adverse health effects. However, for adverse health effects to occur, people must have been exposed to it. A release does not always result in exposure. A person can only be exposed to a contaminant if they come into contact with the contaminant. Health effects resulting from the interaction of an individual with a hazardous substance in the environment depend on several factors. One is the route of exposure: that is, whether the chemical is breathed, consumed with food, soil, or water, or whether it contacts the skin. Another factor is the dose to which a person is exposed, and the amount of the exposure dose that is actually absorbed. Mechanisms by which chemicals are altered in the environment or inside the body, as well as the combination (types) of chemicals are also important. Once exposure occurs, characteristics such as age, sex, nutritional status, genetics, life style, and health status of the exposed individual influence how the contaminants are absorbed, distributed, metabolized, and excreted. Together, those factors and characteristics determine the health effects that may occur as a result of exposure to a contaminant. Much variation in those mechanisms exists among individuals (9).
Health Guidelines
Health guidelines provide a basis for comparing estimated exposures with concentrations of contaminants in different environmental media (soil, air, water, and food) to which people might be exposed.
Non-Cancer Health Effects
ATSDR has developed a Minimal Risk Level (MRL) for contaminants commonly found at hazardous waste sites. The MRL is an estimate of daily exposure to a contaminant below which non-cancer, adverse health effects are unlikely to occur. MRLs are developed for different routes of exposure, like inhalation and ingestion, and for different lengths of exposure, such as acute (less than 14 days), intermediate (15 - 364 days), and chronic (365 days or greater). Oral MRLs are expressed in units of milligrams of contaminant per kilogram of body weight per day (mg/kg/day). MRLs are not derived for dermal exposure. The method for deriving MRLs does not include information about cancer, therefore, an MRL does not imply anything about the presence, absence, or level of cancer risk. If an ATSDR MRL is not available as a health value, then EPA's Reference Dose (RfD) is used. The RfD is an estimate of daily human exposure to a contaminant for a lifetime below which (non-cancer) health effects are unlikely to occur (9).
Cancer Health Effects
The Environmental Protection Agency (EPA) classifies chemicals as Class A, Class B, Class C, Class D, or Class E. This classification defines a specific chemical's ability to cause cancer in humans and animals. According to EPA, Class A chemicals are known human carcinogens, and Class B chemicals are probable human carcinogens. Class B is further subdivided into two groups: Group B1 consists of chemicals for which there is limited evidence of carcinogenicity from epidemiologic studies in humans; and Group B2 consists of chemicals for which there is sufficient evidence of carcinogenicity in animals, but inadequate evidence or no data available from epidemiologic studies in humans. Group C chemicals are possible human carcinogens. Group D chemicals are not classifiable as to human carcinogenicity and Group E chemicals are those for which there is evidence that they are not carcinogenic to humans. For carcinogenic substances, EPA has established the Cancer Slope Factor (CSF) as a guideline. The CSF is used to determine the number of excess cancers resulting from exposure to a contaminant. The National Toxicology Program in its Annual Report on Carcinogens classifies a chemical as a "known human carcinogen" based on sufficient human data. Its classification of a chemical as being "reasonably anticipated to be a carcinogen" (RAC) is based on limited human or sufficient animal data. ATSDR considers the above physical and biological characteristics when developing health guidelines.
Exposure Dose Estimation
To link the site's potential for human exposure with health effects that may occur under site-specific conditions, ATSDR estimates human exposure to the site contaminant from ingestion and/or inhalation of different environmental media (9). The following relationship is used to determine the estimated exposure dose for each site contaminant:
ED = (C x IR x EF) / BW
where:
ED = exposure dose (mg/kg/day)
C = contaminant concentration
IR = intake rate
EF = exposure factor
BW = body weight
Standard body weights for adults, young children, and toddlers are 70 kilograms (kg), 16 kg, and 10 kg, respectively. These weights are approximately 154 pounds (lbs), 35 lbs, and 22 lbs, respectively. The maximum contaminant concentration detected at a site for a specific medium is used to determine the estimated exposure. Use of the maximum concentration will result in the most protective evaluation for human health. For soil, the ingestion rates used are 100 milligrams per day (mg/day) for adults and 200 mg/day for young children. Children exhibiting pica behavior were not evaluated because the contaminated soil is on-site, and it is unlikely that a small child (aged 1 to 3 years old) may venture onto the site and ingest 5000 mg/day of contaminated soil. For water, the ingestion rates used are 2 liters/day for adults and 1 liter/day for school-aged children and toddlers. Some exposures are intermittent or irregularly timed. For those exposures, an exposure factor (EF) is calculated which averages the dose over the exposure period. When unknown, the biological absorption from the environmental medium (soil, water)is assumed to be 100%.
How Risk Estimates are Made
Non-Cancer Risks
For non-carcinogenic health risks, the contaminant intake was estimated using exposure assumptions for the site conditions. This dose was then compared to a risk reference dose (estimated daily intake of a chemical that is likely to be without an appreciable risk of health effects) developed by ATSDR or EPA.
Non-carcinogenic effects, unlike carcinogenic effects, are believed to have a threshold, that is, a dose below which adverse effects will not occur. As a result, the current practice is to identify, usually from animal toxicology experiments, a no-observed-adverse-effect-level (NOAEL), This is the experimental exposure level in animals at which no adverse toxic effect is observed. The NOAEL is then divided by an uncertainty factor (UF) to yield a risk reference dose. The UF is a number which reflects the degree of uncertainty that exists when experimental animal data are extrapolated to the general human population. The magnitude of the UF takes into consideration various factors such as sensitive sub-populations (for example, children, pregnant women, and the elderly), extrapolation from animals to humans, and the incompleteness of available data. Thus, exposure doses at or below the risk reference dose are not expected to cause adverse health effects because it is selected to be much lower than dosages that do not cause adverse health effects in laboratory animals.
The measure used to describe the potential for non-cancer health effects to occur in an individual is expressed as a ratio of estimated contaminant intake to the risk reference dose. If exposure to the contaminant exceeds the risk reference dose, there is concern for potential non-cancer health effects. As a rule, the greater the ratio of the estimated contaminant intake to the risk reference dose, the greater the level of concern. A ratio equal to or less than one is generally considered an insignificant (minimal) increase in risk.
Cancer Risks
Cancer risks are estimated by using site-specific information on exposure levels for the contaminant of concern and interpreting them using cancer potency estimates derived for that contaminant by EPA. An increased excess lifetime cancer risk is not a specific estimate of expected cancers. Rather, it is an estimate of the increase in the probability that a person may develop cancer sometime in his or her lifetime following exposure to that contaminant.
There is insufficient knowledge of cancer mechanisms to decide if there exists a level of exposure to a cancer-causing agent below which there is no risk of getting cancer, namely, a threshold level. Therefore, every exposure, no matter how low, to a cancer-causing compound is assumed to be associated with some increased risk. As the dose of a carcinogen decreases, the chance of developing cancer decreases, but each exposure is accompanied by some increased risk.
There is no general consensus within the scientific or regulatory communities on what level of estimated excess cancer risk is acceptable. Some have recommended the use of the relatively conservative excess lifetime cancer risk level of one in one million because of the uncertainties in our scientific knowledge about the mechanism of cancer. Others feel that risks that are lower or higher may be acceptable, depending on scientific, economic and social factors. An increased lifetime cancer risk of one in one million or less is generally considered an insignificant increase in cancer risk.
Sources of Health Guideline Information
ATSDR has prepared toxicological profiles for many substances found at hazardous waste sites. Those documents present data and interpret information on the substances. Health guidelines, such as ATSDR's MRL and EPA's RfD and CSF are included in the toxicological profiles. Those health guidelines are used by ATSDR health professionals in determining the potential for developing adverse non-carcinogenic health effects and/or cancer from exposure to a hazardous substance. Preparers of this public health assessment have reviewed the profiles for the contaminants of concern at the Hows Corner hazardous waste site.
How Risks at the West Site/Hows Corner Site Are Estimated
People who worked or ventured upon the site were possibly exposed to contaminated soil via inhalation, dermal contact, and incidental ingestion. Individuals were most likely exposed to multiple contaminants via inhalation, ingestion, and dermal contact with water from contaminated residential wells. However, data are very limited on the health effects of multiple contaminant exposure. The effects of multiple contaminant exposure can be additive, synergistic (greater than the sum of the single contaminant exposures), or antagonistic (less than the sum of the single contaminant exposures). Also, simultaneous exposure to contaminants that are known or probable human carcinogens could increase the risk of developing cancer. ATSDR's evaluation of exposures in this public health assessment is limited to individual contaminant exposures; multiple exposures have not been evaluated.
ATSDR has identified one exposure which is known to have occurred on-site. Soils on the site were found to be contaminated with polychlorinated biphenyls (PCBs) and chlorinated hydrocarbons.
ATSDR has also identified one known exposure occurring off-site, for people living near the West Site/Hows Corner site and using water from contaminated residential wells. They were likely exposed to several volatile chlorinated hydrocarbons via inhalation, ingestion, and dermal contact with contaminated water from contaminated residential wells.
The exposure doses associated with these two known exposures are estimated from ATSDR's information regarding possible scenarios, based upon what we know about the history of the site. Because of the uncertainty regarding duration of exposures for most populations, ATSDR is using the following worst case scenarios: 1) all exposed individuals were exposed on a daily basis to the contaminated water or soil; 2) the maximum level of contamination in the sampled wells and soil samples was accessible to all exposed individuals; and 3) 100% of the contaminant could be absorbed. It is assumed that the maximum period of exposure was about 30 years for soil and about 20 years for water. This will allow for the greatest protection of public health. Both exposures have occurred in the past. Neither of these exposures is believed to be still occurring, because the contaminated residential wells are no longer used for potable purposes and the contaminated on-site soil has been remediated to cleanup levels.
Contaminants for which the estimated exposure dose exceeded the health guidelines, those which are carcinogenic, or those for which there are no health guidelines will be discussed further. These contaminants are those indicated in the table below.
| Table 5: Results of Comparison of Estimated Exposure Dose to Health Guidelines for Persons Exposed to Contaminated Residential Well Water and/or On-site Soil | ||||
| Contaminant | Health Guideline | Cancer Class | ||
| Value (mg/kg/day) |
Source | Exceeded by Estimated Exposure Dose |
||
| Polychlorinated Biphenyls | 0.00002 | MRL | YES(soil) | B2 |
| Trichlorobenzenes | 0.01 | RfD | NO(soil) | 3 |
| Tetrachlorobenzenes | 0.0003 | RfD | YES(soil) | 3 |
| Pentachlorobenzenes | 0.0008 | RfD | NO(soil) | 3 |
| 1,1-Dichloroethene | 0.009 | MRL | NO(water) | C |
| 1,2-Dichloroethene | 0.02 | RfD | NO(water) | |
| Tetrachloroethene | 0.01 | RfD | YES(water) No(soil) |
B2-C |
| 1,1,1-Trichloroethane | NONE | NO(water) | ||
| Trichloroethene | 0.7 | iMRL | NO(water) | B2-C |
| iMRL = Intermediate Minimal Risk Level Cancer Class 3 = Not Classifiable RfD = Reference Dose | ||||
Polychlorinated biphenyls (PCBs) were detected in on-site soil at a maximum concentration of 890 mg PCBs/kg of soil (mg/kg). Former on-site workers and visitors could have ingested, inhaled, or had dermal contact with the PCBs in the contaminated soil, waste, and materials.
PCBs are a family of synthetic chemicals that contain 209 individual compounds (known as congeners). There are no known natural sources of PCBs in the environment. PCBs are no longer manufactured or used in the U.S. However, PCBs still remain in the environment from previous spills or improper disposal. PCBs have been widely used as coolants and lubricants in transformers, capacitors, and other electrical equipment.
The estimated exposure doses given the above worst case scenario for exposure to contaminated soils exceeded the chronic oral MRL (0.00002 mg/kg/day). The estimated exposure dose for children exposed via incidental ingestion also exceeds the chronic NOAEL (0.007 mg/kg/day). However, the estimated dose is below the chronic lowest observed adverse health effect level (LOAEL) for less serious effects. In Rhesus monkeys, exposure to PCBs at the estimated exposure dose has resulted in elevated and separated toe nails and prominent toe nail beds. Decreased mean platelet volume and decreased IgM and IgG antibody response to sheep red blood cells have also been shown to occur.
Most of the data regarding adverse health effects in humans from exposure to PCBs comes from occupational studies. In general, these studies have limitations, including lack of sufficient information to determine the relative contributions of the inhalation and dermal routes (the most likely exposure routes in an occupational setting), exposure to other substances, and the absence of analysis of contaminants. Although exposure to PCBs by dermal contact has not been evaluated by ATSDR, it is known that contact with soil can result in absorption of PCBs. Health effects such as chloracne, redness, and skin rashes in people dermally exposed to PCBs have been documented in the literature.
EPA classifies PCBs as Class B2 -- a probable human carcinogen by the oral route. That classification was prompted by animal data. In laboratory animals, exposures have resulted in liver cancer, leukemia, lymphomas, and gastrointestinal tract tumors. Studies of humans (workers) have not provided enough information to determine if PCBs are carcinogenic to humans. Based on EPA's cancer potency factor (7.7 mg/kg/day)-1, ATSDR estimates that there would be a moderate increased risk of developing cancer due to exposure every day to PCBs at the maximum concentration found in on-site soils. This assumes that PCBs are as carcinogenic to humans as they are to animals. It should be noted that ATSDR is not sure of the depth to which the soil samples were taken. Unless these samples were taken at the top three inches it is unlikely that people were exposed to the PCBs at the maximum concentration detected.
According to the literature, people with compromised liver function, infectious hepatitis, and persons taking medications potentially toxic to the liver may be especially sensitive to the adverse health effects of PCBs. Because of the physiologic differences in the detoxification and excretion of PCBs, fetuses exposed to PCBs through the placenta can be more sensitive than adults. Breast-fed infants of PCB-exposed mothers can be exposed through breast milk. Children taking the antibiotic novobiocin also may be sensitive to PCBs.
Tetrachlorobenzenes(9)
Tetrachlorobenzenes (TCBs) are combustible materials used as insecticides, electrical insulators, and dielectric fluids. They are commonly found in conjunction with PCBs. Exposures could have occurred to workers and others who came into contact with TCB-oils and insecticides containing TCB (if used for that purpose on-site). TCBs were found in on-site soils at a maximum concentration of 345 mg/kg. The estimated exposure dose for children, based on the above worst case scenario for soil, exceeds EPA's RfD (0.0003 mg/kg/day). The RfD is based upon the development of kidney lesions in animals. ATSDR has not developed a toxicological profile for these substances at this time. The information based upon the literature reviewed about TCB-induced adverse health effects are from studies involving workers producing TCBs (occupational) and laboratory animals. Based upon these studies, TCBs may be harmful if inhaled or absorbed through the skin, vapors may cause dizziness or suffocation, and dermal contact may irritate or burn the skin and eyes. Workers producing 1,2,4,5-TCB have been shown to develop chromosomal aberrations at exposure doses higher than those estimated for this site. Due to the concentration of the contaminant in the on-site soils and the probable duration of exposure it is unlikely that many people, if any, who visited the site would have been adversely impacted by this contaminant.
1,1-Dichloroethene(10)
1,1-Dichloroethene (DCE) is a clear, colorless liquid man-made chemical used to make certain flexible films such as SARAN® wrap, flame-retardant coatings for fiber and carpet backings, and packaging materials. It smells sweet like chloroform, burns quickly, and evaporates quickly at room temperature.
DCE may enter the body via the lungs, stomach, or intestines. Due to its chemical properties, it could possibly enter the body through the skin. Some of the DCE leaves the body through normal respiratory processes. The remaining DCE is broken-down into other products. Most of these products are excreted in the urine within 1-2 days. One of the by-products (dithioglycolic acid) is more harmful to humans than is the DCE.
There is insufficient information available about health effects in humans after breathing DCE. According to the literature, some people who breathed very high concentrations of DCE at work for several years have developed abnormal liver function. People in closed spaces who breathed large amounts of DCE have lost their breath and fainted. Prolonged inhalation of DCE can induce adverse neurological effects and is possibly associated with kidney and liver damage in humans. No adverse non-carcinogenic health effects are expected to occur from inhalation of site-related DCE.
ATSDR has no information on health effects in humans exposed to DCE via incidental ingestion. EPA has established a long-term drinking water health advisory of 7 micrograms per liter (µg/L), below which DCE in water may not cause health effects. DCE was detected in residential wells at a maximum concentration of 11 µg/L. Based upon the previously described worst case scenario for water ingestion, the estimated exposure doses do not exceed ATSDR's MRL for chronic exposure (0.009 mg/kg/day). Therefore, it is believed that adverse non-carcinogenic health effects from ingestion of well water contaminated with DCE at a concentration of 11 µg/L would not occur.
DCE is classified by EPA as a group C chemical agent (a possible human carcinogen) because information about its carcinogenicity is not complete. ATSDR believes that there would be no apparent increased risk of developing cancer from exposure to DCE at a concentration of 11 µg/L in the contaminated residential well water.
Specific information regarding people who may be unusually susceptible to the toxic effects of DCE were not located. Animal studies indicate that individuals taking certain drugs or who have pre-existing liver, kidney, thyroid, or cardiac disease may be at greater risk for DCE-induced toxicity. Some of the suspect drugs are acetaminophen (Tylenol®), phenobarbital, ethanol (including alcoholic beverages), and thyroxine. Persons who are hyperthyroid, are fasting, elderly, or very young are also more susceptible.
Tetrachloroethene(11)
Tetrachloroethene (PCE) is a manufactured chemical that is widely used in the dry cleaning industry. It is also used to remove grease from metals, to make other chemicals, and to make some consumer products. PCE is a nonflammable liquid at room temperature and evaporates easily into the air, producing a sweet, sharp odor.
PCE was detected in on-site soils at a maximum concentration of 65 mg/kg and in residential wells at a maximum concentration of 2,500 µg/L. PCE can enter the body through the ingestion of contaminated drinking water supplies and via inhalation of the chemical which has been released from water. The primary way PCE enters the body is through inhalation of air contaminated with the chemical. The amount of the chemical that enters the body depends on its concentration in the air, how fast and how deeply you breathe, and how long you are exposed to it. PCE can also enter the body through the ingestion of contaminated drinking water, foodstuffs, and the incidental ingestion of soil.
The health effects of breathing air or drinking water that have low levels of PCE are not known. The estimated exposure dose for persons exposed to on-site soil does not exceed the health guideline, therefore, no adverse non-carcinogenic health effects are expected to have occurred due to those exposures.
The estimated dose for residents exposed to water contaminated with PCE via ingestion exceeds EPA's RfD (0.01 mg PCE/kg/day). However, since the estimated exposure dose based on the above worst case scenario is over 1,000 times lower than the oral NOAEL (941 mg/kg/day), adverse non-carcinogenic health effects due to ingestion of the contaminated water are not expected to occur. Neurological disorders such as decreased reaction times and increased dizziness have been seen in persons exposed occupationally to air contaminated with PCE. However, since the maximum concentration found in the contaminated residential wells is below the inhalation NOAEL (21 ppm air concentration by volume), adverse health effects resulting from inhalation of volatilized PCE from the contaminated water are not expected to occur. If PCE is placed directly on the skin, a portion of it can pass through the skin and into the body. Very little PCE in the air can pass through the skin into the body. No studies were found regarding adverse health effects in animals following dermal exposure to PCE.
Although it has not been shown to cause cancer in people, the U.S. Department of Health and Human Services has determined that PCE may reasonably be anticipated to be a carcinogen. Long-term animal studies using high levels of PCE resulted in liver and kidney cancers. Therefore, EPA classifies PCE as Class B2 chemical agent -- a probable human carcinogen. Assuming PCE is carcinogenic to humans, using EPA's cancer potency factor (0.052 mg/kg/day)-1, and the worst case scenario; the resulting estimated exposure dose indicates that there could be a moderate increased risk of cancer from chronic exposure to PCE at a level of 2,500 µg/L in the contaminated residential well water. Carcinogenic effects are not expected to occur due to exposure to on-site contaminated soil.
In one study, PCE was the most common volatile organic chemical found in the blood of individuals reported to be "chemically sensitive". Since no controls were used it is not clear if PCE was more frequently detected in chemically sensitive individuals or if concentrations of PCE in the blood of chemically sensitive individuals were greater than the concentrations of PCE in the blood of the general population. The developing fetus, children, and especially the developing nervous system may be particularly susceptible to the toxic effects of PCE. As high doses of PCE are known to cause liver and kidney effects, persons with clinical or subclinical renal or hepatic disease may be more susceptible to the effects of PCE.
1,1,1-Trichloroethane(12)
1,1,1-Trichloroethane (TCA) is a colorless synthetic chemical. TCA is used in commercial products, mostly to dissolve other chemicals. It is widely used to dissolve grease from manufactured metal parts. In the home, it may be an ingredient in products such as spot cleaners, glues, and aerosol sprays. In the environment, it can be a liquid or a vapor, or exist dissolved in water and other chemicals. TCA has a sweet yet sharp odor. The liquid form of the chemical evaporates quickly and becomes a vapor in air, which is the form in which it is most commonly found in the environment.
TCA was detected in residential wells at a maximum concentration of 280 µg/L. TCA can enter the body via inhalation of air containing the vaporized form of the chemical. Regardless of how much TCA enters the body most of it will quickly leave the body via normal exhalation. The small amount that is not breathed out is converted to metabolites which exit the body in urine and breath within a few days. In general, the route of exposure does not appear to be an important factor.
ATSDR has not developed MRLs and EPA has not developed an RfD for TCA. It is believed that non-carcinogenic adverse health effects from ingestion of TCA at the maximum concentration should not occur because the estimated exposure dose is below the chronic oral NOAEL of 1500 mg/kg/day (based on animal data). Since the concentration of the chemical is below the chronic inhalation NOAEL (150 ppm air concentration/volume) based upon occupational exposure, adverse health effects resulting from breathing in the chemical at the indicated concentration should not occur. Adverse health effects are not expected to occur due to dermal contact based on the high volatility of TCA and the estimated exposure dose. Overall, exposures associated with the Hows Corner hazardous waste site are not likely to have a deleterious effect on the public's health.
The inability to identify associations between human oral exposure and cancer incidence, as well as the limitations of animal studies, limit the assessment of potential carcinogenic effects in humans after oral exposure to TCA. No studies were found regarding carcinogenic effects in humans following inhalation exposure to TCA. No studies were found regarding cancer in humans and animals after dermal exposure to TCA.
Limited data from animal studies indicate that persons who consume alcoholic drinks may be more susceptible to the acute neurobehavioral effects of TCA. Moderate to heavy drinkers may be more susceptible to hepatotoxicity. Available animal studies however, have not demonstrated that ethanol ingestion will potentiate the hepatotoxicity of TCA. People with diabetes in a state of ketosis may be more susceptible to hepatotoxicity from certain chlorinated alkanes including chloroform and 1,1,2-TCA due to a potentiation from increased ketone levels in the body. Available data, however, indicate that ketones do not appreciably potentiate the hepatotoxicity of 1,1,1-TCA. Thus, people with diabetes in a state of ketosis are not likely to be more susceptible to the hepatotoxicity of TCA than the population at large. Because TCA is associated with some cardiovascular effects, persons with compromised heart conditions may be at additional risk when exposed to high levels of TCA and should avoid these high level exposures.
Trichloroethene(13)
Trichloroethene, or trichloroethylene, (TCE) is a man-made chemical used primarily as a solvent to remove grease, or for production of other chemicals. The automotive and metals industries are the main users. It is also found in some household products like typewriter correction fluid, paint removers, adhesives, and spot removers. TCE is a nonflammable, colorless liquid at room temperature with an odor similar to chloroform or ether.
TCE was detected in residential wells at a maximum concentration of 36 µg/L. ATSDR does not have a chronic MRL for TCE. The estimated dose for residents exposed to the contaminated water via ingestion does not exceed ATSDR's MRL for intermediate exposure (0.7 mg/kg/day). The intermediate MRL, for those chemicals that have both an intermediate MRL and a chronic MRL, is always a higher dose than the chronic MRL. Therefore, it is believed that adverse non-carcinogenic health effects from long-term ingestion of well water contaminated with TCE would not occur since the estimated exposure dose is below the ATSDR MRL. No adverse non-carcinogenic health effects are expected to occur from inhalation of TCE since the concentration of the contaminant in the residential wells is below the NOAEL of 100 ppm. Adverse health effects are not expected to have occurred from dermal exposure to TCE at the maximum concentration found in residential wells.
There is inconclusive evidence concerning the carcinogenicity of TCE. An increased incidence of tumors has been observed in some animals experimentally exposed to TCE by ingestion or inhalation. Additional laboratory studies indicated that some mice exposed to TCE via ingestion develop lung cancer. Additional studies in mice suggest that inhalation exposure may result in liver and lung cancer. However, some of the TCE studies use questionable methods and have inconclusive results, making it difficult to conclude that TCE is an animal carcinogen. For these reasons EPA has not yet given TCE a carcinogenicity classification. Based on the above worst case scenario and the resulting estimated exposure dose, there would be no apparent increased risk of cancer from chronic exposure to TCE at a level of 36 µg/L in the contaminated residential well water.
Limited data indicate that people who smoke may be at increased risk of experiencing toxic
effects from exposure to TCE. Also, people who have worked with TCE for long periods of time
may develop increased dermal sensitivity or other allergic responses to the TCE. Because of the
effect on the metabolism of TCE, people who drink alcoholic substances and/or are being treated
with disulfiram may have increased sensitivity. Others shown to be more susceptible include
people with a history of cardiac rhythm disturbances and people with compromised kidney and
liver function.
B. Evaluation
ATSDR conducts a review of appropriate health outcome data when completed exposures have been identified and when the toxicologic evaluation indicates the likelihood of adverse health effects. Health outcome data may also be reviewed to address health concerns which have been voiced by the community.
The evaluation of health outcome data may give a general picture of the health of a community, or it may confirm the presence of excess disease or illness in the community. However, should elevated rates of a particular disease occur, it may not necessarily be caused by hazardous substances in the environment. Other factors, such as personal habits, socioeconomic status, and occupation may also influence the development of disease. In contrast, even if elevated rates of disease are not found, a contaminant may still have caused illness or disease.
The population surrounding the Hows Corner site is relatively small. Because the available
health outcome information is summarized at the county level, this information may not provide
any meaningful information about the population which is potentially affected by contamination
associated with this site. In addition, because of the cessation of site operations, it would be
difficult to identify the affected or potentially affected former site employees.
C. Community
Based upon ATSDR's review of toxicological information for the contaminants of concern at the Hows Corner hazardous waste site, ATSDR has concluded that adverse non-carcinogenic and carcinogenic health effects may be or have been possible.
Based upon animal data, children exposed in the past to polychlorinated biphenyls (PCBs) in the contaminated on-site soil (has since been removed), at the maximum concentration reported, may have experienced adverse health effects such as a decrease in the concentration of platelets in the blood, skin rashes, chloracne, skin irritation, and decreased IgM and IgG antibody response. Based upon occupational case studies, the tetrachlorobenzenes found in on-site soils were capable of causing dizziness, skin irritation, and burning of the eyes and skin if inhaled or dermally absorbed. However, since it is more likely that exposed person would have been exposed on an intermittent basis, adverse non-carcinogenic health effects are not expected to have occurred.
Data from animal studies indicate that exposure to PCBs in contaminated on-site soils, in the past, may have resulted in a moderate increased risk of developing liver cancer, leukemia, lymphomas, and gastrointestinal tract tumors.
It should be noted that in the absence of hospital records and other medical history, it is difficult to determine whether or not any health problems have or will occur in persons exposed to the contaminants associated with the site. In addition, PCB contaminated soil has been remediated to cleanup levels, and households with wells known to be contaminated have been provided with an alternative water source.
Tetrachloroethylene (PCE) was found in residential well water. Residences with contaminated
well water have since been placed on an alternative water source. Assuming that PCE is a
human carcinogen and a person was exposed at the maximum concentration found for a
prolonged period of time, then it may cause a moderate increased risk of developing carcinogenic effects such as liver and kidney tumors.
In the absence of hospital records and other medical history, it is difficult to determine whether or not any health problems have occurred or will occur in persons exposed to the contaminants associated with the site. The manifestation of carcinogenic health effects would also be determined by other factors in addition to exposure. These factors include life style, nutritional status, sex, age, family traits, and state of health.
ATSDR has reviewed health and toxicological information on the contaminants of concern at the West Site/Hows Corners site. Based upon that review, ATSDR has determined that it may be possible for a person exposed to PCE through the ingestion of contaminated residential well water at the maximum concentration reported to have a moderate increased risk of developing cancer (based upon animal test data). However it should be noted that each individual's potential for developing cancer would depend upon how much of the contaminated water they ingested or inhaled, the duration of exposure, the concentration of the PCE in their water supply, and personal health risk factors.
PCBs in on-site soils (prior to removal) were at a concentration high enough, based upon animal
data, to moderately increase the risk of developing cancer. This is provided that the person was
exposed at the maximum concentration daily. Such exposure is unlikely, however, unless the
soil samples were taken from the top three inches of soil. ATSDR is not sure of the depth to
which the soil samples were taken. The contaminated soils have since been remediated to
cleanup levels and are believed to no longer pose a threat.
Elevation of a disease in a population potentially exposed to hazardous substances at a waste site
requires: a source of contamination, a contaminated environmental medium, a point at which a
person may come in contact with the substance in the contaminated medium, a route for the
medium to enter the body (ingestion, inhalation, or dermal absorption), and one or more people
who could become exposed. Provided workers used personal safety equipment properly and
followed proper procedures for removal of hazardous waste they should be at no increased risk of developing cancer.
For those households that have not connected to the Plymouth Water district supply and are in a potentially affected area, it is important to ensure that their residential wells remain uncontaminated. Residents within the area of the Hows Corner site who are still using their well for domestic purposes, and who are concerned about the quality of their water, may contact the Maine Department of Environmental Protection (207-287-2651) for further information about having their well sampled for contamination.
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