PUBLIC HEALTH ASSESSMENT
LIMESTONE ROAD SITE
CUMBERLAND, ALLEGANY COUNTY, MARYLAND
ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS
In the public health assessment, MDE and ATSDR will evaluate the public health significance of exposure pathways associated with the contaminants of concern listed in this section. This assessment is based on the general toxic potency of these chemicals, and the potential exposures that individuals at this site may experience. Other factors considered in identifying contaminants of concern are:
Local and national background concentrations are available for some contaminants as a measure of compounds that are regularly found in the natural environment. These values do not represent concentrations that are protective of human health. Rather, they add perspective to the risk posed by site-related contamination.
In the data tables that follow in the On-Site and Off-Site Contamination subsections, the contaminants listed do not necessarily cause adverse health effects at the levels found at or near the site. Instead, the contaminants listed are those which will be evaluated further in the public health assessment.
The observed levels of contaminants are evaluated further if they exceed comparison values. Human exposures to concentrations greater than comparison values may, but do not necessarily, cause adverse health effects. Comparison values for cancer-causing chemicals include Cancer Risk Evaluation Guides (CREGs). A CREG is the contaminant concentration associated with one excess cancer case in a population of 1,000,000 if everyone in the population experiences lifetime exposure to that concentration. CREGs are calculated from USEPA's cancer slope (i.e., potency) factors.
Comparison values for health effects other than cancer include Environmental Media Evaluation Guides (EMEGs), Reference Dose Media Evaluation Guides (RMEGs), Lifetime Drinking Water Health Advisories (LTHA), Maximum Contaminant Levels (MCLs), Maximum Contaminant Level Goals (MCLGs), Proposed Maximum Contaminant Levels (PMCLs), Proposed Maximum Contaminant Level Goals (PMCLGs), World Health Organization values (WHO), and occupational guidelines.
EMEGs are ATSDR estimates of contaminant concentrations in specific media (air, water, soil, surface water, or sediment) below which non-cancer, adverse health effects are unlikely to occur, assuming a given level of exposure to that particular medium.
RMEGs are USEPA estimates of the daily exposure to a contaminant that is unlikely to cause adverse non-cancer health effects. MCLs, MCLGs, PMCLs and PMCLGs were developed by USEPA for drinking water. MCLs are enforceable standards representing contaminant concentrations that USEPA deems protective of public health (considering the availability and economics of water treatment technology) assuming a lifetime (70 years) consumption rate of two liters of water per day. MCLGs are non-enforceable goals more stringent than the MCL standards. MCLGs are life-time exposure levels that USEPA believes will result in no known or anticipated adverse health effect, allowing for an adequate margin of safety. PMCLs and PMCLGs are MCLs and MCLGs, respectively, that are being proposed. The Glossary in Appendix C further defines these comparison values.
To identify facilities that could contribute to the groundwater and surface soil contamination near the Limestone Road site, staff from the Environmental Toxicology and Risk Assessment division of Maryland Department of Environment (MDE) searched the Toxic Chemical Release Inventory (TRI) records for 1987, 1988, and 1989. TRI is developed by USEPA from the chemical release information provided by certain industries in compliance with Section 313 of the Superfund Amendments and Reauthorization Act (SARA). One local company was identified in the TRI as a possible, but highly improbable, source of contaminants detected in areas near the Limestone Road Site. Methylene chloride was reported in the TRI as a contaminant of air emissions from this local facility. Methylene chloride was detected in all on and off-site media, although many of the results were qualified as laboratory contaminants because they were also detected in the laboratory or field blank sample. No association between these reported air emissions and results from sampling at the Limestone Road Site can be made with any certainty without additional investigation. Furthermore, this facility is an unlikely source because methylene chloride released to the atmosphere is readily dispersed and transported some distance from its source.
Soil
Surface and subsurface soil from both properties at Limestone Road was sampled in three phases from 62 different locations on and off-site (Figure 1.1). Phase I involved excavating and sampling 34 test pits, dug to a depth of 10 feet in areas where chromium-containing sludges may have been buried. Four soil borings were also taken at this time and sampled continuously at 1.5-foot intervals until bedrock was encountered. During Phase II, five subsurface samples were taken from the site, one was taken from fly ash piles at the Cumberland City Dump, and two were taken from areas north and south of the site to characterize background soils. Phase III was conducted to obtain eight additional background soil samples from off-site areas (1). Because most wastes were buried, the majority of samples were taken from subsurface, rather than the surface soil that would be available for human exposure.
Contaminants of concern are listed in Appendix B, Table 1a. Results from depths greater than one foot would not be available for regular exposure except in an occupational setting involving significant soil excavation. However, concentrations at depth are of interest because they are a potential source of groundwater contamination.
Most metals detected in on-site soils exceeded local and U.S. background concentrations, yet local background soil samples were also high in some of the metals. These elevated levels off-site may originate from the fly ash piles located throughout the area.
On the CC&SC property, the highest chromium concentrations were found in locations identified as dumping areas for metal sludges. These metals appear to be localized in a layer from 1.5 to 6 feet below the surface. A variety of organic (carbon-containing) contaminants were also found on the CC&SC property, with the highest concentrations detected in the same locations as the highest levels of metals.
Such clustering of contamination was not found at the Diggs property. Elevated levels of chromium and other inorganics were scattered throughout the area. The total number of organic compounds detected in test pits on the Diggs property was greater than was found on the CC&SC property. However, most of these compounds, including chlordane, heptachlor epoxide and benzidine, were detected less than three times on either property. With the exception of toluene, none of the organic contaminants were detected in off-site background soil samples.
Results from sampling conducted to date do not adequately define the extent of contamination in soil less than 1 foot deep nor in surface soil (3 inches or less) on and around the site. Because dumping occurred in many areas, boundaries of contamination may not exist, or they may be difficult to define.
Groundwater
Groundwater was sampled on three separate occasions during the RI from monitoring wells on and off the site (see Figure 2). A total of 45 samples were taken from twenty-one monitoring wells over the course of the RI. Two of these wells were located upgradient of the site and were taken to represent background conditions. Contamination in monitoring wells is generally characterized by inorganic (non-carbon) contaminants. There are no clear patterns of contamination among the sampled wells that would characterize a specific plume. However, the presence and levels of organic and inorganic contaminants indicate that the groundwater has been affected by the site. Contaminants of concern in groundwater are listed in Table 2. Contaminants detected above health-based comparison values include bis-2-ethylhexyl phthalate (BEHP), methylene chloride, cadmium, lead, and nickel.
Surface Water
Surface water samples were collected in each of the three sampling phases during the RI. Eleven samples were collected from nine locations during Phase I; during Phase II, these locations were resampled except for two that were unattainable due to low flow conditions, and the background location was replaced with a more appropriate sample. Phase III involved additional sampling of the nine locations with the addition of samples from leachate seeps discharging from the base of the waste mass on the southwestern boundary of the Cumberland City Dump, adjacent to the Diggs property (1). Figure 2 depicts the location of these sampling sites. Contaminants of concern in surface water are listed in Table 3.
All samples contained inorganics in excess of mean background levels and some in excess of USEPA Ambient Water Quality Criteria (designed to protect against adverse health effects from ingesting water and organisms). In general, the highest concentrations were detected at locations SW005 and SW012. BEHP was the only organic contaminant detected in surface water. It was found at low concentrations in three samples taken downstream from the Diggs and city dump properties. This compound was also detected in groundwater and soil (1). As mentioned earlier, BEHP is a common laboratory contaminant and may not actually be present at the site. However, because it was detected in so many different samples, the contaminant is further considered.
Sediment
Sediment samples were collected simultaneously with the surface water samples as described above. Most samples contained levels of inorganic contaminants at or above background concentrations. A number of organic compounds were also detected above background concentrations in samples taken from locations downstream of the site. Contaminant concentrations are given in Table 3.
Soil
Samples were taken from eight off-site locations to determine the background levels of minerals in the area (i.e., metals that are naturally occurring and not present because of site contamination). Although several inorganic contaminants detected on-site were found in these samples, none exceeded levels detected in on-site samples. Toluene was the only organic contaminant detected in these areas.
Groundwater
Twenty-one residential drinking water wells near the Limestone Road site were initially sampled in 1981 by the Allegany Health Department and were tested for heavy metals, including hexavalent chromium. At this time none of these contaminants were found above detection limits, although analytical methods used at that time may not be comparable to those used in 1986, when inorganic compounds were detected in residential wells.
Groundwater from eighteen residential wells near the site was sampled twice in 1985 during the RI and again in 1986 as part of a supplemental sampling plan. Figure 3 depicts the location of these wells (1). Contamination in these wells is generally characterized by inorganic (non-carbon) contaminants. Analyses of the first set of samples were conducted to identify any USEPA priority pollutants present. Inorganic compound were detected; however, no organic compounds were reliably detected. Laboratory blank samples showed signs of contamination indicating that organics detected in the actual sample could have been caused by the same contamination from the laboratory. Therefore, the second set of samples was only analyzed for inorganics based on the conclusion that organics were not actually present in the first set.
However, the results of first-round analyses failed to clearly show that organic contaminants were not present because BEHP and methylene chloride were detected in a small number of groundwater samples. These results were discounted because the compounds were also detected in field and laboratory blanks. The blank samples provide a measure of contamination that has been introduced into a sample set either during collection and transport of samples, or during sample preparation and analysis in the laboratory. Because methylene chloride and BEHP are commonly used in laboratory cleaning and analytical procedures, their presence in blank samples may indicate laboratory contamination. These and other contaminants of concern in groundwater are listed in Table 2.
Contaminants detected in residential wells were also detected in several on-site soil and groundwater samples. To determine if the organic contaminants detected in earlier sampling were actually due to laboratory contamination rather than migration from the Limestone Road Site, another round of residential well water samples was taken in 1986 and analyzed for organic and inorganic contaminants. Although very low levels (1-2 µg/l) of methylene chloride were detected in six wells, results were all below the detection limit (the level that can be detected with a minimum level of accuracy by the analytical method used). These levels were also below the CREG (comparison value) for exposure by ingestion. Furthermore, methylene chloride was not detected in these same wells in earlier sampling rounds.
Because levels were low and there was no apparent pattern of sampling results, the methylene chloride was attributed to contamination from cleaning equipment in the field or in the laboratory.
During this sampling round, a questionnaire was administered to homeowners to determine if any of the metals detected earlier could be attributed to the plumbing materials in the house (lead solder is a common source of lead in drinking water). Lead was detected below the MCL in nine wells where it had not been detected in earlier sampling rounds. Although these results could not confirm a residential source of lead, they do not show a pattern that would indicate that it has migrated from the Limestone site.
In addition to these contaminants, nickel was detected at low concentrations in the same three wells where it was found in previous sampling rounds.
USEPA undertook another round of residential well water sampling in 1990 to further assess the degree of inorganic contamination in six wells and to determine future action on the site. Several contaminants were identified, but none, including lead, exceeded any health-based comparison values.
Because this is a fractured bedrock aquifer, sampling results taken over time are likely to be inconsistent. Groundwater flow patterns are unpredictable and contamination does not tend to move in a plume. Therefore, sampling for organic contaminants at these wells is needed and planned for in the Supplemental RI/FS to further investigate organic contamination presently attributed to field or laboratory contamination.
Surface Water
Four surface water samples were collected from areas upstream of the Limestone Road site (samples discussed in the preceding section designated as on-site are downstream of the site and may not actually be on the site itself). Figure 3 depicts the location of these sampling sites which were established in order to determine "background" concentrations, due to environmental sources other than the Limestone Road site. Contaminants detected in these samples were limited to magnesium and aluminum.
Sediment
Background sediment samples were taken at the same four locations as the surface water samples. Slightly elevated concentrations of arsenic, barium, and chromium were detected in two samples, but were well below levels detected in on-site or downstream samples, indicating that these contaminants are migrating off-site. In addition, BEHP, phenol, acetone, and 2-butanone were also detected in one sample at low concentrations.
C. Quality Assurance and Quality Control
The data presented in this report have undergone quality assurance review. Several organic chemicals identified in groundwater, surface water, soil, and sediment were regarded as laboratory contaminants because they were also identified in the laboratory and/or field blanks. Results indicating the presence of methylene chloride, chloroform, acetone and BEHP were often labeled as laboratory contaminants. While these substances are often used in laboratory cleaning and analytical processes and could occur as a result of laboratory contamination, the prevalence of such a qualification should also be considered in determining the accuracy of such results. Methylene chloride was consistently detected in all media both as a qualified lab contaminant and as a viable result. Its prevalence calls for evaluation of additional sampling results to confirm or reject its qualification as a laboratory contaminant (1).
A wide variety of structures and objects at the Limestone Road Site pose physical hazards to
people who gain access to the property. On the CC&SC property, an old utility building,
formerly used as an "oil processing" facility, is structurally damaged and could collapse. The
Diggs property and Cumberland City Dump, used for storage and disposal, are very dangerous
because of the large number of vehicles, heavy machinery, and appliances that were discarded in
these areas. Such hazards warrant more effective measures to restrict access to these properties,
particularly for young children.
Exposure Pathways evaluated in this public health assessment are listed in Table 4. To determine whether nearby residents are exposed to contaminants migrating from the site, the environmental and human components that lead to human exposure must be evaluated. This pathways analysis consists of five elements:
- a source of contamination,
- transport through an environmental media,
- a point of exposure,
- a route of human exposure, and
- an exposed population.
Exposure pathways are classified as completed, potential, or eliminated. In completed exposure pathways, all five elements exist and exposure to a contaminant has occurred in the past, is occurring, or will occur in the future. In potential exposure pathways, however, at least one of the five elements appears to be missing, but could have existed in the past or may exist now or in the future. These pathways indicate that exposure to a contaminant could have occurred in the past, could be, but is not clearly occurring now, or could occur in the future. An exposure pathway can be eliminated if at least one of the five elements is missing and will never be present. Completed and potential pathways, however, may be eliminated when they are determined to be insignificant (not a threat to public health). Table 3 and the discussion that follows identifies the completed, potential, and eliminated pathways at this site.
Surface Soil
Actual exposure to surface soil is difficult to assess at this site because the condition of the surface soil has changed over time. Aerial photos taken before 1981 suggest that waste material disposed in onsite dumping areas was available for contact with humans. Since 1981 these areas have been covered, but the quality of the cover material is not well characterized. Most sampling data characterize the soil from test pits as deep as 10 feet, which may differ significantly from surface soil that is more available for human exposure. Because most wastes were buried, contaminant levels in deeper strata may not be representative of levels in surface soil (1). Hence, for contaminants only detected in the deeper soil strata, these pathways may not result in any current exposure whatsoever. Samples characterizing site soils were taken from depths ranging from 0-1.5 feet, to 12 feet. Although surface soil available for contact is generally limited to the first 3 inches, this assessment evaluated data characterizing soil from as deep as 12 feet. Until or unless additional data characterizing the first 3 inches is available, this public health assessment will assume that available data from deeper strata are representative of more shallow soil.
Exposure to contaminants in "surface" soil can be considered completed based on the assumption that site-related activities actually do result in incidental soil contact. Because hazardous material was buried and contaminants have been distributed throughout the site, access to most areas on site would result in contact with soil contaminants through incidental ingestion, skin contact, and inhalation of fugitive dust. Most people accidentally ingest small amounts of soil that get on the hands from recreational or occupational activities that involve contact with the ground or dust in the air. Ingestion typically occurs by nail biting or eating food before washing the hands. Individuals including hunters, hikers, other recreational trespassers, and workers involved in site remediation would experience varying degrees of exposure through these routes. There is no way to estimate the number of people exposed because no estimate of the number of trespassers is possible.
Groundwater
Sampling results from two wells in 1985 indicate that past exposure to lead by ingestion of drinking water has occurred at levels exceeding comparison values. As noted earlier, this contamination may have been the result of leaching from plumbing fixtures rather than the Limestone Road Site.
Given that these levels were detected in two homes, the estimated number of people exposed is 6. As noted in the original public health assessment, ATSDR recommended that these two residences use an alternate source of drinking water. However, 1981 sampling did not show these elevated levels, nor did results from the 1990 sampling event. Therefore, it appears that exposure lasted for a maximum of nine years (from 1981 to 1990, if one assumes that exposure began soon after the 1981 sampling at the levels detected in 1985, and continued until the 1990 sampling).
Groundwater
There may be current exposure to low levels of organics in residential well water, although the most recent sampling for organics, in 1986, only found methylene chloride at concentrations below the detection limit and below health-based comparison values. As discussed earlier, additional sampling is needed to clarify the accuracy of these results (i.e., whether they are due to lab contamination or migration from on-site sources). Exposure to contaminants actually present in groundwater may occur by ingestion, dermal contact while bathing, and inhalation while showering.
As discussed earlier, all homes in the vicinity of the site obtain drinking water from the local groundwater aquifer through private wells, with the exception of a few homes where residents choose not to drink their well water. Eighteen residences are located within a half mile downgradient from the Limestone Road site. Due to the rural nature of the area, any new residences would be expected to draw from this aquifer as well. However, county officials have indicated that extensive future development in this area could warrant an extension of the municipal water supply to these homes, although this theoretical development is not expected to occur for quite some time.
Surface Water and Sediment
Potential exposure to any contaminants found in surface water or sediment could result from recreational activity such as boating, swimming, and fishing in Evitts Creek and on the north branch of the Potomac River and its tributaries. These waters receive runoff from the Limestone Road Site as well as the Cumberland City Dump.
Exposure routes associated with these pathways include dermal contact with water and sediment
from swimming or wading. Contaminant concentrations in these media do not greatly exceed
the comparison values, and exposure is seasonal and infrequent. Furthermore, these
contaminants are not expected to be readily absorbed through the skin or to bioaccumulate in
fish tissue. Therefore, these pathways are eliminated from further evaluation because these types
of exposure are not expected to be at levels associated with adverse health effects.
This section will address the potential health effects in persons exposed to site contaminants, evaluate health outcome data, and address all questions raised by the community.
To evaluate potential health effects associated with completed and potential exposure pathways described earlier, ATSDR has developed Minimal Risk Levels (MRLs) for contaminants commonly found at hazardous waste sites. The MRL is an estimate of daily human exposure to a contaminant below which non-cancer, adverse health effects are unlikely to occur. MRLs are developed for each route of exposure, such as ingestion, inhalation, and dermal absorption and for the length of exposure, such as acute (less than 14 days), intermediate (15 to 364 days), and chronic (greater than 365 days). ATSDR also develops Toxicological Profiles on chemicals commonly found at hazardous waste sites. These chemical-specific profiles provide information on health effects, environmental transport, human exposure, and regulatory status.
Arsenic
Arsenic is a naturally occurring element in the earth's crust. Pure arsenic is a gray-colored metal, but this form is not common in the environment. Rather, arsenic is usually found combined with one or more other elements such as oxygen, carbon, chlorine, and sulfur, which determine its form as inorganic or organic. Arsenic combined with inorganic elements is referred to as inorganic arsenic, whereas arsenic combined with carbon and hydrogen is referred to as organic arsenic. It is important to maintain a distinction between inorganic and organic arsenic because the organic forms are usually less toxic than the inorganic forms (5).
Data gathered at the Limestone Road Site do not distinguish arsenic concentrations by specific form. Average soil arsenic concentrations for both the CC&SC and Diggs properties are below the health-based comparison value that is designed to protect against the potential cancer-causing effects of arsenic. Ingestion of higher levels of arsenic have been associated with skin cancer in animal studies and human studies in Taiwanese populations (5).
Although the maximum soil concentration at the CC&SC property (66 ppm) exceeds the health-based comparison value, it is not likely to pose any threat to human health. The sample containing this level of arsenic was taken from a depth of 2.5 to 3.5 feet and would probably not be available for exposure. Furthermore, the comparison value is based on the most toxic inorganic forms of arsenic which may only comprise a percentage of the total arsenic concentration (5). However, surface soil samples (samples collected at 3 inches or less) are needed to fully evaluate possible health effects upon exposure.
Bis(2-ethylhexyl)phthalate (BEHP)
BEHP is an organic compound that was detected at moderate concentrations in groundwater and soil samples at the Limestone Road site.
There are no available studies on the health effects of BEHP in humans (7). Therefore, non-cancer, adverse health effects resulting from exposure cannot be evaluated. However, exposure levels are very low, and exposure has not been confirmed. Therefore, no non-cancer adverse health effects are expected to result.
Animal studies have shown that BEHP can cause cancer and effects on the reproductive system in rats and mice. The liver and testes appear to be the primary target organs for BEHP toxicity (7). Exposure to BEHP concentrations found in monitoring wells may pose an elevated risk of cancer, based on the carcinogenic potency derived by USEPA (7). However, presently there is no exposure to water from these wells.
Levels detected in residential wells taken in 1985 were much lower than those detected in monitoring wells, although the maximum BEHP level detected in one drinking water well exceeded the environmental media comparison value. Exposure to this concentration is not likely to pose a significantly elevated risk of developing cancer if exposure continued at that level (7). BEHP was not detected in subsequent residential well sampling conducted in 1986.
Chromium
Chromium is a naturally occurring element of the earth's crust, present in at least two chemical forms: hexavalent and trivalent chromium. All humans are exposed to low levels of chromium in air and water, but by far the most significant exposure route is through ingestion of food. Trivalent chromium is considered to be a nutrient at low levels and is essential for good health (8).
Hexavalent chromium is more readily absorbed than trivalent chromium and is, therefore, more toxic. Hexavalent chromium (chromium VI) is an irritant, and short-term, high-level exposure can result in adverse health effects at the contact location (for example, ulcers of the skin, irritation and perforation of nasal mucosa, and irritation of the gastrointestinal tract). However, exposure at the Limestone Road site is not great enough to cause these adverse effects (8).
Long-term exposure to hexavalent chromium by ingestion may also cause adverse health effects to the kidney and liver. Trivalent chromium (chromium III) does not produce these effects (8).
Although there are no actual studies available to evaluate the carcinogenicity of hexavalent chromium by ingestion, the current theory about its mechanism of action suggests that cancer is not likely to result from this route of exposure (8).
Evaluation of potential noncarcinogenic effects associated with the ingestion of chromium in soil indicates that daily incidental ingestion could lead to adverse health effects such as kidney and liver damage if chromium is in the hexavalent form (8). However, as with the inhalation route, sufficient exposure to toxic levels is unlikely at the Limestone Road Site because the soil containing these levels is found at a depth where it is not available for exposure.
Dermal exposure to hexavalent chromium throughout the soil matrix may cause an irritating allergic skin reaction known as eczema in some individuals who become sensitized to the chemical. Because this is an allergic reaction that only affects sensitive individuals, it is not as related to concentration as are other toxic effects (8).
Hexavalent chromium was not detected in surface water and only detected in one groundwater sample. Chromium concentrations in these media did not exceed health-based comparison levels for total, trivalent and hexavalent chromium, and, therefore, are not likely to result in adverse health effects (8).
Cyanide
Cyanide is a substance that is found in combination with other man-made and naturally-occurring chemicals in the environment. Cyanide was detected at elevated levels in soil from the CC&SC portion of the Limestone Road Site. Exposure routes for soil include dermal contact and incidental ingestion.
In the form of vitamin B12 (cyanocobalamin), cyanide is needed as part of a healthy diet to prevent iron poor blood, anemia. Effects of exposure to higher levels of cyanide may vary among people of different family traits, age, and sex. Only results from animal studies are available to characterize effects of long-term cyanide ingestion at levels comparable to those detected in soil at the Limestone Road Site (9).
The low concentrations found at this site may cause skin irritation in persons having direct dermal contact with highly contaminated soil. Certain individuals who don't have enough iodine and other essential nutrients in the diet are more susceptible to effects of cyanide on the thyroid gland. In these people, long-term, low level cyanide ingestion can cause cretinism (retarded physical and mental growth in children), or enlargement and overactivity of the thyroid gland (9). Cyanide is not classified as a carcinogen; no cancerous effects are expected to result from exposures (9).
Cadmium
Cadmium is a naturally occurring element in the earth's crust. Cadmium was detected at levels above ATSDR Environmental Media Evaluation Guideline (EMEG) in on-site groundwater and above the EMEG in on-site soil, indicating that exposure to on-site soil and groundwater may pose a risk of adverse health effects (although more thorough surface soil sampling is needed to fully characterize cadmium concentrations available for human exposure). Cadmium was not detected in residential groundwater.
The main route of cadmium exposure at the Limestone Road Site is incidental ingestion of cadmium in soil. It should be noted that the amount of cadmium needed to cause an adverse effect in an exposed person depends on the chemical and physical form of the element (10). In general, cadmium compounds that dissolve easily in water (e.g., cadmium chloride), or those that can be dissolved in the body (e.g., cadmium oxide), tend to be more toxic than those that are hard to dissolve, such as cadmium sulfide. Chronic daily exposure to the more toxic form may cause kidney damage (10). Cadmium is classified as a probable human carcinogen. No cancer slope factor has been developed to be able to determine what risk, if any, is posed to people exposed to cadmium at the site (10). The form of cadmium most prevalent at the Limestone Road Site is not known, and the degree of exposure to cadmium in surface soil is not clear.
Lead
Lead is a naturally occurring inorganic element that is frequently found in small amounts in nature. Lead was detected in groundwater (residential and monitoring wells), on and off-site soil samples, in sediment and in surface water at lower concentrations. Incidental ingestion is the exposure route of concern associated with these media.
Signs and symptoms of lead toxicity depend on lead concentrations in the tissue and the age of the individual. Chronic exposure to low levels of lead can interfere with the blood forming and reproductive systems, kidney function and metabolism, and produce subtle effects on personality, memory, learning, reaction time, psychomotor function, and motor coordination (11). Infants and young children are very sensitive to the toxic effects of lead on the nervous system. Impaired neurological development has been observed in children exposed to relatively low concentrations of lead. At higher concentrations, lead is toxic to the central nervous system and can produce neurological motor dysfunction (11). Lead is classified as a probable human carcinogen, but the non-cancer effects are of more immediate concern (11).
No comparison value has been confirmed as a safe threshold level for lead that would not induce a toxic effect. Current opinion supports the reasoning that toxicity is reduced with reduced exposure. Until the relationship between toxicity and dose is more clearly understood, all exposure to lead should be avoided to the extent feasible (11).
Manganese
Manganese is a naturally occurring substance found in many types of rock. People are regularly exposed to low levels of manganese in water, air, soil, and food (12). A certain amount of manganese in the diet is believed to be necessary for good health. Manganese has caused disease in workers exposed to very high levels of manganese-containing dust in the air for a year or longer. Symptoms of the disease include mental and emotional disturbances and incoordination. It is not known whether or not oral exposure of humans to manganese can cause the disease associated with dust exposure (12).
Manganese has not been found at elevated concentrations in residential wells near the site; it has been found in monitoring wells at levels that are slightly higher than the comparison value. However, this reported concentration was considered to be overestimated due to the way the analytical procedure was performed. Therefore, manganese is not considered a threat to human health at this site.
Methylene chloride
Methylene chloride is a widely used industrial solvent and paint stripper (13). Low levels of methylene chloride were detected in all media tested at the Limestone Road Site. While many of these results were qualified as potential laboratory contaminants, its widespread detection warrants further investigation.
Methylene chloride has caused cancer of the liver and lung in laboratory animals exposed by inhalation to high levels of the chemical over a lifetime. Methylene chloride has also caused liver cancer in laboratory animals following long-term oral exposure. There is no evidence for an increase in cancer deaths in humans occupationally exposed to methylene chloride, but long-term exposure to maximum levels found in off-site groundwater could result in an increased risk of developing cancer (13). Long-term exposure to the 1985 levels could result in an elevated risk of non-cancer effects, such as liver disease, if exposure occurred over a lifetime (13).
Levels detected in residential groundwater at the Limestone Road Site in 1985 exceeded ATSDR's EMEG for exposure by ingestion, but were found at much lower levels in 1986. Therefore, the risk of developing cancerous and non-cancerous health effects may be diminished.
Polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons are a group of chemicals that are both naturally occurring and formed by man during incomplete burning of coal, oil and gas, garbage, or other organic substances. There are over one hundred and fifty different PAH compounds (14). PAH compounds listed below were detected in soil and sediment from the Limestone Road Site. Exposure routes for these media include dermal contact and incidental ingestion, as well as possible, yet limited, inhalation of fugitive dust. Several PAH species were also detected in groundwater from monitoring wells. Although currently there is no human exposure to this groundwater, they may eventually migrate to residential wells through fractured bedrock where groundwater is used for drinking.
Because there are so many PAH compounds of similar chemical and physical properties,
comparison values are only available for a representative group that have been studied
collectively (14). These compounds are:
| acenaphthene acenaphthylene anthracene benz (a) anthracene benzo (a) pyrene benzo (b) fluoranthene benzo (ghi) Perylene benzo (k) fluoranthene |
chrysene dibenzo (a,h) anthracene fluoranthene fluorene Indeno (1,2,3-cd) pyrene phenanthrene pyrene |
PAHs are mostly found in mixtures of two or more compounds. They can occur in the air either attached to dust particles, or in soils or sediment as solids. Most PAHs do not dissolve easily in water, but some readily evaporate into the air. PAHs do not burn easily and endure in the environment from months to years (14).
The majority of PAHs at the Limestone Road Site were detected in low concentrations. Estimated combined exposure to all PAHs exceeds the comparison value for the most toxic compound, benzo(a)pyrene (BaP), assuming the improbable worst-case scenario that all PAHs are as toxic as BaP. Most exposure would presumably occur from incidental ingestion of soil.
PAHs can enter the body quickly and easily by all routes of exposure. This rate is increased when PAHs are administered in oily mixtures. They go to all the tissues of the body that contain fat, and tend to be stored mostly in the kidneys, liver, and fat, with smaller amounts to the spleen, adrenal glands, and ovaries. Most PAHs are metabolized from these tissues within a few days of exposure, and are excreted primarily in the feces and urine (14).
The different PAH compounds vary in potency (the quantity that causes toxicity) and mechanism of action (how they cause adverse effects). Under conditions of short-term, low-level exposure, PAH toxicity is relatively low (14).
The following compounds have been shown to cause cancer in laboratory animals when administered orally (via food), dermally (on the skin), and by inhalation through air: benz(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, dibenz(a,h)anthracene, indeno(1,2,3-c,d)pyrene (14). Studies of long-term human exposure by inhalation have also shown elevated cancer associated with PAH exposure. Such carcinogenic PAHs have been implicated in the proven association between smoking and cancer. Cigarette smoke contains a variety of complex PAH mixtures. Of these contaminants, benzo(a)pyrene is the most extensively studied and is thought to be the most potent carcinogen (14).
There is a growing amount of evidence in animals and humans showing severe immunotoxicity and reproductive toxicity in animals exposed to some carcinogenic PAHs. However, additional research is needed to clarify these mechanisms of action (14).
Based on this information, combined chronic exposure to all PAHs detected in soil, sediment, and groundwater at the Limestone Road site would pose a potential risk of cancer and possibly other adverse health effects to exposed individuals. However, at this time there is no indication that anyone experiences this level of exposure simultaneously.
B. Health Outcome Data Evaluation
Based on the toxicological evaluation of the contaminants of concern for this site, the following health outcomes could be considered plausible (provided that a completed exposure pathway for contact with the chemical of concern has been accurately characterized, and the health effect(s) associated with that particular chemical has been established with animal toxicity studies and human epidemiology):
Maryland's cancer registries (described in the earlier section) were reviewed to identify any elevated incidence rates that could be related to exposures to site contamination. It is important to note that these rates only reflect the number of deaths from cancer rather than the number of cases of cancer. An area with a high cancer mortality rate does not necessarily have a high incidence rate.
As shown in Table 5, cancer mortality for all types is lower in Allegany County than for the State of Maryland. Although specific rates for breast, lung, colon, and cervical cancer appear slightly elevated above the state average, their higher incidence could be explained by a number of other factors besides exposure to site-related contamination. Such factors include access to health care and cancer screening programs, smoking habits and family medical history of such cancers. Furthermore, because the potentially exposed population at the Limestone Road site is small and the overall site cancer risk is low, excess cancer associated with the site would not likely be detectable in the county-wide data.
The County Health Department was contacted to determine if there have been any earlier or more recent reports of these and other illnesses that could be related to exposures to contaminants from the Limestone Road site. None have been reported, nor have any new concerns been raised.
C. Community Health Concerns Evaluation
1. Are neighboring residential water supplies safe?
Based on the more recent sampling results, well water in the vicinity of the Limestone Road site poses no apparent threat to human health. Residential wells have been sampled on four separate occasions in 1985 and 1986, and again in 1990.
Results in 1985 and 1986 suggested that some inorganic contaminants including nickel and lead, and organics including methylene chloride and BEHP were present at levels that pose a risk to human health from long-term exposure. In 1986, the organic contaminants were not detected beyond reliable detection limits or health-based comparison values. In 1990, inorganic concentrations had fallen to below levels of concern.
Methylene chloride, an organic contaminant, was detected once during the RI and in six wells during supplemental sampling. Levels in these wells were attributed to field and laboratory contamination for the following reasons:
- there was no pattern of contamination among the wells,
- results were not replicated in each sampling round, and
- it is a common contaminant because it is so widely used to clean equipment in the field and lab.
Results of additional sampling, planned to confirm these results for both lead and methylene chloride, are expected in the near future. In the meantime, the water is not considered hazardous. Even if contaminants are found to originate in the well, levels are not acutely toxic and would not pose a risk to human health from exposure for several years.
2. Should local residents continue to use Evitts Creek for recreational purposes, including fishing?
Surface water and sediment sampling indicated that some off-site migration of heavy metals including chromium, cadmium, barium, lead, and nickel has occurred. Levels of some of these contaminants exceed USEPA Ambient Water Quality Criteria for the protection of human health. These criteria protect for the potential health threat from ingestion of bioaccumulated contaminants in fish and surface water. However, these criteria were not greatly exceeded and these exposure routes are not likely to be significant because the contaminants are not expected to accumulate in edible portions of fish at levels associated with adverse health effects in humans. Further surface water and sediment sampling is planned during the Supplemental Remedial Investigation to confirm the contaminant concentrations detected in these media; however, current data do not indicate that exposure to contaminants in these media pose a health threat.