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PUBLIC HEALTH ASSESSMENT

AMERICAN SHIZUKI CORPORATION/
OGALLALA ELECTRONICS AND MANUFACTURING
OGALLALA, KEITH COUNTY, NEBRASKA


ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

Sampling has been conducted principally for groundwater at public wells and monitoring wells and for soil gas. Because the information available is not extensive enough to define the lateral limits of the contamination identified, ATSDR considers all of the contamination to be "on site". Review of the sampling data and supporting site-related information suggests that contaminants have been released to the groundwater, soil, and air in the central city area. The narrative and tables in this section address the contaminants that ATSDR has selected to evaluate whether exposure to them has public health significance. Other contaminants reviewed but not selected for further evaluation are not addressed in this assessment. Discussion of the selected contaminants and affected environmental media in this section of the assessment does not imply that human exposure would actually result in adverse health effects. Health effects issues are addressed in a later section.

Contaminant selection considers the following factors:

  1. Concentrations of contaminants in media.
  2. Sample locations, field data quality, and laboratory data quality.
  3. Relationship of concentrations to ATSDR's public health assessment comparison values; also, the unavailability of suitable comparison values.
  4. Community health concerns.

ATSDR also searched the EPA Toxic Chemical Release Inventory (TRI) to determine whether it included information about industrial chemical releases to the environment that might be pertinent to this assessment. TRI did not include any release data for the area (7).

The contaminants selected and the media in which sampling shows they have occurred are summarized in this section and in data tables (Appendix B). The data tables also identify the public health assessment comparison values ATSDR used for selection. The Cancer Risk Evaluation Guide (CREG) was the most frequent comparison value. CREGs are estimated comparison concentrations that are based on an excess cancer rate of one in a million persons and are calculated using EPA's cancer slope factors for specific chemicals. ATSDR's Environmental Media Evaluation Guide was also a comparison value. EMEGs are estimated comparison concentrations that are based on health effects information determined by ATSDR for its Toxicological profiles for specific chemicals.

A. Contamination

Groundwater Data

Review of sampling data shows that several contaminants have been found in groundwater at several locations across the central part of the city: trichloroethylene (TCE), tetrachloroethylene (PCE), benzene, 1,1-dichloroethylene (1,1-DCE), 1,1-dichloroethane (1,1-DCA), and carbon tetrachloride (CCL4). The very limited data reported in reference documents for inorganic components do not suggest that inorganics are a contamination issue. However, ATSDR can not draw meaningful conclusions based on those few data and hence does not address them further in this document.

    Public Water Supply Wells

Samples taken at public wells shows that five (Wells 39-1, 60-1, 64-1, 64-2, and 74-1) within the central city area have produced water containing substantive levels of contamination on one or more occasions. TCE (maximum concentration 220 parts per billion--ppb) is the dominant contaminant detected. Water drawn from Well 63-1 has not shown evidence of contamination during the sampling period. Tables 1A through 1F summarize the available well data by showing maximum concentrations and the most recent concentrations reported. Those data suggest that concentrations have decreased over time in four of the five contaminated wells. For the most recent sampling event reported (March 1993), contamination (TCE) was shown only in Wells 39-1 and 64-1. However, because information about contaminant source(s) and the location and dimensions of affected groundwater zones are incomplete, it seems appropriate to consider that some contaminants might appear, reappear, or increase in concentration in public wells.

Limited testing (eight samples) has been done of water delivered by the distribution system to the users' taps (Table 2). Low levels of TCE were present in three samples; PCE was found at a low concentration in one sample.

    Private Water Supply Wells

Sixteen private wells have been sampled (Table 3). Water from three wells--located in the west, east, and north parts of the central city area--showed low concentrations of TCE. One of those three wells currently is used for residential potable water supply (5).

    Monitoring Wells

Groundwater monitoring wells have been placed at several locations within the central area. The maximum concentrations of selected contaminants and the associated well locations are summarized in Table 4.

Almost all monitoring wells have been placed at, or within a block of, several of the identified businesses: ASC, Bossleman's, Goodall Electric, Keith County Maintenance, Ogallala Electronics, Tip Top, TRW/Goodall, and Quick Electric. Contaminants reported for wells in the vicinity of those businesses are summarized below:

    ASC

Groundwater monitoring has been conducted on the ASC property and on the adjacent fairground to the east. TCE (46 ppb) and PCE (40 ppb) are the predominant chemicals found in water samples from those wells. However, most recent information suggests that levels at most wells are diminishing, are very low, or are "not detected". Only one monitoring well continues to show relatively high concentrations (1)(6)(8).

    Bossleman

About a dozen wells have been installed on, and within a block of, the property. TCE (93.3 ppb) and benzene (4,146 ppb) are the only selected contaminants that have been found at substantial levels. Later, in 1992, benzene was present in only one well (481 ppb). This, together with other information about the pattern of contamination change with time, suggests that the pump and treat activities are capturing much or all of the contaminants beneath the property. However, data are not available to examine changes in TCE levels (1)(2)(9).

    Goodall Electric

Four wells were installed on the former Goodall property on Spruce Street. ATSDR's selected contaminants were not found (1)(10).

    Keith County Maintenance

ATSDR reviewed information prepared in 1992 that said gasoline contamination of groundwater identified previously at that location was no longer present. The accompanying analytical results for benzene (and three other gasoline-related contaminants) showed none were found (11).

    Ogallala Electronics

Monitoring wells have been installed on and within a block of the company's property. TCE (470 ppb), PCE (63 ppb), and benzene (60 ppb) have been found at relatively high concentrations at a few of the wells. However, most recent information suggests that levels at most wells are diminishing, are very low, or are "not detected". Only one well continues to show high concentrations (1)(8)(12).

    Tip Top

A monitoring well within a block of Tip Top sampled twice in 1992 shows that PCE (138.4 ppb) is the dominant contaminant and is present at a relatively high concentration (1)(8).

    TRW/Goodall

NDEQ installed a monitoring well that is within a block of the former TRW/Goodall facility on West 1st Street. TCE (320 ppb) and 1,1-DCE (19.5 ppb) were the principal contaminants. The most recent samples show the level of TCE is substantially reduced, and other contaminants of potential concern were not found (1)(8).

    Quick Electric

The monitoring wells closest to Quick Electric are associated with studies conducted by ASC to the south and east. Information at those well locations cannot be presumed to reflect groundwater conditions at the Quick property.

Soil Gas Data

In 1990, NDEQ, as part of a program to investigate groundwater contamination, initiated soil gas measurements at the potential sources they had identified based on current or past usage of cleaning solvents or the proximity to known areas of groundwater contamination (13). ATSDR has selected several soil gas contaminants: TCE, PCE, 1,1-DCE, cis 1,2-dichloro-ethylene (1,2-DCE), 1,4-dichlorobenzene (1,4-DCB), 1,1,1-trichloroethane (1,1,1-TCA), ethylbenzene, and xylene.

Most of the soil gas samples were taken at, or within a block of, 10 of the identified businesses; no samples were taken by the TRW/Goodall location. Relatively high concentrations of each contaminant were shown at one, or more, sampling locations. The maximum concentrations found for each contaminant are summarized in Table 5. The maximum concentrations reported in the vicinity of each of the businesses are summarized in Tables 6A through 6C.

Other Sampling Data

    ASC

Surface and subsurface soil samples were taken on ASC property at the drum storage area and plant loading docks and in the drainage swale east of the plant boundary; VOCs were less than 1 part per million (ppm) (6)(14)(15).

    Goodall Electric

Subsurface soil samples were analyzed; VOCs were less than 1 ppm (10).

    Ogallala Dump

One sample of the soils that had been placed to cover the landfill was analyzed; the analysis did not include VOCs. A sample of surface water was taken from each of the two adjacent gravel quarries; VOCs were not found (3).

    Ogallala Electronics

Several samples of soils from borings are reported to have been submitted for laboratory analysis of VOCs (1). ATSDR has not located a source for that information.

    South Platte River

River water samples, obtained over many years, are not analyzed for VOCs (16).

B. Quality Assurance and Quality Control

In preparing this assessment, ATSDR presumed that protocols and results for laboratory testing and other activities are substantially valid and used the information in its evaluations. The completeness and reliability of the information could affect the validity of ATSDR's conclusions.

C. Physical and Other Hazards

ATSDR did not observe substantive physical or other hazards associated with the site area. The concentrations of volatile contaminants reported in soil gas are only a small fraction of what would be required to enable fire or explosion to occur. Hence, soil gases do not appear to pose a hazard.


PATHWAYS ANALYSES

ATSDR identifies human exposure pathways by examining environmental and human components that might lead to contact with contaminants. A pathway analysis considers five elements: a source of contamination, transport through an environmental medium, a point of exposure, and a route of human exposure. Exposure pathways are completed when all five elements exist and there is evidence that exposure to a contaminant has occurred in the past, is currently occurring, or will occur in the future. Exposure pathways are potential when one or more of the elements is not clearly defined but could exist. Potential pathways indicate that exposure to a contaminant could have occurred in the past, could be occurring now, or could occur in the future.

ATSDR's analysis of information indicates there are two completed pathways. The principal one is associated with groundwater use; the other involves solvent use in the workplace. Completed pathways elements are summarized in Table 7 (Appendix B).

Two potential exposure pathways appear plausible. The principal one is associated with the possible contamination of interior building air in areas underlain by soil gas contaminants and contaminated groundwater. The other is associated with contaminated soils that could be present wherever chemicals have been released into the ground. Potential pathway elements are summarized in Table 7 (Appendix B).

Table 8 (Appendix B) further characterizes exposed and potentially exposed populations, the associated contaminants, and media.

A. Completed Exposure Pathways

Principal Completed Exposure Pathways

    Public Water Supply Wells

Several contaminants--TCE, PCE, benzene 1,1-DCE and 1,1-DCA--have been found in one or more of several public water supply wells within the central zone since VOC analyses began in 1989. March 1993, analyses--the latest known available--showed VOCs (TCE) present in two of those wells. Those data suggest that contaminant levels, in general, have been decreasing over time at those well locations. However, too little is known about contaminant sources and contaminated groundwater zones to presume that contaminants could not appear, reappear, or increase at the well locations. TCE and PCE have been found in limited sampling of water from users' taps (Table 2).

Water pumped from each well feeds directly into an interconnected distribution system where it may mix with water from other wells and possibly moderate contaminant levels. However, ATSDR believes the well samples and the few tap samples obtained to date provide an incomplete picture of the varying levels of contaminants that have been, and are being, delivered to customers.

ATSDR concludes that some residents, workers, and visitors have been, are now being, and may be exposed in the future to the chemicals in the public water supply principally through ingestion and inhalation (showering). More limited exposure likely occurs through skin contact.

    Private Water Supply Wells

The limited water quality analyses conducted for private wells shows a few have low levels of TCE. Given the large number of private wells still in use, ATSDR believes that some others also are likely to be drawing water contaminated with one or more VOCs. Therefore, some residents and other users of private well water have been, are now being, and may be exposed in the future to chemicals in the groundwater principally through ingestion and inhalation (showering). More limited exposure also occurs through skin contact. Some who use private wells only for irrigation and other nonpotable purposes also are likely to be exposed via incidental ingestion and skin contact and, perhaps, through inhalation.

Other Completed Pathways

    Workplace Interior Air

Where solvents are used at businesses, solvent vapors escape from some types of equipment, maintenance workers periodically service equipment, and some production workers periodically apply solvents in an ambient air environment. Thus, some workers have been exposed in the past, are now being exposed, and will be exposed in the future to solvents principally through inhalation. Exposure through skin contact also is likely to occur, and some exposure to solvent residues through incidental ingestion also is likely. Sampling data are not available to confirm the presence of specific VOCs, but the substantive use of TCE and PCE suggests that at least those would be present at one or more locations.

B. Potential Exposure Pathways

Principal Potential Exposure Pathways

    Soil Gas/Interior Air

Soil gas containing VOCs has been found at essentially every area that has been sampled and could exist elsewhere below ground where chemical releases have occurred and where groundwater is contaminated. Soil gas chemical compounds include TCE, PCE, 1,1-DCE, 1,2-DCE, 1,4-DCB, 1,1,1-TCA, ethylbenzene, and xylene. Soil gas could migrate from below ground and enter and accumulate in buildings; interior air samples are not currently available. If that migration has occurred, building occupants would have been exposed in the past, would now be exposed, or may be exposed in the future through inhalation of contaminants. Migration and exposure are most likely to occur at buildings with basements. ATSDR observed basements at many residences, some commercial buildings, and a few schools and public buildings within the central city area. Concentrations of any soil gas contaminants would be diluted by interior air, but would be in addition to any concentrations that result from showering (as previously noted) or from volatile chemicals used in homes and other buildings.

Other Potential Exposure Pathways

    Soils

Chemical releases into the ground are likely to result in contaminants being retained within the soil. Thus, workers engaged in excavation or who otherwise enter areas where chemicals have been released to soils potentially have been exposed to contaminants. That exposure may have occurred in the past, may be occurring now, or may occur in the future principally through incidental ingestion. Inhalation of contaminated particles and skin contact also are possible exposure routes.


PUBLIC HEALTH IMPLICATIONS

A. Toxicological Evaluation

Introduction

This section discusses health issues for persons exposed to specific contaminants, discusses health outcome data, and addresses specific community health concerns. To evaluate noncancer health effects, ATSDR has developed a Minimal Risk Level (MRL) for certain 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 routes of exposure and for the length of exposure - acute (less than 14 days), intermediate (15 to 364 days), and chronic (equal to or greater than 365 days). ATSDR presents these MRLs in Toxicological Profiles. These chemical-specific profiles provide information on health effects, environmental transport, human exposure, and regulatory status. If an ATSDR MRL is not available, 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 (noncancer) health effects are unlikely to occur.

Cancer is a group of diseases characterized by uncontained growth and spread of abnormal cells. Cancer cells multiply uncontrollably, destroying normal cells, and can spread from their site of origin to other parts of the body. A chemical capable of causing damage leading to cancer is called a carcinogen. The latency period, or length of time between exposure and development of disease, ranges from a few years to decades. ATSDR estimates cancer risks using EPA's cancer potency factor. That method assumes that animal data gathered under high dose exposure conditions can be used to estimate the risk of low dose exposures in humans. The method also assumes there is no safe level of exposure. There is little experimental evidence to confirm or refute those two assumptions. Lastly, the method assumes the 95% upper bound for the risk, rather than the average risk. This means there is a 95% chance that the risk of cancer is actually lower, perhaps by several orders of magnitude.

Health Issues by Contaminant

ATSDR has determined that residents, workers, and visitors are likely to have been, are now being, and may be exposed in the future to chemicals in the public water supply and private/residential well water mainly through ingestion and inhalation (while showering). Those contaminants are listed in Tables 9 and 10, Appendix C. Each contaminant is listed by route of exposure. In calculating estimates of exposure for water, intake rates of 2 liter/day for adults and 1 liter/day for children were used. The mere presence of a contaminant does not imply that harm will result from exposure. For example, a contaminant at a concentration lower than that chemical's MRL or RfD should pose no appreciable public health hazard with respect to noncancerous adverse health effects.

    Benzene

Benzene is a clear, colorless, and highly flammable liquid with a strong sweet odor. Benzene evaporates into the air very quickly and dissolves easily in water. Benzene is produced primarily from petroleum sources and is used mostly to manufacture other chemicals used to make plastics, synthetic rubbers, fibers, and resins. It is also used to make drugs, dyes, pesticides and other agricultural chemicals, lubricants, solvents, and cleaning products (18).

Some residents, workers, and visitors have been exposed, and may be exposed in the future to benzene in public water supply (Table 1A). Future exposure to benzene in groundwater in the area (Table 4) is only possible if the contaminated plume reaches a public or private well water. Although there are no MRLs or RfDs for benzene (Tables 9 and 10), the estimated ingestion doses of benzene, in the only contaminated public well, for adults and children are about 100,000 times lower than the lowest experimental dose of benzene that caused no adverse effects in laboratory animals after six months (three-five days/week) of subchronic/intermediate exposure (18). Moreover, the estimated exposure doses are some 100,000 to 1,000,000 times lower than the lowest experimental dose that caused a decrease of white blood cells in laboratory animals after about 2 years of chronic (long-term) exposure (18). Similarly, ingestion doses of benzene for adults and children, who might be exposed in the future to benzene in groundwater (Table 4), are also lower than the lowest experimental dose of benzene that caused no adverse effects in laboratory animals after six months (three-five days/week) of subchronic/intermediate exposure (18). In addition, mixing of contaminated well water with water from uncontaminated wells possibly moderates contaminant levels. It is highly unlikely that adults and children would suffer any noncarcinogenic health effects because of their exposures to low levels of benzene.

The EPA and the International Agency for Research on Cancer (IARC) consider benzene to be a human carcinogen. According to IARC, many case reports and case series have described the association of leukemia with exposure to benzene, either alone or in association with other chemicals (19). Based on this information, ATSDR has determined that residents who were and may be exposed to benzene from water drawn from the only contaminated public well (Table 1A) are unlikely to develop any additional cancer over their lifetimes because of exposures to low levels of benzene.

    Carbon Tetrachloride

Carbon tetrachloride is a clear liquid that evaporates very easily; therefore it is often found in the environment in the gaseous form. Most carbon tetrachloride that escapes to the environment is found as a gas in the atmosphere. Carbon tetrachloride has a sweet odor and most people can begin to smell it in air at 10 parts per million. Carbon tetrachloride does not occur naturally but has been produced in large quantities to make refrigeration fluid and propellants for aerosol cans. Since refrigerants and aerosol propellants have been found to affect the earth's ozone layer, the production of these chemicals is being phased out. Consequently, the manufacture and use of carbon tetrachloride will probably decline in the future. In the past, carbon tetrachloride was widely used as a cleaning fluid, both in industry and dry cleaning establishments, where it served as a degreasing agent. It was also used in the household to remove spots from clothing, furniture, and carpeting. Carbon tetrachloride was also used in fire extinquishers and as a fumigant to kill insects in grain. These uses were discontinued in the mid-1960s and 1986, respectively (20).

Carbon tetrachloride was detected in one of the monitoring wells along the railroad east of A Street (Table 4). The ingestion dose of carbon tetrachloride for adults who might be exposed in the future does not exceed the RfD (Table 10). Such adults would be unlikely to suffer any noncarcinogenic health effects because of exposure to low levels of carbon tetrachloride. The future ingestion dose for children exceeds the RfD (Table 10). However, the estimated dose is about 10,000 times lower than the doses of carbon tetrachloride that caused no adverse effects in laboratory animals after 2 years of chronic (long-term) exposure (20). It is highly unlikely that children who may be exposed in the future will suffer any adverse health effects because of exposure to low levels of carbon tetrachloride. Moreover, future exposure to the low levels of carbon tetrachloride in groundwater in the area (Table 4) is only possible if contaminated plume reaches a public or private water well.

IARC, the Department of Health and Human Services (DHHS) and the EPA consider carbon tetrachloride to be a carcinogen. An IARC working group reported that there were no adequate data to evaluate the carcinogenicity of carbon tetrachloride. However, three case reports described liver tumors associated with cirrhosis in humans exposed to carbon tetrachloride. One mortality study of laundry and dry cleaning workers exposed to a variety of solvents including carbon tetrachloride indicated excess respiratory cancers, liver tumors, and leukemia (19). Adults and children who may be exposed in the future to carbon tetrachloride through the use of groundwater are not likely to develop additional cancer over their lifetimes because of exposure to low levels of carbon tetrachloride.

    1,1-Dichloroethane

1,1-DCA is a colorless, oily, man-made liquid. It evaporates quickly at room temperature and has an odor like ether, and it burns easily. When released into the environment, 1,1-DCA exists as a vapor rather than a liquid. It is used primarily to make 1,1,1-TCA and other chemicals. It is used as a solvent for paint, varnish and finish removers, and to remove grease. It is no longer used as a surgical anesthetic (21).

DCA was detected in one of the public wells in early 1993 (Table 1D) and also in one of the monitoring wells near the railroad and West A Streets in 1992 (Table 4). However, subsequent samplings in March 1993 did not detect 1,1-DCA in any public water supply wells. Although there are presently no chronic MRL and RfD for 1,1-DCA (Tables 9 and 10), the estimated doses of 1,1-DCA for adults and children are more than 1,000,000 times lower than the lowest experimental dose of 1,1-DCA that caused no adverse effects in laboratory animals after 52 weeks of chronic (long-term) exposure (21). It is unlikely that adults and children who were and who may in the future be exposed to 1,1-DCA will suffer adverse health effects because of exposure to low levels of 1,1-DCA.

EPA considers 1,1-DCA as a possible human carcinogen based on limited animal studies only. IARC and DHHS have found no evidence that 1,1-DCA causes cancer in humans or animals.

    1,1-Dichloroethene

1,1-DCE is also known as vinylidene chloride. It is a man-made chemical and is not found naturally in the environment. It is a clear, colorless liquid that evaporates quickly. It has a mild, sweet smell like chloroform and burns quickly. It is used mainly to manufacture other chemicals such as polyvinylidene chloride (22).

Although 1,1-DCE was detected in two public water supply wells in early 1993, subsequently samplings in March 1993 did not show any contamination (Tables 1D and 1E). The estimated ingestion doses for adults and children do not exceed the MRL or RfD for 1,1-DCE (Table 9). In addition, the estimated doses are about 10,000 - 100,000 times lower than the lowest dose of 1,1-DCE that caused no adverse effects in laboratory animals after 2 years of chronic (long-term) exposure (22). Adverse health effects are unlikely to occur in adults and children because of exposure to low levels of 1,1-DCE. Similarly, residents who in the future might be exposed to 1,1-DCE detected in groundwater at Railroad and West A Streets (Table 4) would unlikely suffer any adverse noncarcinogenic health effects because of the low levels of such an exposure (Table 10).

IARC does not consider 1,1-DCE as a carcinogen. EPA has classified 1,1-DCE as a possible human carcinogen based on limited animal studies only. However, based on this information, ATSDR has determined that residents who were and may in the future be exposed to 1,1-DCE in well water may have no risk of developing additional cancer over their lifetimes because of exposure to low levels of 1,1-DCE.

    Tetrachloroethene

PCE is a colorless, nonflammable liquid with an ether-like odor. It is practically insoluble in water. PCE is used in dry cleaning and textile processing. It is also used to cool gas, insulate fluid, as an anthelminthic, and to manufacture other chemicals and products including fluorocarbons, paint, adhesives, aerosols and coatings (23).

PCE was detected in samples of public supply water wells in 1989 (Tables 1A and 1E), and in one out of eight samples of tap water analyzed (Table 2). However, subsequent analysis in March 1993 did not show PCE contamination, indicating that residents are not currently exposed to PCE through a drinking water pathway. In addition, the estimated past ingestion exposures in adults and children are far lower than the RfD or the intermediate MRL for PCE (Table 9). Therefore, adults and children are unlikely to suffer any noncarcinogenic health effects because of exposure to low levels of PCE. Similarly, the amount of PCE detected in groundwater near East 4th and East B Streets (Table 4) is unlikely to cause any noncarcinogenic health effects in the future because of potential exposure to low levels of PCE (Table 10).

IARC and DHHS consider PCE to be a possible human carcinogen because of animal studies. According to EPA, there is limited evidence that PCE has caused cancer in at least one laboratory rodent species. Although some epidemiological studies suggest a possible association between long-term occupational exposure to PCE and increased lymphatic malignancies and urogenital cancers, the evidence is regarded by IARC as inconclusive because the workers were also exposed to petroleum solvents and other dry cleaning agents as well as PCE (19). Based on this information, ATSDR has determined that persons who were exposed to PCE in public water supply wells and tap water may have no risk of developing additional cancer over their lifetimes because of exposure to low levels of PCE.

    Trichloroethene

TCE is also known as Triclene, Vitran, and other names used in industry. It is a nonflammable, colorless liquid at room temperature with an odor similar to ether or chloroform. It is a man-made chemical that does not occur naturally in the environment. TCE is mainly used as a solvent to remove grease from metal parts. It is also used as a solvent in other ways, and to make other chemicals (24).

TCE has been detected in public supply water wells (Tables 1A, 1B, 1D, 1E and 1F), in 3 of 8 samples of tap water (Table 2), in 3 of 16 private residential wells (Table 3), and in groundwater monitoring wells near West 1st and West D Streets - - a block from Ogallala Electronics (Table 4). Although there are no chronic MRLs or RfDs for TCE, the estimated ingestion doses for adults and children do not exceed the intermediate oral MRL for TCE (Tables 9 and 10). In addition, the estimated doses of TCE were between 10,000 and 1,000,000 times lower than the lowest experimental dose of TCE that caused no adverse effects in laboratory animals after 52 weeks of chronic/long-term exposure (24). In addition, subsequent samplings in March 1993 did not detect TCE contamination in most public water supply wells. Noncarcinogenic health effects are unlikely to occur because of exposure to low levels of TCE.

IARC and DHHS have not classified TCE as a human carcinogen. According to the EPA, there is limited evidence that TCE has caused cancer in at least one rodent species. Based on this evidence ATSDR has determined that adults and children who have been and are likely to be exposed in the future to TCE are unlikely to develop additional cancer over their lifetimes because of exposure to low levels of TCE.

    Solvent Vapors

Some production and maintenance workers who periodically apply solvents or service equipment have been exposed in the past, are now being exposed, and will be exposed in the future to solvents through inhalation. However, sampling data and other information are not available to evaluate these exposures.

Other Exposure Information

Several VOCs including TCE, PCE, 1,1-DCE, 1,2-DCE, 1,4-DCB, 1,1,1-TCA, xylene, and ethylbenzene were detected in soil gas (Tables 5, 6A, 6B, and 6C). ATSDR observed basements at many residences, some commercial buildings, and a few schools and public buildings within the central city area. If soil gas migrates into buildings, occupants would have been exposed in the past, would now be exposed, or may be exposed in the future through inhalation of contaminants. However, indoor air data and other information are unavailable to determine these potential exposures. In addition, workers engaged in excavation or who enter areas where chemicals have been released to soils potentially would be exposed to contaminants principally through skin contact and ingestion of soils/dust. Data and other information for soil are unavailable to determine these potential exposures.

B. Health Outcome Data Evaluation

Review of the Nebraska Vital Statistics Records (25), and the Nebraska Cancer Registry (26) did not show abnormal cancer deaths and incidence rates, or deaths due to other diseases in Keith County when compared to state rates.

C. Community Health Concerns Evaluation

  1. Can drinking water contaminated by site-related chemicals and/or exposure at the workplace cause asthma, lung, and lymph node diseases, and pericarditis?

Toxicological review of environmental data and other information does not indicate that residents or workers have been exposed to levels of site-related contaminants in drinking water at levels that would cause adverse health effects. However, some production and maintenance workers who apply solvents or service equipment have been, are now being exposed, and will be exposed in the future to solvents periodically through inhalation.

Although many organic chemicals can cause asthma, or related conditions, no studies have shown that the type of VOCs detected at the site have caused asthma or pericarditis in humans.

Some epidemiological studies suggest a possible association between long-term occupational exposure to PCE and increased lymphatic malignancies and urogenital cancers. However, the evidence is regarded by IARC as inconclusive because the workers were also exposed to petroleum solvents and other dry cleaning agents. One mortality study of laundry and dry cleaning workers exposed to a variety of solvents including carbon tetrachloride which indicated excess respiratory cancers can also be said to be inclusive for the same reason. Limited animal studies have also shown that dichloroethane (DCA) caused lung tumors in laboratory animals exposed to DCA through the skin. However, this has not been confirmed in humans. Without actual workplace exposure data it is difficult to determine whether or not that exposure could cause any health effects.



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