PUBLIC HEALTH ASSESSMENT
POOLS PRAIRIE SITE
(a/k/a Neosho Wells)
NEOSHO, NEWTON COUNTY, MISSOURI
To determine whether the residents living in the areas of contaminated groundwater
are exposed to contaminants, DOH evaluated the environmental and human components
that lead to human exposure. This pathways analysis consists of five elements
that ATSDR considers necessary for a completed exposure pathway. The five elements
are a source of contamination, transport through an environmental medium, a
point of exposure, a route of human exposure, and an exposed population. An
exposure pathway can be eliminated if at least one of the five elements is missing
and will never be present. Completed pathways require that the five elements
exist and indicate that exposure to a contaminant has occurred in the past,
is currently occurring, or will occur in the future. Potential pathways, however,
require that at least one of the five elements is missing, 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 (27).
Completed Exposure Pathways
Completed exposure pathways existed at the Pools Prairie site until whole-house filtering systems were installed in residences with known trichloroethylene (TCE) contamination above EPA's MCL. Completed exposure pathways still exist in some residences, but levels are below the MCL. The sources of the contamination are the four potential source areas located on the old Fort Crowder property where past releases and improper disposal of TCE occurred. The environmental medium is contaminated groundwater. The point of exposure is at residences that have contaminated private wells. The routes of exposure include ingestion, inhalation, and skin contact. The exposed population is the people using contaminated well water. The time frame for the completed exposure pathway was in the past when residents used contaminated private wells as their sole source of potable water.
Presently, residents with private well contamination above the MCL have been
provided with whole-house filtering systems and are no longer exposed to contaminated
water. The installation of the public water system should provide a long-term
solution and eliminate exposure pathways for those residents presently on whole-house
filtration systems and all others in the new service areas (See Figure 1) as
long as residents connect to the system. For those that don't connect to the
public water system and have wells contaminated above the MCL, a completed current
and future exposure pathway exists. For those with whole-house filtration systems,
a completed future exposure pathway will exist if the units are not properly
maintained. In addition, if wells outside the public drinking water system become
contaminated, a future completed exposure pathway will exist.
Potential Exposure Pathways
Present and future potential exposure pathways exist. Because the contamination remains in the groundwater at the Pools Prairie site, it is possible for residents to be exposed in the present and future if contamination in private wells increases above the MCL or the plume migrates and impacts additional wells. The installation of the public water system should eliminate potential exposure pathways in the two areas (Area 1 and 2) as long as residences connect to the system. Additional potential pathways could exist if the contamination plume moves into an area of private wells outside of the new public water service area where TCE has not been previously detected, or if new wells are drilled into areas of potential groundwater contamination (no drilling restrictions are in place).
There is the potential for exposure at the different contaminated source areas because the contamination is still present. Exposure could occur to remediation workers, the possible trespasser, others who may occupy or work on the site, or if the area is developed or used for another purpose before it is completely remediated. Since SA-2 and SA-3 at the test center are remotely located and somewhat secured, little unauthorized access is expected, although trespass has occurred in the past. Direct contact with highly contaminated materials is a potential source of exposure. Because contamination is located below the surface of the soil, remediation workers are the most likely to be exposed. Workers are expected to use the appropriate personal protection equipment to prevent that exposure. SA-4 is fenced and access is limited only to employees. Surface soil contamination levels detected so far at SA-4 do not pose a health concern. SA-1 is fenced and access is limited. Exposure through contact with the contaminated surface soil is not expected to cause health effects.
This section will discuss the health effects of exposure to specific contaminants. To evaluate 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 each route of exposure, such as ingestion and inhalation, and for the length of exposure, such as acute (less than 14 days), intermediate (15 to 364 days) and chronic (greater than 365 days) (27).
TCE and carbon tetrachloride are the major contaminants found in private wells at the Pools Prairie site. Other chemicals have been detected during the sampling of private wells, but were found to be below their MCL or not at a level of health concern. Exposure doses were calculated using the maximum level of the contaminant detected (310 ppb) and, in the case of cancer, for the maximum length of time of possible exposure (lifetime of exposure, 70 years). To date, it is unlikely that any residents were exposed through ingestion and inhalation to those levels of contamination for that length of time. However, the known maximums were used to consider the worst-case exposure for those residents who may potentially have contaminated wells outside the public water supply distribution area and residents not connecting to the public water supply.
The pathways of ingestion and inhalation are the major pathways of exposure
at the Pools Prairie site. Dermal contact with concentrated levels in an occupational
setting has been found to cause health effects, consisting mostly of dermatitis,
and some individuals can develop hypersensitivity to the chemicals (28). However,
dermal contact with TCE and carbon tetrachloride at the levels present in residential
wells are much lower than the levels reported in occupational settings, and
do not pose a health concern. A discussion of TCE and carbon tetrachloride through
the ingestion and inhalation routes of exposure and their possible health effects
are presented below.
Exposure through ingestion, inhalation, and dermal contact to TCE-contaminated groundwater above EPA's MCL has occurred in the past, is presently occurring at levels below the MCL, and exposure may occur in the future to residents not connected to or outside the new public water system being installed at the Pools Prairie site. TCE was used from 1956 to 1992 at SA-1, from 1956 to 1967 at SA-2, from 1956 to 1973 at SA-3, and from 1957 to 1992 at SA-4 (all dates are approximate). It is believed that TCE was used in large quantities at the different source areas, especially SA-2 and SA-3.
Residents could have been exposed to TCE-contaminated groundwater since the startup of operations in 1956-57, but exposure starting a number of years later is probably a more accurate estimate. In Area 1, the level of TCE has increased from 110 ppb in 1994 in the original private well, through 150 ppb in early 1995 to 180 ppb in 1997. This may indicate that the TCE has gradually been increasing over the years and that residents have not, until recent years, been exposed to these higher levels. In Area 2, levels of TCE have not been as high as in Area 1, but past levels are not known.
People can be exposed through ingestion by drinking contaminated water. Ingestion exposures were calculated using the maximum value of TCE (310 ppb) detected in private wells to determine the worst-case daily ingestion exposure dose for adults and children (see Appendix B). Ingestion exposure at this level is not expected since that level was detected in August 1996 after bottled water had been provided in July 1995. Due to insufficient data, ATSDR does not have intermediate and chronic ingestion guidelines for TCE. In reviewing the available literature on chronic exposure (greater than 365 days) to TCE through ingestion, all the animal studies found used much higher doses than the exposure dose calculated for this site. The lowest No Observed Adverse Effect Levels (NOAELs) dose found in chronic animal studies (50 milligram/Kilo-gram/day (mg/Kg/day)) was over 1,600 times greater than the child dose calculated for the site (0.031 mg/Kg/day). A NOAEL is a chemical specific dose at which no adverse health effects were observed in the study subjects (28). When converted from animal to human, with a protective factor of 100, the NOAEL would still be 16 times greater than the expected child dose.
People can also be exposed to TCE through inhalation while showering, bathing, and other activities. Inhalation exposures were calculated using the maximum value of TCE detected in private wells and assuming that 100% of the TCE was available for inhalation to develop a worst-case inhalation exposure. These calculations can be found in Appendix B. Inhalation exposures were found to be below the recommended level for acute exposure and slightly higher than the recommended level for intermediate exposure. ATSDR has not developed chronic recommendation levels for inhalation exposure to TCE. In reviewing the available animal data, the lowest NOAEL for chronic inhalation of TCE was 100 parts per million (ppm) for male rats. The study had some serious shortcomings (28). This level would be approximately 580 times greater than the calculated residential exposure dose (0.173 ppm) for this site.
In studies of humans who were exposed to TCE contaminated drinking water, varying conclusions have been reached. ATSDR has maintained a TCE Subregistry Baseline data file on approximately 5,000 persons with documented environmental exposure to TCE (along with other chemicals) through private wells. For the report, ATSDR compared health conditions reported by the TCE Subregistry registrants with health conditions reported in a nation-wide survey of the general population. Some health conditions were reported more frequently by certain age groups, and some had higher rates for only men or only women. This study did not confirm the health conditions (they were self-reported) and the study did not completely identify the exposure level. Persons in the study were exposed from 6.5 to 18 years to concentrations varying from less than 1 ppb to 19,380 ppb (determined from limited sampling data, usually one to two sampling events) (29, 30). Findings of the latest follow-up of the study indicate that subregistry participants had a reporting rate above the national norms in various age groups for speech impairment and hearing impairment for children under 10 years of age (only on the baseline study), anemia and other blood disorders, stroke, urinary tract disorders, liver problems, kidney problems, diabetes rates, and skin rashes. Although the findings of ATSDR TCE Subregistry report do not identify a cause and effect relationship between TCE exposure and adverse health effects, they do reinforce the need to continue ongoing follow-up of the participants (30).
Of the reported health problems listed above, only the rate of strokes was reported to increase with increasing concentration of TCE. For the other health problems, their occurrence did not increase with higher exposure levels. If the health problems were related with the exposure to TCE, we would expect the number of people with a specific health problem to increase with higher levels. Therefore, it is unlikely that the reported health problems (anemia and other blood disorders, urinary tract disorders, liver problems, kidney problems, diabetes rates, and skin rashes) are associated with the exposure to TCE in private wells. Of those reporting strokes, a good portion also reported having other health problems including hypertension, diabetes, and being smokers, all of which contribute to the incidence of stroke (29).
Therefore, based on the limited groundwater sampling data available at this
site (no data available on levels before 1994), significant non-cancer adverse
health effects would not be expected from exposure to TCE at this site.
Carbon tetrachloride exposure through ingestion, inhalation, and dermal contact has occurred in the past, may presently be occurring at levels below its MCL, and may occur in the future for residents not connected to or outside the area of the new public water system being installed at the Pools Prairie site. Carbon tetrachloride has been detected in two private wells above the MCL (maximum 8.4 ppb) and in numerous other wells below its MCL of 5 ppb. So far, it has been found almost exclusively in Area 1 (5, 31)
Residents could have been exposed to carbon tetrachloride-contaminated groundwater since the startup of operations in 1956-57. Daily exposure doses were calculated for ingestion and inhalation exposure at the maximum value detected in water (8.4 ppb). This level was used in the calculations to develop a worst-case exposure scenario, but ingestion exposure at this level was not expected since that level was detected in August 1996 after bottled water had been provided in July 1995. These calculations can be found in Appendix B.
People can be exposed through ingestion by drinking contaminated water. Ingestion exposures were calculated to determine a maximum daily exposure dose (see Appendix B). Due to insufficient data, ATSDR does not have chronic ingestion guidelines for carbon tetrachloride (32). However, EPA has developed a chronic Reference Dose (RfD) of 0.0007 mg/Kg/day for carbon tetrachloride (33). An RfD is an estimate of a daily exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable risk of adverse health effects for a lifetime (70 years) of exposure (34). The calculated dose for a child (0.00084 mg/Kg/day) at this site slightly exceeds the RfD. However, the comparison of the child's dose to the RfD is not applicable because a person is only a child for a few years of his or her life. Therefore, no adverse health effects from ingestion exposure to carbon tetrachloride at this site are expected.
People can also be exposed to carbon tetrachloride through inhalation. Inhalation
exposures were calculated to determine a maximum daily exposure dose using the
assumption that 100% of the carbon tetrachloride was available for inhalation
(See Appendix B). Exposures were found to be below the recommended levels for
acute and intermediate exposure. ATSDR has not developed chronic recommendation
levels for inhalation exposure to carbon tetrachloride. The doses for adults
and children at this site were below any NOAELs seen in animal studies (32).
Therefore, significant adverse health effects would not be expected from inhalation
exposure to carbon tetrachloride at this site.
Combination of Chemicals
TCE and carbon tetrachloride can affect the same human target organs (liver
and kidney); therefore, the exposure to the two chemicals should be considered
to be at least additive. However, given the extremely conservative assumptions
used in deriving exposure doses, the likelihood of effects from the combination
of chemicals would be very low. In addition, when exposure is eliminated, mild
damage done to the liver and kidneys is usually repaired because of their regenerative
The American Cancer Society estimates that 40% of the population will develop some type of cancer in their lifetime (35). DOH has calculated the cancer risk for the Pools Prairie site using the maximum detected value of contaminants for a lifetime of exposure (70 years) to develop a worst-case exposure scenario for the site. These calculations can be found in Appendix B. Overall, there may be a slightly increased risk of developing cancer from a lifetime of exposure to contaminated groundwater from this site.
The ability of TCE to cause cancer is presently under review by EPA, is classified as reasonably anticipated to be carcinogenic by the National Toxicology Program (NTP), and is classified as probably carcinogenic to humans (limited human evidence, sufficient evidence in animals) by the International Agency for Research on Cancer (IARC). ATSDR has developed a Cancer Risk Evaluation Guide (CREG) for different chemicals. CREGs are comparison values set by ATSDR to only determine if a chemical is above a level that should be further evaluated. The CREG is a level that if ingested for a lifetime at 2 liters per day, could cause one additional cancer in a population of one million (1x10-6). A CREG for TCE is currently not available since TCE is under review by EPA (33). Humans exposed to TCE for chronic periods via the inhalation and dermal route in the workplace apparently do not experience an increased incidence of cancer. Ingestion exposure to TCE and cancer in humans is controversial, with a number of studies indicating an association and a number of studies not indicating an association (28). Results from the ATSDR TCE Subregistry exposure study did not report an excessive rate of cancer when compared with the general population (29).
Carbon tetrachloride is considered a probable human carcinogen by EPA, is reasonably
anticipated to be a carcinogen by the NTP, and considered possibly carcinogenic
to humans by the IARC. ATSDR currently has a CREG level of 0.3 ppb for carbon
tetrachloride, for a lifetime of exposure in drinking water. Again, CREGs are
used only to determine if the chemical should be further evaluated (33). Based
on the levels found and conservative exposure assumptions, we do not expect
a significant increased risk of developing cancer from carbon tetrachloride
at this site.
Children and Other Sensitive Populations
A sensitive population will exhibit a different or enhanced response to hazardous chemicals than will most persons exposed to the same level of hazardous chemicals in the environment. Reasons may include genetic makeup, age, health and nutritional status, and exposures to other toxic substances. In general, developing fetuses are susceptible to the toxic effects of chemicals (including TCE and carbon tetrachloride) that can cross the placental barrier. The youngest of the population with immature and developing organs (i.e., premature and newborn infants and children) and the elderly with declining organ functions will be more vulnerable to toxic substances, in general, than healthy adults (27).
A number of studies have suggested or shown associations between TCE exposure and children's health effects, but these studies also had flaws which question their validity (28). These studies are discussed below.
In certain residents of Tucson, Arizona, exposed to TCE (6-239 ppb) and other contaminants (dichloroethylene and chromium) in their drinking water from certain wells, an association was found between the elevated levels of TCE in drinking water and congenital heart defects in children whose parents were exposed during the month before conception and the first trimester of pregnancy. Among children whose mothers lived in the areas receiving TCE contaminated water during the first trimester of pregnancy, the rate of congenital heart defects was two and a half times higher than among children of mothers who were not exposed to TCE during pregnancy. Moreover, the rate of congenital heart defects decreased in the previously exposed area after the contaminated wells were shut down. The most significant limitation of the report is that the exposure was ill-defined. Specifically the exact levels of exposure to individuals could not be determined, the areas that received TCE-contaminated were not clearly determined, the first year of exposure was unknown, the actual concentration of TCE varied from year-to-year (though actual concentrations were measured in 1981), and other chemicals were present (28).
In a study of residents exposed to drinking water contaminated with solvents (including TCE at 267 ppb) in Woburn, Massachusetts, there was a suggestion that the combination of eye and ear anomalies and the combination of central nervous system, chromosomal, and oral cleft anomalies in newborns were associated with the contaminated water. However, several scientist have questioned the biological relevance of the unusual groupings of those anomalies for purposes of statistical analysis. The grouping of central nervous system disorders, chromosomal disorders, and oral cleft anomalies is questionable because they are not linked in embryological development. In addition, not enough demographic or medical background information was provided on the subjects in this study to indicate that other potential contributing factors were being considered. In addition, the study was performed following considerable publicity about the well contamination and possible health effects that could potentially affect recall bias of the participants (28).
Also in Woburn, Massachusetts, a case-control investigation (1981) and a follow-up study (1997) was conducted by the Massachusetts Department of Public Health to determine if there was an association between leukemia cases in the city and wells that supplied a portion of the city which were contaminated with TCE (267 ppb), tetrachloroethylene, low levels of other VOCs, and inorganic arsenic. The investigation concluded that the incidence of childhood leukemia was elevated in the city of Woburn and almost half of all cases occurred in the area supplied by the two contaminated wells. Also, the majority of the excess cases were male. The finding of the study suggests that the relative risk of developing childhood leukemia was greater for those children whose mothers were likely to have consumed water from the contaminated well. In contrast, there appeared to be no association between the development of childhood leukemia and the consumption of water from the contaminated wells by the children. Findings in this study are limited by the small numbers of cases and the limited information on exposures (28, 36).
Other sensitive populations including those that consume alcohol or who are treated with disulfiram (a drug used to treat alcohol dependancy) may be at greater risk of TCE poisoning. This occurs because ethanol and disulfiram can both inhibit the metabolism of TCE and cause it to accumulate in the bloodstream, potentiating its effects on the nervous system. Also, those with compromised liver and kidney function may be at a higher risk from exposure to TCE or its metabolites. The liver serves as the primary site of TCE metabolism and the kidney as the major excretory organ for TCE metabolites (28).
Those more susceptible to carbon tetrachloride toxicity include moderate to heavy drinkers, those with significant exposure to TCE and pesticides (DDT, chlordecone, PCBs, and PBBs), drugs (phenobarbitals), and diabetics. For exposure to carbon tetrachloride, no studies were located regarding developmental or reproductive effects in humans after exposure (32).
Dose calculations of past exposureat the Pools Prairie site, using the maximum level of TCE that was detected at the site (although residents are not known to have been exposed at these levels) indicate that according to the lowest adverse effect level of an animal study, the possibility of birth defects from past exposures may potentially exist. However, a review of cancer and birth record data did not reveal an increased incidence of leukemia or birth defects at this site.
Because it is difficult to predict the amount of exposure that a developing fetus may be exposed to at this site, it is also difficult to predict what birth effects or disease, if any, may result from exposure to TCE or carbon tetrachloride at this site. Women who believe they were exposed to TCE during their pregancy and are concerned about possible health impacts on the fetus, should consult their presonal physicians.
Residents with contaminated private wells and those living in the contaminated areas have expressed a number of concerns during Citizen's Advisory Group (CAG) meetings and other meetings held to inform the public about the site. This section will address the following community health-related concerns:
- What health effects will the exposure to the contaminated well water have on me and my children in the present and in the future, such as cancer?
Based on conservative assumptions (using the highest levels of contamination detected) to calculate exposure, significant adverse health effects are not expected from known past exposure to the contaminated well water. Both TCE and carbon tetrachloride are excreted from the body and any mild effects on the liver, kidney, and nervous system are reversible after exposure ends, even after occupational exposure at levels much higher than found at the site. Cancer calculations for past exposures (made assuming that TCE is carcinogenic and exposure occurred at the maximum level and time) indicated that overall, there doesn't appear to be a significant risk of developing cancer from past exposure to contaminated groundwater at the site. However, cancer calculations were also made for a lifetime of exposure at the maximum level of contamination to those who do not connect to the public water system. Assuming 70 years of exposure to the highest level of TCE detected (310 ppb), it appears there is a potential for an elevated risk of cancer for a lifetime of exposure.
- Has my exposure to the TCE contamination in my well been the cause of rashes, dizziness, or other symptoms?
Rashes, dizziness, as well as other symptoms from exposure (inhalation and dermal contact) to TCE and carbon tetrachloride have been seen in industry when working with pure TCE or TCE at very high concentrations. Considering that the maximum detected level was 310 ppb, it seems very unlikely that any of the mentioned health effects would be caused by the contamination in the groundwater, unless a person is sensitized to these particular chemicals. Persons having these symptoms should consult their private physicians.
- Are my livestock being affected by drinking water from an open trough filled from a contaminated well?
It is unlikely that livestock are being affected by the low levels of contamination in their water supply. TCE and carbon tetrachloride are very volatile and evaporate quickly from surface water and surface soil. Considering the levels of contaminants present in groundwater and that, once exposed to the atmosphere, the chemicals evaporate very quickly from the watering tanks into the open air, the concentrations present for the livestock to drink would be much lower than the level present in the well water. Also, since both VOCs do not bioaccumulate (build up in the animal) and what small concentration that may get into their system is excreted (as in humans), there is no harmful effect expected to the livestock or humans that consume them.
Other concerns expressed by residents include the decline in their property values and the stigma of living near and affected by a site that is proposed for the NPL. Additional concerns include: not wanting to be annexed into the city of Neosho, a preference for individual wells, frustration with the bureaucracy, a desire for more private well sampling and faster reporting of results, not knowing what they are drinking since the level of contamination may have changed since their well was last sampled, as well as other non-health related concerns. These concerns are beyond the scope of this public health assessment and some may fall under the authority of local and regulatory agencies.
On December 14, 1999, DOH held a public availability session to present the public comment version of the Pools Prairie Site Public Health Assessment to the public and to gather and discuss any further concerns residents may have. No additional health concerns were presented in person at the meeting or received in the mail. Some technical comments were received on the document and are discussed in Appendix C.