EAST MULTNOMAH COUNTY GROUND WATER CONTAMINATION
GRESHAM, MULTNOMAH COUNTY, OREGON
A. On-Site Contamination
Because the proposed National Priorities List (NPL) site incorporates the total known area of groundwater contamination and possible future migration of groundwater contamination, there is no off-site contamination. Therefore, this public health assessment will not have a separate section for discussion of off-site contamination. This Environmental Contamination and Other Hazards section is divided into three subsections. The first subsection discusses the environmental contamination found at the sources of the groundwater contamination. The environmental contamination found off the source properties is discussed in subsection two. The last subsection will discuss the contamination found in residential wells near the sources of contamination.
In order to determine what environmental contaminants might constitute a concern, the Agency for Toxic Substances and Disease Registry (ATSDR) staff has evaluated all available environmental monitoring data from 1985 to present. Comparison values were used as a basis for evaluation of the data and to determine which contaminants should be looked at more closely. Comparison values are estimated health-based environmental concentrations below which no known or anticipated adverse effect on the health of persons should occur. The values allow adequate margins of safety. Appendix 3 contains descriptions of the comparison values used in this public health assessment.
A contaminant is selected for further evaluation if the contaminant concentration in a valid environmental sample exceeds comparison values. The presence of a contaminant on the lists in the tables of this section does not mean that either exposure to the contaminant or adverse health effects have occurred or will occur. Inclusion in the list indicates only that the potential for human exposures to the selected contaminants and the potential for adverse human health effects as a result of any exposures to the selected contaminants are discussed in more detail in later sections of this public health assessment.
1. Environmental Contamination at the Sources of the Groundwater Contamination
To date, the U.S. Environmental Protection Agency (EPA) and the Oregon Department of Environmental Quality (ODEQ) have identified three sources of the groundwater contamination: Boeing Company, Cascade Corporation, and Swift Adhesives (1,4). Environmental investigations at each facility have identified several causes for the groundwater contamination. At the Boeing facility, waste material from Boeing and other former owners/operators at the property had been disposed of at various locations. The Boeing Company is remediating both the Troutdale Gravel Aquifer (TGA) groundwater contamination and the sources of contamination (i.e., pumping and treating the contaminated groundwater and soil remediation) at its facility (5-7).
Leaking underground storage tanks and the former degreasing operations were the main sources of environmental contamination at the Cascade Corporation facility (8-14). The contamination from underground storage tanks and the degreasing operations are being remediated (i.e., removal of the contaminated soils and tanks and pumping and treating the contaminated TGA groundwater are underway).
The cause of the environmental contamination at the Swift Adhesives plant was land disposal of waste adhesives (15-17). These wastes were removed in 1990. Swift Adhesives is presently evaluating methods of remediating the groundwater contamination found at and near its facility.
The environmental investigations have identified the extent of contamination at the three facilities. Appendix 4, Tables 1, 2, and 3 present the results of the investigations for the Boeing Company, Cascade Corporation, and Swift Adhesives, respectively. Environmental samples taken at these facilities were checked for all of the compounds on the EPA Target Compound List. Only chlorinated organic solvents (i.e., 1,2-dichloroethane; 1,1-dichloroethylene; cis-1,2-dichloroethylene; tetrachloroethylene; 1,1,1-trichloroethane; trichloroethylene [TCE]; and vinyl chloride) were detected above health comparison values (5-17).
Chlorinated organic solvents have been detected in the soils and groundwater at each facility. Most of the soil contamination is located several feet below the ground surface and is generally not accessible to people unless the soil is excavated (5-17).
Because most of the waste materials and the leaking storage tanks were buried, surface soil contamination is unlikely.
Analytical results of groundwater samples taken at the Boeing Company and Cascade Corporation facilities indicate that the contamination has migrated into the two upper groundwater regional aquifers in Multnomah County (i.e., the TGA and the Troutdale Sandstone Aquifer [TSA]) (5-14). The results of the groundwater investigations at the Swift Adhesives facility indicate chlorinated organic solvents have not entered the regional aquifers but have migrated into a local perched aquifer (localized lens of groundwater which is separated from a regional aquifer) (15-17).
Cascade Corporation formerly had a well at its facility. The groundwater obtained from this well was used for process water; it was never used as a source of drinking water (8). Analytical results of samples taken from this well indicated that TCE was in the well (upwards of 410 micrograms of TCE per liter of water [µg/L]). This well was abandoned.
There are no bodies of surface water at any of the source areas. Therefore, surface water and sediment samples were not taken. Because no foodstuff is grown or produced at these facilities, biota samples were not taken.
No ambient air samples were taken at the three source facilities. Air monitoring (e.g., monitoring using Hnu or other portable air monitoring equipment) was conducted during the site investigations. The monitoring activities did not detect any significant air contamination at these facilities (5-17).
A preliminary environmental investigation at the Firestone facility (see Appendix 1, Figure 1 for location) indicates that there might be some groundwater contamination at that location (4). Based on the Swift Adhesives investigation and the spatial distribution of contaminants at Firestone, it is unlikely that the source of the detected contaminants at Firestone are from an upgradient source. Monitoring of downgradient wells of this facility have not shown any contamination.
2. Environmental Contamination Beyond the Property Lines of the Sources
Appendix 4, Tables 4, 5, and 6 present the results of the environmental investigations conducted away from the three known sources of groundwater contamination within the proposed NPL site (Boeing Company of Portland, Cascade Corporation, and Swift Adhesive, respectively) (5-17). These results indicate that the groundwater contamination found at the three facilities has moved beyond the property lines (see Appendix 1, Figure 3).
The groundwater contamination that originated from the Cascade Corporation facility has moved towards the north, northeast and northwest. The northwest portion of the Cascade groundwater contamination has moved onto and beyond the property of the Boeing Company. The groundwater contamination that originated from the Boeing Company has mixed with the Cascade groundwater contamination (5-14). Appendix 1, Figures 2 and 3 depict the approximate extent of groundwater contamination within the regional groundwater aquifers at the proposed NPL site. The groundwater contamination from Swift Adhesive facility is not depicted in Appendix 1, Figures 2 and 3 because the groundwater contamination from the Swift Adhesive has not moved into the regional aquifer system.
Surface water samples have been taken from the two springs near the Cascade facility, from the drainage ditch near the Cascade facility, and from the Columbia Slough near the Boeing facility. Sediment samples were also taken from the drainage ditch and the Columbia Slough (5-14). No environmental contaminants were detected above health comparison levels in the sediment and surface water samples taken from the drainage ditch near the Cascade facility (8-14). Chlorinated organic solvents above health comparison values were detected in the surface water samples taken from the springs and the Columbia Slough (see Appendix 4, Tables 4 and 5) (5-14). No soil contamination was found beyond the property lines of the sources (5-17).
The Boeing Company and Cascade Corporation are evaluating methods of remediating the groundwater contamination that has migrated from their facilities.
3. Residential Well Contamination
Residential wells located near the three sources of groundwater contamination have been sampled (4-7,11-13). A detailed well inventory has been conducted by ODEQ, Boeing Company, and Cascade Corporation. Analytical results of these samples indicate that TCE and tetrachloroethylene have migrated into some wells at levels above comparison values (see Appendix 4, Table 7).
The highest residential well contamination was found near (northeast) and downgradient of the Cascade Corporation facility (i.e., TCE as high as 105 µg/L). Contaminated residential wells downgradient of the Boeing Company are reported to have TCE as high as 40 µg/L (7). There are no contaminated residential wells near the Swift Adhesive facility.
B. Quality Assurance and Quality Control
ATSDR was able to obtain quality assurance and quality control (QA/QC) information for most of the data presented in this public health assessment. This information indicates appropriate QA/QC was performed for the samples. The conclusions presented in this public health assessment are based in part on the data presented. The validity of the conclusions, therefore, depends on the accuracy and reliability of the data provided.
C. Physical and Other Hazards
No physical or other hazards were noted during the ATSDR site visit except those normally found at an industrial facility or residential area.
D. Review of Toxic Chemical Release Inventory (TRI) Data
To identify facilities that might contribute to the environmental contamination within the proposed East Multnomah County Groundwater Contamination NPL Site and to determine whether people maybe exposed to hazardous substances in addition to their possible exposures from the proposed NPL site, ATSDR searched the 1987-1991 files of the Toxic Chemical Release Inventory (TRI) databases for site-related contaminants being discharged within the proposed NPL site (18). TRI was developed by the EPA from chemical release (air, water, and soil) information provided by certain industries.
Several limitations of TRI data should be noted (19). The air release data in TRI could be estimates or actual measurements. Many of the reported data are estimates based on conservative (overestimated) scenarios. Consequently, the levels of emissions recorded in TRI are often biased on the high side. In addition, reporting is restricted to specific chemicals that are used or released above specified amounts. Finally, investigators believe there have been and still are industries that do not report releases. Representatives of smaller industries might not be aware that reporting requirements exist or that they are responsible for such reports.
The search of TRI indicates that only one facility within the proposed NPL site has released site-related chemicals to the environment (18). For the five years for which TRI data were evaluated and available, the Boeing Company reported that it released an average of 157,653 pounds of 1,1,1-trichloroethane per year to the ambient air. The significance of this emission is discussed in the Potential Pathways section of this public health assessment.
In this section of the Public Health Assessment, the possible environmental exposure pathways are evaluated to help determine whether individuals have been, are, or will be exposed to site-related contaminants. The pathway analysis consists of five elements:
An environmental exposure pathway is considered complete when there is good evidence that all five elements exist (20). The presence of a completed pathway indicates that human exposure to contaminants has occurred in the past, is occurring, or has the potential to occur in the future. When one or more of the five elements of an exposure pathway are missing, that pathway is considered potential. The presence of a potential exposure pathway indicates that human exposure to contaminants could have occurred in the past, could be occurring, or could occur in the future. An exposure pathway can be eliminated from consideration if at least one of the five elements is missing and will never be present. If there is uncertainty about the site-relatedness of the contaminants of concern in an exposure pathway, the pathway will be evaluated as if the contaminants were site-related.
The completed, potential, and no known environmental exposure pathways are discussed below. In addition, Tables 1 and 2 in Appendix 5 present the estimates of the number of exposed individuals at the proposed East Multnomah County Groundwater Contamination National Priorities List (NPL) site. The population estimate for the completed environmental exposure pathway was developed by using a computer geographic information system (GIS). The approximate extent of groundwater contamination (Appendix 1, Figure 3) was digitized and correlated to the 1990 U.S. Census information. The results of the GIS analysis is presented in Appendix 1, Figure 5.
A. Completed Environmental Exposure Pathways
There is good evidence that people have been, are being, and can be exposed (ingestion, inhalation, and skin contact) to site-related contaminants via residential drinking water wells. Analytical results of environmental samples taken from the regional groundwater aquifers (Troutdale Gravel Aquifer [TGA] and Troutdale Sandstone Aquifer [TSA]) indicate that various chlorinated organic solvents have moved beyond the property boundaries of the Boeing Company and Cascade Corporation facilities. Many residences near these facilities obtained their drinking water from the regional groundwater aquifers via private wells. Analytical results of samples taken from the private wells show that trichloroethylene (TCE) and tetrachloroethylene have migrated into some of the wells at levels above health comparison values.
Because of the complex hydrogeology within the proposed NPL site, it is not possible to determine precisely when each well became contaminated. Because of the total extent of groundwater contamination (see Appendix 1, Figure 2), the average linear velocity of groundwater within the TGA and TSA aquifers (0.1 to 2.3 feet per day and 0.07 to 0.3 feet per day, respectively), and the fact that the industrial operations have been conducted at the Boeing Company and Cascade Corporation facilities since the 1963 and 1953 respectively, it is possible that the drinking water wells near the Boeing Company and Cascade Corporation facilities might have been contaminated for more than 10 years. No matter when TCE and tetrachloroethylene entered the residential drinking water wells, it is likely that the initial concentrations would have been well below health comparison values (i.e., 3 micrograms of TCE per liter of water [µg/L] and 0.7 µg/L for tetrachloroethylene) (5). The TCE and tetrachloroethylene residential drinking water well concentrations would have slowly increased over time until the concentrations in some of the well water reached the levels detected recently (a maximum of 105 µg/L for TCE and 3 µg/L for tetrachloroethylene) (see Appendix 4, Table 7).
Most of the people with contaminated wells have been given alternative drinking water sources. However, two homeowners have refused to accept alternative drinking water and might still be obtaining drinking water from the contaminated well they jointly use. Until the regional groundwater contamination is remediated, the level of contamination in the well is likely to increase over time, because higher concentrations of site-related contaminants have been monitored upgradient from this well. The complex hydrogeology within the proposed NPL site makes it difficult to predict how high the level of contamination in the well might become. Groundwater samples from monitoring wells upgradient from this contaminated well indicate that TCE contamination of around 100 µg/L is near this well. Therefore, it is possible that the contamination in this residential well may eventually become contaminated with TCE at that level.
Nineteen wells have been shown to be contaminated. In addition, Boeing Company and its predecessors operated two production wells that were used for drinking water supply prior to 1986.
It is estimated that 1,076 people live within the area that encompasses the approximate extent of groundwater contamination (see Appendix 1, Figure 5). These people might have been exposed to site-related contaminants if they obtained drinking water from private or trailer park wells. This estimate is probably an overestimation of the exposed population because not everyone who lived within the groundwater contamination area relied upon wells for their drinking water.
Only two families have chosen to continue using water from a well known to be contaminated at levels of public health concern. These are the only persons known to have ongoing exposure to contaminated water at levels of public health concern.
There are several private wells in use that have detectable levels of TCE (below health comparison values). In addition, the mobile home park wells are possibly being used for irrigation water and for swimming pool water. Human exposures to contaminated water from these wells are not likely to be at levels of health concern.
There are no other known completed environmental exposure pathways related to the proposed East Multnomah County Groundwater NPL site.
B. Potential Environmental Exposure Pathways
There are five environmental exposure pathways through which people could have possibly been exposed to site-related contaminants. People could possibly be exposed to site-related contaminants because of future migration of contaminated groundwater into drinking water wells, worker exposures, contaminated subsurface soil being disturbed, discharges to the ambient air, and surface water contamination.
1. Future Groundwater Migration
Three wells for the City of Portland's backup water system are downgradient of the contaminated groundwater areas (i.e., wells that withdraw water from the TSA or SGA). Analytical sampling results of these wells indicate the wells are not presently contaminated with site-related contaminants. Pumping tests of these wells indicate that site-related contaminants could possibly migrate into the city wells if these wells are used for an extensive period of time (years) and the areas of groundwater contamination are not controlled or remediated. The City of Portland wells in the TSA and SGA are not now being used as a drinking water supply.
In addition to the City of Portland wells, there are several residential and small community wells (West Interlachen Corporation, Interlachen Corporation, and the Blue Lake Co-op) downgradient of the contaminated groundwater areas. These wells could also become contaminated with site-related contaminants if the areas of groundwater contamination are not controlled or remediated. Analytical results of samples taken from these wells indicate the wells are not contaminated with site-related compounds and are not contaminated with any other chemical at levels of health concern.
If these wells are used and become contaminated, people could be exposed in the future to site-related contaminants at levels of public health concern via ingestion, inhalation, and skin contact.
EPA, the Oregon Department of Environmental Quality (ODEQ), Boeing Company, and Cascade Corporation are evaluating ways to control and remediate the areas of groundwater contamination, and have taken interim measures to control migration while the city of Portland pumps from supply wells that only withdraw water from the Blue Lake Aquifer. (Note: Pump tests indicate that it is unlikely that the contaminants will enter the Blue Lake Aquifer.)
According to EPA, 750,000 people use the affected groundwater aquifers for standby or as their primary drinking water sources. If the groundwater contamination is not remediated or controlled and if the TSA and SGA City of Portland supply wells are used, there is the potential that these wells could be contaminated and all of the people could possibly be exposed to some site-related contaminants.
2. Worker Exposures
When waste materials were disposed of at the Boeing Company, Cascade Corporation, and Swift Adhesive facilities, workers could have been exposed via ingestion, inhalation, and skin contact in the past to chlorinated organic solvents. The extent of exposure would depend upon what personal protection equipment (e.g., gloves, protective clothing, and respirator) the workers wore; the length of contact; and the amount of waste material ingested, inhaled, and accumulated on the skin. The Agency for Toxic Substances and Disease Registry (ATSDR) does not have adequate information to estimate how extensive the occupational exposures might have been.
In addition to material handling, waste disposal, and other occupational exposures, workers at the Boeing Company and Cascade Corporation facility might have inhaled site-related contaminants found in the Boeing Company and Cascade Corporation industrial wells. Depending on how the well water was handled inside the plants, the chlorinated organic solvents in the well water could have volatilized into the work areas of the plants. ATSDR does not have adequate information to estimate how extensive the exposures might have been.
Boeing Company of Portland and Cascade Corporation are pumping contaminated groundwater out of the ground at their facilities. The contaminated groundwater is being treated by an air stripping process at each facility. This air stripping process results in the emission of chlorinated organic solvents into the air. Workers at these facilities could inhale these air contaminants. Evaluations conducted by Boeing Company and Cascade Corporation indicate that the air strippers are discharging at levels below regulatory limits. Although the levels are below regulatory limits, the workers are presently being exposed to low levels of chlorinated organic solvents in addition to the exposures from the past. ATSDR is not able to evaluate the public health implications of the continued low level inhalation exposure to workers exposed in the past to higher concentrations of chlorinated organic solvents from drinking water because the scientific information concerning this type of exposure situation is not clear.
3. Subsurface Soil
Analytical results of soil samples taken at the Boeing Company, Cascade Corporation, and Swift Adhesive facilities indicate that subsurface soils were contaminated with chlorinated organic solvents above health comparison values. Individuals could have been exposed via inadvertent consumption, inhalation (i.e., dust), and skin contact with the contaminated soil whenever these soils were excavated or disturbed. Because of the inadvertent nature of these possible exposure pathways and because the subsurface soils are not disturbed frequently, it is unlikely that people have been exposed to any significant amounts of site-related contaminants above levels of health concern from soil.
4. Ambient Air
A search of the EPA Toxic Chemical Release Inventory (TRI) database indicates that the Boeing Company released approximately 157,653 pounds (average) of 1,1,1-trichloroethane per year into the ambient air during the years 1987 through 1991. People living near the Boeing facility might have inhaled and might still be inhaling some of the 1,1,1-trichloroethane being released to the ambient air. This possible exposure route is in addition to the drinking water exposures to chlorinated organic solvents. Because no ambient air monitoring data is available, ATSDR is not able to determine the extent of human exposure associated with this air discharge.
5. Surface Water
Environmental samples taken from the Shepard Spring, the Taggart Spring, and the Columbia Slough indicate that chlorinated organic solvents (see Appendix 4, Tables 4 and 5) have migrated from the groundwater into these bodies of water. Neither the springs nor the slough are currently being used as a drinking water source. The Shepard Spring was used in the past to water livestock. The Columbia Slough has been and is being used for recreation. People could potentially have been exposed, could be exposed now, and could be exposed in the future to the surface water contaminants via inadvertent consumption and inhalation of the surface water and skin contact with the water or volatilized solvents. However, these exposures are not likely to occur very frequently and are not likely to result in exposures to any significant amounts of site-related contaminants above levels of health concern.
C. No Known Environmental Exposure Pathways
None of the chlorinated organic solvents detected at the proposed East Multnomah County Groundwater Contamination NPL site accumulate in animals or plants (21-27). Therefore, it is unlikely people will be exposed to foodstuffs contaminated with site related contaminants.
As discussed in the Pathways Analyses section, the residential drinking water wells exposure pathway is considered completed (i.e., human exposure occurred or is occurring) for persons who used or use contaminated wells. The contaminants of concern - those detected above comparison values - in this pathway are trichloroethylene (TCE) and tetrachloroethylene. No other nonoccupational exposure pathways are apparent for persons living in the affected area.
The Toxicological Evaluation portion of this section discusses the possible health hazard from past and future exposures to the two contaminants of concern in the residential drinking water wells. The community health concerns are addressed in the Community Health Concerns Evaluation section. The reasons that health outcome data were not evaluated are discussed in the Health Outcome Data Evaluation section.
A. Toxicologic Evaluation
1. Introduction
Typically, the toxicological evaluation in a public health assessment is a comparison of the exposure dose - the amount of a substance individuals in an exposure pathway are exposed to daily - to an appropriate health guideline. For noncarcinogens, this is usually the Agency for Toxic Substances and Disease Registry's (ATSDR's) Minimal Risk Levels (MRLs) or the U.S. Environmental Protection Agency's (EPA's) Reference Doses (Rfds). The MRLs and Rfds are estimates of daily human exposure to a contaminant below which noncarcinogenic adverse health effects are unlikely to occur (20). That means that any exposure dose below the appropriate MRL or Rfd does not represent a hazard to human health excluding cancer risks. However, for exposure doses above an MRL or Rfd, there is a wide zone of uncertainty whether adverse health effects will occur. Therefore, a review of the toxicological literature is done to determine whether the specific exposure situation represents a hazard to public health. The results of the comparison of exposure doses to health guidelines and the methodology for calculating the exposure doses are described in Appendix 6.
Adults and children exposed to the maximum levels of TCE (105 micrograms of TCE per liter of water [µg/L]) in the residential drinking water did not exceed the intermediate health guidelines (exposure durations of 15 through 364 days). However, there is some indication from recent studies that health effects from exposures of more than a year might occur at the TCE levels found in the residential drinking water supply. Because of this, the possible health consequences of exposure to TCE will be discussed in the next subsection. In addition, the limitations of the recent studies will be discussed.
Adults and children exposed to the maximum levels of tetrachloroethylene (3 µg/L) in residential drinking water did not result in human exposres that exceed the chronic health guidelines. Therefore, it is unlikely that adverse health effects would occur to people exposed to tetrachloroethylene contaminated residential drinking water.
TCE and tetrachloroethylene are considered probable human carcinogens (28). The risk of carcinogenic health effects from TCE and tetrachloroethylene exposure was evaluated using the methods described in Appendix 6. Based on this evaluation, the past exposures to TCE and tetrachloroethylene in the residential drinking water wells represents no apparent increased risk of cancer. However, two homeowners are presently using a contaminated drinking water well and have refused alternative drinking water supplies. It is possible that the amount of TCE and tetrachloroethylene will increase in the well. Thus, people ingesting the contaminated water from the well might have a low increased risk of developing cancer.
2. Discussion of Possible Health Consequences
The possible health consequences of exposure to TCE are described in the following paragraphs.
Health assessors determine the possibility of health consequences by comparing the exposure to the results of epidemiologic evaluations of human exposures to a chemical. If valid human data are not available, information from properly conducted animal studies is used. The type of data used for an evaluation is indicated for each chemical.
Several recent studies of individuals exposed to TCE in drinking water identified several health effects which had rates greater than rates in comparison groups (29-34). The health effects reported in those studies were stroke and impaired hearing (29); slowed eye blink response (30,31); several abnormal neurophysiological and neuropsychological parameters (31); impairment of the immune system (32); increased occurrence of the symptoms related to lupus (33); and congenital cardiac malformations (34). Those studies are discussed in this section.
When results were compared with results for respondents to the National Health Interview Survey, elevated rates for several health outcomes were found in participants in the ATSDR TCE exposure registry (29). These outcomes included (for various age and sex groups) speech impairments, hearing impairments, hypertension, stroke, liver problems, anemia and other blood disorders, diabetes, kidney disease, urinary tract disorders, heart conditions, and skin rashes. Only the rates for strokes and impaired hearing were related to the concentration of TCE. The approximately 4,300 participants in this registry were exposed to 2 to 19,380 µg/L of TCE in drinking water for up to 18 years. These results are limited by the lack of confirmation of the health conditions and less than complete identification of exposure levels. The results do not establish a cause-and-effect relationship between exposure and adverse health outcomes.
Significantly slower eye blink responses were identified in TCE-exposed individuals from Woburn, Massachusetts and Tucson, Arizona (30,31). Those slower responses were considered a subclinical effect (i.e., not harmful). The validity of these results is limited by the nonrandom selection of the participants and the lack of an identification of a dose-response relationship. In addition, a recent study of workers exposed for an average of 16 years to TCE concentrations many times stronger than those found in Arizona and Massachusetts found no change in the eye blink response (35).
Impairment of the immune system was observed in TCE-exposed individuals from Woburn, Massachusetts (32). This immunologic impairment was evidenced by altered T-cell ratios (T-cells are a type of white blood cell), increased incidence of autoantibodies, increased infections, and recurrent rashes. The validity of these results is limited by the nonrandom selection of the participants (they were all relatives of children who had leukemia) and the lack of identification of a dose-response relationship.
Increased occurrence of the 10 symptoms used to diagnose lupus was identified in TCE-exposed individuals from Tucson, Arizona (33). The validity of these results is limited by the non-random selection of the participants and the lack of identification of a dose-response relationship.
Another study of the TCE contamination in Tucson found that the rate of total congenital cardiac malformations was higher in the area where TCE-contaminated water was probably ingested than in areas without TCE contamination. These results are limited by uncertainty about the extent of the contamination and the lack of information needed for evaluation of a dose-response relationship.
The results of the studies reviewed indicate that further investigation of low dose TCE exposures is needed. However, they do not offer any evidence about a cause-effect relationship between TCE exposure and specific health effects. Thus they do not offer any assistance in interpreting the possibility of health consequences from the exposure to TCE in the East Multnomah residential drinking water wells.
Based on studies of workers and laboratory animals, the past exposure to TCE in the proposed East Multnomah County Groundwater Contamination National Priorities List (NPL) site area residential drinking water wells does not appear to be a high enough concentration to result in noncarcinogenic health effects (26).
B. Health Outcome Data Evaluation
In this section, the reasons why cancer data for Multnomah County were not evaluated are discussed. In addition, the guidelines that ATSDR follows for evaluating information from health outcome databases are reviewed.
In a public health assessment, available health outcome databases are identified for the area near the site. From those data, ATSDR selects health outcomes for further evaluation based on biological plausibility or community health concerns (20).
For biological plausibility, the decision to evaluate health outcome data depends on whether a completed exposure pathway exists for a chemical suspected of causing the health outcome of concern (20). The selection of a noncarcinogenic health outcome is based on a review of the toxicologic literature for that contaminant of concern.
When a contaminant of concern has been identified as a carcinogen, health outcomes for the major anatomical sites are usually selected for evaluation (20). Designation of a chemical as a carcinogen (for purposes of health outcome data evaluation) is based on the following:
A latency period of at least 10 years between exposure and diagnosis has been observed in most studies of human cancer (20). If exposure began less than 10 years before collection of the latest data available, analysis of health outcome data for cancer incidence or mortality is not likely to be useful, particularly if the exposure level is low.
Even when health outcomes do not meet ATSDR's guidelines for biological plausibility, health outcome data can be evaluated as a basis for addressing community health concerns.
For the proposed East Multnomah County Groundwater Contamination NPL site, cancer is considered a biologically plausible health outcome for the following reasons:
2) people were exposed to this contaminant in the residential drinking water-wells (i.e., they were in a completed exposure pathway) for more than 10 years.
Based on current scientific studies, developmental or birth defects are not considered biologically plausible health outcomes. Neither TCE nor tetrachloroethylene is strongly associated with those effects (24,26).
The county was the smallest population unit for which health outcome data were readily available. It would be impossible to detect any elevation of health outcomes that could possibly be associated with site-related exposures because of the tremendous difference in populations (i.e., Multnomah County [570,000] vs. the exposed population [less than 1,076]). Therefore, cancer data for Multnomah County were not evaluated in this public health assessment.
C. Community Health Concerns Evaluation
The community health concerns identified during the public availability sessions are addressed as follows:
Is the incidence of cancer elevated within the proposed NPL site?
RESPONSE
Are the symptoms indicated by a mother related to the proposed NPL site?
RESPONSE
Can stillbirths and birth defects in horses be caused by the contaminants found in the spring water?
RESPONSE
