Skip directly to search Skip directly to A to Z list Skip directly to site content

PUBLIC HEALTH ASSESSMENT

POTTER COMPANY
WESSON, COPIAH COUNTY, MISSISSIPPI


ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

In order to determine what environmental contaminants may be a concern, ATSDR has evaluated all of the available environmental monitoring data (1986 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 health-based thresholds below which no known or anticipated adverse effect on the health of persons should occur. The values allow an adequate margin of safety. The comparison values used for each contaminant are identified in the contaminant tables (Tables 1 - 3) found in this section. Appendix 2 contains a description of the comparison values used in this public health assessment.

A contaminant is selected for further evaluation if the contaminant in a valid environmental sample exceeds comparison values. The presence of a contaminant on the list in the tables of this section does not mean that either exposure to the contaminant or adverse health effects has occurred or will occur. Inclusion in the lists 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 will be discussed in more detail in later sections of this Public Health Assessment.

A. On-Site Contamination

As discussed previously, an extensive environmental sampling program has been conducted at the proposed Potter Company NPL site. This sampling has delineated the extent of soil and groundwater contamination. The analytical results of the sampling program (1986-1990) are presented in Table 1.

TABLE 1 - ENVIRONMENTAL CONTAMINANTS DETECTED ABOVE HEALTH COMPARISON VALUES AT THE PROPOSED POTTER COMPANY NATIONAL PRIORITIES LIST SITE (1,6,8)



Contaminant
Range in Surface Soil (µg/kg) Range in Subsurface Soil (µg/kg) Comparison Value for Ingestion (µg/kg)* Range in Groundwater (µg/l) Comparison Value for Ingestion (µg/l)* Comparison Value Source*
1,2-Dichloroethane ND1 ND 8,000 ND 0.4 CREG
1,1-dichloroethylene ND ND 1,000 ND-408 0.06 CREG
Trans-1,2-dichloroethylene ND ND 40,000 ND-374 200 RMEG
Tetrachloroethylene ND ND-30 10,000 ND-42 0.7 CREG
1,1,1-Trichloroethane ND ND-91 11,000 ND-480 200 LTHA
1,1,2-Trichloroethane ND ND 10,000 ND-5 0.6 CREG
Trichloroethylene ND-10 ND-850 60,000 ND-26,000 3 CREG
Polychlorinated Biphenyls ND-12,500,000 ND-20,000,000 90 ND 0.005 CREG
* - See Appendix 2 for a description of the comparison values and their sources.
1 - ND is nondetect.
µg/kg - micrograms of contaminant per kilogram of soil
µg/l - micrograms of contaminant per liter of water
The bold indicates those contaminants whose concentrations are above the comparison value.

PCBs

PCB (primarily Aroclor 1254) surface soil (top three inches of soil) and subsurface soil contamination were found at the locations where waste fluids (mixtures of TCE and PCBs) were reported to have been discharged (See Appendix 1, Figure 1) (1,8). The highest surface soil contamination was found on the east side of the frame storage building (Area 1). It has been reported that waste fluids from the degreasing operation (previously located in the frame storage building) were deposited directly onto the ground at this location. Waste fluids were also discharged onto the ground at the north-side of the manufacturing building (Area 3). Elevated levels of PCBs were also detected at this location.

After being discharged onto the ground, the waste fluids and contaminated surface soil (via surface water runoff - rain) moved downhill towards and into the ditch at the southern part of the Potter Company property (3). Analytical results of samples taken from these natural drainage areas indicated that PCB surface soil contamination existed at these locations (Areas 2 and 5). The waste fluids and contaminated surface soil also moved onto the former Byrd property (purchased by Potter Company in 1988). Analytical results of samples taken at the former Byrd property indicate PCB surface soil contamination upwards of 3,300 micrograms of contaminant per kilogram of soil (µg/kg or ppb) and subsurface soil contamination upwards of 4,700 µg/kg. The health comparison value (ingestion) for PCBs in soil is 90 µg/kg.

Because PCBs tend to stick or absorb very strongly to soils, PCBs normally do not move very deeply underground (10). However, the ability for PCBs to move deeper underground is greatly enhanced in the presence of organic solvents (e.g., TCE and TCA)(9). Therefore, it is possible the PCB surface soil contamination at the proposed Potter NPL site could have migrated into the groundwater. In 1987 and 1988, a limited number of groundwater samples (nine) were analyzed for PCBs. The results of the chemical analysis indicates PCBs are not present in the groundwater above the detection limits (0.05 µg/l or ppb). However, most of the samples analyzed for PCBs (eight) were taken from the southern most on-site groundwater monitoring wells (MW-36 and MW-38, see Appendix 1, Figure 2 for the locations of the monitoring wells). Only one groundwater sample from the area of highest groundwater contamination was analyzed for PCBs (MW-35). Additional sampling results from the areas of high groundwater contamination are needed to confirm that PCBs have not migrated into the groundwater.

All of the PCB soil contamination greater than 10,000 µg/kg (10 ppm) at the Potter Company property and greater than 1,000 µg/kg (1 ppm) at the former Byrd property and in the drainage ditch was removed by the remedial activities conducted by Potter in 1988 (2).

TCE and TCA

TCE and TCA were dumped onto the ground along with the PCBs (1). Both TCE and TCA tend not to adhere very well to soils (11,12). Therefore, they tend to either volatilize (evaporate) into the air or migrate down through the soil. Analytical results of surface and subsurface soil samples indicate no significant (not above health comparison values) contamination of TCE, TCA, or any of their biological breakdown products (i.e., naturally occurring bacteria in soils tend to change TCE and TCA into 1,2-dichloroethane, 1,1-dichloroethylene, and trans-1,2-dichloroethylene).

In addition to discharging waste fluids directly onto the ground, waste fluids were also discharged to the septic systems formerly used by Potter (see Appendix 1, Figure 1 for locations) (1). Analytical results of subsurface soil and septic tank sludge samples indicate PCBs (up to 4,600 µg/kg), TCE (up to 850 µg/kg), and TCA (up to 91 µg/kg) were discharged at these locations.

Analytical results of groundwater samples taken from the on-site groundwater monitoring wells (1988-1990) clearly indicate the groundwater is contaminated with TCE, TCA, and their biological breakdown products (6). The highest TCE [26,000 micrograms of contaminant per liter of water (µg/l or ppb)] and TCA (480 µg/l) groundwater contamination was found in the monitoring well (MW-35B) next to the area where the degreasing fluids were dumped onto the ground. The highest concentration of TCE and TCA biological breakdown products was found in the monitoring well (MW-27) nearest the abandoned septic tank next to the metal warehouse.

B. Off-Site Contamination

Table 2 presents the results of the environmental monitoring program conducted in the surrounding community near the proposed Potter Company NPL site. Surface soil samples were taken in the unnamed stream. Groundwater samples were collected from the groundwater monitoring wells installed by contractors working for the Potter Company.

Analytical results of the surface soil samples taken in the unnamed stream indicate PCB contamination upwards of 103,800 µg/kg (1,4,8). The highest concentration of PCBs were found right next to the Potter Company property line. The surface soil PCB contamination above 1,000 µg/kg (1 ppm) in and next to the unnamed stream was removed by the Potter Company.

Analytical results from the groundwater samples taken from the monitoring wells clearly indicate that TCE, TCA, and their biological breakdown products have moved off the Potter Company property (6). The groundwater contaminants have entered the three water-bearing zones underlying Wesson. In general, the highest concentration of contaminants have been found close to the Potter property. Appendix 1, Figure 2 delineates the total extent of groundwater contamination by TCE above the detection limit of 0.5 ppb in the deeper groundwater zones.

Table 2 - ENVIRONMENTAL CONTAMINANTS DETECTED ABOVE HEALTH COMPARISON VALUES IN THE SURROUNDING COMMUNITY NEAR THE PROPOSED POTTER COMPANY NATIONAL PRIOITIES LIST SITE (1,6,8)



Contaminant
Range in Surface Soil (µg/kg) Comparison Value for Ingestion (µg/kg)* Range in Groundwater (µg/l) Comparison Value for Ingestion (µg/l)* Comparison Value Source*
1,2-Dichloroethane ND 8,000 ND-27 0.4 CREG
1,1-dichloroethylene ND 1,000 ND-527 0.06 CREG
Trans-1,2-dichloroethylene ND 40,000 ND-201 200 RMEG
Tetrachloroethylene ND 10,000 ND-18 0.7 CREG
1,1,1-Trichloroethane ND 11,000 ND-2,439 200 LTHA
1,1,2-Trichloroethane ND 10,000 ND2-11 0.6 CREG
Trichloroethylene ND 60,000 ND-4,500 3 CREG
Polychlorinated Biphenyls ND-103,800 90 ND** 0.005 CREG
* - See Appendix 2 for a description of the comparison values and their sources.
1 - ND is nondetect.
µg/kg - micrograms of contaminant per kilogram of soil
µg/l - micrograms of contaminant per liter of water
** - Only one groundwater sample was analyzed for polychlorinated biphenyls.
The bold indicates those contaminants whose concentrations are above the comparison value.

Table 3 - ENVIRONMENTAL CONTAMINANTS DETECTED ABOVE HEALTH COMPARISON VALUES IN WESSON DRINKING WATER WELLS (5,13)



Contaminant
Wesson Municipal Drinking Water Well Number 1 (µg/l) Wesson Municipal Drinking Water Well Number 2 (µg/l) Wesson Municipal Drink Water Distribution System (µg/l) Residential Drinking Water Wells (µg/l) Comparison Value for Ingestion (µg/l)* Comparison Value Source (µg/l)*
1,2-Dichloroethane ND1 ND ND ND 0.4 CREG
1,1-dichloroethylene ND-2 ND-2 ND-1 ND 0.06 CREG
Trans-1,2-dichloroethylene ND-13 ND-13 ND-1 ND 200 RMEG
Tetrachloroethylene ND ND ND ND 0.7 CREG
1,1,1-Trichloroethane ND-1.6 ND ND ND 200 LTHA
1,1,2-Trichloroethane ND ND ND ND 0.6 CREG
Trichloroethylene 88-327 120-848 ND-219 ND-30 3 CREG
Polychlorinated Biphenyls ND** ND** NA NA 0.005 CREG
* - See Appendix 2 for a description of the comparison values and their sources.
1 - ND is nondetect and NA is not analyzed.
µg/l - micrograms of contaminant per liter of water
** - Only one sample was analyzed for polychlorinated biphenyls.
The bold indicates those contaminants whose concentrations are above the comparison value.

The groundwater monitoring data indicate that the contamination originating from Potter Company migrated into the Wesson Municipal drinking water well numbers 1 and 2 (6). TCE was first detected in these wells in August 1987 (5). Table 3 lists the contaminants detected above health comparison values in the Wesson Municipal Well number 1, Well number 2, and the distribution system.

The concentrations of contaminants in the distribution system were significantly reduced when the aerator at the Wesson water treatment plant was modified in May 1988 (5). Analytical results of samples taken after the modification indicate that TCE concentration fell to about 14 µg/l. After the new wells (Well numbers 3 and 4) were connected and the old wells (Well numbers 1 and 2) were closed (June 1989), the TCE concentration in the Wesson Municipal Drinking water distribution system was below detection limits (less than 0.5 µg/l).

The State of Mississippi identified and sampled all of the active residential drinking water wells in the Wesson area (13). Analytical results of these samples indicate that only one residential well was contaminated with TCE. This well is located northwest of the proposed Potter Company NPL site. ATSDR was told that this well is no longer used for drinking water and that the residence associated with this well was connected to the Wesson drinking water distribution system.

In addition to sampling the active residential drinking water wells, the State of Mississippi also sampled the spring the City of Wesson previously used as its only source for drinking water (1922 to 1974) (5). Analytical results of this sample indicate that the spring was not contaminated with TCE.

Only one groundwater sample taken from a monitoring well (MW-37) was analyzed for PCBs (10). The results of this analysis indicates PCBs were not present in the groundwater at that location and time (1988). The State of Mississippi checked for the presence of PCBs in Wesson well numbers 1 and 2 in 1988 (5). These one time sampling results indicate PCBs were not present. Additional sampling from the areas of higher groundwater contamination is needed to confirm that PCBs have not migrated into the groundwater and off-site.

C. 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.

D. 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.

E. Review of Toxic Chemical Release Inventory (TRI) Data

To identify possible facilities that could contribute to the environmental contamination in Wesson, ATSDR searched the 1987-1991 files of the Toxic Chemical Release Inventory (TRI) databases for Copiah and Lincoln Counties. 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 (14). The air release data in TRI may 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, it is believed there have been and still are industries that do not report releases. Smaller industries may not be aware that reporting requirements exist or that they are responsible for such reports.

The search of TRI did not identify any facilities that could have contributed to the contamination in Wesson (15).

PATHWAYS ANALYSES

In this section of the Public Health Assessment, the possible environmental pathways are evaluated to help determine whether individuals have, are, or will be exposed to site-related contaminants. Environmental pathways can be completed or potential. A completed pathway indicates that human exposure to contaminants has occurred in the past, is occurring, or will occur in the future (16). 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 exposure has and never will occur. 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 and potential environmental exposure pathways, as well as those for which there is no known exposure, are discussed below.

TABLE 4 - COMPLETED ENVIROMENTAL EXPOSURE PATHWAYS AT THE PROPOSED POTTER COMPANY NATIONAL PRIORITIES LIST SITE

Pathway Name Point of Exposure Route of Exposure Exposed Population Time of Exposure Contaminants of Concern Estimated Exposed Population
Wesson Municipal Drinking Water Supply Drinking Water Inhalation
Skin Contact
Citizens of Wesson and Students at the Copiah-Lincoln Community College Past
(Assumed to have occurred for 15 years)

Trichloroethylene
1,1-dichloroethylene

2,300

A. Completed Environmental Exposure Pathways

Table 4 lists the components of the groundwater environmental exposure pathway which is considered the only completed (i.e., human exposure has occurred or is occurring) and the estimated number of individuals in this pathway.

There is good evidence that humans were exposed (ingestion, inhalation, and skin contact) in the past to site-related contaminants via the Wesson municipal drinking water distribution system (6). Analytical results of environmental samples taken from the local groundwater aquifers indicates that TCE, TCA, and the biological breakdown products of TCE and TCA have migrated into the three layers of the local groundwater aquifer. The City of Wesson well numbers 1 and 2 tap these aquifers (5). Analytical results of samples taken from Wesson well numbers 1 and 2 show that TCE, TCA, 1,1-dichloroethylene, and total 1,2-dichloroethylene have migrated into the wells. Drinking water samples were taken from the Wesson municipal drinking water distribution system. Analytical results of these samples confirm that TCE, 1,1-dichloroethylene, and total 1,2-dichloroethylene were in the water drunk by the citizens of Wesson from September 1987 through June 1989. The contaminated wells were replaced with uncontaminated wells (Wesson well numbers 3 and 4) in June 1989.

No information is presently available to indicate when the Wesson wells became contaminated. The City of Wesson started to use well number 1 in 1974.(1) Prior to 1974, drinking water came from a spring; however analytical results of a sample taken from the spring indicates that this source of drinking water was not contaminated. Therefore, it is not likely humans were exposed to site-related contaminants (i.e., TCE, 1,1-dichloroethylene, and total 1,2-dichloroethylene) prior to 1974.

In order to determine how long Wesson well numbers 1 and 2 were contaminated, one would have to model the groundwater system. ATSDR will try to model the groundwater system in the near future. For the purpose of this assessment, ATSDR will assume the worse case situation, the wells were contaminated from 1974-1989 (15 years).

The 1980 U.S. Census indicates the City of Wesson had a population of 1,313 (2). All of these individuals received their drinking water from the Wesson municipal drinking water distribution system. In addition to the city residences, students at the Copiah-Lincoln Community College (approximately 1,000 students) also received their drinking water from the Wesson municipal drinking water distribution system. Therefore, the exposed population for this proposed NPL site is approximately 2,300.

There are no other completed environmental exposure pathways related to the proposed Potter Company NPL site.

B. Potential Environmental Exposure Pathways

Table 5 lists the components of the four environmental exposure pathways considered to be potential, and the estimated number of individuals in each pathway. These possible environmental exposure pathways are surface and subsurface soil, future migration of the contaminated groundwater into drinking water wells, worker exposures during degreasing operations and waste material handling, and air.

1. Surface and Subsurface Soil

Analytical results of surface and subsurface soil samples indicate wide spread PCB contamination (1). The PCB (primarily Aroclor 1254) soil contamination was found on the Potter Company property, the Byrd property, and in the unnamed stream off the Potter property. By 1993, all of the PCB soil contamination greater than ten ppm at the Potter Company property and greater than one ppm at the Byrd property or in the unnamed stream was removed by the remedial activities conducted by Potter Company. Therefore, humans were possibly exposed to the PCB soil contamination from 1953 (the start of Potter Company activities at this location) to 1993.

Individuals, primarily children, could have been exposed in the past to the surface and subsurface soil PCB contamination via inadvertent consumption and skin contact with the soil on hands or food items, mouthing of objects, or the ingestion of nonfood items (pica). In addition, these individuals could have inhaled the soil contaminants whenever the surface and subsurface soil were disturbed (e.g., dust and particulate matter). All children mouth or ingest non-food items to some extent. The degree of pica behavior varies widely in the population, and is influenced by nutritional status and the quality of care and supervision. Groups that are at increased risk for pica behavior are children aged 1-3 years old, children from families of low socioeconomic status, and children with neurologic disorders (e.g., brain-damage, epilepsy, mental retardation). Because of the inadvertent nature of this possible exposure pathway, it is not possible to estimate the number of exposed individuals.

Because of the remedial actions conducted by the Potter Company, it is unlikely individuals will be exposure to PCB contaminated soil currently and in the future at or near the proposed Potter Company NPL site.

TABLE 5 - POSSIBLE ENVIRONMENTAL EXPOSURE PATHWAYS AT THE PROPOSED POTTER COMPANY NATIONAL PRIOITIES LIST SITE

Pathway Name Point of Exposure Route of Exposure Exposed Population Time of Exposure Contaminants of Concern Estimated
Exposed
Population
Surface and Subsurface Soil Potter Company Property, the Byrd Property, and the Unnamed Stream Ingestion
Inhalation
Skin Contact
Individuals Working at or Visiting Potter Company and entering the Unnamed Stream Past Polychlorinated Biphenyls Unknown
Future Groundwater Migration Drinking Water Ingestion
Inhalation
Skin Contact
Customers of the Wesson and the Lincoln Rural Water Association Drinking Water Systems Future Trichloroethylene Unknown
Worker Exposures Degreasing and Waste Handling Operations Ingestion
Inhalation
Skin Contact
Potter Company Employees Past CurrentFuture Trichloroethylene (Past)
Polychlorinated Biphenyls (Past)
1,1,1-Trichloroethane (Past, Current, Future)
Less Than 10
Air Degreasing Operations Inhalation Residents Near the Potter Company Past Current Future Trichloroethylene (Past)
1,1,1-Trichloroethane (Past, Current, Future)
Unknown

2. Future Groundwater Migration

Although not contaminated now, four public drinking water wells appear to be in the direct path of the groundwater contamination. The Wesson well numbers 4 and 5 and the Lincoln Rural Water Association well numbers 1 and 2 are approximately one mile east and southeast of the leading edge of the groundwater contamination (see Appendix 1, Figure 3). If the groundwater contamination continues to move east/southeast, these wells could possibly become contaminated. Individuals who rely upon these wells for drinking water could then be exposed (ingestion, inhalation, and skin contact) to site-related contaminants (e.g., TCE). However, the Mississippi Bureau of Pollution Control has approved Potter Company's plan for groundwater remediation system. The remediation system should become operational in the first quarter of 1995. The goal of this system is to prevent future migration of contaminated groundwater.

Because this exposure could possibly occur in the future, the size of the exposed population can not be estimated.

3. Worker Exposure

When material was degreased and the waste fluids from the degreasing operations were dumped onto the ground, Potter Company employees could have been exposed (ingestion, inhalation, and skin contact) in the past to TCE, TCA, and PCB. In addition to the potential past exposures, Potter Company employees could be presently or in the future exposed to TCA during degreasing operations and waste fluid disposal (currently the waste fluids are reportedly disposed of in accordance with hazardous waste regulations). The extent of exposure would depend upon what personal protection equipment the workers wore (i.e., gloves, protective clothing, and respirator) and the length of contact, both of which would affect the amount of waste material ingested, inhaled, or accumulated on the skin. Less than ten employees are involved with degreasing operations and disposal of the waste fluids.

4. Air

TCE and TCA could have volatilized into the air and migrated off the Potter Company property. Individuals not employed at Potter could inhale (past, current, future) the TCE or TCA. The distance to the nearest residence is less than 150 feet away (the Byrd residence). Therefore, it is possible that some TCE or TCA discharged to the air from the degreasing operation could have migrated off-site. Because air monitoring data is not available, it is not possible to confirm or deny whether humans could have come in contact with TCE or TCA via air emissions.

C. No Known Environmental Exposure Pathways

Analytical results of samples taken from the Wesson and the Lincoln Rural Water Association drinking water distribution systems indicate there is no site-related contamination. Therefore, there is currently no exposure to site-related contaminants via drinking water.

PCBs are known to bioaccumulate in plants and animals (9). However, there is no evidence that PCB contaminated soil or water was used to raise food stuff. In addition, fishing is not conducted in the stream where PCB contamination occurred (the stream is frequently dry). Therefore, it is unlikely individuals would be exposed to PCB via food.

PUBLIC HEALTH IMPLICATIONS

As discussed in the Pathways Analyses section, the Wesson Municipal Drinking Water Supply exposure pathway is considered completed (i.e., human exposure occurred). The contaminants of concern in this pathway are trichloroethylene (TCE), and 1,1-dichloroethylene.

The Toxicological Evaluation portion of this section will discuss the possible health hazard from past exposure to the two contaminants of concern in the Wesson Municipal Drinking Water Supply. The community's concern about cancer will be addressed in the Health Outcome Data Evaluation section which describes cancer mortality data.

A. Toxicological Evaluation

Introduction

Typically, the toxicological evaluation in a public health assessment is a comparison of the exposure dose (i.e., the amount of a substance individuals in an exposure pathway are exposed to daily) to an appropriate health guideline. In this evaluation, the health guidelines are ATSDR's Minimal Risk Levels (MRLs). The results of the comparison of the exposure doses to the MRLs for each chemical is described in Table 6, and the methodology for calculating the exposure doses in Appendix 3.

Neither the adult, nor the child exposure doses for the maximum levels of 1,1-dichloroethylene (1 µg/l) and TCE (219 µg/l) in the Wesson Municipal Water Supply exposure pathway exceed the MRLs for those chemicals. Usually, any exposure dose below the appropriate MRL does not represent a hazard to human health (16). However, the only available health guideline for TCE is for an exposure of less than a year. 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 Wesson Municipal Water Supply. Because of this, the possible health consequences of exposure to TCE will be discussed.

TCE is considered a probable human carcinogen and 1,1-dichloroethylene a possible human carcinogen (17). The risks of carcinogenic health effects from 1,1-dichloroethylene and TCE exposure were evaluated using the methods described in Appendix 4. Based on this evaluation, the past exposure to 1,1-dichloroethylene in the Wesson Municipal Water Supply System represents no apparent increased risk of cancer. There was a low increased risk of cancer from past exposures to TCE.

TABLE 6 - COMPARISON OF ESTIMATED EXPOSURE DOSE TO HEALTH GUIDELINES FOR INGESTION1

CONTAMINANT

EXPOSURE PATHWAY

HEALTH GUIDELINE

SOURCE

HEALTH GUIDELINE EXCEEDED BY EXPOSURE DOSE
trichloroethylene Wesson Municipal Water Supply 0.7 mg/kg/day IMRL2 NO
1,1-dichloroethylene Wesson Municipal Water Supply 0.009 mg/kg/day CMRL3 NO
1 - An explanation of how exposure doses are calculated can be found in Appendix 3.
2 - IMRL is intermediate minimal risk level.
3 - CMRL is chronic minimal risk level.


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 then information from properly conducted animal studies are used. The type of data used for an evaluation is indicated for each chemical.

Trichloroethylene (TCE)

Noncarcinogenic Health Effects

Based on studies of workers and laboratory animals, the exposure to TCE in the Wesson water supply does not appear to be of a high enough concentration to result in noncarcinogenic health effects (11). However, several recent studies of individuals exposed to TCE in drinking water identified several health effects which had rates greater than comparison groups (18-23). The health effects reported in those studies were stroke and impaired hearing (18); slowed eye blink response (19,20); several abnormal neurophysiological and neuropsychological parameters (20); impairment of the immune system (21); increased occurrence of the symptoms related to lupus (22); and congenital cardiac malformations (23).

Elevated rates for several health outcomes were found in participants in the TCE exposure registry when compared with respondents to the National Health Interview Survey (18). 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 ppb 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 (19,20). Those slower responses were considered a subclinical effect (i.e., not harmful). The validity of these results is limited by the non-random selection of the participants and the lack of a identification of a dose-response relationship. In addition, a recent study of workers exposed for an average of 16 years to many times the TCE concentrations found in Arizona and Massachusetts found no change in the eye blink response (24).

Impairment of the immune system was observed in TCE-exposed individuals from Woburn, Massachusetts (21). This immunologic impairment was evidenced by altered T-cell ratios (T-cells are a type of white blood cell), increased incidence of auto-antibodies, increased infections, and recurrent rashes. The validity of these results is limited by the non-random selection of the participants (they were all relatives of children who had leukemia) and the lack of a identification of a dose-response relationship.

Increased occurrence of the ten symptoms used to diagnose lupus was identified in TCE-exposed individuals from Tucson, Arizona (22). The validity of these results is limited by the non-random selection of the participants and the lack of a 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 compared to areas without TCE-contamination. These results are limited by uncertainty about the extent of the contamination and the lack of exposure information to evaluate 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 Wesson water supply.

Carcinogenic Health Effects

The levels of TCE found in the Wesson Municipal Water Supply represent a low increased risk of cancer. However, there is a great deal of uncertainty about the carcinogenicity of TCE. Studies of workers exposed to TCE did not identify an increase of cancer (11). Investigations of exposures to TCE in drinking water from Woburn, Massachusetts and several New Jersey communities suggest increases of leukemia. However, both studies have numerous methodological problems. Evaluations of the series of animal studies vary from a determination of TCE as probable human carcinogen by EPA to "not classifiable for cancer" determinations by the International Agency for Research on Cancer. An evaluation of cancer data for the City of Wesson would help address this uncertainty.

B. Health Outcome Data Evaluation

We evaluated cancer mortality data for Copiah County. The number of deaths due cancer in Copiah County was not greater for the 14 anatomical sites or combination of anatomical sites evaluated than what would be expected from the numbers for the State of Mississippi. Cancer data were evaluated because they were identified as biologically plausible health outcomes.

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 (16). 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 (16). Designating a chemical as a carcinogen (for purposes of health outcome data evaluation) is based on classification as such by the National Toxicology Program (NTP), the International Agency for Research on Cancer (IARC), the United States Environmental Protection Agency (EPA), and the United States Occupational Safety and Health Agency (OSHA).

A latency period of at least 10 years between exposure and diagnosis has been observed in most studies of human cancer (16). If exposure began less than 10 years prior to 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 to address community health concerns.

For the proposed Potter Company NPL site, cancer is considered a biologically plausible health outcome because: trichloroethylene (TCE) is considered a probable human carcinogen (11), and people were exposed (i.e., they were in a completed exposure pathway) to this contaminant in the Wesson Municipal Water Supply for up to 15 years. Cancer mortality data were available and were evaluated. Cancer incidence data were not evaluated in this public health assessment because the State of Mississippi does not have a Cancer Incidence Registry.

Developmental or birth defects were not considered biologically plausible health outcomes. Neither TCE and 1,1-dichloroethylene are strongly associated to those effects (11,25).

Cancer Mortality Data

To identify cancer mortality rates, ATSDR reviewed mortality data on 14 anatomical sites or combination of anatomical sites for Copiah County for 1979-1991. Those data came from a database maintained by the Office of Analysis and Epidemiology of the National Center for Health Statistics, Centers for Disease Control and Prevention. The anatomical sites evaluated were lung; lip, mouth, and throat; digestive tract and pancreas; liver and gall bladder; bone, connective and soft tissue; skin; breast; female reproductive; male reproductive; bladder and kidney; lymphatic; leukemia; all other sites; and all sites combined. Information specific to the City of Wesson area was not available.

The age-adjusted rates for Copiah County were compared to the rate for Mississippi. Because Copiah is split evenly between African-Americans and Whites, comparisons were made for both groups.

The number of deaths due cancer in Copiah County was not greater for the 14 anatomical sites or combination of anatomical sites evaluated than what would be expected from the numbers for the State of Mississippi.

Evaluations of cancer mortality data have limitations. A major limitation is that the data evaluated were for Copiah County, not the City of Wesson. The population of Wesson (1,313) makes up about 5% of the population of Copiah County (26,952). Because of this disparity, effects on the population of Wesson may not identified. An evaluation of cancer mortality data for just Wesson needs to be done to eliminate this limitation.

Another limitation is that the cancer mortality data used did not include information on personal risk factors (smoking, diet, alcohol, etc.) or on occupational and environmental exposures to chemicals. Analyses of those data can only be descriptive and cannot be used to determine associations with possible agents. There is an inherent five percent chance that any excess in observed cancer cases is due to random variation alone.

A third limitation is whether mortality data reflect the actual frequency of a disease (i.e., deaths plus those who survive) (26). Factors such as quality of health care, high survival rates, and misclassification of cause of death can lead to differences in mortality rates even though the true frequency of the disease has not changed.

C. Community Health Concerns Evaluation

The one identified community health concern, "Is the rate of cancer in Wesson elevated?", can not be fully addressed. Only county-wide cancer mortality were available for evaluation. This evaluation is described in the preceding section, and, as discussed, a review of data for Wesson is needed to fully address this concern about elevated cancer rates.

1 Letter dated 9/27/94 from Jeffrey Novak, First Environment, Kennesaw, Georgia.


Next Section       Table of Contents

  
 
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #