United States
Environmental Protection
^ W ^1 Agency
Neurotoxicity of
Tetrachloroethylene
(Perchloroethylene)
Discussion Paper
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External Review Draft
www.epa.gov/ncea
Neurotoxicity of Tetrachloroethylene (Perchloroethylene)
Discussion Paper
NOTICE
THIS DOCUMENT IS A PRELIMINARY DRAFT. It has not been formally
released by the U.S. Environmental Protection Agency and should not at this
stage be construed to represent Agency policy. It is being circulated for comment
on its technical accuracy.
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC 20460
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DISCLAIMER
This document is a draft for discussion purposes only and does not constitute U.S.
Environmental Protection Agency policy. Mention of trade names or commercial products does
not constitute endorsement or recommendation for use.
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TABLE OF CONTENTS
List of Tables iv
List of Figures iv
Preface v
Authors and Contributors vi
1. HUMAN STUDIES 1
1.1. REVIEW OF INDIVIDUAL STUDIES 2
1.1.1. Acute Controlled Exposure Studies 3
1.1.1.1. Stewart et al. (1970) 3
1.1.1.2. Hake and Stewart (1977) 4
1.1.1.3. Altmann et al. (1990, 1992) 6
1.1.2. Chronic Exposure Studies 8
1.1.2.1. Lauwerys et al. (1983) 8
1.1.2.2. Seeber (1989) 9
1.1.2.3. Cai etal. (1991) 10
1.1.2.4. Nakatsuka etal. (1992) 11
1.1.2.5. Ferroni etal. (1992) 12
1.1.2.6. Cavalleri et al. (1994), Gobba et al. (1998) 13
1.1.2.7. Echeverria et al. (1995) 16
1.1.2.8. Altmann et al. (1995) 19
1.1.2.9. Spinatonda et al. (1997) 21
1.1.2.10. Schreiber et al. (2002) 22
1.2. SUMMARY OF NEUROPSYCHOLOGICAL EFFECTS IN LOW- AND
MODERATE-EXPOSURE STUDIES 26
2. ANIMAL STUDIES 29
2.1. INHALATION STUDIES 29
2.1.1. Summary of Animal Inhalation Neurotoxicity Studies 33
2.2. ORAL AND INTRAPERITONEAL STUDIES 33
3. PRELIMINARY SUMMARY OF NEUROTOXIC EFFECTS FOR DISCUSSION .... 36
REFERENCES 45
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LIST OF TABLES
Table 1. Summary of neuropsychological effects of tetrachloroethylene in humans 38
Table 2. Summary of animal inhalation neurotoxicology studies 40
Table 3. Summary of oral neurotoxicity animal studies 42
LIST OF FIGURES
Figure 1. Visual contrast sensitivity functions for control and exposed children (top), adults
that were identified as having impaired function (i.e., 5 of the total 11) and their
matched controls (middle), and the control and exposed individuals over 60 years
of age 43
Figure 2. Summary of the relationship between dose levels and treatment duration 44
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PREFACE
This discussion paper was developed by the U.S. Environmental Protection Agency (EPA)
to serve as background material for a workshop discussion with experts regarding neurotoxicity
of tetrachloroethylene. Subsequent to these discussions, a revised review of neurotoxicity will be
incorporated into a comprehensive health assessment document (toxicological review document)
that will be peer reviewed and released for public comment. This work was undertaken by staff
in the National Center for Environmental Assessment (NCEA) for EPA's Office of Air Quality
Planning and Standards.
Tetrachloroethylene is a widely used solvent. It is produced commercially mainly for use
in dry cleaning, textile processing, and metal cleaning operations. It has the following end-use
pattern: 55% as a chemical intermediate, 25% for metal cleaning and vapor degreasing, 15% for
dry cleaning and textile processing, and 5% for other unspecified uses (ATSDR, 1997).
Although dry cleaning facilities are a significant source of atmospheric emissions of
tetrachloroethylene, their use of tetrachloroethylene has declined by more than 60% over the last
10 years due to the introduction of equipment with vapor recovery (U.S. EPA, 2003).
Tetrachloroethylene is also released into groundwater where it can persist for years because of
the limited contact between groundwater and air. When people are exposed, it is readily
absorbed by all exposure routes and is widely distributed throughout the body.
Tetrachloroethylene is listed as a hazardous air pollutant under the Clean Air Act, a toxic
pollutant under the Clean Water Act, a contaminant under the Safe Drinking Water Act, a
hazardous waste under the Resource Conservation and Recovery Act, and a hazardous substance
under the Comprehensive Environmental Response, Compensation, and Liability Act
(Superfund). It is a toxic chemical with reporting requirements under the Emergency Planning
and Community Right-to-Know Act, and under the Toxic Substances Control Act. In addition,
certain releases must be reported to the Toxics Release Inventory. Because of this wide use and
the need for regulatory decisions under various environmental statutes, EPA is soliciting expert
advice on the significance of the available information on the neurotoxicity of
tetrachl oroethy 1 ene.
The relevant literature was reviewed through June 2003.
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AUTHORS AND CONTRIBUTORS
The National Center for Environmental Assessment within EPA's Office of Research and
Development was responsible for the preparation of this document.
Chemical Manager
Robert E. McGaughy
Washington Division
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC
Authors
Deborah Rice
Washington Division
National Center for Environmental Assessment
Office of Research and Development
Environmental Protection Agency
Washington, DC
Cheryl Siegel Scott
Washington Division
National Center for Environmental Assessment
Office of Research and Development
Environmental Protection Agency
Washington, DC
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1. HUMAN STUDIES
The nervous system is a major target organ in humans exposed to tetrachloroethylene by
inhalation, and a range of effects on neurologic function are well documented for both acute and
chronic exposure. Section 1.1.1 of this paper contains a description of three reports of
controlled inhalation exposures. The studies by Stewart et al. (1977) and Hake and Stewart
(1977) were funded primarily by the National Institutes of Occupational Safety and Health
(NIOSH). These studies are considered to be protective of human subjects, as U.S.
Environmental Protection Agency (EPA) and other federal agencies subscribe fully to principles
such as those articulated in EPA's Protection of Human Subjects Rule ("the Common Rule"), 40
CFR Part 26. A description of the studies by Altmann et al. (1990, 1992) is also included
because the Agency for Toxic Substances and Disease Registry used these studies to develop an
acute minimal risk level (MRL) (ATSDR, 1977). EPA considers these studies to be "third party
studies." No information is provided in the published papers regarding the procedures the study
investigators adopted for informed consent or protection of human subjects, and staff of the
National Center for Environmental Assessment (NCEA) have contacted study investigators
requesting this information.
Acute controlled inhalation exposures of 100 ppm tetrachloroethylene and higher have
induced symptoms consistent with depression of the central nervous system (CNS), including
dizziness and drowsiness (ATSDR, 1997). Changes in electroencephalograms (EEGs) have been
noted with controlled inhalation exposures at 100 ppm (Stewart et al., 1977). Acute exposure to
lower levels of tetrachloroethylene has induced alterations in neurobehavioral function. For
example, Altmann et al. (1990, 1992) reported increases in the latency of visually evoked
potentials (VEPs) among volunteers with inhalation exposure to 50 ppm for 4 hours per day for 4
days as compared with latency among subjects exposed to 10 ppm (the control group in this
study). The observations by these investigators indicate that visual system dysfunction such as
delayed neuronal processing time and altered contrast perception is related to tetrachloroethylene
exposure.
A number of epidemiologic studies of the prevalence or cross-sectional design are
available for subchronic or chronic exposure to tetrachloroethylene. The subchronic and chronic
epidemiologic studies are discussed in Section 1.1.2 of this paper. These studies (Lauwerys et
al., 1983; Seeber, 1989; Cai et al., 1991; Nakatsuka et al., 1992; Ferroni et al., 1992; Cavalleri et
al., 1994; Gobba et al., 1998; Spinatonda et al., 1997; Echeverria, et al., 1995) examined a
number of neurobehavioral or neurotoxic outcomes among workers in dry cleaning operations.
Two other studies, Altmann et al. (1995) and a pilot study by Schreiber et al. (2002), examined
residents or day care workers exposed to tetrachloroethylene through living or working in close
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proximity to a dry cleaning establishment. Exposure concentrations to tetrachloroethylene in
these two studies (mean and median concentrations) are approximately an order of magnitude
lower than the time-weighted-average concentrations of the dry cleaner studies.
Together, these epidemiologic studies (Seeber, 1989; Ferroni et al., 1992; Cavalleri et al.,
1994; Gobba et al., 1998; Spinatonda et al., 1997; Echeverria, et al., 1995; Altmann et al., 1995;
Schreiber et al., 2002) provide some evidence that chronic exposure to tetrachloroethylene
affects visual spatial function. Findings from the dry cleaner studies further indicate that tasks
requiring the processing of visual information (color vision, reaction time, coding speed, visual
memory, visual contrast perception) are particularly vulnerable to alterations from exposure to
tetrachloroethylene. Altmann et al. (1995) and Schreiber et al. (2002) observed effects on visual
function among residents living in close proximity to a dry cleaning business, and Schreiber et
al. (2002) also reported this effect in nine day care workers exposed to tetrachloroethylene from
a nearby dry cleaning establishment.
Color vision is another domain assessed in tetrachloroethylene exposed populations.
Acquired dyschromatopsia (loss of color vision) is a well-known adverse effect of exposure to
solvents (Geller and Hudnell, 1997), and studies suggest that blue-yellow dyschromatopsia is
associated with lower-level solvent exposure (Muttray et al., 1997). Moreover, dyschromatopsia
is considered an important sign of neurotoxicity (Lucchini et al., 2000). Color vision testing has
been reported for four populations of dry cleaners (Nakatsuka et al., 1992; Cavalleri et al., 1994;
Gobba et al., 1998; Valic et al., 1997) and among workers exposed to mixtures of solvents that
historically contained 10% tetrachloroethylene (Muttray et al., 1997).
Three studies (Seeber, 1989; Ferroni et al., 1992; Altmann et al., 1995) assessed fine
motor control, and all found no effect.
1.1. REVIEW OF INDIVIDUAL STUDIES
The following subsections present detailed descriptions of the human studies on
tetrachloroethylene exposure. As part of this review, NCEA staff have critically read each of
these studies and have also relied heavily upon study descriptions contained in the New York
State ambient air criteria document (NYS DOH, 1997). For some studies, more detailed
information of study procedures was provided in correspondence between the principal
investigator and staff of the New York State Department of Health; this correspondence is cited
below.
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1.1.1. Acute Controlled Exposure Studies
1.1.1.1. Stewart, R.O., E.D. Baretta, H.C. Doddand T.R. Torkelson. 1970. Experimental
human exposure to tetrachloroethylene. Arch. Environ. Health. 20:225—229.
Sixteen healthy adults were exposed to single and repeated exposures of 100 ppm for a
period of 7 hours, with five subjects repeatedly exposed for 5 days. During or after exposure,
study investigators recorded subjective symptoms, administered a number of neurological tests
to exposed subjects, collected blood and urine samples to assess affects on clinical parameters,
and collected alveolar breath samples. Additionally, visual acuity and depth perception were
measured in exposed subjects. Although not stated in the published report, it is assumed from
the design of this study that investigators were not blinded when administering the neurological
tests. Additionally, the paper does not discuss whether informed consent was obtained, nor does
it describe the procedures used by study investigators.
All subjects reported the ability to detect odor, and this perception decreased over the
course of daily and weekly exposure. Of the subjects exposed to a single 7-hour exposure, eye
and nose irritation was reported by 60% of the subjects, a slight frontal headache by 25%, slight
light-headedness by 25%, feeling slightly sleepy by 40%, and difficulty in speaking by 25%.
Some of these complaints were made during the first 2 hours. Of five healthy men exposed to
100 ppm for 7 hours per day on 5 consecutive days, one reported a mild frontal headache during
each exposure (this subject also had chronic sinusitis, but this condition did not preclude his
participation in the study) and two consistently reported mild eye and throat irritation. Other
symptoms were not reported, and individual responses during exposures to 0 ppm were not
assessed.
Three tests of equilibrium (a modified Romberg test1, where an individual stands on one
foot with eyes closed and arms at side; a heel-to-toe test; and a finger-to-nose test) were
performed every 60 minutes during each day of exposure. After 6 hours, neurobehavioral tests
of motor function (the Crawford manual dexterity and Flanagan coordination tests), cognitive
function (arithmetic test), and motor/cognitive function (inspection test) were also performed.
Three of the subjects had increased difficulty in maintaining their equilibrium when tested within
the first 3 hours of exposure (i.e., performance on the Romberg test was impaired). The three
subjects were able to perform the test normally when given a second chance. Performance on
the other tests was not impaired. An additional subject, exposed during the third day of testing,
showed a slight deterioration in his Romberg test and complained of slight dizziness and slight
impairment of his intellectual faculties after 1 hour of exposure. This subject was known to
study investigators as being susceptible to the CNS-depressant effects of solvents. No
1 The Romberg test measures CNS depression.
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improvement in his Romberg test occurred during the next hour, and he was removed from the
test chamber. This subject performed the test normally when retested 30 minutes later.
Overall, these investigators concluded that there were CNS effects in some subjects
exposed to 100 ppm, as supported by the findings of light-headedness and abnormal modified
Romberg tests. Additionally, these investigators discussed the possibility of a range of
individual susceptibility to tetrachloroethylene.
1.1.1.2. Hake C.L., andR.D. Stewart. 1977. Human exposure to tetrachloroethylene:
inhalation and skin contact. Environ. Health Perspect. 21:231-238.
This review article summarizes a number of previous studies carried out by these authors,
including four controlled exposure studies primarily funded by the NIOSH. Hake and Stewart
identified these studies as Study A, Study B, Study C, and Study D.
Study A was designed to examine the effect of exercising on tetrachloroethylene blood
concentration. Neurological tests were not administered to the one study subject.
As part of a 5-week study, three or four healthy men (Study B) and four healthy women
(Study C) were exposed 1, 3, or 7.5 hours per day, 5 days per week, to 0, 20, 100, or 150 ppm
tetrachloroethylene. The published paper does not contain a description of the schedule or the
total duration of exposure to individual exposure concentrations. These investigators assessed
neurological, physiological, and/or behavioral responses as well as subjective symptoms among
exposed subjects.
Reports of symptoms (e.g., headache) varied among individuals, but, overall, complaints
during exposure were similar to those during exposure to 0 ppm tetrachloroethylene. All
subjects were able to detect the odor of tetrachloroethylene at every level of exposure; the odor
became less noticeable or disappeared as an exposure progressed on both a daily and weekly
basis.
The evaluation of EEG recording made during exposure suggested altered patterns
indicative of cortical depression in both male and female subjects exposed to 100 ppm
tetrachloroethylene for 7.5 hours. Recordings of visual evoked responses and equilibrium tests
were normal in men and women.
The performance of men on neurobehavioral tests of cognitive function (arithmetic),
motor function (alertness), motor/cognitive function (inspection), and time estimation were not
statistically significantly affected by any exposure. The performance of men on a second test of
motor function (Flanagan coordination) was statistically significantly decreased (p<0.05) when
compared with the response at 0 ppm on at least 1 day during the weeks of 100 ppm and 150
ppm tetrachloroethylene exposure. The performance on physiological tests (tests not identified
in published paper) of female subjects exposed to 100 ppm for 5 days was not affected.
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Stewart et al. (1977) discuss the conclusions of Study B and Study C, concluding that (1)
there was considerable interindividual variation in response to tetrachloroethylene vapors, (2)
EEG analysis indicated preliminary signs of narcosis in most subjects exposed to 100 ppm for
7.5 hours, (3) impairment of coordination may occur in subjects exposed to 155 ppm for 7.5
hours, and (4) the effects were likely attributable to tetrachloroethylene and not a metabolite.
Study D was a complex study with 12 healthy adults (6 men and 6 women) of
interactions on behavioral and neurological function associated with inhaled tetrachloroethylene
and oral doses of alcohol or diazepam, a tranquilizer. A full description of this study was
provided to NIOSH (Stewart et al., 1977). Individuals were typically exposed for 5.5 hours to 0
ppm on Monday or Tuesday, 100 ppm on Wednesday and Friday, and 25 ppm on Thursday
during each of the 11 weeks of exposure and were given a placebo capsule, alcohol, Valium, or
nothing during each period. Numerous neurological tests were performed throughout each
exposure, and the authors took great efforts to ensure that all testing was done in a double-blind
mode.
Exposure to 25 or 100 ppm tetrachloroethylene for 5.5 hours did not increase the overall
prevalence of reported symptoms (e.g., headache) or alter the subjects' mood. Exposure-related
increases in the strength and persistence of the tetrachloroethylene odor were perceived by the
subjects. Exposure did not significantly reduce performance on two equilibrium tests (Romberg
and heel-to-toe) and two neurobehavioral tests of motor function (Michigan eye-hand
coordination test and rotary persuit test). At 100 ppm, there was a statistically significant
decrease (/K0.05) in scores on a third test of motor function (Flanagan coordination test) on
some days of exposure. Statistical analyses performed by the investigators revealed no effect of
tetrachloroethylene exposure alone on EEGs and no interactive effects between
tetrachloroethylene and either alcohol or Valium.
The study authors (Hake and Stewart, 1997; Stewart et al., 1977) concluded that
performance on the three neurobehavioral tests of motor function was not consistently affected
by exposure to 100 ppm tetrachloroethylene, although exposure did have a significant but
inconsistent detrimental effect on the performance of the Flanagan coordination test.
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1.1.1.3. Altmann, L., A. Bottgor andH. Wiegand. 1990. Neurophysiological and
psychophysical measurements reveal effects of acute low-level organic solvent exposure in
humans. Int. Arch. Occup. Environ. 3:493—499. Altmann, L., H. Wiegand, A. Bottger, F.
Eistwmelor and G. Winneke. 1992. Neurobehavioral and neurophysiological outcomes of
acute repeatedperchloroethylene exposure. Appl. Psych. 41:269—279.
These studies, conducted in Germany, reports intentional inhalation exposure of human
subjects to tetrachloroethylene for the purpose of measuring potentially adverse health outcomes.
The publication provides no information about ethical principles expoused by the U. S.
Government for exposure to human subjects. Therefore, the principal author has been contacted
and information has been requested regarding procedures that were used to select the subjects
and inform them about the nature of the exposure, institutional procedures that were taken to
review the design of the study, and ethical standards and guidelines that the institution was
operating under at the time of the study. To date, no response has been received. Although the
report is not of crucial importance in the evaluation of chronic neurotoxic effects of
tetrachloroethylene, the human subjects issue associated with the report is still of interest.
Altmann et al. (1990, 1992) used neurophysiological and neurobehavioral techniques to
evaluate the neurological effects of tetrachloroethylene on healthy adults exposed to 10 ppm or
50 ppm for 4 hours on 4 consecutive days. All subjects denied prior occupational exposure to
solvents and drug use at the time of the study. Visual acuity of all subjects was normal or
corrected to normal. The study was a single-blind study (subjects were not told their level of
exposure) and subjects were randomly assigned to either group. Sixteen subjects were exposed
to 10 ppm and 12 subjects were exposed to 50 ppm, but neurophysiological measurements were
made on only 22 subjects (12 at the low level and 10 at the high level). There was no unexposed
control group.
Three neurophysiological measurements were taken on the day before exposure started
and on each of the four exposure days: (1) VEPs in response to black and white checkerboard
patterns were measured; the VEPs of some subjects (exact number not reported) were also
measured on the day after exposure ceased; (2) a visual contrast sensitivity (VCS) test (a test of
the central spatial vision that determines the minimum contrast necessary for an individual to see
patterns of various sizes) was given to five subjects (three from the low-exposure group and two
from the high-exposure group); (3) recordings of brainstem auditory-evoked potentials (BAEPs)
(neurophysiological measurements of the electrical signals generated by the hearing system in
response to auditory stimuli) were made to evaluate the peripheral hearing loss of the subjects.
All measurements were started 2 hours after a subject entered the chamber and were completed
within 1 hour.
A German version of the Neurobehavioral Evaluation System was used to assess motor,
motor/cognitive, and cognitive function of subjects. The battery included nine tests (finger
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tapping, eye-hand coordination, simple reaction time, continuous performance, symbol digit,
visual retention, pattern recognition, digit span, and paired associates). A vocabulary test and a
test of emotional state (moods) were also given. Each subject was assessed with a complete
battery of tests during the pre-exposure baseline assessment and at the end of the study. Subsets
of the battery covering motor function and mood were given repeatedly at the beginning and end
of each 4-hour exposure period.
Tetrachloroethylene was not detected in blood samples collected before the start of the
first exposure period. The detection limit was less than 0.0005 mg/L. Mean tetrachloroethylene
blood levels increased slightly over the 4-day period. Among subjects exposed to 10 ppm, mean
blood levels were 0.33, 0.36, 0.4, and 0.38 mg/L at the end of days 1, 2, 3, and 4 of exposure,
respectively. Among subjects exposed to 50 ppm, mean blood levels were 1.1, 1.2, 1.4, and 1.5
mg/L at the end of days 1, 2, 3, and 4 of exposure, respectively.
On the first day of testing, faint solvent odor was reported by 33% and 29% of the
subjects exposed to 10 ppm and 50 ppm, respectively. On the fourth day, these incidences
changed to 17% and 36%, respectively. The VEP patterns of subjects during the third hour of
exposure to 50 ppm on days 1, 2, 3, and 4 of exposure were significantly different (p<0.05) from
those measured on the control day, and the differences became progressively greater on
successive exposure days. One set of VEP patterns on the day after the end of the exposure
period appeared different from the control day values (statistical significance was not reported).
VEP patterns in subjects during exposure to 10 ppm were different from their patterns on the
control day, but the differences were not statistically significant (p>0.05). There were
significant differences (/K0.05) between the VEP patterns of subjects exposed to 10 ppm and
those exposed to 50 ppm.
Data on contrast sensitivity indicated greater effects at 50 ppm than at 10 ppm; effects
were most pronounced on the last day of exposure. However, statistical analysis was not
reported, and the data are limited by the small number of subjects. There were no indications of
peripheral hearing loss at either exposure level.
Neurobehavioral test results were reported for only those tests given repeatedly on 4
consecutive days (finger tapping, eye-hand coordination test, simple reaction time, continuous
performance, and moods). There were significant post-exposure performance deficits (p<0.05)
among subjects exposed to 50 ppm when compared with the group exposed to 10 ppm in tests of
motor/cognitive function (continuous performance test for vigilance) and motor function (eye-
hand coordination), and a near-significant difference (p=0.09) on a test of motor function (simple
reaction time). In all cases, the degree of improvement shown by the subjects exposed to 50 ppm
was less than that shown by the subjects exposed to 10 ppm. There were no exposure-related
effects on the finger-tapping or moods test.
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The study authors concluded that visual function in healthy, young adult males is mildly
affected by tetrachloroethylene exposures to 50 ppm, maintained for 4 hours on each of 4 days
(Altmann et al., 1990), and they stated that the impaired performance on tests of motor/cognitive
and motor function suggests that 50 ppm cannot be considered a NOAEL for neurobehavioral
endpoints indicative of CNS depression (Altmann et al., 1992).
1.1.2. Chronic Exposure Studies
1.1.2.1. Lauwerys, R., J. Herbrand, J.P. Bucket, A. Bernard and J. Gaussin. 1983. Health
surveillance of workers exposed to tetrachloroethylene in dry-cleaning shops. Int. Arch.
Occup. Environ. Health. 52:69—77.
Lauwerys et al. (1983) studied 26 workers (24 women and 2 men) occupationally
exposed to tetrachloroethylene in six dry cleaning shops in Belgium for a mean of 6.4 years. The
controls (31 women and 2 men) were workers in a chocolate factory (20) or an occupational
health service (13) who did not report occupational exposure to organic solvents. Several
characteristics of the two groups were similar (sex ratio, mean age [32.9 vs. 34.5 years], and
level of education). However, 13 of the 26 dry cleaning workers—but only 9 of the 33
controls—were smokers. Neurobehavioral tests of motor function (simple and choice reaction
time), sensory function (critical flicker fusion), and cognitive function (sustained attention test)
were given twice to each worker, once before work and once after work. Both groups were
tested in the middle of the work week. Individuals also were questioned about chronic
symptoms related to nervous system disturbances. Blood samples for tetrachloroethylene
measurements and liver function tests were collected before work. Urine samples for kidney
function tests were collected after work.
The mean tetrachloroethylene air concentration (8-hour TWA) was 21 ppm and the range
of TWA values was 9 to 38 ppm, using results from active sampling of personal air. The mean
tetrachloroethylene blood level (30 minutes after the end of work) was 1.2 mg/L (range of means
from the shops was 0.6 to 2.4 mg/L). There was no significant connection between air
concentrations and blood levels.
Seventeen of 22 symptoms related to nervous system disturbances were more prevalent
among the workers than among unexposed controls. However, none of the differences were
statistically significant, and there was no relationship with duration of exposure. Two symptoms
particularly affected were memory loss (7/26 vs. 3/33) and difficulty falling asleep (11/26 vs.
6/33). None of the mean scores of the dry cleaning workers on the four neurobehavioral tests
were significantly lower (/K0.05 ) than those of the control group. The prevalence of abnormal
scores (those beyond the 5th or 95th percentile of the control group) did not vary significantly
between the two groups.
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1.1.2.2. Seeber, A. 1989. Neurobehavioral toxicity of long-term exposure to
tetrachloroethylene. Neurotoxicol. Teratol. 11:579—583.2
Seeber et al. (1989) evaluated the neurobehavioral effects of tetrachloroethylene on 101
German dry cleaning workers (machine operators, ironers, touch-up workers, counter attendants,
and other employees) who were employed in coin-operated or while-you-wait shops, which were
all affiliated with one organization. The workers were separated into a low-exposure group (50
women, 7 men) or a high-exposure group (39 women, 5 men). A third group of 84 sales
personnel (64 women, 20 men) from several department stores and receptionists from large
hotels served as unexposed controls. Predominant characteristics of both groups included
primarily standing work, contact with customers, and moderate physical exercise, all against the
background of somewhat matching skills. The mean ages of the low-exposure, high-exposure,
and control groups were 38.2, 38.4, and 31.8 years, respectively.
Details on air monitoring methods were sparsely reported, but mean tetrachloroethylene
concentrations (8-hour TWA) for the low- and high-exposure groups were 12 (± 8) ppm and 53
(± 17) ppm, respectively, using results from active sampling of room air and passive sampling of
personal air. The mean duration of occupational exposure for the low- and high-exposure groups
was 11.8 and 10.6 years, respectively.
A number of tests of neuropsychological functioning were administered, including
standardized tests of symptoms and personality; tests of sensorimotor function, including finger
tapping and aiming; and the Mira and Santa Ana dexterity tests, which are published
standardized tests. Threshold of perceptual speed was assessed by recognition of stimuli flashed
briefly on a screen; whether this procedure used a standardized instrument is unclear, but it is
assumed that it did not. Choice reaction time was also determined using "nine light and tone
stimuli." It is not clear whether the auditory and visual stimuli occurred together or whether
some trials consisted of an auditory stimulus and other visual tests. Details of the timing of the
stimulus presentation were not provided. One of the response variables, "delayed reactions,"
was not defined. The typical dependent variable measured in this task—response reaction
time—apparently was not measured. Subtests of the Wechsler Intelligence Test (digit span, digit
symbol, and cancellations) were used, as was recognition of words, faces, and digits. The
instrument used and the scoring of the last three tests are not described. Intelligence was
assessed using the logical thinking subtest of the German Performance Test System.
Each subject was examined during a 1.5-day stay at a clinic located at a large institute for
occupational medicine. Each subject came to the clinic in the evening hours, stayed overnight,
2 Dr. Seeber provided additional information on this study in written correspondence to
the New York State Department of Health dated January 19 and May 20, 1996. This information
appears in NYS DOH (1997).
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and started the examination and testing process the next morning. The clinic examined
numerous people daily, and the dry cleaners and the control group were a small part of the daily
routine of the clinic staff. Neurobehavioral tests were given by two specialized clinic staff, who
did not question the subjects about exposure status. However, clinic psychologists (six at the
time of the study) did inquire about the exposure and living conditions of the subjects. Because
the dry cleaner groups and the control group differed in gender ratios, age, and scores on the
intelligence test, stratified analysis was used to statistically control the influence of these
confounding factors on test scores. The groups also differed in alcohol consumption, so a
separate analysis was used to examine the role of alcohol on effects associated with
tetrachl oroethy 1 ene.
Performance of both the low-exposure and high-exposure groups differed significantly
(/K0.01) from that of the unexposed control group on the threshold of perceptual speed and
"delayed responses" on a choice reaction time task, both of which are measures of information
processing speed (p=0.08 and 0.03 for low and high exposure, respectively). Both exposed
groups also had worse scores (/K0.01) on two tests of attention (digit reproduction and digit
symbol) and on visual scanning (cancellations). The low-exposure group also showed
significantly higher scores than the control group on questionnaires on neurological signs
(/K0.01) and emotional liability (/K0.05), Scores of the high-exposure group for these measures
appeared higher than those for the control group; however, the scores were not statistically
significantly different. There were no differences between groups on the other tests. Controlling
for group differences in alcohol consumption did not alter any test results.
1.1.2.3. Cai, S.X., M.Y. Huang, Z. Chen, Y.T. Liu, C. Jin, T. Watanabe, H. Nakatsuka, K.
Seiji, O. Inoue andM. Ikeda. 1991. Subjective symptom increase among dry-cleaning workers
exposed to tetrachloroethylene vapor. Ind. Health. 29:111—121.
Cai et al. (1991) evaluated the CNS effects of tetrachloroethylene exposure among 56 dry
cleaning workers (27 women and 29 men) from three shops in China. The control group (37
women and 32 men) was of similar mean age (34 years vs. 35 years for dry cleaning workers),
but the male dry cleaning workers were 4 years younger than the male controls and the women
were 4.9 years older than the female controls. The controls were recruited from the same
factories as the dry cleaning workers but from workshops without known solvent exposures. The
geometric mean tetrachloroethylene air concentration (8-hour TWA) was 20 ppm and the range
of TWA values was 4 to 97 ppm, using results from passive sampling of personal air. The mean
duration of occupational (tetrachloroethylene) exposure was 3 years.
The prevalence of symptoms of tetrachloroethylene exposure was significantly higher
among the dry cleaning workers (men, women, and men and women combined) (/K0.001), than
among the unexposed controls. Five symptoms (dizziness, drunken feeling, floating sensation, a
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heavy feeling in the head, and facial flushes) in men and women (combined) were significantly
more prevalent among the dry cleaning workers than among the controls (/K0.001). Nasal
irritation and unusual smell were also reported significantly more often by the dry cleaning
workers than by controls (p<0.05). Similar findings were reported when the workers were asked
about the symptoms they had noticed during the 3 months before the study. The investigators
found exposure-related increases in the prevalence of subjective symptoms among dry cleaning
workers exposed to 21 ppm (8-hour TWA).
1.1.2.4. Nakatsuka, H., T. Watanabe, Y. Takeuchi, N. Hisanaga, E. Shibata, H. Suzuki,
M. Y. Huang, Z. Chen, Q.S. Qu andM. Ikeda. 1992. Absence of blue-yellow color vision loss
among workers exposed to toluene or tetrachloroethylene, mostly at levels below occupational
exposure limits. Int. Arch. Occup. Environ. Health. 64:113—117.
Nakatsuka et al. (1992) evaluated the effects of tetrachloroethylene exposure on the color
vision of 64 dry cleaning workers (34 women and 30 men) in China. The workers were from the
same shops studied by Cai et al. (1991). Control workers (72 women and 48 men) were
recruited from the clerical sections of dry cleaning shops and from other factories (paint
production plants or plants producing tetrachloroethylene from trichloroethylene). The mean
ages of the dry cleaning workers (34 years for men, 35 years for women) were lower than those
of the controls (34 years for men, 33 years for women). Lanthony's new color test was carried
out by ophthalmologists or occupational health doctors in charge of the factories under one of
two lighting conditions (natural sunlight or a daylight fluorescent light).
The geometric mean air concentrations of tetrachloroethylene (averaging time not
reported) were 16 and 11 ppm for the men and women, respectively, using results from passive
sampling of personal air. The overall geometric mean was 13 ppm.
There was no significant difference in the performance of the dry cleaning workers and
unexposed controls on Lanthony's new color test. The percentages of men and women dry
cleaning workers who correctly separated colored caps from monochromatic caps were not
significantly different from the percentages in the corresponding control group. The study
authors noted concluded that they found no distinct case of color vision loss among the dry
cleaning workers.
The test used to evaluate study subjects, Lanthony's new color test, is not considered as
sensitive as the Lanthony's D-15 desaturated panel test (Geller and Hudnell, 1997).
Additionally, the investigators did not match exposed subjects and their controls on a number of
important covariates, nor did they present results in a quantitative manner (use of the CCI)
(Gobba, 2000).
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1.1.2.5. Ferroni, C., L. Selis, A. Mutti, D. Folli, E. Bergamaschi and I. Franchini. 1992.
Neurobehavioral and neuroendocrine effects of occupational exposure to perchloroethylene.
Neurotoxicol. 13: 243-247.3
Ferroni et al. (1992) evaluated neuroendocrine and neurobehavioral effects of
tetrachloroethylene exposure among 60 female dry cleaners and 30 unexposed controls who
were comparable in age (mean ages 39.7 and 37.6 years, respectively) and vocabulary level.
Each dry cleaning shop in a small town outside of Parma, Italy, was visited. The workers were
invited to participate in the study, which was part of a preventive health program implemented
by the local health office and professional associations of small businesses. There were no
refusals. Controls were selected from the workers at a hospital who cleaned clothes using a
water-based process. Their jobs were essentially the same as those of the dry cleaners, but they
were not exposed to any organic solvents. Both groups filled out a questionnaire on their
characteristics and health; medication, including oral contraceptives; life style; and current and
past jobs. Both groups met the following criteria: no history of metabolic disorders, no history
of psychiatric disorders, and low level of daily alcohol intake. The two groups were similar in
height, weight, body mass index, smoking habits, and use of medication, but alcohol intake was
about 5% higher (p<0.03) in the control group than in the dry cleaner group.
Workers and controls were given five neurobehavioral tests (part of the Swedish
Performance Evaluation System, "adapted" Italian version: finger tapping with both dominant
hand and nondominant hand, simple reaction time, digit symbol test, shape comparison-
vigilance, and shape comparison-response to stress). All subjects were examined in the morning
before their work shift in the same room by the same examiners (NYS DOH, 1997). The tests
were part of a computer-based battery, and the same machines and software were used to
administer the tests and score the results. The same sequence of tests and protocols were used
for all subjects. Although the examiners were not blind to the status of the subjects (dry cleaner
or control), the examiners and the dry cleaners were blind to the worker's exposure level (NYS
DOH, 1997). Serum prolactin levels were measured in all subjects; all samples were taken just
before the neurobehavioral tests. Samples from dry cleaners and controls were alternated and
analyzed in the same experimental runs. For women, only those samples obtained during the
proliferative phase of the menstrual cycle were used for comparison between groups (41 dry
cleaners and 23 controls).
Workplace air samples were randomly collected throughout the work week during
summer and winter to account for variability related to either the work cycle or seasonal
3 Dr. Mutti provided details on the selection process of exposed and control subjects and
also clarified reported results to Dr. Ken Bodgen, New York State Department of Health, in
written correspondence dated July 29 and September 5, 1995 (see NYS DOH, 1997).
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environmental fluctuations. The median tetrachloroethylene air concentration (4-hour TWA)
was 15 ppm and the range of TWA values was 1 to 67 ppm. The subjects' range of
tetrachloroethylene blood levels was 0.012 to 0.864 mg/L (median = 0.145 mg/L) (incorrectly
expressed in Ferroni et al. [1992] as 12,864 and 145 mg/L [NYS DOH, 1997]). The mean
duration of occupational exposure was 10 years.
The dry cleaners showed significantly reduced performance when compared with the
unexposed, matched controls in three tests (simple reaction time, p<0.0001; vigilance, p<0.005;
and stress, p<0.005), as reported in a single sentence in the results section in Ferroni et al.
(1992). Performance on the finger-tapping test (both hands) and digit symbol test was not
affected (NYS DOH, 1997). Additionally, the mean serum level of prolactin was significantly
higher in the workers than in the matched controls (/K0.001). None of the three measures of
exposure (duration of exposure and air or blood concentration of tetrachloroethylene) was
significantly associated with decreased test scores or increased serum prolactin levels among the
dry cleaners.
The study authors concluded that tetrachloroethylene exposure in dry cleaning shops may
impair performance and affect pituitary function but that the cross-sectional design prevents
distinguishing acute effects from chronic effects. They also noted, however, that the most likely
bias of cross-sectional studies is a spontaneous selection of the sample (i.e., workers who believe
exposure is making them sick or workers who actually become sick may quit work prematurely
and not be included in the study). This is known as selection bias and would lead to an
underestimate of the actual or underlying risk
1.1.2.6. Cavalleri, A., F. Gobba, M. Paltrinieri, G. Fantuzzi, E. Righi and C.L. Aggazzoti.
1994. Perchloroethylene exposure can induce colour vision loss. Neuroscience Lett.
179:162—166.4 Gobba, F., E. Righi, G. Fantuzzi, G. Predieri, L. Cavazzuti and G. Aggozzotti.
1998. Two-year evaluation of perchlorothylene-induced color-vision loss. Arch. Environ.
Health 53:196-198.
In a study on the effects of tetrachloroethylene exposure on the color vision of dry
cleaners, Cavalleri et al. (1994) compiled a list of all the dry cleaning shops in the municipality
of Modena, Italy, (110 shops employing 189 workers) and randomly selected 60 dry cleaners
from 28 premises for recruitment into the study (Aggazzotti et al., 1994). Only full-time workers
(n = 52) were asked to participate, and 2 declined. All 50 workers provided, via questionnaires,
information on work history, health status, occupational and hobby use of solvents, drinking and
smoking habits, and drug use. Thirty-five of the 50 dry cleaners (33 women, 2 men) met the
4 Dr. Cavalleri provided additional information on this study in written correspondence
to the New York State Department of Health dated October 8, 1996 (see NYS DOH, 1997).
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inclusion criteria; others were excluded for hypertension, smoking more than 30 cigarettes a day,
alcohol consumption exceeding 50 g of alcohol per day, oculo-visual pathology, or working less
than 1 year. Another worker was excluded because a matched control could not be found.
The controls were factory workers who were not occupationally exposed to solvents or
other neurotoxic chemicals; they were selected and recruited into the study using the same
methods that were used for dry cleaners. The controls (n = 35) were from factories in the
Modena area and met the same inclusion criteria as the dry cleaners and were matched to dry
cleaners by gender, age (±3 years), alcohol consumption (±10 g/day), and cigarette use (±5
cigarettes per day). The mean age of both groups (35 years) and the percentages of each group
that were smokers (43%) or alcohol drinkers (71%) were the same.
All subjects appeared healthy and met minimal status of visual acuity. None of the
subjects reported hobby exposure to solvents or other substances toxic to the eye. There were no
known systematic differences between exposed and control groups or between machine
operators and ironers.
Color vision was assessed using Lanthony's D-15 desaturated panel test, in which
subjects are asked to put a series of small round "caps" in order by color. The types of errors
made can distinguish specific types of color vision deficiency; for example, red-green color
blindness (common in males) or blue-yellow color blindness, which is produced by solvent
exposure (Mergler and Blain, 1987; Mergler et al., 1987, 1988a, b, 1991; Campagna et al., 1995,
1996). Test scores are based on the ability of each subject to recombine a set of 15 caps colored
with desaturated colors according to a definite chromatic sequence, with each mistake increasing
the score above a perfect score of 1.00. A formula (the CCI) is used to calculate total errors.
This test assesses specific visual neurotransmitters and circuits from the retinal ganglion cells in
the eye to higher visual areas.
Exposed and control subjects were tested in a random order (NYS DOH, 1997). All
subjects were tested at the same time of day (in the morning, before work) under the same
lighting conditions by the same investigator. With respect to exposed subjects, the investigator
was unaware of both the exposure levels and the job (operator or ironer) of each dry cleaner.
For all dry cleaners, the mean tetrachloroethylene air concentration (8-hour TWA) was 6
ppm and the range of TWA values was 0.4-31 ppm, using results from passive sampling of
personal air. For operators (N = 22), the mean air concentration 8-hour TWA was 7 ppm and the
range of TWA values was 0.4-31 ppm. For ironers (N = 13), mean air concentration (8-hour
TWA) was 5 ppm and the range of TWA values was 0.5-11 ppm. The mean duration of
occupational exposure was 8.8 years. Tetrachloroethylene concentrations were also measured in
alveolar air for a subset of these dry cleaners, with a high correlation observed between
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tetrachloroethylene concentration in alveolar air and the 8-hour TWA levels in ambient air (r =
0.8,/?<0.001) (Aggazzotti etal., 1994).
Only 3 dry cleaning workers, as opposed to 13 controls, had scored a perfect test score
(/K0.01), Mistakes were made mainly in the blue-yellow range. Overall, the workers showed
poorer performance on the test as compared to controls, as they had a significantly higher mean
CCI (p=0.03). The effect was statistically significant among operators but not among ironers.
The observation for ironers may reflect a lower statistical power in this group due to fewer
subjects (13 ironers vs. 22 operators). There also was a statistically significant positive
correlation (/KO.O l) between TWA air concentrations and the CCI (r = 0.52), which remained
after multivariate analysis considered previous tetrachloroethylene exposure duration, age,
number of cigarettes per day, and calculated daily intake of alcohol as covariates. The effect on
color vision may not be rapidly reversible; preliminary data showed that some workers did not
improve their scores when retested after 4 weeks of vacation (NYS DOH, 1997). Moreover, the
finding among some of these workers by poorer performance on this test in the follow-up study
by Gobba et al. (1998), described below, suggests that color vision impairment is a chronic
effect. The CCI values were not associated with two other measures of tetrachloroethylene
exposure (mean duration and an integrated index of exposure, yearly TWA level). The study
authors suggested that this may reflect the difficulty in controlling for the interactive effects of
age and exposure and accurately evaluating exposure.
Gobba et al. (1998) reexamined color vision after a period of 2 years in 33 of the 35 dry
cleaners and ironers examined by Cavalleri et al. (1994). Two subjects had retired during the 2-
year period between examinations. These investigators used the Lanthony D-15 test, the test
used by Cavalleri et al. (1994), to assess color vision, and performance was compared to a
subject's score from the initial survey (self-control). Tetrachloroethylene concentration in the
occupational setting was determined in the breathing zone using personal passive samplers.
Monitoring was carried out during the afternoon shift, as Cavalleri et al. (1994) did not show any
differences between morning and afternoon samples. Gobba et al. (1998) found
tetrachloroethylene concentration had increased during the 2-year period for 19 subjects
(geometric mean, from 1.67 ppm at the first survey to 4.35 ppm at the second survey), identified
as Group A, and had decreased for 14 subjects (geometric mean, from 2.95 ppm to 0.66 ppm),
identified as Group B. For the 33 workers overall, tetrachloroethylene concentration did not
change over the 2-year period (geometric mean, from 2.4 ppm to 1.94 ppm at the second survey,
p>0.05).
Color vision had deteriorated between the two surveys for the entire group, a reflection of
the color vision loss among Group A subjects, whose exposure had increased in the second
survey. As found in the first survey, perception of the blue-yellow range of color was affected
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the most, with few subjects presenting a red-green deficit. Color vision performance for the
entire group was related significantly to age (r = 0.45) and tetrachloroethylene concentration (r =
0.39). The mean CCI score for Group A subjects was statistically significantly different between
the two surveys, and analysis of variance methods that controlled for an effect of age further
supported the finding of color vision deterioration among these subjects. For Group B, subjects
who experienced lower exposure concentrations by the second survey, the CCI score did not
change from that of the initial survey. Additionally, analysis of variance did not show any
differences between the first and second surveys.
Overall, the findings of Cavalleri et al. (1994) and Gobba et al. (1998) are in agreement
with previous studies on other solvents (Geller and Hudnell, 1997; Mergler et al., 1996; Mergler
and Blain, 1987), the blue-yellow range of color vision was primarily affected in the dry
cleaners, with only a few workers showing an effect on red-green perception. This suggests a
retinal location for the effects (Pokorny and Smith, 1986) or, alternatively, post-receptor
processing deficits, perhaps the result of a distal axonopathy of the optic nerve (Mergler, 1995;
Spencer and Schaumburg, 1978).
1.1.2.7. Echeverria, D., R.F. White and C. Sampaio. 1995. A behavioral evaluation of PCE
exposure in patients and dry cleaners: a possible relationship between clinical and preclinical
effects. J. Occup. Environ. Med. 37:667—680.
Echeverria et al. (1995) assessed neurobehavioral effects and mood disturbances in four
patients diagnosed with tetrachloroethylene encephalopathy. Subject 1 was exposed chronically
over a 1-year period when the interior woodwork of her home was mistakenly treated with
tetrachloroethylene. The three other cases were occupationally exposed. Subject 2 was exposed
during two separate periods: first, for 3 years in a dry cleaning establishment, and second, for 7
years cleaning parts. Subject 3 was exposed for 16 years as a dry cleaning worker. Subject 4
was also exposed as a dry cleaning worker, but her duration of employment was not reported.
Subjects 2, 3, and 4 were working with tetrachloroethylene when first tested. Air monitoring
data were not available; however, occupational health physicians diagnosed each case with
tetrachloroethylene encephalopathy on the basis of symptoms, neurophysiological assessment,
and their own examinations.
A large battery of standard neurobehavioral tests was given to each subject. For most
tests, impairment was inferred clinically when a subject's score was greater than one standard
error of measurement below expectation, which is less restrictive than the criterion (more than
two standard deviations below mean) commonly used in neurobehavioral testing to separate
normal from abnormal scores (Lezak, 1995). Test results for the four subjects most consistently
indicated complaints of fatigue and confusion, accompanied by cognitive deficits on tests
assessing memory, motor, visuospatial, and executive function. Repeated testing of subjects 3
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and 4 indicated post-exposure improvement on neurobehavioral tests of all the affected
functional domains, although performance on some of the more difficult tests in each domain
remained impaired. These results suggest an association between CNS effects and
tetrachloroethylene exposure, but a conclusion of a causal relationship is precluded by the lack
of data on the duration and severity of the tetrachloroethylene exposure.
The investigators also assessed the performance of 65 dry cleaning workers on
neurobehavioral tests designed to detect the same impairments noted in the clinical cases. The
testing was conducted in 1986. The owners of 125 shops in Detroit, Michigan, were contacted,
and 23 agreed to allow their workers to participate in the study. Within each shop, operators
were matched on education and age (± 5 years) with a lower-exposure subject.
The subjects (35 men and 30 women) were grouped into three categories of chronic
tetrachloroethylene exposure (low, moderate, and high), based on type of shop (wet-transfer or
dry-to-dry), job title (counter clerk, presser, or operator), and years of employment. All the
operators were placed in the high-exposure category. There was no unexposed control group.
Dry cleaning workers placed in the chronic exposure categories of low, moderate, and high had
been employed at their main job for 2.1, 3.9, and 14.6 years, respectively. Theirmean age was
40.9, 40.6, and 43 years, respectively. The three groups were also characterized by estimates of
current exposure (low, medium, and high), which corresponded to mean tetrachloroethylene air
concentrations (8-hour TWA) of 11, 23, and 41 ppm, respectively, for counter clerks, pressers,
and operators in the more common wet-transfer shops (17 of 23 shops). Estimated air
concentrations for counter clerks, pressers, and operators in the dry-to-dry shops were 0.5, 10,
and 11 ppm, respectively. The estimates were based on a relationship between breath and air
concentrations derived from a larger independent study (Solet et al., 1990). The study authors
noted that the estimates were comparable to those found in other surveys of dry cleaning
facilities in the United States.
All subjects were tested in groups of two in the afternoon after work on the first or
second day of their work week. The tests were conducted in a minivan. Each subject provided a
breath sample and completed a medical, symptom, work history, and hobby questionnaire. The
subjects were administered six neurobehavioral tests, a test of verbal skills, and questionnaires
on emotional states (moods) and CNS symptoms. The neurobehavioral test battery consisted of
one test of motor/cognitive function (symbol digit) and five tests of cognitive function (digit
span, trailmaking A and B, visual reproduction, pattern memory, and pattern recognition),
including three tests of an individual's ability to process and remember visuospatial stimuli (the
latter three tests).
Multivariate analysis was used to evaluate the relationship between a chronic index of
lifetime exposure and performance on neurobehavioral tests, after adjusting for the confounding
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variables of current exposure, a 3-year index of exposure, age, education, verbal skill, alcohol
consumption, hours of sleep, fatigue, mood, symptoms, medication, and secondary exposures to
neurotoxicants. After adjustment for factors affecting performance, the scores of the dry
cleaning workers with high chronic exposure were statistically significantly lower (/K0.01) than
those of the workers with low chronic exposure in three tests of visual function: visual
reproduction, pattern memory, and pattern recognition. Adjusted scores were reduced from 6 to
15%; the two most sensitive tests were those that measured short-term memory of visual designs.
These impairments of visually mediated function were consistent with the impairment of
visuospatial functions observed in the four patients previously studied by Echeverria et al., who
were diagnosed with tetrachloroethylene encephalopathy. Other effects seen in the patients
(mood changes and decreased cognitive function in nonvisual tests) were not found in the dry
cleaning workers with high lifetime exposures. Among complaints by the dry cleaning workers,
only the number of complaints of dizziness from standing up rapidly and "solvent-induced
dizziness" over the previous 3 months was significantly elevated (p<0.04) in the high-exposure
group.
The study authors concluded that effects on visuospatial function were consistently found
in subjects employed as operators for an average at 14.6 years and exposed to an estimated
tetrachloroethylene 8-hour TWA air concentration of 41 ppm, suggesting a vulnerability of
visually mediated functions with tetrachloroethylene exposure. This conclusion was based on
the impaired performance of the high-exposure group when compared with a group of dry
cleaning workers with low lifetime exposure, including 16/22 workers who were probably clerks
in wet-transfer shops where the mean current exposure level was 12 ppm. This exposure level is
substantially above background ambient levels, and whether the performance of the low-
exposure group was impaired when compared with that of a group without occupational
exposure (i.e., an unexposed control group) is not known. The lack of an unexposed control
group limits the ability of the study to characterize fully the magnitude of the effects on
visuospatial ability and to detect exposure-related symptoms or effects on tests of nonvisual
cognitive ability. It also limits the extrapolation of the results to other populations exposed to
tetrachl oroethy 1 ene.
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1.1.2.8. Altmann, L., H.F. Neuhann, U. Kramer, J. Witten andE. Jermann. 1995.
Neurobehavioral and neurophysiological outcomes of chronic low-level tetrachloroethylene
exposure measured in neighborhoods of dry cleaning shops. Environ. Res. 69:83—89.
Altmann et al. (1995) used neurophysiological and neurobehavioral techniques to assess
the effects of long-term exposures to tetrachloroethylene. A total of 19 tetrachloroethylene-
exposed subjects (residents of Mulheim, Germany) were chosen from a population of 92 subjects
living in neighborhoods close to dry cleaning facilities. Three criteria were used to select
subjects: (1) a tetrachloroethylene blood level above 0.002 mg/L, (2) a period of living above or
next to a dry cleaning facility for at least 1 year, and (3) no occupational exposure to organic
solvents. The mean age of the exposed subjects was 39.2 years (range, 27-58 years) and the
mean duration of living near a dry cleaning facility was 10.6 years (range, 1-30 years). The
daily activity pattern of the exposed subjects was not reported.
A total of 30 controls were selected from volunteers; their mean age was 37.2 years
(range, 24-63 years). One or two controls, matched for age (± 1 years, but 3 years in one case
and 6 years in another case) and gender, were chosen for each exposed subject. The control
subjects were recruited mainly from the staff of a public health office or an institute for
environmental hygiene, and none reported a history of solvent exposure. Voluntary consent was
obtained from all subjects prior to the initiation of testing.
All subjects were given medical examinations. Five exposed (26%) and seven control
subjects (23%) were excluded for various medical reasons, including impaired vision, diseases
with potential neuropathy, hypertension, and joint impairment. The reasons for exclusion were
similar in both groups. All subjects met standards for visual acuity and vibration perception.
The final exposed group was composed of 5 men and 9 women and the control group was
composed of 9 men and 14 women. The two groups did not differ with regard to consumption of
alcoholic beverages, regular medication, smoking, or body mass index, but they did differ in
degree of education.
VEPs in response to black-and-white checkerboard patterns were recorded for all
individuals. Vibration perception using a tuning fork—a crude measure of peripheral
neuropathy—was assessed at the ankle. Five tests included in the Neurobehavioral Evaluation
System developed in the United States and adapted for testing on a German population were
used: finger-tapping speed with the index finger of both the dominant and the nondominant
hand; hand-eye coordination using a joy stick to follow a sine wave on a computer screen; a
continuous performance test for assessment of vigilance, which requires a response to a specific
stimulus appearing on the computer screen and failure to respond to other stimuli; simple
reaction time, which requires the fastest possible response to a simple visual stimulus (measured
twice); and visual memory on the Benton visual retention test, which requires a match of a
previously displayed stimulus out of several choices after a short delay interval. All of these
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tests are commonly used to assess occupationally exposed adults, and the software for testing
and analysis is available for purchase. All testing was completed in a single 3-hour session;
testing times were selected randomly for both exposed or control subjects.
Blood samples were taken once in the examination room immediately before testing (all
subjects) and, if possible, once when the exposed subjects were at home. The mean blood level
for exposed subjects, based on samples collected in the examination room, was 0.0178 mg/L
(standard deviation, 0.469 mg/L). For seven of the nine exposed subjects, blood concentrations
in samples collected at home were higher than those in samples collected in the examination
room. None of the blood concentrations in the control group exceeded the detection limit of
0.0005 mg/L. For the exposed subjects (data from 13 apartments), indoor air sampling indicated
that the mean (7-day TWA) air concentration was 0.7 ppm (standard deviation, 1 ppm) and the
median was 0.2 ppm. For the control group, the mean and median values were 0.0005 ppm
(standard deviation, 0.0005 ppm) and 0.0003 ppm. There was a good correlation between home
indoor air concentrations and blood levels of tetrachloroethylene in the exposed subjects (r =
0.81). The correlation was much lower when the examination room blood samples were used (r =
0.24).
After adjusting for covariates and possible confounders of age, gender, and education,
there were statistically significant group differences between the adjusted mean scores of
exposed and control subjects on three neurobehavioral tests (simple reaction time, /K0.05 for test
1 andp<0.01 for test 2; continuous performance, p<0.05; and visual retention, /K0.05), In all
cases, the exposed subjects had slower response times or more errors than the unexposed
controls. No statistically significant differences were observed between the performance of the
exposed and control groups on the finger-tapping or eye-hand coordination tests, which are
measures of fine motor function or on VEP, which would be expected to be less sensitive than
direct measurement of visual function, or on vibration perception at the ankle using a tuning
fork.
The relationship between indoor tetrachloroethylene concentration and individual
performance was not reported, so it was not possible evaluate concentration-response
relationships. Because the responses in the exposed group for the tests highlighted above
(simple reaction time, continuous performance, visual retention) were statistically significantly
different from those of the control group, whether or not the covariates were considered, an
approximate estimate of the impact of the tetrachloroethylene exposures can be derived by
comparing the reported response levels for the two groups. The degree of change from control
was approximately 15-20% for this subset of tests.
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1.1.2.9. Spinatonda, (7., /?. Colombo, E.M. Capodaglio, M. Imbriani, C. Pasetti, G. Minuco
and P. Pinelli. 1997. Studio dei processi di produzione della praola: applicazione in un
gruppo di soggetti esposti cronicamente a solventi organici (parte II) [Study on speech
production processes: application for a group of subjects chronically exposed to organic
solvents (part II). Med Lav. 19:85—88.
Spinatonda et al. (1997) assessed the effect of tetrachloroethylene exposure on vocal
reaction times among 35 dry cleaners and 39 unexposed controls. Controls were matched to
exposed individuals for age (mean age of 35 years for both groups) and education. The
published paper did not identify the population from which exposed and controls were drawn,
the inclusion criteria for exposed subjects and controls, and hence, whether potential study
subjects were excluded, nor was information presented as to whether controls were of the same
sex as exposed subjects or whether they held jobs similar to those of the tetrachloroethylene-
exposed dry cleaners. The investigators did not identify the length of exposure in a
tetrachloroethylene-exposed j ob.
Exposure was assessed by a "grab sample" and not as a weighted average (as expressed
in other occupational studies reviewed in this section). Exposure monitoring indicated a median
concentration of tetrachloroethylene of 8 ppm (range, 2-136 ppm). An index of cumulative
exposure to tetrachloroethylene was also developed for each exposed subject by multiplying the
tetrachloroethylene concentration by the number of years worked.
The latency to vocal response to the stimulus (reading) and duration of vocal response
were measured in each subject after the presentation of a sequence of words on a computer
screen. For each condition, subjects were asked to say the word immediately or following delays
of 0.1 or 0.5 seconds. The test was performed using a random sequence of concrete or
meaningless disyllabic words. These tests were carried out at the place of employment for dry
cleaners and in a clinical setting for controls, indicating that the investigators were not blinded as
to a subject's exposure status.
Compared with the control group, the exposed group had statistically significantly longer
mean reaction times and/or vocalization durations under all response conditions (immediate or
delayed response) with either real or meaningless words. Furthermore, statistically significantly
positive correlations were observed between cumulative tetrachloroethylene exposure and
immediate reading and delayed reading tasks (r = 0.69 and r = 0.73, respectively). No
information on alcohol consumption or other potential differences between exposed subjects and
controls was reported, precluding an analysis of how these factors may have affected the
observed association between tetrachloroethylene and reaction time.
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1.1.2.10. Schreiber, J.S., H.K. Hudnell, A.M. Geller, D.E. House, K.M. Aldous, M.E. Force,
K. W. Langguth, E.J. Prohonic and J.C. Parker. 2002. Apartment residents' and day care
workers' exposure to tetrachloroethylene (perc) and deficits in visual contrast sensitivity.
Environ. Health Perspect. 110: 655—664.
Schreiber et al. (2002) reported the findings from two different studies that administered
visual tests to assess neurologic function in two populations: apartment residents and day care
employees who had potential environmental tetrachloroethylene exposure due to close proximity
to dry cleaning facilities.5 All participants—or their guardians in the case of the residential
study—signed voluntary consent forms prior to study commencement.
For the residential study, a total of 17 tetrachloroethylene-exposed subjects (11 adults
between the ages of 20 and 50, 2 adults over the age of 60, and 4 children) from six families that
had resided for an average of 5.8 years (6 years median) in two apartment buildings in New York
City. This was an affluent, English-speaking, white population living near New York City's
Central Park (telephone communication from K. Hudnell, U.S. EPA, to D. Rice, U.S. EPA).
Control subjects were recruited from among NYS DOH employees in Albany, New York, and
their families and were age- and gender-matched to exposed apartment residents; control
subjects were considered representative of the general population not living near dry cleaning
facilities. All controls were white except for one Asian individual. In some cases, more than
one control participant was matched to an exposed subject, in which case the visual function test
scores of controls were averaged to yield a single point. Mean age was 34.5 years for exposed
apartment residents and 33.2 years for control subjects.
Nine adult staff (all females) of a day care facility agreed to participate in the day care
study. Controls were age- and gender-matched acquaintances of the exposed participants, local
retail shop employees, NYS DOH employees, or staff from other local day care centers with no
known tetrachloroethylene exposure. All subjects in the exposed and control groups were white
(telephone communication from K. Hudnell, U.S. EPA, to D. Rice, U.S. EPA). Mean age was
27.7 years for control participants and 27.2 years for day care staff; mean duration of
employment at the center for exposed subjects was 4 years.
5 The apartment residents lived in two separate buildings in New York City that each
contained a dry cleaning business. The residential study served as a pilot for a larger study that
is investigating visual effects among tetrachloroethylene-exposed residents. The day care study
was part of an investigation of staff and children carried out by NYS DOH and the Centers for
Disease Control and Prevention and reported in Schreiber et al. (2002). The day care facility,
located in Albany, New York, was in a building that also housed a business that did dry cleaning.
All visual testing for both studies was carried out by the same investigator using the same testing
apparatus.
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Both study populations and their controls were given a questionnaire to obtain
information on sociodemographics; lifestyle factors such as exposure to direct or passive smoke,
alcohol consumption, and exercise; medical history; and neurotoxicant exposure in addition to
the visual tests. Exposed participants had no known exposure to other neurotoxicants, ongoing
illness, current use of neuroactive drugs, or a medical history indicative of neurologic
dysfunction, and both exposed participants and controls reported low or moderate alcohol
consumption which did not differ between either exposed group and their controls. The
investigators also administered visual tests of acuity, contrast sensitivity, and color
discrimination to exposed subjects and their referents. The investigators were not blinded as to a
subject's status as either exposed or nonexposed.
The assessment of tetrachloroethylene exposure of residents consisted of
tetrachloroethylene concentrations in indoor air and personal air samples, exhaled breath, and
blood, which were collected at the time of visual testing. Testing was performed during a period
of active dry cleaning for four of the families and 1 month after closure of the facility for the
remaining two families in the residential study. Additionally, adult residents provided urine
samples, which were analyzed for tetrachloroethylene as well as for three products of its
metabolism: TCA, trichloroethanol, and the urinary acetyl metabolite. Two exposed participants
were mothers who were breastfeeding, and they provided breast milk samples.
Ambient concentrations of tetrachloroethylene were also available for all study
participants for an earlier time frame (from 1 to 3 months before the date of visual testing), when
active dry cleaning was occurring in both apartment buildings. These measurements were used
by NYS DOH to identify study sites. Concentrations of airborne tetrachloroethylene levels in
apartment rooms were higher in these samples than in the monitoring data obtained at the time of
the visual testing. Median concentrations in these samples, which were taken during the day
during active periods of dry cleaning, were 0.21 ppm (mean = 0.36 ppm: range, 0.10-0.9 ppm).
Airborne tetrachloroethylene concentrations had decreased in samples collected at the time of
visual testing; median tetrachloroethylene concentration was 0.09 ppm (mean = 0.18 ppm; range,
0.01-0.78 ppm). Tetrachloroethylene levels in blood correlated well with levels in room air,
personal air, and breath.
Atmospheric monitoring of the day care facility before closure of the dry cleaning
business showed airborne concentrations of tetrachloroethylene ranging from 0.27 to 0.35 ppm,
with median and mean concentrations of 0.32 ppm. Samples obtained at the time of visual
testing, 5 weeks after removal of the dry cleaning machines, approached background
concentrations (range, 0.0012-0.0081 ppm).
Visual function testing consisted of visual acuity, contrast sensitivity, and color vision.
The visual acuity test assesses the ability to discriminate high frequencies at high contrast; for
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example, reading successively smaller black-on-white letters as part of an examination for
corrective lenses. This typically measures the optics of the eye rather than the neurological
integrity of nervous system circuitry. In neither assessment did groups differ in acuity, and
individuals wore corrective lenses as appropriate for subsequent testing.
The contrast sensitivity function assesses the integrity of visual pathways. The visual
system processes spatial information as a Fourier analysis of sine wave frequencies. Testing of
contrast sensitivity is performed by determining the ability of the visual system to detect sine
waves of a number of different frequencies tested individually, thereby breaking spatial visual
function into its essential components. The stimuli for testing consisted of disks displaying sine
waves oriented vertically or 15 degrees to the left or right of the vertical. The subject indicated
the orientation of the stimulus either verbally or by a hand gesture. For each of the test
frequencies, the contrast between the light and dark portions of the sine wave was decreased
until the subject could no longer detect the sine wave pattern. That contrast was considered the
threshold for that particular frequency.
Group mean scores for VCS across spatial frequencies were statistically significantly
lower in exposed residents than in controls and in day care employees as compared with
controls, indicating poorer visual function in the exposed groups. An exposure-response analysis
did not show an association between poorer performance and increasing tetrachloroethylene
concentration. Among apartment residents, mean scores of VCS in all four children and in both
older adults (>60 years of age) were lower than the 12th percentile score of all control subjects.
(The 12th percentile represents the two control subjects with the poorest performance out of the
17 total data points.) In contrast, only 5 of the 11 adults aged less than 60 years scored below the
12th percentile as compared to controls (Figure 1).
The spatial vision of the four children was poor enough that it would likely negatively
impact normal activities. For example, at the highest frequency tested, the exposed children
required three times as big a difference in the light versus dark part of the grid in order to be able
to see the grid. This frequency did not correspond with the detection of fine detail of a scene but
rather with the ability to identify small objects. Similar deficits were observed at lower
frequencies as well, with the exception of the lowest frequencies that correspond with the ability
to distinguish the outlines of large objects. It is unknown whether the difference between groups
would have been statistically significant on the basis of the adults under 60 years alone.
However, day care employees also had a statistically significantly lower group mean VCS score
across all spatial frequencies as compared with the control group (data not shown). No
differences between exposed residents or day care employees and their respective controls were
observed for visual acuity scores (group means).
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Educational differences between residents and their controls were not considered to have
confounded the observation of VCS differences between exposed subjects and controls; other
studies have looked for but have not found this variable to explain observed differences in VCS
in other populations (Mergler et al., 1991; Frenette et al., 1991). Deficits in VCS function are a
well-known consequence of solvent exposure in industrial workers (Bowler et al., 1991;
Broadwell et al., 1995; Campagna et al., 1995; Donoghue et al., 1995; Frenette et al., 1991;
Hudnell et al., 1996a; Mergler et al., 1991). Therefore, the effects of tetrachloroethylene on
contrast sensitivity function are not an unexpected finding.
Moreover, urban-rural differences between exposed and control subjects is not thought to
strongly bias findings. For example, Kaufman et al. (1988) did not show that urban or rural
residence was related to performance on specific subtests of the Wechsler Adult Intelligence
Scale, although associations were seen with other variables such as sex, age, and education.
In the residential study, exposed subjects were retested twice after the initial assessment,
6 to 10 months and 17 to 21 months after closure of the dry cleaning facility. Performance
across frequencies appeared to worsen over successive episodes (statistical comparisons were
not performed) (NYS DOH, 2000a). These results provide evidence that the visual deficits were
permanent and perhaps became even worse after closure of the dry cleaning facilities. Control
subjects from the initial testing were not retested; however, there is no reason to expect that
performance of unexposed subjects would deteriorate. This failure of improvement in function
with decreased exposure is consistent with failure of improvement in color vision loss in
industrial workers following significant reduction in tetrachloroethylene exposure (Gobba et al.,
1998).
Color vision was also assessed in both the residential and the day care groups. Subjects
were asked to put a series of small round "caps" in order by color. The types of errors made
could distinguish specific types of color vision deficiency: for example, red-green color
blindness, which is common in males, or blue-yellow color blindness, which is associated with
solvent exposure (Mergler and Blain, 1987; Mergler et al., 1987, 1988a, b, 1991; Campagna et
al., 1995, 1996). Neither group was statistically significantly impaired on this test, although the
performance of the exposed groups was worse than that of controls, as indicated by the scores on
the CCI, particularly in the residential group. These results suggest that VCS is a more sensitive
measure of solvent (tetrachloroethylene) exposure than is color vision.
Regarding these permanent changes in contrast sensitivity, it is important to understand
that these changes in nervous system pathways are probably not confined to the visual system,
but are indicators of nervous system damage in brain areas, which are not as easy to assess as
sensory system function, for which normal variability is relatively small compared to other
endpoints.
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1.2. SUMMARY OF NEUROPSYCHOLOGICAL EFFECTS IN LOW- AND
MODERATE-EXPOSURE STUDIES
It is important to compare performance across studies in order to determine whether it is
possible to identify a pattern of neuropsychological deficits produced by tetrachloroethylene
(Table 1). Deficits in blue-yellow color vision, a well-established effect of solvents, were
observed in the Muttray et al. (1997) study of workers previously exposed to a mixture of
solvents that contained tetrachloroethylene (not described in Section 1.1.2) and in the high-
exposure (7 ppm) but not the low-exposure (5 ppm) groups in Cavalleri et al. (1994).
Additionally, the lack of improvement in color vision among dry cleaners studied by Cavalleri et
al. (1994) whose exposure to tetrachloroethylene had decreased over a 2-year period (Gobba et
al., 1998) suggests impaired color vision may be a persistent chronic effect. In a recent
residential study of tetrachloroethylene exposure at a much lower concentration (0.4 ppm) than
previously studied (Schreiber et al., 2002), there was a decrement in color vision, although it was
not statistically significant. This suggests that color vision impairment might be caused by low
tetrachloroethylene concentrations, but more information is needed to confirm the Schreiber et
al. (2002) observations.
Deficits in spatial vision, as measured by tests for visual contrast sensitivity (VCS), are
also a well-established effect of exposure to solvents (Bowler et al., 1991; Broadwell et al.,
1995; Campagna et al., 1995; Donoghue et al., 1995; Frenette et al., 1991; Hudnell et al., 1996a,
b; Mergler et al., 1991). Schreiber et al. (2002) was the only study to measure VCS. Moderate
deficits were observed in adults in both the day care and residential populations. The severe
deficit in the residential study is quite surprising. By comparison, the magnitude of the deficit in
VCS was much more severe, for example, than deficits in monkeys exposed to a relatively high
dose of methylmercury, a neurotoxicant that affects vision preferentially (Rice and Gilbert,
1990).
Three studies assessed fine motor control using various instruments, and all three found
no effect. Two of these studies—an occupational study with relatively higher exposure (Ferroni
et al., 1992) and the Altmann et al. (1995) residential study—also assessed simple reaction time,
a task that uses a motor response and demands a relatively modest amount of attention; results
were positive in both studies.
These findings on simple reaction time are in contrast to those of Lauwerys et al. (1983)
who did not observe any statistically significant differences on this test between dry cleaners and
their referent. These investigators also did not find a statistically significant difference in the
prevalence of self-reported symptoms among exposed subjects compared to controls, an
observation inconsistent with Cai et al. (1991), who reported exposure-related increases in the
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prevalence of subjective symptoms among dry cleaning workers exposed to 20 ppm (mean 8-
hour TWA) tetrachloroethylene.
Speed of information processing was assessed in four studies, Seeber (1989), Ferroni et
al. (1992), Echeverria et al. (1995), and Spinatonda et al. (1997). Seeber (1989) used two tasks.
Effects were observed in both groups on a task requiring recognition of briefly presented stimuli.
In a choice reaction time task, effects were borderline in the lower-exposure group and negative
in the higher-dose group. Spinatonda et al. (1997) found effects on response to vocal and visual
stimuli. Conversely, the times on the finger tapping test were not statistically significantly
different between dry cleaner and referents in Ferroni et al. (1992). Speed of information
processing also was not shown in Echeverria et al. (1995) to be affected by cumulative
tetrachloroethylene exposure.
Ferroni et al. (1992) and Altman et al. (1995) assessed vigilance using a continuous
performance procedure in which the subject faces a screen that presents one of several different
stimuli at random intervals. The subject must make a response to a specified stimulus and not to
the others. This test measures sustained attention and is correlated with performance on tests of
executive function. Both studies found deficits as a result of tetrachloroethylene exposure on
this task.
Seeber (1989) found effects on two tests of attention that are subsets of the Weschler IQ
tests and so were designed to be sensitive to performance within the normal range. These
investigators also found positive effects on a visual scanning test that is usually used to assess
laterality of brain damage but has also proved sensitive to toxicant (lead) exposure (Bellinger et
al., 1994). In contrast, Echeverria et al. (1995) and Ferroni et al. (as described in NYS DOH,
1997) did not find effects on digit span or digit symbol despite higher levels of exposure as
compared with Seeber (1989).
The effects of tetrachloroethylene on tests of visuospatial function are of particular
interest in light of the effects identified on tests of visual function per se. Echeverria et al.
(1995) found effects on tests of pattern memory, visual reproduction, and pattern recognition in
the absence of effects on attention (digit symbol and digit span) or executive function
(Trailmaking A and B). One hypothesis is that these effects may be the result of deficits in
visual function or higher-order processing in the visual system, given that lower exposures
produced frank visual deficits. Seeber (1989) also reported impaired visuospatial recognition in
both exposure groups, and Altmann et al. (1995) observed deficits on a test of visuospatial
function at much lower exposures than those of the other two studies.
The pattern of effects observed in these studies shows a consistency between the
occupational studies and studies of residents. The finding of decrements in visuospatial function
and visual function per se in occupationally exposed dry cleaners are supportive of the observed
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deficits in visual function in one residential population (Schreiber et al., 2002) as well as the
findings in a second residential population (Altmann et al., 1995). Moreover, contrast sensitivity
function may be a more sensitive endpoint than color vision loss, as previously discussed.
The human studies all have limitations. Most importantly, these studies were designed to
identify a hazard and not to identify an exposure concentration associated with no adverse effect.
In some studies, investigators were not blinded as to subject status, a potential source of bias,
particularly in situations in which the investigator interacted directly with the subject during
testing. None of these studies included a large number of subjects—fewer than 100 in most
cases. All studies used a cross-sectional design, which is weaker than a longitudinal design for a
number of reasons, including a greater potential for selection bias and exposure misclassification
(the latter of which would bias the results toward the null). Several studies provided insufficient
details on the population from which controls were selected (Seeber, 1989; Spinatonda et al.,
1997; Ferroni et al., 1992) or the details provided raise concerns regarding the appropriateness of
the control group (Seeber, 1989; Spinatonda et al., 1997; Schreiber et al., 2002 [residents only];
Ferroni et al., 1992). For some of the occupational studies, the descriptions of behavioral testing
procedures or results were insufficient or ambiguous (Ferroni et al., 1992; Seeber, 1989;
Spinatonda et al., 1997).
These studies do have important strengths. They describe susceptibility to
tetrachloroethylene toxicity in humans, eliminating the need for quantitative extrapolation from
animal models. Moreover, two studies (Cavalleri et al., 1994; Spinatonda et al., 1997) reported
exposure response gradients, providing greater confidence of tetrachloroethylene as the causal
exposure. Several studies (Altmann et al., 1995; Schreiber et al., 2002; Echeverria et al., 1995)
employed multiple measures of exposure (ambient monitoring, personal monitoring, and in some
cases, biological monitoring) with a high degree of correlation between ambient concentration
and biological metrics such as blood tetrachloroethylene concentration, suggesting ambient
exposure as a reasonable exposure metric.
Individual studies have taken appropriate means to minimize bias and potential
confounding. Study investigators have either (1) matched exposed and control subjects on a
number of important factors such as age, alcohol consumption, and/or education (Cavalleri et al.,
1994; Spinatonda et al., 1997; Schreiber et al., 2002; Altmann et al., 1995; Echeverria et al.,
1995), (2) excluded subjects whose diseases or conditions may have been associated with
neurologic deficits (Altmann et al., 1995; Cavalleri et al., 1994; Ferroni et al., 1992; Echeverria
et al., 1995), (3) shown no difference in group means between exposed subjects and their
referents on a number of factors such as alcohol consumption (Schreiber et al., 2002; Ferroni et
al., 1992), or (4) provided results in which statistical analysis (regression analyses) of the data
accounted for a number of joint factors on the outcome measure (Altmann et al., 1995; Seeber,
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1989; Echeverria et al., 1995). These measures give greater confidence that the decrement in
neurological performance observed in these studies was more likely caused by
tetrachloroethylene exposure.
Effects on spatial vision are well-known consequences of solvent exposure in industrial
workers (Bowler et al., 1991; Broadwell et al., 1995; Campagna et al., 1995; Donoghue et al.,
1995; Frenette et al., 1991; Hudnell et al., 1996a; Mergler et al., 1991). Other organic solvents,
as well as alcohol, induce effects on memory and color vision (Altmann et al., 1995; Mergler et
al., 1991; Hudnell et al., 1996a, b). Mergler and Blain (1987) also identified several hypotheses
for organic solvent-related dyschromatopsia, including effects on the neuron. Both VCS deficits
and color discrimination deficits are commonly present prior to detectable pathology in the retina
or optic nerve head, making this one of the earliest sign of disease (Regan, 1989). Effects in the
visual system may also have "downstream" consequences on neurological tests that use visual
stimuli or require a visually mediated response (Grandjean et al., 2001; Hudnell et al., 1996b).
The consistency of the human observations suggest a common mode of action of organic
solvents, including tetrachloroethylene, to degrade pattern vision. By analogy, these
observations support an inference of tetrachloroethylene-induced neurobehavioral effects.
2. ANIMAL STUDIES
2.1. INHALATION STUDIES
Mattsson et al. (1998) studied the effects of exposure to tetrachloroethylene acutely or for
13 weeks on flash-evoked potentials (FEPs), somatosensory-evoked potentials (SEPs), EEGs,
and rectal temperature in Fischer 344 rats. During the acute (pilot) study, male rats were
exposed to 0 or 800 ppm tetrachloroethylene for 6 hours per day for 4 days and tested before and
after exposure on the fourth day. Changes in FEP, SEP, and EEG components were observed.
In the subchronic study, the above endpoints plus BAEPs and caudal nerve conduction velocity
were determined in male and female rats exposed to 0, 50, 200, or 800 ppm for 6 hours per day
for 13 weeks. Testing was performed during the week following cessation of exposure.
Changes in FEP were observed at the highest dose. Several measures of BAEP were affected at
50 ppm but not at higher doses. BAEP power was also affected at 800 ppm. Other measures
were not affected. The finding of an overall greater effect following short-term (4-day) exposure
as compared with longer-term exposure is similar to the findings of Moser et al. (1995) on a
number of measures of a neurotoxicity battery.
The effects of exposure to 90-3600 ppm tetrachloroethylene for 1 hour on motor activity
was examined in male MRI mice (Kjellstrand et al., 1985). A strong odor (cologne) was used as
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the control condition. Total activity was monitored during the dark period during exposure and
for several hours thereafter. All doses produced increased activity during exposure, which
decreased over several hours after cessation of exposure. Although apparently no statistical
analyses were performed, it is clear from the figures that the lowest dose produced an average
performance well outside the boundary of the 95% confidence intervals of the cologne-treated
controls and that it was dose-dependent. Tetrachloroethylene induced motor activity at
concentrations lower than those of the other organic solvents tested (methylene chloride, toluene,
trichloroethylene, 1,1,1 -trichloromethane).
De Ceaurriz et al. (1983) exposed male Swiss OF1 mice to 596, 649, 684, or 820 ppm
tetrachloroethylene for 4 hours. Immediately following exposure, subjects were immersed in a
cylinder filled with water and the duration of immobility was observed for 3 minutes. The term
"behavioral despair" has been coined for this initial immobility, and the length of immobility is
shortened by antidepressant administration. Tetrachloroethylene exposure also shortened the
period of immobility, with a no-observed-effect level (NOEL) of 596 ppm.
Wang et al. (1993) exposed male SD rats to 300 ppm tetrachloroethylene continuously
for 4 weeks or to 600 ppm for 4 or 12 weeks. Exposure to 600 ppm at either duration resulted in
reduced brain weight gain, decreased regional brain weight, and decreased DNA in frontal cortex
and brainstem but not hippocampus. Four specific proteins (S-100, glial fibrallary acidic protein,
neurone-specific enolase, and neurofilament 68 kD polypeptide) were decreased at 4- and/or 12-
week exposures to 600 ppm; 300 ppm had no effect on any endpoint.
In a study from the same laboratory (Rosengren et al., 1986), Mongolian gerbils of both
sexes were exposed to 60 or 300 ppm tetrachloroethylene for 3 months, followed by a 4-month
solvent-free period. Changes in both S-100 (an astroglial protein) and DNA concentrations in
various brain regions were observed at the higher concentration, and decreased DNA in frontal
cortex was observed after exposure to 60 ppm. The higher concentration also produced
decreased brain but not body weight. The results at 60 ppm were replicated in a follow-up study
(Karlsson et al., 1987).
In a related study (Briving et al., 1986), Mongolian gerbils were exposed for 12 months
to tetrachloroethylene at 120 ppm. At the end of exposure, out of a total of 8 amino acids
assayed, taurine was significantly decreased in the two brain regions assessed (hippocampus and
cerebellum), and glutamine was elevated in the hippocampus. y-Aminobutyric acid (GABA)
levels were unaffected, as were uptake of GABA and glutamate.
The effect of tetrachloroethylene on neurotransmitter levels in the brain was explored in
male SD rats exposed continuously to 200, 400, or 800 ppm for a month (Honma et al., 1980a,
b). The 800 ppm dose produced a decrease in ACh in the striatum, and there was a dose-related
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increase in a peak containing glutamine, threonine, and serine in whole-brain preparations.
GAB A, NE, 5-HT, and other amino acids were not affected.
White male and female MRI mice were exposed to 9, 37, 75, or 150 ppm
tetrachloroethylene continuously for 30 days to 150 ppm for one of several exposure periods
ranging from 5 to 30 days or to 150 ppm for 30 days with various recovery periods (Kjellstrand
et al., 1984). Other groups were exposed intermittently on several dosing and exposure regimens
that resulted in a TWA of 150 ppm for 30 days. Plasma butyrylcholinesterase (BuChE) levels,
organ weights, liver morphology, and motor activity were assessed. BuChE was elevated after
continuous exposure to 37 ppm or greater. Liver weight was increased at all doses following
continuous exposure, and body weight decreased at 37 ppm or above. Motor activity results
following continuous exposure were not reported. BuChE and liver weight were both elevated at
a TWA of 150 ppm for 30 days, regardless of the length of the exposure pulse. This was true
even for a 1-hour exposure (at 3600 ppm) as well as at the lowest concentration (225 ppm). All
concentrations of intermittent exposure also increased motor activity. A recovery period
reversed the effects on BuChE, whereas liver weight was still slightly elevated at 150 days after
cessation of exposure. Changes in liver morphology were detected following exposure to 9 ppm
for 30 days and reversed after cessation of exposure.
The effects of exposure to 200 ppm tetrachloroethylene 6 hours per day for 4 days in
male SD rats were examined on a number of endpoints (Savolainen et al., 1977a, b). Rats were
killed on the fifth day following a further 0 to 6 hours of exposure. Tetrachloroethylene levels
were highest in fat, followed by liver, cerebrum, cerebellum, lung, and blood. Tissue levels
increased in all tissues over the 6 hours of exposure. Brain RNA content decreased, and brain
nonspecific cholinesterase was increased on the fifth day, although no statistical comparisons
were performed. Locomotion in an open field was increased immediately following the end of
exposure on the fourth day, with no difference 17 hours after exposure, although no statistical
comparisons were made. Brain protein, GSH, and acid proteinase were unaffected.
A series of experiments was performed on the effects of tetrachloroethylene on brain
lipid patterns. Exposure to 320 ppm for 90 days (Kyrklund et al., 1990) or 30 days (Kyrklund et
al., 1988) in male SD rats resulted in changes in the fatty acid composition of the cerebral cortex,
which persisted after a 30-day recovery period (Kyrklund et al., 1990). Similar results were
observed in the cerebral cortex and hippocampus after exposure to 320 ppm in the Mongolian
gerbil (sex unspecified) in the presence of reduced brain weight (Kyrklund et al., 1987).
Exposure of male Mongolian gerbils to 120 ppm for 12 months also resulted in decreases in
long-chain, linolenic acid-derived fatty acids in the cerebral cortex and hippocampus (Kyrklund
et al., 1984).
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Kyrklund and Haglid (1991) exposed pregnant guinea pigs to airborne
tetrachloroethylene continuously from gestation days (GDs) 33 through 65. The exposure was
continuous at 160 ppm except for 4 days at the beginning and end of the exposure period, when
it was reduced to 80 ppm. In the control group there were three dams with litter sizes of four,
three, and two pups, and in the exposed group there were three dams with litter sizes of two
each. The pup body weights differed between litters. In the data analysis, three pups in the
control group were eliminated and the six pups in the treatment and control groups were
assumed to be independent, which is an invalid assumption. According to the authors' analysis,
the offspring had a slightly altered brain fatty acid composition, with a statistically significantly
reduced stearic acid content in the treatment group, which is consistent with the authors' earlier
findings in rats. This conclusion might have been different if the investigators had grouped
litters rather than pups as independent groups. The results suggest that tetrachloroethylene could
have reduced the litter size, but a much larger study would be necessary to establish reduced
litter size as an effect of tetrachloroethylene.
Nelson et al. (1980) of NIOSH investigated developmental neurotoxicity in SD rats by
exposing pregnant dams to tetrachloroethylene at concentrations of 100 ppm or 900 ppm during
both early pregnancy (GDs 7-13) or late pregnancy (GDs 14-20). The investigators made
morphological examinations of the fetuses and performed behavioral testing and neurochemical
analysis of the offspring. There were no alterations in any of the measured parameters in the 100
ppm groups. At 900 ppm there were no skeletal abnormalities, but the weight gain of the
offspring as compared with controls was depressed about 20% at weeks 3-5. Developmental
delay was observed in both the early and late pregnancy groups. Offspring of the early
pregnancy-exposed group performed poorly on an ascent test and on a rotorod test, whereas
those in the late pregnancy group underperformed on the ascent test only at postnatal day 14.
However, later in development (days 21 and 25), their performance was higher than that of the
controls on the rotorod test. These pups were markedly more active in the open field test at days
31 and 32.
There were no effects on running in an activity wheel on days 32 or 33 or avoidance
conditioning on day 34 and operant conditioning on days 40 to 46. Neurochemical analyses of
whole-brain (minus cerebellum) tissue in 21-day-old offspring revealed significant reductions in
acetylcholine levels at both exposure periods, whereas dopamine levels were reduced among
those exposed on GDs 7-13. Unfortunately, none of the statistics for the 100 ppm treatments
were presented. The authors observed that more behavioral changes occurred in offspring
exposed during late pregnancy than in those exposed during early pregnancy.
A multigeneration study of the effects on rats exposed to airborne concentrations of
tetrachloroethylene was performed by Tinston (1994). The investigators observed several
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developmental effects. Of interest here were the signs of CNS depression (decreased activity
and reduced response to sound) observed for the first 2 weeks in both adult generations and
when the exposure was resumed on day 6 postpartum in the F1 generation (adults and pups).
These effects disappeared about 2 hours after cessation of the daily exposure. Other overt signs
of tetrachloroethylene poisoning among the adults included irregular breathing and piloerection
at both 1000 and 300 ppm. These changes stopped concurrently with cessation of exposure or
shortly thereafter.
2.1.1. Summary of Animal Inhalation Neurotoxicity Studies
In order to compare the animal inhalation neurotoxicity studies with each other and to
discover whether there is any relationship across studies between the lowest-observed-adverse-
effect level (LOAEL) and the duration of treatment, the data were summarized (Table 2) and
then plotted as the log (duration, weeks) versus log (LOAEL) (Figure 2). The plot shows that
there is no systematic trend in the relation between the LOAEL and treatment duration. It also
shows that the LOAEL varies over a 22-fold range: from 37 ppm for 30 days for increased brain
butyrylcholinesterase in mice observed by Kjellstrand et al. (1984) to 800 ppm for 13 weeks for
alteration in the FEP in rats observed by Mattsson et al. (1998). Other observations at
comparatively low concentrations are decreased DNA in gerbils by Rosengren et al. (1986) and
Karlsson et al. (1987) at 60 ppm and increased motor activity in mice at 90 ppm observed by
Kjellstrand et al. (1985). The LOAEL for these studies as a group is therefore in the range of 37
to 90 ppm, and the effects at these levels are changes in neurotransmitter levels and increased
motor activity. Changes in fatty acid composition were observed at somewhat higher
concentrations (320 ppm).
2.2. ORAL AND INTRAPERITONEAL (i.p.) STUDIES
A study in male SD rats assessed the acute or short-term effects of tetrachloroethylene by
gavage on several screening tests (Chen et al., 2002). A single dose of 500 mg/kg to adult rats
produced changes on three different tests of pain threshold, locomotor activity, and seizure
susceptibility threshold following pentylenetetrazol infusion, whereas 50 mg/kg had statistically
significant effects on seizure threshold only. In the short-term study, young 45-50 gm rats were
dosed 5 days per week for 8 weeks with 5 or 50 mg/kg. Behavioral testing began 3 days after the
last dose. Locomotion was affected only at the high dose, whereas both doses produced effects
on the other four endpoints. The 8-week exposure resulted in retarded weight gain in both
treated groups, which was about 10% at the end of the dosing period.
The interpretation of these results is problematic. The tests are all observational in
nature, requiring scoring by the observer. It does not state in the paper that the observer(s) was
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blind to the treatment group of the animals, which is essential for such tests to be valid. In fact,
because there were differences in weight between control and treated rats, it would probably be
easy to distinguish treated from control animals simply by looking at them. Further, the paper
does not state whether all animals were tested by the same person for each task or, if not,
whether there was any indication of interobserver correlation. The potential effect of the
difference in weight between the control and the treated groups on these measures is also
unknown. Given that the differences between the control and the treated groups in response
latency to painful stimuli is tenths or one-hundredths of a second with no dose-response, these
issues are of serious concern.
Umezu et al. (1997) assessed various behavioral endpoints in 8-week-old ICR male mice
at the beginning of the experiment. Righting reflex was affected after single-dose i.p.
administration of tetrachloroethylene at 4000 but not at 2000 mg/kg or lower, and ability to
balance on a wooden rod was decreased at 2000 but not at 1000 mg/kg or lower. Response rate
on a fixed-ratio 20 (FR20) schedule—which requires 20 responses for each reinforcement—was
affected at 2000 but not at 1000 mg/kg or lower 30 minutes after administration. In a procedure
in which a thirsty mouse was shocked every 20th lick of a water spout, mice dosed with 500
mg/kg but not with higher or lower doses received an increased number of shocks. In an FR20-
FR20 punishment schedule, responding in the punishment condition was increased at 1000 but
not at 500 mg/kg or lower. A puzzling aspect of this study is the mention in the methods section
of "breeding animals," with no further explanation. If the investigators bred their own mice,
there is no indication of how pups were assigned to treatment groups.
Moser et al. (1995) examined the effects of a number of potentially neurotoxic agents,
including tetrachloroethylene, on a neurotoxicity screening battery in adult female Fischer 344
rats following either a single gavage dose (acute exposure) or repeated gavage doses over 14
days (subacute exposure). For the acute study, subjects were tested 4 and 24 hours following
exposure. After acute exposure, a lowest-observed-effect level of 150 mg/kg was identified for
increased reactivity to being handled 4 hours after dosing, with increased lacrimation, decreased
motor activity, abnormal gate, decreased response to an auditory stimulus, decreased ability to
right, and increased landing foot splay at higher doses at 4 and/or 24 hours post-dosing. A
NOEL was not identified. In the subacute study, no endpoints were significantly different from
those of controls at doses of 50-1500 mg/kg. This presumably represents behavioral adaptation
following repeated exposure to tetrachloroethylene.
Locomotor activity was monitored in MRI mice gavaged with 5 or 320 mg/kg
tetrachloroethylene for 7 days beginning at 10 days of age (Fredriksson et al., 1993). Twelve
male pups from three or four litters were assigned to each treatment group. Locomotion, rearing,
and total activity (vibration of the cage) were measured for 60 minutes at 17 and 60 days of age.
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Locomotor activity of treated mice in both dose groups was statistically significantly increased,
and rearing behavior decreased as compared with controls for all three measures at 60 days of
age but not at 17 days. However, the results of this study are uninterpretable as an effect of
tetrachloroethylene exposure for two reasons: (1) the results at 320 mg/kg were no different than
those at 5 mg/kg, indicating that something besides exposure was causing the effect, and (2)
littermates were used as independent observations in the statistical analysis. This invalid
procedure can increase the apparent a and result in erroneous statistical results. For example,
Holson and Pearce (1992) demonstrated that for body weight, using three or four littermates as
independent observations, as in the above study, results in the nominal a increasing from 0.05 to
0.23-0.38. Similar litter effects have been demonstrated for behavioral data (Buelke-Sam et al.,
1985).
Locomotor activity was assessed in 6-week-old male Wister rats following i.p. doses of
100, 500, or 1000 mg/kg tetrachloroethylene for 3 consecutive days, with activity being
monitored for at least 1 week following cessation of administration (Motohashi et al., 1993).
Animals were monitored 24 hours per day, and locomotor activity (measured as change in
electrical capacitance of a circuit beneath the floor of the cage) was analyzed by time-series
analysis and spectral analysis. All doses of tetrachloroethylene changed circadian rhythm in a
dose-dependent manner, with the increased activity at the start of the dark period delayed by
tetrachloroethylene exposure. Recovery took 3 to 5 days after cessation of exposure.
Operant performance on a fixed-ratio 40 schedule of reinforcement was assessed in adult
male SD rats gavaged with 160 or 480 mg/kg tetrachloroethylene immediately before testing
(Warren et al., 1996). The lower dose produced no effect on response rate over the 90-minute
session, whereas the higher dose produced a transient rate decrease, recovering after 20 to 40
minutes in three of six animals and inducing a complete cessation of response in two of the six
animals. Tetrachloroethylene concentrations increased rapidly after administration in blood,
brain, fat, liver, and muscle. For the duration of the 90-minute period of testing, blood
tetrachloroethylene levels were approximately linearly related to the administered dose, but brain
tetrachloroethylene levels were similar for both dose groups.
A summary of the oral neurotoxicity animal studies is presented in Table 3. For the six
oral neurotoxicity studies in rodents reviewed here, only one (Fredriksson et al., 1993) described
effects lasting more than 1 week. In that study the effect (increased motor activity) was the same
at 5 and 320 mg/kg, and the results cannot be interpreted as an effect of tetrachloroethylene
treatment, as explained above. The lowest LOAEL occurring in the four remaining studies is
100 mg/kg for delayed onset of circadian activity in rats (Motohashi et al., 1993). This LOAEL
is an i.p. dose describing transient neurological effects and is not comparable to inhalation or
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ingestion LOAELs without pharmacokinetic modeling of an appropriate dose metric. No
information is available for irreversible neurological effects via the oral route.
3. PRELIMINARY SUMMARY OF NEUROTOXIC EFFECTS FOR DISCUSSION
Taken together, the preponderance of epidemiologic evidence is supportive of an
association between subclinical neurobehavioral system effects and tetrachloroethylene
exposure. The pattern of effects on vision may be consistent with decrements in visually
mediated functions, as suggested by Echeverria et al. (1995). The test for VCS is sensitive to
neurological dysfunction associated with many diseases affecting the nervous system (NYS
DOH, 2000b). Moreover, VCS deficits as well as color discrimination deficits are commonly
present prior to detectable pathology in the retina or optic nerve head, making this one of the
earliest signs of disease (Regan, 1989). Additionally, other organic solvents, as well as alcohol,
induce effects on memory and color vision (Altmann et al., 1995; Mergler et al., 1991; Hudnell
et al., 1996a, b). The consistency of these observations suggest a common mode of action of
organic solvents to degrade pattern vision. Hence, these observations, by analogy, add support
to an inference of tetrachloroethylene-induced neurobehavioral effects.
The human studies on dry cleaning workers chronically exposed to tetrachloroethylene
indicate that tasks requiring the processing of visual information (color vision, reaction time,
coding speed, and visual memory) are particularly vulnerable to alterations from exposure to
tetrachloroethylene (Seeber et al, 1989; Ferroni et al., 1992; Cavalleri et al., 1994; Echeverria et
al., 1995; Spinatonda et al., 1997).
One study of tetrachloroethylene exposure in residences near a dry cleaning facility
(Altmann et al., 1995) and a pilot study of tetrachloroethylene exposure in residences and in a
daycare center located near a dry cleaning facility (Schreiber et al., 2002) found decrements in
several neurological parameters at lower exposures than did the studies of occupational
exposures cited above. This indicates that CNS effects can occur at a lower concentration than
inferred from the studies of dry cleaners, which have been of exposures several-fold higher than
those in these residential studies. LOAELs in the human studies of CNS effects range from 0.3
ppm to 41 ppm.
Alcohol by itself cannot explain the observed deficits in neurobehavioral functions,
because statistical analyses of the epidemiologic observations controlled for this covariate.
However, effects from the interaction between tetrachloroethylene exposure and alcohol
consumption were not well investigated in these studies. Valic et al. (1997) showed greater
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decrements in color vision among subjects with both exposures when compared with individuals
with solvent exposure only or with neither exposure.
There are no human studies investigating drinking water or other oral exposures to
tetrachloroethylene and neurotoxic effects.
The research in animal models (rodents) on the effects of tetrachloroethylene on
functional endpoints consists almost exclusively of screening studies (functional observation
battery, motor activity) or effects on sensory system function, as assessed by evoked potentials.
Effects on motor activity and motor function have been observed with some consistency
following either adult or developmental exposure. Changes in VEPs were also reported
following acute but not subchronic exposure. In addition, changes in brain DNA or protein
levels and lipid composition were altered following inhalation exposure, with changes observed
in the cerebellum, hippocampus, and frontal cortex. Although tests of cognitive function have
apparently not been performed in rodents, the neurochemistry changes observed in the
hippocampus and frontal cortex are consistent with observed effects on cognition and memory in
humans. Therefore, effects observed in humans and in rodent models exhibit a reasonable
degree of congruence.
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Table 1. Summary of neuropsychological effects of tetrachloroethylene in humans
o
u>
00
Neurological
test
Study, number of subjects, exposure level
Cavalleri
et al.
(1994)
Echeverria
et al. (1995)a
Ferroni et
al. (1992)
Seeber et al.
(1989)
Spinatonda
et al. (1997)
Altmann et
al. (1995)
Schreiber et al. (2002)
Lauwerys
et al.
(1983)
Nakatsuka
et al. (1992)
Residents
Day care
70
65
90
185
74
37
34
18
59
184
7 pmm
11 ppm
23 ppm
41 ppm
15 ppm
12 ppm
53 ppm
8 ppm
0.7 ppm
0.4 ppm
0.1 ppm
21 ppm
15 ppm
Contrast
sensitivity
(spatial
vision)
+
+
Color
confusion
index
(Yellow-blue)
+/-b
trend +, not
statistically
significant
C
Fine
motor
function
-
-
-
Simple
RT
(attention,
motor)
+
+
Continuous
performance
(vigilance)
+
+
Visuo spatial
function
+, +, +
pattern
recognition,
reproduction,
memory
+
digit
reproduction
+
Benton
-------
Table 1. Summary of neuropsychological effects of tetrachloroethylene in humans (continued)
Neurological
test
Study, number of subjects, exposure level
Cavalleri
et al.
(1994)
Echeverria
et al. (1995)a
I c mi n i et
al. (1992)
Seeber,
(1989)
Spinatonda
et al. (1997)
Altmann et
al. (1995)
Schreiber et al. (2002)
Lauwerys
et al.
(1983)
Nakatsuka
et al.
(1992)"
Residents
Day care
70
65
90
185
74
37
34
18
59
184
7 pmm
11 ppm
23 ppm
41 ppm
15 ppm
12 ppm
53 ppm
8 ppm
0.7 ppm
0.4 ppm
0.1 ppm
21 ppm
15 ppm
Information
processing
speed
+ perceptual
threshold
+ "delayed
reaction" on
choice
reaction time
+
vocal
reproduction
Digit span,
digit symbol
+ dry
cleaners4,
- ironersd
(both)
+/-, +
Cancellation
(visual
scanning)
+
Stress
reaction
time
¦
Trailmaking
(executive
function)
H
ffl
O
V
o
c
o
H
W
a Field study, no unexposed controls.
b Positive in dry cleaners, negative in ironing workers with lower exposure.
c Using less sensitive test instrument and data analysis procedure than the other studies.
d Cavalleri et al. (1994) showed an effect in dry cleaners but not ironers with lower exposure.
+ = positive effect, impaired performance in exposed group
- = no effect of tetrachloroethylene
-------
Table 2. Summary of animal inhalation neurotoxicology studies
o
oo
o
Subjects
Effect
LOAEL (ppm)
Reference
Fischer 344 rats
Changes in FEP, SEP, EEG
Increase in late component of FEP
800, 4 days
800, 13 weeks
Mattsson et al.
(1998)
MRI mice, males
Increase in motor activity
90, 1 hour
Kj ell strand et al.
(1985)
Swiss 0F1 mice,
males
Decrease in duration of immobility
649, 4 hours
De Ceaurriz et al.
(1983)
SD rats
Decreased weight gain
Behavioral changes, more extensive for late pregnancy
exposure
Decreased brain acetylcholine
0, 100, 900 on days
7-13 or on days 14-20
NOAEL = 100
LOAEL = 900
Nelson et al. (1980)
SD rats, males
Reduced brain weight, DNA, protein
600, 12 weeks
Wang et al. (1993)
Decrease in brain DNA, increase in brain cholinesterase
200
Savolainen et al.
(1977a, b)
Change in fatty acid composition of cerebral cortex
320, 12 weeks
320, 4 weeks
Kyrklund et al.
(1990, 1988)
Neurotransmitter changes, brain regions
800, 4 weeks
Honma et al.
(1980a, b)
Mongolian gerbils
Decrease in DNA, frontal cortex
Decrease in brain weight
60, 12 weeks
300, 12 weeks
Rosengren et al.
(1986)
Same as above
60, 12 weeks
Karlsson et al. (1987)
Taurine, glutamine changes in brain regions
120, 12 months
Briving et al. (1986)
Decrease in brain weight, change in fatty acids
320, 12 weeks
Kyrklund et al.
(1987)
-------
Table 2. Summary of animal inhalation neurotoxicology studies (continued)
Subjects
Effect
LOAEL (ppm)
Reference
Mongolian gerbils
(con't)
Decreased brain long-chain fatty acids
120, 52 weeks
Kyrklund et al.
(1984)
Decrease in brain stearic acid after in utero exposure
(questionable findings)
160, gestation days 33 to
65
Kyrklund and Hagid
(1991)
NMRI mice, males
and females
Increase in butyrylcholinesterase
37, 4 weeks
Kj ell strand et al.
(1984)
Motor activity changes
150, 4 weeks
Kj ell strand et al.
(1984)
Rats, multigeneration
study
CNS depression in first 2 weeks of F1 and F2
generations, which ceased 2 hours after daily
exposures
0, 100, 300, 1000
Tinston (1994)
LOAEL = Lowest-observed-adverse-effect level
FEP = Flash-evoked potential
SEP = Somatosensory-evoked potential
EEG = Electroencephalogram
NOAEL = No-observed-adverse-effect level
-------
Table 3. Summary of oral neurotoxicity animal studies
Subjects
Effect
Dose
Reference
SD rats, male
Pain threshold, pain susceptibility, weight gain
decrement
Interpretation is unclear
5, 50 mg/kg daily for 8 weeks
Chen et al. (2002)
Operant responses stopped immediately after 480
mg/kg dose, then 2/3 of animals recovered by 40
minutes
No effect at 160 mg/kg
Brain tetrachloroethylene concentrations were the
same at both doses
Gavage single dose at 0, 160, 480
mg/kg
Warren et al.
(1996)
ICR mice,
male
NOAEL/LOAEL:
Righting reflex: 2000/4000 ppm
Balance: 1000/2000 ppm
Reinforcement: 1000/2000 ppm
Punishment: 500/1000 ppm
Single intraperitoneal doses at 0,
500, 1000, 2000, 4000 mg/kg
Umezu et al.
(1997)
F344 rats,
female
Increased reactivity, decreased motor activity,
decreased righting ability, increased landing foot
splay, abnormal gait after one dose
No effect after repeated doses
Single doses: 150 mg/kg is LOEL
Repeated dosing for 14 days: 1500
mg/kg is NOEL
Moser et al. (1995)
NMRI mice,
postnatal
exposure
Increased locomotion and decreased rearing at day
60 in both dose groups (invalid analysis of data)
No effect immediately after treatment
Gavage treatment 5, 320 mg/kg daily
for postnatal days 10-16
Fredriksson et al.
(1993)
Wistar rats,
male
Transient delay in circadian activity, dose-related
Intraperitoneal doses 0, 100, 500,
1000 mg/kg-day for 3 days
LOAEL =100 mg/kg-day
Motohashi et al.
(1993)
NOAEL = No-observed-adverse-effect level
LOAEL = Lowest-observed-adverse-effect level
LOEL = Lowest-observed-effect level
NOEL = No-observed-effect level
-------
Control, <18 years old
Exposed, <18 years old
Spatial Frequency (Cycles/Degree)
>
>
'<75
£
0)
w
£
o
o
TO
3
(/)
>
160 -
140 -
120 -
100 -
' Exposed, 18-60
Control, 18-60
Spatial Frequency (Cycles / Degree)
160 -
140 -
120 -
(J)
£
0)
w
£
o
o
TO
3
Control, >60 years old
Exposed, >60 years old
Spatial Frequency (Cycles/Degree)
Figure 1. Visual contrast sensitivity functions for control and exposed children (top), adults that
were identified as having impaired function (i.e., 5 of the total 11) and their matched controls
(middle), and the control and exposed individuals over 60 years of age. The X axis represents the
frequency of the stimulus bars, with finer bars toward the right. The Y axis represents the inverse of the
contrast at which the subject could no longer distinguish the orientation of the bars (threshold). For any
frequency, a higher contrast sensitivity threshold represents better visual function. It is apparent that the
group of children is relatively more impaired than the impaired group adults.
Source: Schreiber et al., 2002
10/14/03
43
DRAFT—DO NOT CITE OR QUOTE
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Animal Neurotoxicity Inhalation Studies
Duration vs. LOAEL
100
J2
(D
0)
J 1
0
1 o>
Q
O.Of
_l
0.001
10 100 1000
Log (LOAEL, ppm)
Figure 2. Summary of the relationship between dose levels and treatment duration.
10/14/03
44
DRAFT—DO NOT CITE OR QUOTE
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DRAFT—DO NOT CITE OR QUOTE
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