Perchloroethylene exposure can induce colour vision loss

Reanalysis of Trichloroethylene and Tetrachloroethylene Metabolism to Glutathione Conjugates Using Human, Rat, and Mouse Liver in Vitro Models to Improve Precision in Risk Characterization

BACKGROUND

Both trichloroethylene (TCE) and tetrachloroethylene (PCE) are high-priority chemicals subject to numerous human health risk evaluations by a range of agencies. Metabolism of TCE and PCE determines their ultimate toxicity; important uncertainties exist in quantitative characterization of metabolism to genotoxic moieties through glutathione (GSH) conjugation and species differences therein.

OBJECTIVES

This study aimed to address these uncertainties using novel in vitro liver models, interspecies comparison, and a sensitive assay for quantification of GSH conjugates of TCE and PCE, S-(1,2-dichlorovinyl)glutathione (DCVG) and S-(1,2,2-trichlorovinyl) glutathione (TCVG), respectively.

METHODS

Liver in vitro models used herein were suspension, 2-D culture, and micropatterned coculture (MPCC) with primary human, rat, and mouse hepatocytes, as well as human induced pluripotent stem cell (iPSC)-derived hepatocytes (iHep).

RESULTS

We found that, although efficiency of metabolism varied among models, consistent with known differences in their metabolic capacity, formation rates of DCVG and TCVG generally followed the patterns human ≥ rat ≥ mouse , and primary hepatocytes > iHep . Data derived from MPCC were most consistent with estimates from physiologically based pharmacokinetic models calibrated to in vivo data.

DISCUSSION

For TCE, the new data provided additional empirical support for inclusion of GSH conjugation-mediated kidney effects as critical for the derivation of noncancer toxicity values. For PCE, the data reduced previous uncertainties regarding the extent of TCVG formation in humans; this information was used to update several candidate kidney-specific noncancer toxicity values. Overall, MPCC-derived data provided physiologically relevant estimates of GSH-mediated metabolism of TCE and PCE to reduce uncertainties in interspecies extrapolation that constrained previous risk evaluations, thereby increasing the precision of risk characterizations of these high-priority toxicants. https://doi.org/10.1289/EHP12006.

A pilot study characterizing tetrachloroethylene exposure with exhaled breath in an impacted community

Martinsville, Indiana overlays four groundwater contamination plumes, including a U.S. Environmental Protection Agency (EPA)-designated Superfund site. The primary contaminants are tetrachloroethylene (PCE), trichloroethylene (TCE), and other volatile organic compounds (VOCs). Martinsville represents many similar communities facing the challenge of groundwater and soil contamination and vapor intrusion, where residents are often frustrated by the lack of help in understanding and addressing the problem. The objective of this study was to evaluate PCE in exhaled breath to identify and quantify exposure to PCE and to explore the extent and level of PCE exposure among community residents. We measured chlorinated VOCs in exhaled breath samples from 38 healthy individuals who lived either in a contamination area or outside any plume area. We also measured VOCs in indoor air and tap water samples collected from 10 homes. PCE was detected in all exhaled breath samples (mean: 6.6 μg/m³; range: 1.9-44 μg/m³) and tap water samples (mean: 0.74 μg/L; range: 0.39-0.92 μg/L). PCE was detected in six of nine (66%) homes with air concentrations ranging from 1.6 to 70 μg/m³, exceeding the EPA action level of 42 μg/m³. We did not detect TCE or any other chlorinated VOCs in these samples. PCE exposure occurred among individuals living on the EPA Superfund site, as well as among those living on other plume sites and those living outside any known plumes. Preventive measures should focus on identifying highly exposed groups and reducing their exposures, followed by addressing moderately elevated exposures in the community. Our results demonstrated that PCE in exhaled breath can be used as an effective tool in community engaged environmental health research to evaluate the extent and level of community exposure, increase awareness, and promote residents' participation in research and site cleanup decision-making.

Evaluation of Occupational Exposure to Perchlorethylene in a Group of Italian Dry Cleaners Using Noninvasive Exposure Indices

Recent data suggest a general trend in decreased occupational exposure to perchlorethylene (PCE) in the dry-cleaning sector. The aims of this study were to confirm this trend to lower exposure levels in a group of Italian dry cleaners and to evaluate the current occupational PCE exposure in these works using noninvasive biological indices. Environmental exposure was assessed by personal sampling in 60 operators working in 21 dry cleaning shops in North Italy. PCE in the exhaled alveolar air (PCEalv), urinary concentration of PCE and of trichloroacetic acid (TCA) (PCEu and TCAu respectively), were measured as biological exposure indices. Median PCE environmental concentration in the whole sample was 10.6 mg/m3 (i.e., less than the 25% of the levels measured in the same area in a previous study). All values were less than 10% of the occupational limits. PCEu measured in samples collected at the end of the work shift resulted the biological markers having the strongest correlation with environmental PCE (r = 0.81). PCEalv also resulted in a high correlation (r = 0.66), while a lower correlation was found for TCAu measured at the end shift (r = 0.32). According to our results, PCEu can be proposed as a valid, noninvasive, and easily reliable exposure index to evaluate PCE exposure at the low levels currently observed in dry cleaners, therefore representing a promising alternative to invasive blood sample collections needed to determine PCE blood concentration.

Towards sustainable and safe apparel cleaning methods: A review

Perchloroethylene (PERC) is a compound commonly used as a solvent in dry cleaning, despite its severe health and environmental impacts. In recent times chemicals such as hydrocarbons, GreenEarth(®), acetal and liquid carbon dioxide have emerged as less damaging substitutes for PERC, and an even more sustainable water-based wet cleaning process has been developed. We employed a systematic review approach to provide a comprehensive overview of the existing research evidence in the area of sustainable and safe apparel cleaning methods and care. Our review describes traditional professional dry cleaning methods, as well as those that utilise solvents other than PERC, and their ecological attributes. In addition, the new professional wet cleaning process is discussed. Finally, we address the health hazards of the various solvents used in dry cleaning and state-of-the-art solvent residue trace analysis techniques.

Toluene inhalation exposure for 13 weeks causes persistent changes in electroretinograms of Long-Evans rats

Studies of humans chronically exposed to volatile organic solvents have reported impaired visual functions, including low contrast sensitivity and reduced color discrimination. These reports, however, lacked confirmation from controlled laboratory experiments. To address this question experimentally, we examined visual function by recording visual evoked potentials (VEP) and/or electroretinograms (ERG) from four sets of rats exposed repeatedly to toluene. In addition, eyes of the rats were examined with an ophthalmoscope and some of the retinal tissues were evaluated for rod and M-cone photoreceptor immunohistochemistry. The first study examined rats following exposure to 0, 10, 100 or 1000ppm toluene by inhalation (6hr/d, 5d/wk) for 13 weeks. One week after the termination of exposure, the rats were implanted with chronically indwelling electrodes and the following week pattern-elicited VEPs were recorded. VEP amplitudes were not significantly changed by toluene exposure. Four to five weeks after completion of exposure, rats were dark-adapted overnight, anesthetized, and several sets of electroretinograms (ERG) were recorded. In dark-adapted ERGs recorded over a 5-log (cd-s/m(2)) range of flash luminance, b-wave amplitudes were significantly reduced at high stimulus luminance values in rats previously exposed to 1000ppm toluene. A second set of rats, exposed concurrently with the first set, was tested approximately one year after the termination of 13 weeks of exposure to toluene. Again, dark-adapted ERG b-wave amplitudes were reduced at high stimulus luminance values in rats previously exposed to 1000ppm toluene. A third set of rats was exposed to the same concentrations of toluene for only 4 weeks, and a fourth set of rats exposed to 0 or 1000ppm toluene for 4 weeks were tested approximately 1year after the completion of exposure. No statistically significant reductions of ERG b-wave amplitude were observed in either set of rats exposed for 4 weeks. No significant changes were observed in ERG a-wave amplitude or latency, b-wave latency, UV- or green-flicker ERGs, or in photopic flash ERGs. There were no changes in the density of rod or M-cone photoreceptors. The ERG b-wave reflects the firing patterns of on-bipolar cells. The reductions of b-wave amplitude after 13 weeks of exposure and persisting for 1year suggest that alterations may have occurred in the inner nuclear layer of the retina, where the bipolar cells reside, or the outer or inner plexiform layers where the bipolar cells make synaptic connections. These data provide experimental evidence that repeated exposure to toluene may lead to subtle persistent changes in visual function. The fact that toluene affected ERGs, but not VEPs, suggests that elements in the rat retina may be more sensitive to organic solvent exposure than the rat visual cortex.

Exposure to organic solvents used in dry cleaning reduces low and high level visual function

PURPOSE

To investigate whether exposure to occupational levels of organic solvents in the dry cleaning industry is associated with neurotoxic symptoms and visual deficits in the perception of basic visual features such as luminance contrast and colour, higher level processing of global motion and form (Experiment 1), and cognitive function as measured in a visual search task (Experiment 2).

METHODS

The Q16 neurotoxic questionnaire, a commonly used measure of neurotoxicity (by the World Health Organization), was administered to assess the neurotoxic status of a group of 33 dry cleaners exposed to occupational levels of organic solvents (OS) and 35 age-matched non dry-cleaners who had never worked in the dry cleaning industry. In Experiment 1, to assess visual function, contrast sensitivity, colour/hue discrimination (Munsell Hue 100 test), global motion and form thresholds were assessed using computerised psychophysical tests. Sensitivity to global motion or form structure was quantified by varying the pattern coherence of global dot motion (GDM) and Glass pattern (oriented dot pairs) respectively (i.e., the percentage of dots/dot pairs that contribute to the perception of global structure). In Experiment 2, a letter visual-search task was used to measure reaction times (as a function of the number of elements: 4, 8, 16, 32, 64 and 100) in both parallel and serial search conditions.

RESULTS

Dry cleaners exposed to organic solvents had significantly higher scores on the Q16 compared to non dry-cleaners indicating that dry cleaners experienced more neurotoxic symptoms on average. The contrast sensitivity function for dry cleaners was significantly lower at all spatial frequencies relative to non dry-cleaners, which is consistent with previous studies. Poorer colour discrimination performance was also noted in dry cleaners than non dry-cleaners, particularly along the blue/yellow axis. In a new finding, we report that global form and motion thresholds for dry cleaners were also significantly higher and almost double than that obtained from non dry-cleaners. However, reaction time performance on both parallel and serial visual search was not different between dry cleaners and non dry-cleaners.

CONCLUSIONS

Exposure to occupational levels of organic solvents is associated with neurotoxicity which is in turn associated with both low level deficits (such as the perception of contrast and discrimination of colour) and high level visual deficits such as the perception of global form and motion, but not visual search performance. The latter finding indicates that the deficits in visual function are unlikely to be due to changes in general cognitive performance.

Retinal and visual system: occupational and environmental toxicology

Occupational chemical exposure often results in sensory systems alterations that occur without other clinical signs or symptoms. Approximately 3000 chemicals are toxic to the retina and central visual system. Their dysfunction can have immediate, long-term, and delayed effects on mental health, physical health, and performance and lead to increased occupational injuries. The aims of this chapter are fourfold. First, provide references on retinal/visual system structure, function, and assessment techniques. Second, discuss the retinal features that make it especially vulnerable to toxic chemicals. Third, review the clinical and corresponding experimental data regarding retinal/visual system deficits produced by occupational toxicants: organic solvents (carbon disulfide, trichloroethylene, tetrachloroethylene, styrene, toluene, and mixtures) and metals (inorganic lead, methyl mercury, and mercury vapor). Fourth, discuss occupational and environmental toxicants as risk factors for late-onset retinal diseases and degeneration. Overall, the toxicants altered color vision, rod- and/or cone-mediated electroretinograms, visual fields, spatial contrast sensitivity, and/or retinal thickness. The findings elucidate the importance of conducting multimodal noninvasive clinical, electrophysiologic, imaging and vision testing to monitor toxicant-exposed workers for possible retinal/visual system alterations. Finally, since the retina is a window into the brain, an increased awareness and understanding of retinal/visual system dysfunction should provide additional insight into acquired neurodegenerative disorders.

Human health effects of tetrachloroethylene: key findings and scientific issues

BACKGROUND

The U.S. Environmental Protection Agency (EPA) completed a toxicological review of tetrachloroethylene (perchloroethylene, PCE) in February 2012 in support of the Integrated Risk Information System (IRIS).

OBJECTIVES

We reviewed key findings and scientific issues regarding the human health effects of PCE described in the U.S. EPA's Toxicological Review of Tetrachloroethylene (Perchloroethylene).

METHODS

The updated assessment of PCE synthesized and characterized a substantial database of epidemiological, experimental animal, and mechanistic studies. Key scientific issues were addressed through modeling of PCE toxicokinetics, synthesis of evidence from neurological studies, and analyses of toxicokinetic, mechanistic, and other factors (tumor latency, severity, and background rate) in interpreting experimental animal cancer findings. Considerations in evaluating epidemiological studies included the quality (e.g., specificity) of the exposure assessment methods and other essential design features, and the potential for alternative explanations for observed associations (e.g., bias or confounding).

DISCUSSION

Toxicokinetic modeling aided in characterizing the complex metabolism and multiple metabolites that contribute to PCE toxicity. The exposure assessment approach-a key evaluation factor for epidemiological studies of bladder cancer, non-Hodgkin lymphoma, and multiple myeloma-provided suggestive evidence of carcinogenicity. Bioassay data provided conclusive evidence of carcinogenicity in experimental animals. Neurotoxicity was identified as a sensitive noncancer health effect, occurring at low exposures: a conclusion supported by multiple studies. Evidence was integrated from human, experimental animal, and mechanistic data sets in assessing adverse health effects of PCE.

CONCLUSIONS

PCE is likely to be carcinogenic to humans. Neurotoxicity is a sensitive adverse health effect of PCE.

Review of the epidemiologic literature on residential exposure to perchloroethylene

Perchloroethylene is a solvent that is widely used for dry cleaning. There has been considerable interest in the toxicity of this chemical because of the potential for low-level exposure among a large portion of the US population. Although substantial epidemiologic literature exists on high-level occupational exposure to perchloroethylene, there are relatively few studies dealing with lower-level residential exposure. In the current paper, the author reviews this limited residential literature, with special emphasis on strengths, limitations, and consistency. Reviewed studies primarily address neurobehavioral, cancer, and reproductive endpoints. Most studies used an ecological or cross-sectional design, with exposure defined by either drinking-water contamination or proximity to dry cleaning. In general, reviewed studies were highly exploratory, with inconsistencies and potential for bias that detract from interpretation of study findings. The magnitudes of reported effects are frequently incompatible with the effects reported from much higher occupational and human-chamber exposures. Overall, few reliable conclusions can be drawn from this sparse and highly limited body of literature.

Long-term perchloroethylene exposure: a meta-analysis of neurobehavioral deficits in occupationally and residentially exposed groups

The literature concerning the neurobehavioral and neurophysiological effects of long-term exposure to perchloroethylene (PERC) in humans was meta-analyzed to provide a quantitative review and synthesis in the form of dose-effect curves. The useable database from this literature comprised studies reporting effects of long-term exposure to PERC, effects that included slowed reaction times, cognitive deficits, impaired color vision, and reduced visual contrast sensitivity. For the meta-analyses, dose was defined as the product of the concentration inhaled PERC and the duration of exposure, expressed in unites of ppm-h/1000 (for numerical convenience). Dose-related results were highly variable across studies. Reports involving low exposure concentrations characteristic of nonoccupational exposures consistently produced effects of a magnitude that were comparable to those reported for higher concentration occupational studies. If this finding is reliable and general, studies of occupationally exposed persons may underestimate the magnitude of effects of PERC and other chemicals in the total population. Given the limited scope of the available data for PERC and its methodological and reporting problems (small sample sizes, testers were not blind to the subjects' exposure conditions, and the timing and location of testing were insufficiently documented), it seems important to test this conclusion with a well-documented study of two groups (occupational and nonoccupational exposure) in which subjects are evaluated in randomized order, using the same procedures and with the testers kept blind to the status of the subjects.

[Usefulness of color vision test for early detection of neurological damages by neurotoxic substances]

This paper reviews the published literature that is concerned with color vision impairment from industrial and environmental exposure to neurotoxic substances, and we evaluated whether testing for color vision impairment could be an affordable procedure for assessing these neurotoxic effects. In general, most cases of congenital color vision impairment are red-green, and blue-yellow impairment is extremely rare. However, most of the acquired color vision impairment that is related to age, alcohol or environmental factors is blue-yellow impairment. Therefore, many studies have been performed to identify this relationship between exposure to neurotoxic substances, such as organic solvents and heavy metals, and the prevalence of blue-yellow color vision impairment. The test for color vision impairment is known to be very sensitive to the early signs of nervous system dysfunction and this can be useful for making the early diagnosis of neurotoxic effects from exposure to very low concentrations of toxic substances.

Characterization of the effects of inhaled perchloroethylene on sustained attention in rats performing a visual signal detection task

The aliphatic hydrocarbon perchloroethylene (PCE) has been associated with neurobehavioral dysfunction including reduced attention in humans. The current study sought to assess the effects of inhaled PCE on sustained attention in rats performing a visual signal detection task (SDT). Due to its similarities in physiological effect to toluene and trichloroethylene (TCE), two other commonly used volatile organic compounds (VOCs) known to reduce attention in rats, we hypothesized (1) that acute inhalation of PCE (0, 500, 1000, 1500 ppm) would disrupt performance of the SDT in rats; (2) that impaired accuracy would result from changes in attention to the visual signal; and (3) that these acute effects would diminish upon repetition of exposure. PCE impaired performance of the sustained attention task as evidenced by reduced accuracy [P(correct): 500 to 1500 ppm], elevated response time [RT: 1000 and 1500 ppm] and reduced number of trials completed [1500 ppm]. These effects were concentration-related and either increased (RT and trial completions) or remained constant [P(correct)] across the 60-min test session. The PCE-induced reduction in accuracy was primarily due to an increase in false alarms, a pattern consistent with reduced attention to the signal. A repeat of the exposures resulted in smaller effects on these performance measures. Thus, like toluene and TCE, inhaled PCE acutely impaired sustained attention in rats, and its potency weakened upon repetition of the exposure.

Potential health effects of occupational chlorinated solvent exposure

Based on toxicology, metabolism, animal studies, and human studies, occupational exposure to chlorinated aliphatic solvents (methanes, ethanes, and ethenes) has been associated with numerous adverse health effects, including central nervous system, reproductive, liver, and kidney toxicity, and carcinogenicity. However, many of these solvents remain in active, large-volume use. This article reviews the recent occupational epidemiology literature on the most widely used solvents, methylene chloride, chloroform, trichloroethylene, and tetrachloroethylene, and discusses other chlorinated aliphatics. The impact of studies to date has been lessened because of small study size, inability to control for confounding factors, particularly smoking and mixed occupational exposures, and the lack of evidence for a solid pathway from occupational exposure to biological evidence of exposure, to precursors of health effects, and to health effects. International differences in exposure limits may provide a "natural experiment" in the coming years if countries that have lowered exposure limits subsequently experience decreased adverse health effects among exposed workers. Such decreases could provide some evidence that higher levels of adverse health effects were associated with higher levels of solvent exposure. The definitive studies, which should be prospective biomarker studies incorporating body burden of solvents as well as markers of effect, remain to be done.

Effect of petroleum derivatives and solvents on colour perception

BACKGROUND

Occupational exposure to various neurotoxic chemicals has been shown to be associated with colour vision impairment. It seems that this can occur at low exposure levels, sometimes well below the recommended occupational threshold limits. This study was undertaken to determine the effect of exposure to petroleum derivatives (polyethylene, polystyrene) and solvents (perchloroethylene) on colour perception.

METHODS

Colour vision was assessed using the Ishihara plates, the D-15 test and the Farnsworth Munsell 100 Hue test. Two factories using petroleum derivatives and three dry cleaning premises were chosen at random. A total of 93 apparently healthy employees were recruited from the five workplaces. Two age-matched control groups comprising 56 people, who were support staff of the university with no exposure to petroleum, solvents or their derivatives, were also recruited.

RESULTS

All subjects passed the Ishihara test, showing that none had a congenital red-green defect. Some of the exposed employees failed the D-15 and had abnormally high FM100 Hue scores. All control subjects passed all the colour vision tests. The D-15 test showed that 28 per cent (26 of 93) of exposed employees had a colour vision defect whereas the FM 100 Hue test found that 63 per cent (59 of 93) had a colour vision defect. Most defects were of the blue-yellow type (22.6 per cent) when using the D-15 test. However, with the FM 100 Hue test, most defects were of the non-polar type with no specific axis (50.5 per cent). Mean total error scores calculated from the FM100 Hue test for exposed employees were statistically significantly higher than those of the control subjects.

CONCLUSION

Employees directly exposed to petroleum derivatives and solvents have a higher risk of acquiring colour vision defects compared to subjects who are not.

Colour vision and occupational toluene exposure: results of repeated examinations

Potential effects of human occupational exposures to toluene on colour vision were investigated in a follow-up study over 4 years with three repeated examinations. Colour vision was measured with the Lanthony desaturated colour vision test D-15d, and the colour confusion index (CCI) was calculated. The mean current exposures were 26+/-21 ppm for printers (high toluene level) and 3+/-4 ppm for end-processors (low toluene level). The mean exposure durations were 23+/-6 years for "long-time exposed" and 7+/-2 years for "short-time exposed" subjects. Repeated analyses (n=162) and multiple regressions (maximum available n=267) did not reveal significant effects of toluene with respect to intensity or duration of current or long-term exposure. Age and occupational qualification were significantly associated with CCI in both kinds of analysis, whereas alcohol consumption (carbohydrate-deficient transferrin, CDT) and smoking habits (cigarettes per day) were not. It is concluded that current industrial exposure limits of toluene provide sufficient protection against possible disturbance of colour vision.

Does Occupational Exposure to Organic Solvents Affect Colour Discrimination?

This review assesses the evidence regarding the effects of occupational exposure to organic solvents on colour discrimination and investigates exposure-response relationships and reversibility. This review also considers the current state of knowledge of the possible mechanisms underlying changes in colour vision, and the human health significance of any reported changes. Among the commonly used organic solvents, styrene has been investigated the most thoroughly. Studies of styrene-exposed workers in Germany, Italy and Japan provide a sufficiently consistent body of evidence to support a robust conclusion that styrene does cause an impairment of colour discrimination relative to age-matched controls. Generally, the impairment of colour discrimination observed in styrene-exposed workers tends to be of the tritan (blue-yellow) type, although some cases of red-green impairment have also been found. The limited information available on exposure-response relationships indicates that the effects on colour discrimination would not be expected at 8-hour time weighted average (8 h TWA) exposures <20 ppm, although a precise threshold cannot be determined. The data on reversibility are limited and inconclusive. The results from the most rigorous study in which this aspect was investigated point to a reversibility of effects after a 4-week exposure-free period, whereas results from a study with limitations suggest a persistence of effect. The effects of toluene, tetrachloroethylene or mixed solvent exposure have also been investigated, although the information available is generally less reliable than for styrene. For toluene, it can be confidently concluded that this solvent does not have an acute effect on colour discrimination, even when exposures are relatively high (50-150 ppm 8 h TWA, and 290-360 ppm 30 minutes TWA). However, studies are inconclusive on whether long-term or repeated exposure to toluene can cause a persistent impairment of colour discrimination. There are few studies that have specifically investigated the effects of tetrachloroethylene on colour discrimination. Among these studies, none has examined the potential for any acute effects of this solvent vapour. A large-scale study in Japanese workers showed no effects of long-term exposure to tetrachloroethylene concentrations in the region of 12-13 ppm. However, the test methodology used was relatively insensitive to changes in colour discrimination, hence the results do not provide reassurance for an absence of subtle effects. A study in Italian dry-cleaners suggested a slight impairment of colour discrimination relative to controls, associated with relatively low exposures to tetrachloroethylene (mean 8 h TWA exposure approximately 6 ppm). The studies concerning the effects of mixed solvent exposure on colour discrimination are based on workers exposed to solvents in paints and lacquers, workers from the printing and petrochemical industries, people working in or living near to microelectronics factories and children exposed to solvents prenatally. However, these studies are subject to design limitations or methodological irregularities, such that no conclusions regarding the effects of mixed solvent exposure on colour discrimination can be drawn. Overall, the only credible evidence for an effect of solvents on colour discrimination derives from the studies on styrene. Because of limitations in the data for other solvents it is not possible to determine whether the evidence for styrene reflects a generic property of solvents. The mechanisms of styrene-induced effects on colour discrimination have not been properly investigated and can only be the subject of speculation. One conclusion that can be drawn is that pathological changes to the ocular system, such as changes to the lens, are unlikely to be involved. This is because there is an absence of convincing evidence for such changes from medical examinations conducted in epidemiological studies of solvent-exposed workers. Also, it seems unlikely that effects on colour discrimination are a nonspecific consequence of more generalised CNS depression, given that styrene-induced effects on colour discrimination appear to occur below the threshold for narcotic effects. The effects of styrene on colour discrimination are subtle and involve an impairment of the ability to discriminate accurately between closely related shades of the same colour rather than 'colour blindness'. There is no valid basis for using colour discrimination as a marker for other forms of solvent-induced neurotoxicity.

Perchloroethylene in Alveolar Air, Blood, and Urine as Biologic Indices of Low-Level Exposure

We studied the reliability of biologic indices for monitoring perchlorethylene (PCE) exposure at low environmental solvent concentrations. Environmental monitoring was performed by personal sampling, biologic monitoring by measuring PCE in alveolar air (PCE-Alv), blood (PCE-B), and urine (PCE-U) in 26 low-exposed dry-cleaners. Correlation coefficients (r) between environmental PCE and PCE-B, PCE-Alv, and PCE-U were 0.94, 0.81, and 0.67 respectively. A high correlation was also found among biologic indices: r value was 0.96 between PCE-B and PCE-Alv, 0.95 between PCE-B and PCE-U, and 0.87 between alveolar PCE-Alv and PCE-U. The examined biologic indices proved sensitive enough for biologic monitoring of low exposure to PCE and can give substantially similar information in terms of exposure evaluation. PCE-Alv offers some advantages because it correlated better with exposure and is analytically simpler.

Color vision impairment in workers exposed to neurotoxic chemicals

Recent research shows that occupational exposure to several solvents, metals and other industrial chemicals can impair color vision in exposed workers. Occupation-related color vision impairment usually results in blue-yellow color discrimination loss or, less frequently, a combination of blue-yellow and red-green loss. The eyes may be unequally involved, and the course is variable depending on exposure and other factors. The pathogenesis of occupational color vision loss has not been elucidated; it may be due to, e.g. a direct action of neurotoxins on receptors, possibly on the cone's membrane metabolism, and/or to an interference with neurotransmitters within the retina. Other possible pathogenetic mechanisms, such as a direct effect to the optic nerve, have also been suggested. Occupational color vision loss is usually sub-clinical, and workers are unaware of any deficit. It can be assessed using sensitive tests, such as the Farnsworth-Munsell 100 Hue (FM-100) or the Lanthony D-15 desaturated panel (D-15 d). The latter is the most widely used for studies in groups of exposed workers, and offers the possibility of a quantitative evaluation of the results by calculation of the Bowman's Color Confusion Index (CCI), or of the Vingrys' and King Smith's Confusion Index (CI). Other advantages of D-15 d are the possibility to perform the test directly at the workplace, and the reproducibility when performed in standardized conditions. In most cases, occupation-related color vision impairment is correlated to exposure levels, and has often been observed in workers exposed to environmental concentrations below the current occupational limit proposed by the ACGIH. Progression with increasing cumulative exposure has been reported, while reversibility is still discussed. Acquired color vision impairment related to occupational exposure to styrene, perchloroethylene (PCE), toluene, carbon disulfide, n-hexane, solvent mixtures, mercury and some other chemicals are discussed. Results show that color vision testing should be included in the evaluation of early neurotoxicity of chemicals in exposed workers. The D-15 d would be useful in the surveillance of workers exposed to solvents and other chemicals toxic to the visual system.

Occupational exposure to chemicals and sensory organs: a neglected research field

The effect of industrial chemicals on the sensory perception of exposed workers has received scant attention from the medical community to date, and the scientific literature is mainly limited to some case-reports or isolated studies. Possible explanations for this include the complexity of sensory perception, and the lack of agreement among researchers on methods for testing large groups of subjects. Nevertheless, some published studies showed that vision, hearing and olfactory function can be affected by various industrial metals and solvents, and some data exist also for touch and taste. This review discusses the main industrial chemicals involved. The pathogenesis of the toxicity of chemicals to sensory perception may be related to an action on receptors, nerve fibers, and/or the brain; probably, different pathogenetic mechanisms are involved. One of the main problems in this research field is that most of the studies to date evaluated the effect of a single industrial chemical on a single sense: as an example, we know that styrene exposure can impair smell and also hearing and vision but we have little idea whether different senses are impaired in the same worker, or whether each impairment is independent. In addition, workers are frequently exposed to different chemicals: co-exposure may have no effect, or result in both an increase or a decrease of the effect, as was observed for hearing loss, but studies on this aspect are largely insufficient. Research shows that both occupational and environmental exposure to industrial chemicals can affect sense organs, and suggests that the decline of perception with age may be, at least partly, related to this exposure. Nevertheless, available evidence is incomplete, and is largely inadequate for an estimation of a "safe" threshold of exposure. Good quality further research in this field is needed. This is certainly complex and demands adequate resources, but is justified by the ultimate result: the possibility to prevent an avoidable part of the decline in sensory function with age.

Color discrimination impairment in workers exposed to mercury vapor

OBJECTIVE

To study color discrimination impairment in workers exposed to elemental mercury (Hg) vapor.

SUBJECTS

Twenty-four male workers from a chloralkali plant exposed to Hg vapor, aged 42+/-9.8 years, duration of exposure 14.7+/-9.7 years, were examined. The 8h TWA air-borne Hg concentration in workplace was 59 microg/m(3); mean Hg urinary excretion (HgU) was 20.5+/-19.3 microg/g creatinine; mean Hg urinary excretion after the administration of a chelating agent, sodium 2,3-dimercapto-1-propane-sulfonate (DMPS), was 751.9+/-648 microg/48h. Twenty-four age- and gender-matched control subjects were compared. Visual acuity, alcohol intake, smoking habits, and history of diseases or drugs potentially influencing color vision were registered.

METHODS

The Lanthony 15-Hue desaturated test (L-D15-d) was used to assess color vision. The results were expressed quantitatively as Bowman's Color Confusion Index (CCI), and qualitatively according to Verriest's classification of acquired dyschromatopsias.

RESULTS

The CCI was significantly higher in the exposed group than in the control (mean CCI 1.15 versus 1.04; P=0.04). The proportion of subjects with errorless performance on the Lanthony test was significantly lower in the Hg exposed group compared to referents (52% versus 73%; P=0.035). The exposed group showed higher frequency of type III dyschromatopsias (blue-yellow confusion axis) in comparison with the control group (12.5% versus 8.3%), however, the difference did not reach statistical significance. Multiple regression did not show any significant relationship between the CCI, and age, alcohol consumption, or measures of exposure.

CONCLUSION

In agreement with previous studies by Cavalleri et al. [Toxicol. Lett. 77 (1995) 351; Environ. Res. Sec. A 77 (1998) 173], the results of this study support the hypothesis that exposure to mercury vapor can induce sub-clinical color vision impairment. This effect was observed at an exposure level below the current biological limit for occupational exposure to mercury. This raises doubts on the actual protection afforded by this limit concerning the effect of mercury on color vision.

Color vision and occupational chemical exposures: I. An overview of tests and effects

The paper presents a summary of the literature published until December 2000 on effects from some industrial chemical exposures on color perception, as well as short descriptions of the tests applied. Several different tests have been used to study acquired alterations of color vision. These changes are frequently found in the blue-yellow axis. Many of the tests were originally designed to detect congenital alterations in the red-green axis, and thus have relatively low sensitivity when studying chemically induced deficits in color perception. At present, the Lanthony D15-desaturated panel seems most suitable for application in industrial settings, since it is clearly the most sensitive and easily administered test. Color vision seems to be a physiological function very sensitive to several chemicals. The potency of industrial chemicals to induce color vision deficiencies has often been investigated during the last two decades. The chemicals most frequently studied are different solvents and mercury. Pronounced effects on color perception have been reported following chronic exposure to organic solvents such as styrene, carbon disulphide, perchloroethylene, n-hexane and solvent mixtures, and to organic as well as inorganic mercury. The effect of occupational toluene exposure seems not as well established, since only slight effects and several negative studies have been reported. For some of these compounds the effect on color vision has been further established through the finding of clear dose-effect relationships. In a few cases, even acute exposure situations, e.g. exposure to toluene for a few hours or acute alcohol intake, seem to affect color perception. Follow-up studies are needed to investigate the possible reversibility of effects in relation to discontinued or reduced exposures.

Mortality in dry-cleaning workers: an update

BACKGROUND

A cohort of 1,708 dry-cleaning workers identified from union records was exposed to perchloroethylene (PCE), a known animal carcinogen and probable human carcinogen, for at least 1 year before 1960. Many workers also had exposure to Stoddard solvent, a petroleum-based dry-cleaning solvent.

METHODS

Vital status was updated through 1996 and life table analyses conducted.

RESULTS

The cohort had excess cancer mortality (271 deaths, standardized mortality ratio [SMR] 1.25, 95% confidence interval [CI] 1.11-1.41). Elevated SMRs for tongue, bladder, esophagus, intestine, lung, and cervical cancer, pneumonia, and diseases of the stomach and duodenum were statistically significant.

CONCLUSION

The current study confirms findings of prior updates and other studies that dry-cleaning workers have excess cancer mortality at several sites. Although important lifestyle and socioeconomic risk factors exist for both cervical and esophageal cancer mortality, excesses of these sites in the PCE only subcohort and among workers with longer duration of PCE exposure suggest an association with PCE exposure.

Dose-related color vision impairment in toluene-exposed workers

Occupational exposure to various neurotoxic chemicals can impair color vision. We evaluated this possibility in toluene-exposed workers. Thirty-three rubber workers and 16 referents were studied. We estimated toluene exposure by measuring urinary excretion of the unmodified form of the solvent (i.e., TolU). Color vision was tested with the Lanthony D-15 desaturated panel, and the outcomes were expressed quantitatively with the Color Confusion Index and the Total Confusion Index. Toluene-exposed workers had a subclinical reduction in color vision, compared with referents. We related this effect to solvent cumulative exposure--estimated as the product of urinary excretion of unmodified toluene by previous toluene exposure duration. This approach supports the hypothesis that impairment progresses as exposure continues. In the examined group of workers, toluene exposure was within the occupational limit proposed by the American Conference of Governmental Industrial Hygienists. The observed loss in color vision raises doubts on the real protection afforded by this limit--at least for effects of the solvent on the eyes. Finally, the Total Confusion Index was a more sensitive index than the Color Confusion Index in the evaluation of toluene-related color-vision impairment, suggesting that this index should be adopted in future studies of the effects of chemicals on color perception.

Factors influencing tetrachloroethylene concentrations in residences above dry-cleaning establishments

Indoor air quality has been increasingly recognized as a significant public health problem. Proximity to industrial or commercial sources contributes to contamination in homes. Air sampling was conducted at 12 residences in 8 buildings that housed dry cleaners and 6 residential control sites. The authors found that concentrations of tetrachloroethylene, a dry-cleaning solvent, were elevated significantly in residences located in buildings that also housed dry-cleaning establishments (mean = 2.0 mg/m3) relative to their concentrations in control residences (mean = < 0.07 mg/m3 [p < .001]). Tetrachloroethylene concentrations remained elevated when the cleaners were closed on weekends (p < .01). The authors verified that colorimetric detector tubes were a useful screening tool for residences. Also identified were factors that could affect tetrachloroethylene concentrations. The use of exhaust fans and the implementation of required inspection and maintenance requirements by dry cleaners were associated significantly with reduced tetrachloroethylene concentrations in residences (p < .01). In all cases, tetrachloroethylene concentrations exceeded "minimal risk levels" posited by the Agency for Toxic Substances Disease Registry for chronic exposure to tetrachloroethylene. Residents who live in buildings that house dry cleaners may be exposed at concentrations that are of public health concern. Measures that might reduce this exposure were also identified.

Optic neuritis with residual tunnel vision in perchloroethylene toxicity

CASE REPORT

In a 57-year-old female owner of a dry-cleaning shop, we describe the association of severe bilateral optic neuritis with unexpectedly high concentrations of perchloroethylene/metabolites in the blood and of chloroform in urine. Visual disturbances consisted of complete blindness for 9 days in the left eye, for 11 days in the right eye, with bright phosphenes and pain on eye rotation. Only central (2-3 degrees radius) vision recovered in the following months.

CONCLUSION

Although environmental concentrations of perchloroethylene were within normal limits, we measured five-fold increases in vapors emitted when ironing freshly dry-cleaned fabrics, and suggest that inhalation of perchloroethylene vapors was the cause of this case of ocular nerve toxicity, recapitulating a previous report of major perchloroethylene toxicity.

Reversible color vision loss in occupational exposure to metallic mercury

Color vision was evaluated in twenty-one mercury exposed workers and referents matched for sex, age, tobacco smoking, and alcohol habits. The Lanthony 15 Hue desaturated panel (D-15 d) was applied. In the workers, mean urinary Hg (HgU) was 115+/-61.5 microg/g creatinine; in all but one the values exceeded the biological limit (BEI) proposed by the American Conference of Governmental Industrial Hygienists. A dose-related subclinical color vision impairment was observed in Hg-exposed workers compared to the referents. Just after the survey, working conditions were improved. Twelve months later the workers were reexamined. Mean HgU was 10.0 microg/g creatinine and in no subjects was the BEI exceeded. Color perception was significantly improved compared to the first examination and, furthermore, no differences were observed between exposed workers and referents. The results add evidence that the color vision loss observed during the first part of the study was related to Hg exposure and, moreover, show that this effect is reversible. These data indicate that metallic Hg can induce a reversible impairment in color perception. This suggests that color vision testing should be included in studies on the early effects of Hg. The possibility of applying the D-15 d as an early effect index in the biological monitoring of Hg exposed workers should also be entertained.

Two-year evolution of perchloroethylene-induced color-vision loss

Progression of perchloroethylene-induced color-vision impairment was studied in 33 dry-cleaner workers at 12 establishments in Modena, Italy. In an initial survey, we evaluated exposure with personal passive samplers, and we assessed color vision with the Lanthony D-15 desaturated panel. Two years later, workers were reexamined. In 19 workers (subgroup A), exposure to perchloroethylene had increased (median of 1.7 ppm versus 4.3 ppm, respectively), whereas in the remaining 14 workers (subgroup B) exposure was reduced (2.9 ppm versus 0.7 ppm, respectively). Color vision worsened in subgroup A, but no vision changes were apparent in subgroup B. The results indicated that an increase in exposure during a 2-y period, even if slight, can cause color vision to deteriorate. A similar slight reduction in exposure did not lead to color-vision improvement; perhaps this lack of improvement resulted from (a) an insufficient reduction in exposure, (b) an insufficient reduction in duration of exposure, or (c) irreversible perchloroethylene-induced color-vision loss.

The urinary excretion of solvents and gases for the biological monitoring of occupational exposure: a review

'In the field' application of the measurement of urinary excretion of unmodified solvent for the biological monitoring of exposed workers has been investigated in many recent papers. The results obtained for several solvents are reviewed. The values of correlation coefficients (r) and regression lines obtained for benzene, toluene, xylene, styrene, n-hexane, cyclohexane, 2- and 3-methylpentane, methyl chloride, tetrachloroethylene, carbon tetrachloride, methyl chloroform, p-dichlorobenzene, nitrous oxide, halothane, isoflurane, enflurane, acetone, methyl ethyl ketone and methyl isobutyl ketone are presented. The correlations observed were generally good: r values range from 0.50-0.97, and the majority are between 0.84 and 0.90. The regression lines reported for the same solvent in different studies present some variability: this is possibly due to an inadequate control of factors influencing the relationship between external dose and absorption, such as differences in body burden, work load, individual characteristics, etc. These factors are discussed. As a whole, results reported in the literature show that measuring of urinary excretion of unmodified solvents provides a highly sensitive and specific exposure index, and can also be applied for the biological monitoring of occupational exposure to low levels of solvents or to solvent mixtures. Nevertheless, for an adequate assessment of biological limit values, further studies evaluating the reproducibility of regression lines are needed, given that the aspects influencing the correlation between external dose and urinary excretion are fully controlled. Another crucial aspect is the correlation with early effects: even though this has yet to be evaluated for several solvents, for others such as styrene and perchloroethylene a good correlation was obtained, further supporting the usefulness of the measurement of urinary excretion of solvent for the biological monitoring of occupational exposure.