Absence of blue-yellow color vision loss among workers exposed to toluene or tetrachloroethylene, mostly at levels below occupational exposure limits

Prenatal and early childhood exposure to tetrachloroethylene (PCE) and non-medical use of prescription drugs: A retrospective cohort study in Cape Cod, MA

BACKGROUND

Between 1968 and 1983, public drinking water supplies of Cape Cod, Massachusetts were contaminated with the chlorinated solvent tetrachloroethylene (PCE). We previously found an affinity for risk-taking behaviors, including the use of illicit drugs, following prenatal and early childhood exposure to PCE. Using newly collected data, we investigated the risk of non-medical use of prescription drugs (NMUPD) following prenatal and early childhood PCE exposure.

METHODS

Participants were identified from a retrospective cohort study ("Cape Cod Health Study") via cross-matching birth certificates and water system data. The original self-administered questionnaire gathered data on demographics, work and medical history, and alcohol and illicit drug use from 618 individuals (363 exposed and 255 unexposed). The follow-up survey added questions on non-medical use of prescription pain relievers, tranquilizers, stimulants and sedatives. A validated leaching and transport model was used to estimate exposure to PCE exposure in drinking water.

RESULTS

There was a wide distribution of cumulative prenatal and early childhood PCE exposure levels (range: 0.04 g-3722.2 g). PCE exposed subjects had a 1.92-fold increase in risk of any non-medical use of prescription drugs [Adjusted RR: 1.92, (95% CI: 1.31, 2.83)]. Furthermore, the association followed a dose-response relationship where the risk of NMUPD was higher for those exposed to PCE levels greater than or equal the median level versus those exposed to levels less than the median [Adjusted RR: 2.05 (95% CI: 1.34, 3.15) vs. 1.83 (95% CI: 1.20, 2.79) (p-value for trend < 0.01)]. Additionally, we found moderate increases in risk by level of non-medical use (any non-medical use, non-medical use of 1 or more categories of prescription drugs, or 2+ categories) as well as by category of drug for pain relivers, stimulants and tranquilizers.

CONCLUSION

We found that prenatal and early childhood exposure to PCE was associated with a moderate increase in the risk of NMUPD. Exposed subjects had dose-related increased risks of NMUPD of pain relievers, tranquilizers, and stimulants. This study has a number of limitations and is the first to report this association. Additional longitudinal studies of populations exposed to PCE during early life should be conducted to examine its long-term neurotoxic effects.

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.

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.

Systematic literature review of uses and levels of occupational exposure to tetrachloroethylene

Tetrachloroethylene has been one of the most widely used chlorinated solvents in the United States. This review provides a basis for tetrachloroethylene exposure assessment in population-based case-control studies. We performed literature searches in MEDLINE, TOXLINE, NIOSHTIC, and the NIOSH Health Hazard Evaluation databases using relevant search terms. We calculated weighted arithmetic means from the measurement data and compiled these into three summary tables by type of operation: (1) dry cleaning, (2) degreasing, and (3) other operations. We identified 258 relevant documents, of which 179 (69%) contained useful descriptive information. Within the dry cleaning industry, the overall arithmetic mean (AM) for personal tetrachloroethylene exposures was 59 ppm (range: 0-4636, n = 1395). Machine operators who transferred wet garments to a dryer had the highest levels (AM = 150 ppm [range: 0-1000, n = 441]) of the jobs in this industry. The AM for personal measurements associated with degreasing was 95 ppm (range: 0-1800, n = 206). In addition, we identified several other sources of substantial tetrachloroethylene exposure, including cleaning mining equipment, testing coal, cleaning animal coats in taxidermy, and cleaning and duplicating film. Exposure assessment in population-based, case-control studies is a complex process requiring substantial resources. Researchers conducting these types of studies will be able to use results of the measurements to quantify tetrachloroethylene exposure levels for various jobs.

Acquired dyschromatopsia among petrochemical industry workers exposed to benzene

Exposure to organic solvents, which are widely used in industry, can lead to dysfunction of the nervous system. However, controversy continues about the nature of early-stage damage to the nervous system from low-grade chronic exposure to organic solvents. Since loss of color-vision can be a sensitive early marker of neurotoxic damage, the main aim of this study was to investigate the association between low-level chronic exposure to organic solvents, especially benzene, and acquired dyschromatopsia. The study initially comprised 1236 workers who were employed at a large petrochemical distillation factory. After excluding those workers who may have had color-vision impairment due to congenital or acquired eye diseases and those with other medical conditions, 908 males who had worked for at least 6 months were included in the final analysis. Those who worked only in the office were categorized as nonexposed, while those who worked at outside facilities were divided into three groups of approximately equal size according to their estimated cumulative exposure levels to benzene (low, medium, high). Color-vision was assessed using the Lanthony D-15 desaturated panel color test. The results showed that the color-confusion index (CCI) was positively related to age. In the qualitative assessment of types of color-vision loss, the prevalence of total dyschromatopsia was significantly higher with increasing cumulative exposure levels in the left eye (p<0.05) but not in the right eye. The significance for the prevalence of type III dyschromatopsia was borderline in the left eye (p=0.0571). The relationship between acquired dyschromatopsia and exposure level also showed an increase in the odds ratio in the left eye but not in the right eye. Taken together, these results suggest that chronic low-level exposure to benzene can lead to acquired dyschromatopsia.

Impairments of Colour Vision Induced by Organic Solvents: A Meta-Analysis Study

The impairment of colour discrimination induced by occupational exposure to toluene, styrene and mixtures of organic solvents is reviewed and analysed using a meta-analytical approach. Thirty-nine studies were surveyed covering a wide range of exposure conditions. Those studies using the Lanthony Panel D-15 desaturated test (D-15d) were further considered. From these for 15 samples data on colour discrimination ability (Colour Confusion Index, CCI) and exposure levels were provided, required for the meta-analysis. In accordance with previously reported higher CCI values for the exposed groups, the computations yielded positive effect sizes for 13 of the 15 samples, indicating that in the great majority of the studies the exposed groups showed inferior colour discrimination. However, the meta-analysis showed great variation in effect sizes across the studies. Possible reasons for inconsistency among the reported findings are discussed. These pertain to exposure-related parameters, as well as to confounders such as conditions of test administration and characteristics of subject samples. Those factors vary considerably among the studies and might have greatly contributed to divergence in measured colour vision capacity, thereby obscuring consistent effects of organic solvents on colour discrimination.

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.

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.

Color vision and occupational toluene exposure

We examined the relationship between acquired color vision loss and exposure to toluene and total hydrocarbons among 125 male workers. Seventy-two toluene-exposed printers were compared with 34 workers from the same photogravure plant with ambient background exposure, and with 19 workers from a bookbinding plant located in the same town (nonexposed). Environmental mean toluene exposure level at workstation was estimated from individual 8-h sampling. Historic exposure data from the last 30 years were used to construct two cumulative exposure indices, one for toluene and one for total hydrocarbons. Airborne toluene levels were overall lower than the current Threshold Limit Value (TLV) of 50 ppm. Color vision was assessed by the Lanthony D-15 desaturated panel. Color vision loss was quantitatively established by the Color Confusion Index (CCI) and classified by type of acquired dyschromatopsia according to Verriest's classification. CCI was positively related to current airborne toluene levels, and cumulative exposure indices for toluene and total hydrocarbons (.18< or =r< or =.35). Odds ratios of acquired dyschromatopsia were significant for current airborne toluene, toluene, and total hydrocarbon past exposure (1.27 [1.02-1.58], 1.21 [1.04-1.39], 1.15 [1.02-1.31], respectively). In conclusion, this study suggests that the Lanthony D-15 desaturated panel detects early neurotoxic effects among workers exposed to toluene.

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.

Impairment of colour vision in workers exposed to organic solvents

OBJECTIVES

To investigate loss of colour vision related to exposure to solvents and the role of three enzyme polymorphisms in modifying the risk in exposed workers.

METHODS

A sample was studied of 68 male dockyard workers and 42 male community controls with and without neuropsychological symptoms from a previous cross sectional study. Indices of cumulative and intensity based exposure to solvents were calculated for all subjects. Alcohol, drug, and smoking histories were obtained. Colour vision was tested by Lanthony D15d colour vision test. Genotype of glutathione S-transferase M1 and T1 and N-acetyltransferase 2 polymorphisms were determined.

RESULTS

The relation between impairment of colour vision and exposure to solvents was investigated with multiple regression techniques. Increasing annual exposure to solvents was significantly associated with reduced colour vision (p=0.029). Impairment of colour vision was not associated with neuropsychological symptoms as measured by the Q16 solvent symptom questionnaire. No significant association was found between acquired impairment of colour vision and genetic polymorphisms when GSTM1, GSTT1 or NAT2 phenotypes were included in the analyses.

CONCLUSIONS

Exposure to mixed solvents is associated with impairment in colour vision, the risk increases with increasing exposure. The risk of impairment of colour vision was not altered in this study by the presence of different GSTM1, GSTT1 or NAT2 polymorphisms.

Colour vision loss in workers exposed to elemental mercury vapour

We evaluated colour vision in 33 workers exposed to elemental mercury (Hg) vapour and in 33 referents matched for sex, age, alcohol consumption and cigarette smoking. The results were expressed as colour confusion index (CCI). In the workers urinary excretion of Hg (HgU) ranged from 28 to 287 micrograms/g creatinine. Subclinical colour vision loss, mainly in the blue-yellow range, was observed in the workers. This effect was related to exposure, as indicated by the correlation between HgU and CCI (r = 0.488, P < 0.01). In the workers whose HgU exceeded 50 micrograms/g creatinine, mean CCI was significantly increased compared to the matched referents. The results suggest that exposure to elemental Hg inducing HgU values exceeding 50 micrograms/g creatinine can induce a dose-related colour vision loss.

Occupational and environmental exposure to perchloroethylene (PCE) in dry cleaners and their family members

Perchloroethylene exposure in 28 dry-cleaning establishments and in 25 homes occupied by dry cleaners in Modena, Italy, was investigated. Environmental air samples and alveolar air samples from dry cleaners (n = 60) and from their family members (n = 23) were collected. The degree of perchloroethylene on the dry-cleaning premises varied widely from establishment to establishment. Spot sampling ranged from 0.6 to 75 mg/m3, whereas sampling by personal passive dosimeters ranged from 2.6 to 221.5 mg/m3 (8-h time weighted average values). Perchloroethylene in alveolar air samples collected at the end of the work day correlated closely with the 8-h time weighted average values (r = .750, p = .001), and correlated also with alveolar air samples collected at home in the evening (r = .665, p = .001) and the following morning (r = .549, p < .001). Perchloroethylene levels inside the homes of dry cleaners appeared significantly higher than in 29 houses selected as controls (Mann Whitney U test, p < .001). Perchloroethylene in alveolar air samples collected at home suggests that nonoccupational exposure to perchloroethylene for family members of dry cleaners exists.

Perchloroethylene exposure can induce colour vision loss

We evaluated colour vision in 35 dry-cleaners exposed to perchloroethylene (PCE) and in a paired number of controls matched for sex, age, alcohol consumption and cigarette smoking. A subclinical colour vision loss, mainly in the blue-yellow range, was present in dry-cleaners. This effect was related to PCE exposure levels, and appeared at environmental concentrations of the solvent well below the current exposure limits for exposed workers. The results suggest that PCE exposure, even at low environmental levels, can induce a dose-related impairment of colour vision.