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 429.8 years, duration of exposure14.79.7 years, were examined. The 8 h TWA air-borne Hg concentration in workplace was 59 mg/m3; mean Hg urinaryexcretion (HgU) was 20.519.3 mg/g creatinine; mean Hg urinary excretion after the administration of a chelatingagent, sodium 2,3-dimercapto-1-propane-sulfonate (DMPS), was 751.9648 mg/48 h. Twenty-four age- and gendermatchedcontrol subjects were compared. Visual acuity, alcohol intake, smoking habits, and history of diseases or drugspotentially influencing color vision were registered. Methods: The Lanthony 15-Hue desaturated test (L-D15-d) was usedto assess color vision. The results were expressed quantitatively as Bowman’s Color Confusion Index (CCI), andqualitatively according to Verriest’s classification of acquired dyschromatopsias. Results: The CCI was significantlyhigher in the exposed group than in the control (mean CCI 1.15 versus 1.04; P ¼0.04). The proportion of subjects witherrorless performance on the Lanthony test was significantly lower in the Hg exposed group compared to referents (52%versus 73%; P ¼0.035). The exposed group showed higher frequency of type III dyschromatopsias (blue–yellowconfusion axis) in comparison with the control group (12.5% versus 8.3%), however, the difference did not reachstatistical significance. Multiple regression did not show any significant relationship between the CCI, and age, alcoholconsumption, 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 tomercury vapor can induce sub-clinical color vision impairment. This effect was observed at an exposure level below thecurrent biological limit for occupational exposure to mercury. This raises doubts on the actual protection afforded by thislimit concerning the effect of mercury on color vision.