Color Discrimination Impairment in Workers Exposed to Mercury Vapor

Abstract 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 8 h TWA air-borne Hg concentration in workplace was 59 μg/m 3 ; mean Hg urinary excretion (HgU) was 20.5±19.3 μg/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 μg/48 h. 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.