Mercury toxicity in the Amazon: contrast sensitivity and color discrimination of subjects exposed to mercury

• Published in: Brazilian journal of medical and biological research Vol. 40; no. 3; pp. 415 - 424
• Main Authors: Rodrigues, A.R., Souza, C.R.B., Braga, A.M., Rodrigues, P.S.S., Silveira, A.T., Damin, E.T.B., Côrtes, M.I.T., Castro, A.J.O., Mello, G.A., Vieira, J.L.F., Pinheiro, M.C.N., Ventura, D.F., Silveira, L.C.L.
• Format: Journal Article
• Language: English
• Published: Brazil Associação Brasileira de Divulgação Científica 01.03.2007
• Subjects: Adolescent; Adult; Aged; Amazon riverside communities; BIOLOGY; Brazil; Case-Control Studies; Color Perception - drug effects; Color vision; Color Vision Defects - chemically induced; Color Vision Defects - diagnosis; Contrast sensitivity; Contrast Sensitivity - drug effects; Environmental Exposure - adverse effects; Environmental Pollutants; Humans; Male; Medical Laboratory Personnel; MEDICINE, RESEARCH & EXPERIMENTAL; Mercury - toxicity; Mercury - urine; Mercury exposure; Middle Aged; Mining; Occupational Diseases - chemically induced; Occupational Diseases - diagnosis; Occupational Exposure - adverse effects; Spectrophotometry, Atomic; Time Factors; Visual dysfunction; Brazil; Mercury toxicity; Color vision; Mercury exposure; Visual dysfunction; Contrast sensitivity; Amazon riverside communities
• ISSN: 0100-879X; 1414-431X; 0100-879X; 1414-431X
• DOI: 10.1590/S0100-879X2007000300018

We measured visual performance in achromatic and chromatic spatial tasks of mercury-exposed subjects and compared the results with norms obtained from healthy individuals of similar age. Data were obtained for a group of 28 mercury-exposed subjects, comprising 20 Amazonian gold miners, 2 inhabitants of Amazonian riverside communities, and 6 laboratory technicians, who asked for medical care. Statistical norms were generated by testing healthy control subjects divided into three age groups. The performance of a substantial proportion of the mercury-exposed subjects was below the norms in all of these tasks. Eleven of 20 subjects (55%) performed below the norms in the achromatic contrast sensitivity task. The mercury-exposed subjects also had lower red-green contrast sensitivity deficits at all tested spatial frequencies (9/11 subjects; 81%). Three gold miners and 1 riverine (4/19 subjects, 21%) performed worse than normal subjects making more mistakes in the color arrangement test. Five of 10 subjects tested (50%), comprising 2 gold miners, 2 technicians, and 1 riverine, performed worse than normal in the color discrimination test, having areas of one or more MacAdam ellipse larger than normal subjects and high color discrimination thresholds at least in one color locus. These data indicate that psychophysical assessment can be used to quantify the degree of visual impairment of mercury-exposed subjects. They also suggest that some spatial tests such as the measurement of red-green chromatic contrast are sufficiently sensitive to detect visual dysfunction caused by mercury toxicity.