Cross-sectional study to assess the association of color vision with mercury hair concentration in children from Brazilian Amazonian riverine communities

•Study of color vision and its relation to Hg exposure.•Children from the Tapajós basin had higher mercury exposure than those from the Tocantins.•Tapajos children with higher Hg levels performed slightly worse on color vision testing. Mercury exposure in the Brazilian Amazon region has been an important concern since the 1980s, when gold mining activities contaminated many Amazonian river basins and the fish therein. Mercury exposure in humans can lead to changes in neural function. The visual system has been used as a functional indicator of methylmercury (organic) and mercury vapour (inorganic) toxicity. Children are particularly vulnerable to this metal exposure. To compare the color vision of children from riverine communities of mercury-exposed (Tapajós basin) and non-exposed Amazonian rivers (Tocantins basin). The study sample was 176 children, aged 7–14 years old. Children from two locations in the mercury-exposed Tapajós river basin, Barreiras (n = 71) and São Luiz do Tapajos (n = 41), were compared to children from Limoeiro do Ajuru (n = 64), a non-exposed area in the Tocantins river basin. No caregiver reported that any children had contact with mercury vapour during their lifetime, and probably most of the mercury in their bodies was obtained by fish consumption. Because of this, we decided to evaluate the mercury exposure by total mercury levels in hair samples, a good marker for organic mercury, and not in the urine, a marker for inorganic mercury. Color vision was assessed by the Lanthony Desaturated D-15 test. We used the Vingrys and King-Smith method (1988) to quantify the hue ordering test. The primary visual outcomes from this analysis were C-index (magnitude of the hue ordering error) and angle of the hue ordering. The Tapajós children had a higher mean hair mercury level (mean: 4.5 μg/g; range: 0.26–22.38 μg/g) than that of Tocantins children (mean: 0.49 μg/g; range: 0.03–1.91 μg/g) (p 0.05). There was a weak linear correlation in the average C-index obtained from both eyes and the total mercury concentration. Multiple logistic regression analysis indicated that the location of the community and the age had a greater influence on the visual outcomes than the sex of the children and within-locale v