Background

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.

Objective

To compare the color vision of children from riverine communities of mercury-exposed (Tapajós basin) and non-exposed Amazonian rivers (Tocantins basin).

Methods

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.

Results

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). Mean difference was approximately 4.01 μg/g with a 95% confidence interval of 2.79–5.23. The results of the Lanthony D-15d test showed no significant difference between the C-index mean values of the Tapajós and Tocantins groups (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 variation in mercury concentration.

Conclusion

Our results suggest a difference in one aspect of vision, that is, color vision, between children living in two different river basins in the Brazilian Amazon. The association may be related to Hg exposure but also appeared related to the location of the community and age.

中文翻译：

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横断面研究评估巴西亚马逊河沿岸社区儿童的色觉与汞头发浓度的关系

背景

自1980年代以来，巴西亚马逊地区的汞暴露一直是一个重要问题，当时金矿开采活动污染了许多亚马逊河流域及其中的鱼类。人体接触汞会导致神经功能发生变化。视觉系统已用作甲基汞（有机）和汞蒸气（无机）毒性的功能指标。儿童特别容易受到这种金属暴露的影响。

客观的

比较来自暴露于汞（Tapajós盆地）和未暴露的亚马逊河（Tocantins盆地）的河流社区儿童的色觉。

方法

研究样本为176名7至14岁的儿童。将来自暴露于汞的塔帕霍斯河盆地中两个地点的儿童，Barreiras（n = 71）和圣路易斯·塔帕霍斯（n = 41），与来自Limoeiro do Ajuru（n = 64）的非接触区儿童进行了比较。托坎丁斯河流域。没有看护者报告说，任何儿童在其一生中都接触过汞蒸气，并且他们体内大部分的汞可能是通过食用鱼类获得的。因此，我们决定通过头发样品中的总汞含量来评估汞的暴露，后者是有机汞的良好标志，而不是尿液中的无机汞的标志。通过Lanthony饱和D-15测试评估色觉。我们使用了Vingrys和King-Smith方法（1988）来量化色相排序测试。

结果

Tapajós儿童的平均头发汞含量（均值：4.5μg/ g；范围：0.26–22.38μg/ g）高于Tocantins儿童（均值：0.49μg/ g；范围：0.03–1.91μg/ g）（ p ＜0.05）。平均差异约为4.01μg/ g，95％置信区间为2.79–5.23。Lanthony D-15d试验的结果表明，Tapajos和Tocantins组的C指数平均值之间无显着差异（p> 0.05）。从两只眼睛获得的平均C指数与总汞浓度之间的线性相关性较弱。多元逻辑回归分析表明，社区的位置和年龄对视觉结果的影响大于儿童的性别和汞浓度在区域内的变化。

结论

我们的研究结果表明，居住在巴西亚马逊河两个不同流域的儿童在视觉方面（即彩色视觉）方面存在差异。这种关联可能与汞的暴露有关，但也与社区的位置和年龄有关。