Variation In Mercury Concentrations Research Articles

Microbial Mercury Reduction Potential In Gold Mining Waste: Bacillus Subtilis And Pseudomonas Aeruginosa Study

This study aims to investigate the potential of Bacillus subtilis and Pseudomonas aeruginosa in removing mercury from wastewater generated by Artisanal and Small-scale Gold Mining (ASGM) in Tatelu and Talawaan Villages, North Minahasa, Indonesia. Following the ban on mercury use in gold processing, there is a need for effective mercury-free processing technologies to mitigate environmental and health impacts. The research begins with the cultivation of rejuvenated bacteria, followed by a preliminary test to establish bacterial growth curves. This test provides guidelines for the duration of stirring during subsequent biodegradation processes. The biodegradation test involves mercury content analysis of wastewater samples, followed by Minimum Inhibitory Concentration (MIC) testing using lactose broth as the bacterial growth medium. The MIC test helps determine the variations in mercury concentrations and the efficacy of the selected bacteria in degradation. The objectives of this study are to assess the capability of Bacillus subtilis and Pseudomonas aeruginosa in removing mercury from ASGM wastewater. The findings hold significant potential for the development of efficient and economically viable biotreatment technologies for addressing mercury contamination in hazardous waste produced by small-scale gold mining. The innovative technology proposed in this study can be readily adopted by other gold mining industries to ensure compliance with stringent environmental and health standards.

MERCURY BACKGROUND IN BOTTOM SEDIMENTS OF THE EASTERN ARCTIC

On the basis of dated bottom sediment cores, layers accumulated in the pre-industrial period were selected. They determine the mercury concentrations, which are the geochemical background for the selected water areas. The variability of mercury concentrations in the sediments of the inner shelf is small (20–30 μg/kg) and can be used as a basis for environmental assessment in the economic development of the Arctic regions.

The distribution and dynamics of residual mercury from the Chisso chemical plant in sediments of the Yatsushiro Sea, western Kyushu, Japan: have recent sedimentations lowered surface mercury concentrations?

To determine the long-term dynamics of mercury discharged from Chisso chemical plant between 1932 and 1968, the vertical variation in mercury concentrations in Yatsushiro Sea sediments was studied from 2013 to 2020 at 31 locations and compared to the mercury concentration distribution obtained in 1996. The results suggest that new sedimentation occurred after 1996, but the mercury concentrations at the surface ranged from 0.2 to 1.9mgkg-1, which did not decrease significantly over a 20-year period. It was estimated that approximately 17 t of mercury remained in the southern Yatsushiro Sea sediment, which is equivalent to 10-20% of the total mercury discharged between 1932 and 1968. From results of WD-XRF and TOC measurement, it was suggested that mercury in sediment had been transported with suspended particles derived from sludges from the chemical plant and further suggests that the suspended particles derived from the sediment surface layer are still slowly diffusing.

Factors related to fish mercury concentrations in Iowa lakes.

Mercury contamination in aquatic ecosystems is a global concern due to the health risks of consuming contaminated fishes. Fish mercury concentrations are influenced by a range of biotic and abiotic factors that vary among regions, but these complex interactions are difficult to disentangle. We collected bluegill (Lepomis macrochirus), white and black crappie (Pomoxis annularis; P. nigromaculatus), largemouth bass (Micropterus salmoides), walleye (Sander vitreus), muskellunge (Esox masquinongy), and northern pike (E. lucius) from waterbodies throughout Iowa and analyzed them for mercury concentrations. We used land use, water chemistry, and fish characteristics to explain variation in mercury concentrations among and within systems. Mercury concentrations were generally low and undetectable (< 0.05mg/kg) in 43% of fish analyzed. Detected mercury concentrations were highest in largemouth bass, muskellunge, northern pike, and walleye, lowest in black and white crappie and bluegill, and positively related to fish length and age. Mean lake depth, pH, watershed area to lake area ratio, and percent of watershed as open water were positively related to fish mercury concentrations whereas lake area and percent of watershed as agriculture, developed, forested, and grassland were negatively related to mercury concentrations. Additionally, mercury concentrations were higher in shallow natural lakes compared to other lake types. Our results indicate fish mercury concentrations are lower in Iowa lakes compared to other regions. Models we developed in this study can be used to identify other waterbodies that may have elevated mercury concentrations that can guide fish mercury monitoring programs.

Utilization of Nanochitosan as Adsorbent of Mercury (Hg) in Gold Ore Processing Waste

Mercury pollution in gold ore processing wastewater can cause environmental and health problems. A large amount of mercury pollution causes neurological disease, paralysis, loss of sense of taste, irregular speech, and death. One effective method to reduce mercury amount in the environment is adsorption. Adsorption performance is affected by several factors such as surface area of material, deacetylation degree (DD), and adsorption condition, which is indicated by contact time and mercury concentration. Nanochitosan is used in this research. Effect of deacetylation degree (85%; 87%; 95%), contact time (30;60;90;120 minutes), and variation of mercury concentration (5;10;15;20;25;30 ppm) on adsorption performance was investigated in this research. Nanochitosan in this research is characterized by FTIR, SEM-EDX, BET-BJH, and pH PZC. AAS measures adsorption performance in this research. The result shows that nanochitosan, which has the best adsorption performance, is nanochitosan with a deacetylation degree of 95%, at a contact time of 60 minutes, and mercury concentration is 15 ppm.

Spatial variation in mercury concentrations in polar bear (Ursus maritimus) hair from the Norwegian and Russian Arctic

We examined spatial variation in total mercury (THg) concentrations in 100 hair samples collected between 2008 and 2016 from 87 polar bears (Ursus maritimus) from the Norwegian (Svalbard Archipelago, western Barents Sea) and Russian Arctic (Kara Sea, Laptev Sea, and Chukchi Sea). We used latitude and longitude of home range centroid for the Norwegian bears and capture position for the Russian bears to account for the locality. We additionally examined hair stable isotope values of carbon (δ13C) and nitrogen (δ15N) to investigate feeding habits and their possible effect on THg concentrations. Median THg levels in polar bears from the Norwegian Arctic (1.99 μg g−1 dry weight) and the three Russian Arctic regions (1.33–1.75 μg g−1 dry weight) constituted about 25–50% of levels typically reported for the Greenlandic or North American populations. Total Hg concentrations in the Norwegian bears increased with intake of marine and higher trophic prey, while δ13C and δ15N did not explain variation in THg concentrations in the Russian bears. Total Hg levels were higher in northwest compared to southeast Svalbard. δ13C and δ15N values did not show any spatial pattern in the Norwegian Arctic. Total Hg concentrations adjusted for feeding ecology showed similar spatial trends as the measured concentrations. In contrast, within the Russian Arctic, THg levels were rather uniformly distributed, whereas δ13C values increased towards the east and south. The results indicate that Hg exposure in Norwegian and Russian polar bears is at the lower end of the pan-Arctic spectrum, and its spatial variation in the Norwegian and Russian Arctic is not driven by the feeding ecology of polar bears.

Сигналы ртути подземных вод Култукского полигона во время подготовки и реализации Байкало-Хубсугульской сейсмической активизации 2020–2021 гг.

From 5-year monitoring of groundwater in the Kultuk area, long-period (about 2.5 years) and short-period (months) variations in mercury concentration have been established. Long-period variations are associated with the preparation and implementation of the Baikal-Khubsugul seismic reactivation; short-period ones – directly with earthquakes. Mercury concentrations was low in groundwater in 2015, when seismogenic deformations developed in a state of crustal compression, and generally increased to 2020–2021, when seismogenic deformations occurred under extention. The course of the seismic process was reflected in a successive change in mercury/redox potential rеlationship in groundwater. It is proposed that the anomalous behavior of mercury during seismic activity resulted in increasing its concentration in the sedimentary layers of the second half of the 18th century through the present.

Variations in mercury concentrations in the muscles of fish in biotopes within the water body and in different water bodies of Russia

Abstract. In recent decades, researchers from Papanin Institute for Biology of Inland Waters Russian Academy of Sciences have been studying mercury concentrations in the muscles of fish from water bodies situated in different natural and climatic zones. Overall, more than 5000 fish samples from 102 lakes and 35 rivers in Russia were analysed. In the absence of local sources of mercury entering the water body, its concentrations in the fish muscles varied in wide ranges, exceeding two orders of magnitude. Minimum concentration (&lt;0.03 mg/kg wet weight) was recorded in the muscles of omul, rotan (Chinese sleeper), minnow, and bleak (Lake Baikal, Transbaikalia and European Russia). Maximum mercury concentration (2-3 mg/kg wet weight) was recorded in the muscles of perches from lakes in the northwest of Russia (Vologda and Novgorod regions, Karelia). Most of the measurement results ranged from 0.05 to 0.30 mg/kg wet weight. Differences in mercury concentrations in the muscles of fish of the same species, similar in size and from one water body, as a rule, did not exceed ranges of one order of magnitude. In the absence of local mercury sources, mercury concentrations in fish muscles from closely spaced water bodies could have more than tenfold differences.

Does mercury emission from small-scale gold mining cause widespread soil pollution in Ghana?

The use of mercury in small-scale gold mining is globally the largest anthropogenic source of mercury in the environment. In countries like Ghana, where small-scale gold mining is a highly important economic sector, the activity is also expected to cause local pollution. This study is based on a hypothesis that the mining activity in Ghana is causing more widespread soil pollution also outside active mining sites, and that the main part of regional differences in soil concentrations of mercury might come from pollution. Little systematic and dependable data has been collected to assess the extent of mercury contamination of soils in areas outside active mining areas. The regional aspect of mercury pollution from mining has not been studied in Ghana or other countries with a large small-scale gold mining sector. Systematic collection of soil samples on a 25×25km2 net covering the entire country was carried out to ensure the representativeness of data and to allow calculation of spatial trends. The soil concentrations found in one-third of the country, where most intensive mining takes place, are three times higher than concentrations in the rest of the country. This difference cannot be explained by sources of natural variation in mercury concentrations but can be explained by decades of atmospheric deposition. It is therefore likely that the mining activity has caused a more widespread increase in soil concentrations, also outside active mining sites. The mercury concentrations found are on average 0.024mgkg-1, which is low compared to published studies from other countries and regions and estimated world averages. All measured concentrations are well below soil quality criteria for human health. The build-up of soil concentrations in the mining area is still problematic because mercury is a hazardous substance in the environment.

Untangling causes of variation in mercury concentration between flight feathers.

Bird feathers are one of the most widely used animal tissue in mercury biomonitoring, owing to the ease of collection and storage. They are also the principal excretory pathway of mercury in birds. However, limitations in our understanding of the physiology of mercury deposition in feathers has placed doubt on the interpretation of feather mercury concentratoins. Throughout the literature, moult sequence and the depletion of the body mercury pool have been taken to explain patterns such as the decrease in feather mercury from the innermost (P1) to the outermost primary feather (P10) of the wing. However, it has been suggested that this pattern is rather a measurement artefact as a result of the increased feather mass to length ratio along the primaries, resulting in a dilution effect in heavier feathers. Here, we attempt to untangle the causes of variation in feather mercury concentrations by quantifying the mercury concentration as μg of mercury (i) per gram of feather, (ii) per millimetre of feather, and (iii) per day of feather growth in the primary feathers of Bulwer's Petrel Bulweria bulwerii chicks, effectively controlling for some of the axes of variation that may be acting in adults, and monitoring the growth rate of primary feathers in chicks. The mercury concentration in Bulwer's Petrel chicks' primaries increased from the innermost to the outermost primary for all three concentration measures, following the order of feather emergence. These observations confirm that the pattern of mercury concentration across primary feathers is not an artefact of the measure of concentration, but is likely an effect of the order of feather growth, whereby the earlier grown feathers are exposed to higher blood mercury concentrations than are later moulted feathers as a result of blood mercury depletion.

Seasonal Dynamics and Interannual Variability in Mercury Concentrations and Loads through a Three-Reservoir Complex.

The Hells Canyon Complex (HCC) along the Snake River (Idaho-Oregon border, U.S.A.) encompasses three successive reservoirs that seasonally stratify, creating anoxic conditions in the hypolimnion that promote methylmercury (MeHg) production. This study quantified seasonal dynamics and interannual variability in mercury concentrations (inorganic divalent mercury (IHg) and MeHg) and loads at four reservoir inflow and outflow locations through the HCC (2014-2017). We observed (1) that the HCC is a net sink for both IHg and MeHg, (2) interannual variability in IHg and MeHg loads largely reflecting streamflow conditions, and (3) seasonal variability in particulate IHg loading at the inflow (greatest from February to April) and MeHg export from the outflow (greatest from September to December) of the HCC. Seasonal export of MeHg was evidenced by increases in monthly mean concentrations of unfiltered MeHg (approximately 2-fold) and the percentage of total mercury (THg) as MeHg (≥4-fold) coincident with reservoir destratification. Despite evidence of seasonal export of MeHg from the HCC, annual loads indicate a 42% decrease in unfiltered MeHg from HCC inflow to outflow. Results from this study improve the understanding of seasonal variability in mercury transport through and transformation within a reservoir complex.

Mercury in White Sea bottom sediments: distribution, sources, and deposition chronology

For the first time, vertical and lateral distribution patterns of mercury in White Sea bottom sediments have been determined. An abrupt change in the nature of mercury concentrations has been revealed, with a general tendency to decrease with depth. Natural variations in mercury concentrations within 0.01 - 0.03 μg/g dry weight (dw) have been established. An upper value of 0.03 μg/g dw is taken for the natural background content of the element. The distribution of mercury concentrations in the sequence of bottom sediments is influenced by both anthropogenic and natural factors and processes. With distance from the marine -estuary boundary of the Northern Dvina River, the river’s role in supplying mercury to the White Sea is reduced, and global and regional atmospheric mass transfer take over. The mercury content is used as an indicator of landslide processes in Kandalaksha Gulf of the White Sea. The accumulation chronology of mercury in White Sea sediments is studied, and the proportion of anthropogenic mercury is calculated.

Mercury as an indicator of foraging ecology but not the breeding hormone prolactin in seabirds

Marine predators are frequently exposed to contaminants through diet, and thus contaminants like mercury have the potential to be used as tracers of foraging ecology. Mercury’s neurotoxic and endocrine-disrupting effects can have far-ranging consequences for both individuals and populations, and thus mercury concentrations could also be indicative of wildlife health. Because blood samples are relatively non-invasive and easy to obtain in seabird colonies, we investigated whether blood-based mercury concentrations were representative of foraging ecology and breeding hormone concentrations in seabirds. Blood-based mercury carbon and nitrogen stable isotopes, and the reproductive hormone, prolactin, were sampled from two seabird species that exhibit different foraging strategies in Western Australia: Great-winged Petrels (Pterodroma macroptera) are pelagic squid-specialists whose populations are under-studied; Flesh-footed Shearwaters (Ardenna carneipes) are coastal foragers that associate with fishing vessels, and are a species listed as Vulnerable in Western Australia. Mercury was six times higher in Great-winged Petrels (geometric mean ± SE: 3.360 ± 0.180 μg g−1 ww, n = 15) than Flesh-footed Shearwaters (0.554 ± 0.109 μg g−1 ww, n = 12). There was a significant difference in δ15N between species, and within-species variation in δ13C mirrored variation in mercury concentrations, supporting the view that foraging ecology plays a central role in mercury exposure. Furthermore, Great-winged Petrels’ mercury concentrations are among the highest reported in seabirds. However, no relationship between mercury and prolactin concentrations was detected. Overall, these results demonstrate that mercury can be used as a foraging ecology tracer in these populations but may not be a good indicator of seabirds’ breeding hormones like prolactin, though mercury may affect other aspects of reproduction that we did not measure. These results may aid in future assessment of population trends in these, and other, species.

Non-lethal sampling of avian indicators reveals reliable geographic signals of mercury despite highly dynamic patterns of exposure in a large wetland

Mercury is a global contaminant with special relevance for aquatic food webs, where biomagnification can result in strong effects on apex predators. Non-lethal sampling of tissues such as blood and feathers is often used to assess mercury risk and spatiotemporal variability of mercury exposure on avian populations. However, the assumption that samples from individuals within a population are representative of local mercury exposure underpins those approaches. While this assumption may be justified, it is rarely expressed quantitatively. Further, the stability of the tissue/exposure relationship over time or space may depend on the sampling medium used, since some tissues and age classes may be better at reflecting local or short-term changes in exposure. Here, we present analyses of mercury concentrations from three tissues (albumen, blood and feathers) of the same individual great egret (Ardea alba) nestlings from breeding colonies in the Florida Everglades collected over three consecutive years. The interaction of year and colony location explained at least 50% of the observed variation in mercury concentration in all the sampled tissues. Annual colony-wide average Hg concentrations in any of the sampled tissues correlated with average Hg concentrations in the other two tissues from the same colony (R2 > 0.53 in every case), while concentrations in albumen, blood and feathers from the same individual correlated poorly (R2 < 0.23 in every case). We suggest that despite high variation between and within individuals of the same colony, annual colony-averaged mercury concentrations in albumen, nestling blood or feathers can be representative indicators of annual geographic differences in mercury exposure. These results support the use of non-lethal sampling of nestling tissues to reflect local mercury exposure over large spatial scales.

Mercury in White Sea Bottom Sediments: Distribution, Sources, and Deposition Chronology

For the first time, vertical and lateral distribution patterns of mercury in White Sea bottom sediments have been determined. An abrupt change in the nature of mercury concentrations has been revealed, with a general tendency to decrease with depth. Natural variations in mercury concentrations within 0.01–0.03 µg/g dry weight (dw) have been established. An upper value of 0.03 µg/g dw is taken for the natural background content of the element. The distribution of mercury concentrations in the sequence of bottom sediments is influenced by both anthropogenic and natural factors and processes. With distance from the marine–estuary boundary of the Northern Dvina River, the river’s role in supplying mercury to the White Sea is reduced, and global and regional atmospheric mass transfer take over. The mercury content is used as an indicator of landslide processes in Kandalaksha Gulf of the White Sea. The accumulation chronology of mercury in White Sea sediments is studied, and the proportion of anthropogenic mercury is calculated.

A comparison of fish tissue mercury concentrations from homogenized fillet and nonlethal biopsy plugs

The use of biopsy plugs to sample fish muscle tissue for mercury analyses is a viable alternative to lethal sampling; however, the practice has yet to be widely implemented in routine monitoring due to concerns about variability of mercury concentrations in fish muscle tissues. Here we examine distribution of mercury in fillets of four fish species (Walleye, Northern Pike, Smallmouth Bass and Lake Trout), suitability of left/right side of fillet for biopsy sampling, and appropriateness of re-using a biopsy punch. The results showed that average mercury concentrations in left and right fillets of fish are similar. Mercury concentrations in biopsy plug samples, taken from the anterior dorsal area of the fish fillet, were statistically equivalent to the mercury concentrations in homogenized fillets. There was no discernible cross contamination between samples when a biopsy punch was reused after washing in hot soapy water, and as such, biopsy punches can be recycled during sampling to reduce the sampling cost. If a tissue mass collected from a specific site on the fillet is insufficient, then we suggest sampling corresponding locations on the other fillet rather than sampling two adjacent sites on one fillet to obtain more tissue. The results presented here can improve the accuracy of fillet biopsy plug sampling, minimize fish mortality for mercury monitoring, and reduce labor and material costs in monitoring programs.

Alpine accentors as monitors of atmospheric long-range lead and mercury pollution in alpine environments.

Mercury and lead are deposited in the West Carpathians as long-range transported air pollution. The Alpine accentor (Prunella collaris) was recognized as a cost-effective biomonitor, and used to investigate the bioavailability of contaminants in large alpine areas. The outer tail feathers and blood of the alpine accentors were used for assessment of atmospheric mercury and lead contamination, respectively. Mean mercury levels in feathers of accentors averaged at 1.15μg/g (SE = 0.105, n = 40). There were no temporal variations in mercury concentrations. Mean blood lead levels were at 5.2μg/dL (SE = 0.5, n= 27), showing a slight decreasing trend from July to October. Juveniles were not more susceptible to lead accumulation than adults. Bone lead concentrations that increase with age reflect a bioaccumulation effect. A statistically significant negative correlation was found between the length of erythrocytes and the concentration of lead, which may show the first symptoms of microcytosis. In comparison to aquatic ecosystems, the biogeochemical factors that influence methylmercury availability in alpine habitats are not yet completely known and require further investigation. Our findings show that birds in alpine terrestrial ecosystems may contain surprisingly high levels of methylmercury. The mercury levels in the feathers of accentors probably indicate that alpine autotrophs make sufficient amounts of mercury available to the terrestrial food web. The blood lead levels of accentors likely approach the threshold level for further hematological effects. We found a clear tendency in erythrocytes to change their shape from ellipsoid to smaller and rounder with increasing amounts of lead in their blood. The shape of bird erythrocytes appears to be a very sensitive indicator of critical levels of lead in the alpine environment.

A case study and a meta-analysis of seasonal variation in fish mercury concentrations.

Mercury contamination in aquatic ecosystems is a concern due to health risks of consuming fish. Fish mercury concentrations are highly variable and influenced by a range of environmental factors. However, seasonal variation in mercury levels are typically overlooked when monitoring fish mercury concentrations, establishing consumption advisories, or creating accumulation models. Temporal variation in sampling could bias mercury concentration estimates of accumulation potential. Thus, the objectives of this study were to first evaluate seasonal variation of largemouth bass (Micropterus salmoides) axial muscle mercury concentration from two Iowa, USA impoundments. Second, we conducted a meta-analysis to evaluate if seasonal variation in mercury concentration is dependent upon mean mercury concentration, waterbody type, or fish trophic level or mean length. Largemouth bass were collected four times between May and October (24-36 fish per month) from Twelve Mile (2013) and Red Haw (2014) lakes. Largemouth bass axial muscle mercury concentrations were variable within and between lakes, ranging from undetectable ( < 0.05 mg/kg) to 0.54 mg/kg. Largemouth bass mercury concentrations were similar across months in Twelve Mile but varied temporally in Red Haw and were highest in July, intermediate in May and September, and lowest during October. Results of the meta-analysis suggest that seasonal variation in mercury concentrations is more likely to occur as mean mercury concentration of the population increases but is unrelated to waterbody type, trophic status, and fish size. Understanding seasonal variation in fish mercury concentrations will aid in the development of standardized sampling programs for long-term monitoring programs and fish consumption advisories.

Variation in mercury concentration in juvenile Magellanic penguins during their migration path along the Southwest Atlantic Ocean

The vulnerability of seabirds related to their migratory dynamics is frequently linked to environmental problems along the migration path. In this context, Magellanic penguins (Sphenicus magellanicus) seem to be vulnerable to an extensive range of environmental disturbances during their northward migration along the Atlantic waters of South America, which include by catch, marine debris ingestion, overfishing and environmental contamination. In this study, we investigate mercury accumulation in muscle and hepatic tissues of juveniles penguins collected along the Brazilian coast during three migratory seasonal years (2006, 2008 and 2012) and three areas along a latitudinal gradient. We found significant differences in Hg levels across the years, with higher hepatic Hg levels found in tissues of penguins sampled in 2008. The higher Hg levels in samples of penguins from 2008 might be attributed to variations in body condition or Hg uptake, associated with the trophic imbalance linked to an extreme El Niño event during that year. Significant differences in Hg accumulation across the latitudinal areas were also observed. The penguins sampled at the farthest area from the breeding ground presented the higher levels of Hg and also the poorest body condition. Body condition and other traits may influence the levels of chemical pollutants and decrease the migratory success rate in the juvenile age phase, compromising population dynamics.

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

BackgroundMercury 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. ObjectiveTo compare the color vision of children from riverine communities of mercury-exposed (Tapajós basin) and non-exposed Amazonian rivers (Tocantins basin). MethodsThe 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. ResultsThe 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. ConclusionOur 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.