Auzier Guimarães et al. 2025 — Mercury in fish from the Tapajós River Basin: systematic review and health risk
This systematic review compiled 36 studies published between 1992 and 2022 covering 143 fish species (14,113 individuals, 735 mean Hg values) from the Tapajós River Basin in the Brazilian Amazon, a region heavily impacted by artisanal gold mining. Mercury concentrations in fish muscle tissue ranged from 0.01 to 3.82 mg/kg across all trophic levels, with piscivorous species showing the highest levels and clear spatial clustering in the middle Tapajós, upper Tapajós, and Teles Pires sub-basins, which are identified as Hg contamination hotspots closely associated with illegal gold mining activity. Using the Target Hazard Quotient (THQ) at the local average consumption of 116.25 g/capita/day, 89% of the 129 food-fish species evaluated showed THQ ≥1 in at least one sub-basin, indicating a potential chronic health risk to riverside populations; 75% of evaluated food species should be consumed in quantities below the local average daily intake to avoid health risks. Received July 2024, accepted October 2024, published October 30, 2024 online; printed in ACS Environ. Au 2025, 5, 86–100.
Key numbers
- Literature base: 36 studies, 1992–2022, PRISMA protocol
- Species covered: 143 fish species, 14,113 individuals, 735 mean Hg values
- Total Hg range across all species and trophic levels: 0.01–3.82 mg/kg (muscle tissue)
- Trophic levels: TL1 herbivorous/detritivorous (42 sp.), TL2 omnivorous (26 sp.), TL3 invertivorous/planktivorous (21 sp.), TL4 piscivorous (54 sp.)
- Piscivorous species exceeding ANVISA limit (1 mg/kg for piscivorous fish): 16 species (29%)
- Piscivorous species exceeding WHO limit (0.5 mg/kg): 36 species (67%)
- Nonpiscivorous species range: 0.01–0.98 mg/kg; several TL2/TL3 species exceeded 0.5 mg/kg ANVISA/WHO limit at mining-impacted sites
- THQ ≥1 (at 116.25 g/capita/day, 70 kg BW, RfD 0.0001 mg/kg/day for MeHg): 115/129 food-fish species (89%) in at least one sub-basin
- Middle Tapajós: 90% of food-fish species (n=91) had THQ ≥1 — most dangerous sub-basin
- Lower Tapajós: 76% of food-fish species; Upper Tapajós: 85%
- Teles Pires: 85% (n=28); Jamanxim: 89% (n=8)
- 75% of 129 evaluated food-fish species should be consumed below 116.25 g/capita/day to avoid health risks
- Maximum observed: Brachyplatystoma filamentosum mean 3.82 mg/kg; several Cichla spp. and Hoplias spp. commonly >1 mg/kg
- Highest contamination sub-basins: middle/upper Tapajós and Teles Pires (gold mining hotspots)
- Daily fish consumption range in Tapajós communities: 8 g to 217 g per capita/day (average used for THQ: 116.25 g)
- ANA sub-basin classification: Lower Tapajós, Middle Tapajós (authors’ subdivision), Upper Tapajós, Jamanxim, Juruena, Teles Pires
Methods (brief)
Systematic review following PRISMA guidelines; databases searched: Web of Science, PubMed, Scopus, Observatório do Mercúrio (Pan-Amazon georeferenced platform). Data extraction: collection site, coordinates, sampling year, species, trophic level, sample size, mean Hg concentration. Mercury reported as total Hg (tHg) in muscle tissue; methylmercury (MeHg) reported where source studies specified. Spatial analysis: Inverse Distance Weighting interpolation in QGIS 3.30; Kruskal–Wallis ANOVA with Bonferroni post-hoc for sub-basin comparison (p<0.05); Moran’s I spatial autocorrelation for piscivorous species. Temporal analysis across three decades (1992–2001, 2002–2011, 2012–2022); Kruskal–Wallis and simple linear regression. THQ and Maximum Safe Consuming Quantity (MSCQ) calculated using ANVISA and WHO reference doses. Oral RfD for MeHg: 0.0001 mg/kg/day. Note: the review reports tHg as the primary metric from most source studies; MeHg measurements are from a minority of source papers. The two measures are not substituted; tHg values dominate the dataset.
Implications
Certification: Provides a comprehensive evidence base for Hg (tHg and MeHg) contamination in freshwater fish from a high-risk mining-affected region. The 89% THQ ≥1 finding supports the principle that high fish consumption in contaminated areas constitutes a serious dietary mercury exposure pathway for vulnerable populations. For HMT&C purposes, this review underscores the relevance of origin-of-catch data for fish products targeting frequent consumers.
Courses: Core content for the mercury/fish dietary exposure module. Illustrates trophic biomagnification directly with data; shows that even lower trophic level fish can exceed limits at mining-impacted sites. The variation between sub-basins (76%–90% THQ ≥1) illustrates that geographic origin of catch is a critical variable that cannot be treated as uniform.
App: The study does not provide product-level data for commercially packaged foods but is directly relevant to risk scoring for fresh or frozen Amazonian freshwater fish. tHg range 0.01–3.82 mg/kg, piscivorous median substantially higher than nonpiscivorous, should inform any fish-type-specific contamination estimate.