Mercury contamination and human exposure

Overview

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Key numbers

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ment in the form of metallic or elemental Hg (Hg0), matã (Prochilodus brevis), the Piau (Leporinus sp.),
eral deposits and/or volcanic activities. However, responded with 86,000 tones, approximately 17% of
ties have developed recommendations that establish fisheries in northeastern Brazil (Table 1). For three
Table 1 Species, common name, total Hg concentrations, size and the percentage of methyl-Hg (mean, standard deviation and size
Species Common name Total Hg (ng g−1 w.w.) LT (cm) n Methyl-Hg (%) n
Fish samples were obtained from major reser- by immersion for 24 h in a 10% Hg-free HCl solu-
NaBH4 (Lacerda et al., 2014; Moura & Lacerda, μL of each sample, and 50 μL of 1% sodium tetra-
2018, 2022). The limit of detection (LOD) was cal- ethyl borate. Ethylated extracts were taken to a final
average recoveries varying from 88 to 101%. The Rand automated methyl-Hg system. Certified refer-
limit of quantification (LOQ) of the procedure was ence material (Tuna Fish-BCR-463) analyzed using
the LOD multiplied by 10 (USEPA, 2000) and was the same procedure yielded an average recovery of
1.0 ng.g−1. Concentration values obtained were not 82%. The average LOD was 0.02 ng.g−1 and LOQ
Exposure risk estimates considered total Hg concen- taminants, where a THQ < 1 means no potential risk
from 54.8% in P. squamosissimus (Hake) from the arid vegetation surrounding the Castanhão Reservoir
Castanhão Reservoir to 100% in S. rhombeus (Pira- create completely different environmental conditions
rhombeus feeds mainly on fish (> 80%), particu- concentration favoring predation, as hypothesized for
nile S. rhombeus are specialized on preying fish fins, the reservoir. The results (Table 1) showed that the
(100%, both in frequency and relative weight of food for the Hg and methyl-Hg contents, size-Hg relation-
tribute with 33.3% and 2.1% frequency, respectively, tive correlation with, whereas in the fluvial habitat
although these two items sum up only 2.7% in weight Hg concentrations increase with size (Fig. 2). Unfor-
from northeastern Brazil are in the same range of centrations were well over it (1,700 ng.g−1 w.w.)
presented significantly lower Hg concentrations than greater than 30 meals per month (Table 3). It is worth
wild fish from areas not affected by the fish farms, sumer group (Table 4) and was lower for children
Exposure estimates showed no significant risk of THQ < 1 means no potential risk of adverse effects
(Table 2). This result highlights the very low levels ering the high consumption (in a subsistence basis),
than the local per capita fish consumption (FCNE), the sive exposure to Hg (Tables 3 and 5). These results
subsistence consumption rate (FCsubs), which means Nogueira et al. (2025), which showed that exposure
Prochilodus rubrotaeniatus 4.86 1.19 4.14 4.73 5.65 1.38 4.82 5.50 2.82 6.89 2.40 2.74
Prochilodus rubrotaeniatus Rio Cocó 0.50 0.21 0.59 0.52 102 84 120 105
Table 4 Safe fish screening Consumer FCNE = 0.0245 FCWHO = 0.0285 FCSUBS = 0.142
Prochilodus rubrotaeniatus 0.05 0.12 0.04 0.05 0.06 0.14 0.05 0.06 0.28 0.69 0.24 0.27

Methods (brief)

niloticus). Overall, concentrations were very low and those of the same species but sampled in reservoirs.
ment in the form of metallic or elemental Hg (Hg0), matã (Prochilodus brevis), the Piau (Leporinus sp.),
Prochilodus argenteus (Fl) Curimata 6.2 ± 1.5 (3.2–8.4) 20.2 ± 4.5 (19.0–31.0) 9 94.5 (81.7–100) 5
(Piranha), individuals were sampled from reservoirs et al. (2023) that describes the continental aquatic
and rivers, while for Oreochromis niloticus (tilapia), fauna of the state of Ceará. Samples were collected
individuals were sampled from fish farms and open directly in rivers and reservoirs using traditional
reservoirs. Total Hg concentrations were quantified in fishery techniques. When available, samples were
cies. For two species (e.g. H. malabaricus (Traíra) samples were packaged and preserved in Styrofoam
and Leporinus friderici (Piau)), the sample size was with ice until they arrived at the laboratory for
with caution. Fish Hg concentrations are reported in treatment and digestion of the samples were previ-
Fish samples were obtained from major reser- by immersion for 24 h in a 10% Hg-free HCl solu-
variations. All sampling sites occur in the larger philized sample were weighed directly in metal-free
Species were acquired directly from fishermen and 200 °C for 30 min, after digestion, 1 mL of hydro-
the sampled watershed
vapor atomic absorption spectrophotometry (CV- For sample ethylation it was added to each tube
AAS, NIPON® NIC RA-3), after Hg reduction with 300 μL of a 2 mol.L−1 acetate buffer (pH 4.5), 30
NaBH4 (Lacerda et al., 2014; Moura & Lacerda, μL of each sample, and 50 μL of 1% sodium tetra-
2018, 2022). The limit of detection (LOD) was cal- ethyl borate. Ethylated extracts were taken to a final

Implications

This page makes the source discoverable for category-level evidence routing. Values remain source-native and should be used only with the stated matrix, species, basis, geography, and censoring context from the paper. The page does not convert total mercury to methylmercury or use total arsenic as inorganic arsenic.

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised