Majlesi et al. 2017 — Hg, Cd and Pb in muscle of three freshwater fish species, Khersan River, Iran

Majlesi and colleagues measured mercury (total Hg by hybrid-system AAS), cadmium, and lead (both by graphite-furnace AAS) in muscle tissue of three wild-caught freshwater fish species — rainbow trout (Oncorhynchus mykiss), pike (Esox lucius), and common carp (Cyprinus carpio) — landed by local fishermen on the Khersan River (largest tributary of the Karun River, southwest Iran) in May–June 2016. Mean muscle concentrations were lowest in rainbow trout (Hg 0.023, Cd 0.110, Pb 1.12 mg/kg) and highest in common carp (Hg 0.027, Cd 0.155, Pb 1.45 mg/kg), with pike intermediate (Hg 0.026, Cd 0.162, Pb 1.34 mg/kg). Mercury and cadmium were below the WHO, FAO, FDA, and EC fish-tissue limits in every species; lead exceeded the WHO (0.5 mg/kg) and EC Regulation 1881/2006 (1.0 mg/kg) limits in all three species and the NOAA (1.28 mg/kg) limit in pike and common carp. Lead and cadmium concentrations correlated negatively and significantly with fish weight (r = −0.517 for Pb, r = −0.568 for Cd; P < 0.05); length correlations were negative but non-significant. The authors attribute the elevated lead burden to urban, rural, and agricultural wastewater entering the river upstream of the sampling reach.

Key numbers

All muscle-tissue values are mean ± standard deviation in mg/kg (= µg/g). The paper does not state wet- vs dry-weight basis explicitly; the methods describe oven-drying samples at 65 °C to constant weight before taking the 0.5 g aliquot for wet-acid digestion, suggesting a dry-weight basis, but the authors compare the reported values directly to WHO/EC regulatory limits (which are wet-weight) without conversion. Basis flagged as ambiguous; see Verification notes.

Mean ± SD muscle concentrations by species (Table 1):

• Rainbow trout (Oncorhynchus mykiss): Hg 0.023 ± 0.004; Cd 0.110 ± 0.028; Pb 1.120 ± 0.130 mg/kg
• Pike (Esox lucius): Hg 0.026 ± 0.006; Cd 0.162 ± 0.023; Pb 1.340 ± 0.079 mg/kg
• Common carp (Cyprinus carpio): Hg 0.027 ± 0.005; Cd 0.155 ± 0.018; Pb 1.450 ± 0.086 mg/kg
• ANOVA: no inter-species difference for Hg (P > 0.05); trout significantly lower than pike and carp for Cd (P < 0.05); all three species differ from one another for Pb, with trout < pike < carp (P < 0.05); Pb in every species exceeded the WHO/EC limit (marked with * in Table 1).

Reference limits compared in Table 2 (mg/kg):

• FAO (2000): Hg 0.5; Cd 0.5; Pb 2
• WHO (2000): Hg 0.5; Cd 0.5; Pb 0.5
• ROPME (1999): Hg 0.5; Cd 0.07–0.75; Pb 0.01–1.28
• FDA (2001): Hg 0.5–1; Cd 4; Pb 1.7
• EC Regulation No. 1881/2006: Hg 0.5–1; Cd 0.5; Pb 1
• NOAA (2009): Hg 0.5; Cd 4; Pb 1.28

Fish biometrics (Table 3, mean ± SD):

• Pike: weight 666 ± 86 g; length 38 ± 7 cm
• Rainbow trout: weight 534 ± 112 g; length 34 ± 16 cm
• Common carp: weight 423 ± 123 g; length 26 ± 25 cm

Pearson correlations of muscle metal vs. fish size (Table 4):

• Length × Hg r = −0.246 (P = 0.393); Length × Cd r = −0.312 (P = 0.195); Length × Pb r = −0.283 (P = 0.165)
• Weight × Hg r = −0.256 (P = 0.275); Weight × Cd r = −0.568 (P = 0.032, significant); Weight × Pb r = −0.517 (P = 0.018, significant)

Discussion-section single-species means cited as a separate decomposition (p. 157):

• Pike Cd 0.052 mg/kg; common carp Cd 0.045 mg/kg; rainbow trout Pb 0.22 and 0.33 mg/kg (“respectively”). These values do not match the Table 1 means and appear in the discussion without clear sourcing; flagged as an internal inconsistency, the Table 1 values are taken as authoritative.

Methods (brief)

Cross-sectional sampling of trout, pike, and common carp by local fishermen on the Khersan River in May–June 2016. Fish were placed on ice, transported to the lab, length-and-weight measured (biometric board to 1 mm; digital scale to 0.01 g), muscle dissected, and stored frozen at −70 °C until analysis. Sample preparation: muscle dried in an oven at 65 °C for 120–150 min to constant weight; 0.5 g of dried tissue digested by a wet-acid method in a 250 mL flask with 25 mL concentrated H₂SO₄, 20 mL 7 M HNO₃, and 1 mL 2 % sodium molybdate (with boiling chips), followed by addition of 20 mL of 1:1 concentrated HNO₃:HClO₄ above the condenser; heated until white acid fumes ceased; cooled; 10 mL distilled water added; heated 100 min to a clear solution; brought to volume in a volumetric flask. Hg, Cd, and Pb were measured on a Perkin Elmer 4100ZL atomic absorption spectrometer — mercury via a hybrid-system approach with 5 mL of 5 % ammonium pyrrolidine carbamate added to 10 mL of digestate, mixed 20 min, 2 mL methyl isobutyl ketone added, mixed 30 min, centrifuged at 2500 g for 10 min to transfer analytes to the organic phase; cadmium and lead via graphite-furnace AAS with a palladium-matrix modifier; calibration via standards using Winlab 32 software and EDL cathode-ray source. Mercury is reported as total mercury (no methylmercury speciation). Statistical analysis in SPSS 19: one-way ANOVA for inter-species comparisons and Pearson correlation for metal-vs-size relationships; P < 0.05 significance threshold. No LODs, reference materials, recoveries, or replicate structure are reported.

Implications

Certification: contributes total-Hg, Cd, and Pb occurrence data for wild-caught freshwater fish (rainbow trout, pike, common carp) from a single Iranian river system, with Pb exceedances of WHO/EC limits in all three species and species-level differentiation in Cd and Pb (trout lowest). Useful for the freshwater-fish product category as one input on baseline Pb burden in rivers with significant urban/agricultural wastewater pressure; weak on speciation (tHg only) and reporting (no replicate-level disclosure, basis ambiguous, internal inconsistency in discussion-section values).

Courses: illustrates the inverse weight-metal relationship in wild freshwater fish (significant for Cd and Pb in this dataset), the routine practice of comparing fish-tissue values to multiple international limits with divergent stringency (WHO Pb 0.5 vs EC 1.0 vs FDA 1.7 vs FAO 2.0 mg/kg), and the importance of explicit wet/dry basis reporting.

App: total-Hg, Cd, and Pb point data for three named freshwater species from a single Iranian river, year 2016. Limited utility beyond regional occurrence input due to small per-species n and ambiguous reporting basis.

Wiki pages updated on ingest

• mercury
• cadmium
• lead
• freshwater-fish
• fish
• fish-freshwater

Verification notes

• Per-species sample size is not stated; methods text reads “Six fish species were collected” (paper measures only three species, likely an English-translation error). Recorded as null; sample_population field documents the ambiguity.
• Wet vs dry weight basis: not stated in the paper. Methods describe oven-drying to constant weight before the 0.5 g digestion aliquot is taken, which would yield dry-weight values; the authors then compare directly to WHO/EC limits (defined on wet weight) without explicit conversion. Reported here as the authors reported them, with the basis ambiguity flagged in Key numbers.
• Discussion-section paragraph on p. 157 reports Cd in pike and common carp as 0.052 and 0.045 mg/kg and Pb in rainbow trout as “0.22 and 0.33 mg/kg,” which do not match Table 1 means or any obvious decomposition; the Table 1 values are taken as authoritative and the discrepancy is flagged.
• DOI not printed in the PDF; the publisher (Shiraz University of Medical Sciences, ijns.sums.ac.ir) hosts the article at the access_url above. License terms are not displayed on the article landing page; treated as publisher-hosted with unspecified reuse terms.

Page history

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