Heavy Metal Index

Heavy metal content in farmed rainbow trout in relation to aquaculture area and feed pellets

Source access

Publication
Foods and Raw Materials
Year
2019
Authors
Majlesi M; Malekzadeh J; Berizi E; Akbartabar Toori M
Source type
peer reviewed
License
CC BY 4.0

Majlesi et al. 2019 — Heavy metals in farmed rainbow trout, Yasuj, Iran

Majlesi and colleagues measured mercury (total Hg by cold-vapour atomic absorption), cadmium, and lead in the muscle tissue of farmed rainbow trout (Oncorhynchus mykiss) sampled from six farms across three aquaculture sites in Yasuj, southwest Iran, during February–April 2018. The three sites differed by water-supply contamination probability: site A close to the spring source, site B downstream of cities and villages, and site C downstream of a rural area. Three commercial feed-pellet mixtures (I, II, III) used in the farms were also analysed. Overall mean muscle concentrations were 0.022 mg/kg Hg, 0.105 mg/kg Cd, and 1.07 mg/kg Pb (dry weight). Mercury and cadmium in edible tissue were below the maximum permissible limits set by the WHO, FDA, FAO, and EC; lead (1.07 mg/kg) exceeded the WHO limit (0.5 mg/kg) and the EC limit (1.0 mg/kg) but remained below the FDA (1.7 mg/kg) and FAO (2.0 mg/kg) limits. Fish from the lower-contamination spring-fed site A carried the lowest cadmium and lead concentrations. Cd and Pb concentrations correlated negatively and significantly with fish weight, and biomagnification factors for all three metals were below 1, indicating no biomagnification from feed to fish.

Key numbers

All fish-tissue values are means in mg/kg (= µg/g) on a dry-weight basis (samples oven-dried at 105 °C before digestion); feed-pellet values are mean ± SD in mg/kg.

Overall muscle-tissue means (Table 1):

  • Hg (tHg): 0.022 mg/kg
  • Cd: 0.105 mg/kg
  • Pb: 1.070 mg/kg

Site-specific muscle-tissue means (Fig. 2 / text):

  • Hg: site A 0.021 ± 0.0027; site B 0.023 ± 0.0026; site C 0.024 ± 0.0027 mg/kg (site A vs others not significant, P > 0.05)
  • Cd: site A 0.076; site B 0.119; site C 0.120 mg/kg (sites B and C significantly higher than A, P < 0.05)
  • Pb: site B highest at 1.171 mg/kg; sites C and A reported at 0.893 mg/kg (P < 0.05); fish from sites B and C significantly higher than site A

Maximum permissible limits compared (Table 1, µg/g):

  • WHO (2007): Hg 0.5, Cd 0.5, Pb 0.5
  • FDA (2001): Hg 0.05–1.0, Cd 4.0, Pb 1.7
  • FAO (2007): Hg 0.5, Cd 0.5, Pb 2.0
  • EC Reg. 1881/2006: Hg 0.5–1.0, Cd 0.5, Pb 1.0
  • Result: Hg and Cd below all limits; Pb (1.07) above WHO (0.5) and EC (1.0), below FDA (1.7) and FAO (2.0)

Commercial feed-pellet mixtures (Table 4, mean ± SD mg/kg):

  • Pellet I: Pb 5.8 ± 0.365, Cd 0.61 ± 0.093, Hg 0.075 ± 0.013
  • Pellet II: Pb 4.52 ± 0.259, Cd 0.54 ± 0.106, Hg 0.063 ± 0.018
  • Pellet III: Pb 4.15 ± 0.384, Cd 0.66 ± 0.076, Hg 0.071 ± 0.026
  • Pellet I Pb (5.8 mg/kg) exceeded the European Commission standard for feed
  • Fish fed pellet II: Hg 0.05, Cd 0.076, Pb 0.893 mg/kg; pellet III produced higher Hg and lower Cd in muscle vs pellets I and II (P < 0.05)

Health-risk parameters, this study (Table 3):

  • EDI (mg/kg bw/day): Hg 0.17×10⁻⁵, Cd 0.84×10⁻⁵, Pb 0.86×10⁻⁴
  • EWI (mg/kg bw/week): Hg 0.12×10⁻⁴, Cd 0.59×10⁻⁴, Pb 0.6×10⁻³
  • PTWI %: Hg 0.30, Cd 0.84, Pb 2.41
  • RfD (mg/kg bw/day): Hg 0.0003, Cd 0.001, Pb 0.004
  • THQ: Hg 0.0059, Cd 0.008, Pb 0.021; TTHQ 0.0349 — all THQ < 1 (no non-carcinogenic risk pattern; intake pattern Pb > Cd > Hg)

Biomagnification factors (Table 5; BMF = C_fish / C_feed):

  • Site A: Pb 0.15, Cd 0.11, Hg 0.28
  • Site B: Pb 0.25, Cd 0.22, Hg 0.36
  • Site C: Pb 0.37, Cd 0.22, Hg 0.38
  • All BMF < 1 (no biomagnification); pattern Hg > Pb > Cd

Size correlations (Table 7, Pearson):

  • Weight vs Pb r = −0.580 (P = 0.012, significant); vs Cd r = −0.519 (P = 0.027, significant); vs Hg r = −0.266 (P = 0.286, ns)
  • Length correlations non-significant for all three metals

Exposure parameters used: fish ingestion rate 25.2 g/day (Iran), average adult body weight 65 kg, exposure frequency 365 days/year, exposure duration 60 years, fresh-to-dry conversion factor 0.208.

Note: the per-group sample size is reported inconsistently across the paper (text states five fish per farm / 10 per site; Fig. 2 caption states five fish per group; Fig. 3 caption states six fish per group; Table 6 caption states eight fish per group). The total fish sample is ~30. This is a reporting inconsistency in group sizes only; it does not affect the reported metal concentrations.

Methods (brief)

Rainbow trout (Oncorhynchus mykiss) collected Feb–April 2018 from six raceway farms across three sites in Yasuj (site A near spring; site B downstream of cities/villages; site C downstream of a rural area). Fillets and feed pellets oven-dried at 105 °C for 1 h, then microwave-digested (MARSXpress, CEM) in 6 mL concentrated HNO₃ (Romil Ltd.) plus 2 mL H₂O₂ (Merck), filtered and made up to 50 mL with ultrapure water. Hg, Cd, and Pb were determined by cold-vapour atomic absorption with a Perkin Elmer 4100 (FIMS 400, Perkin Elmer Inc.); blanks processed to control contamination. Mercury reported as total mercury (no methylmercury speciation). Statistical analysis in SPSS 19.0: one-way ANOVA with Duncan’s post-hoc test, and Pearson correlation for metal-vs-size relationships; P < 0.05 significance. Human-health risk assessed via EDI, EWI, PTWI %, target hazard quotient (THQ), and total THQ; biomagnification factor (BMF) computed as fish-to-feed concentration ratio.

Implications

Certification: provides total-Hg, Cd, and Pb occurrence data (dry weight) for farmed freshwater rainbow trout from an Iranian production region, including site-level variation tied to water-supply contamination and feed-pellet metal content. Lead in muscle (1.07 mg/kg dry weight) exceeded WHO and EC limits while Hg and Cd remained below all compared limits, relevant to provenance and feed-quality considerations for farmed freshwater fish.

Courses: useful for illustrating how aquaculture water source and commercial feed composition jointly drive heavy-metal accumulation in farmed fish, and for the negative metal-vs-fish-size relationship and sub-1 biomagnification factor concepts.

App: total-Hg, Cd, and Pb data for farmed freshwater rainbow trout contribute to species- and product-level contamination profiles; values are dry-weight and from a single Iranian region.

Wiki pages updated on ingest

Verification notes

Fresh-context audit subagent (2026-05-30) verdict REVISE; all five checks were clean except minor Check 2 concerns, resolved as follows:

  • Audit flagged the per-group sample-size note as incomplete for omitting Fig. 3’s “six fish per group”; verified against PDF p. 5 (Fig. 3 caption) — correct, added Fig. 3’s six-fish count to the reconciliation note.
  • Audit flagged matrices fish-tissue as not enumerated in the four-list taxonomy snapshot; verified — fish-tissue is an established bare-string matrices value used on 21 existing source pages (e.g. zolfaghari2018, melnyk2021). False positive; no change.
  • Audit flagged WHO in jurisdictions: as loose; verified — WHO is an established jurisdictions value across the corpus (e.g. zolfaghari2018, meng2023). False positive; no change.
  • Numerical fidelity (Tables 1–7), speciation (tHg, no MeHg), Methods, Part 12 brand firewall, and Part 2 wiki/HMTc firewall all confirmed clean against the source PDF.

Page history

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