Lozano-Bilbao et al. 2023 — Metals in five tuna species from the Canary Islands

Lozano-Bilbao and colleagues measured Al, Cd, Cr, Cu, Fe, Li, Pb, and Zn by inductively coupled plasma optical emission spectrometry (ICP-OES) in muscle of 75 tuna specimens (15 each of Acanthocybium solandri, Katsuwonus pelamis, Thunnus albacares, Thunnus obesus, and Thunnus thynnus) caught by the Canarian fishing fleet in the eastern Atlantic in 2021. Thunnus thynnus, the largest and longest-lived species in the panel, presented the highest mean concentrations of every metal measured, including a mean Fe of 137.8 ± 100.9 mg/kg (about 8 to 28 times the mean of the other species), a mean Cd of 0.051 ± 0.039 mg/kg, and a mean Pb of 0.280 ± 0.188 mg/kg. The authors report that 75% of T. thynnus specimens exceeded the 0.05 mg/kg cadmium limit they attribute to Regulation (CE) No 420/2011 for fish meat, and 40% of T. thynnus specimens exceeded the 0.30 mg/kg lead limit attributed to Regulation (EC) No 1881/2006 for fish muscle meat; on those grounds they recommend that T. thynnus from this region be further monitored before commercialization. Mercury was not analyzed in this study (sample tissue was reported as insufficient, and Hg plus isotopes were deferred to later work).

Key numbers

Wet-weight muscle concentrations (Table 2, mg/kg w.w.; n = 15 per species).

• Acanthocybium solandri (wahoo):

  • Al: mean 0.515 ± 0.214; min 0.326; max 0.949 mg/kg.
  • Cd: mean 0.007 ± 0.003; min 0.000; max 0.010 mg/kg.
  • Cr (total): mean 0.118 ± 0.065; min 0.055; max 0.218 mg/kg.
  • Cu: mean 0.301 ± 0.074; min 0.195; max 0.395 mg/kg.
  • Fe: mean 4.639 ± 1.489; min 2.398; max 6.616 mg/kg.
  • Li: mean 0.009 ± 0.003; min 0.006; max 0.016 mg/kg.
  • Pb: mean 0.009 ± 0.003; min 0.006; max 0.014 mg/kg.
  • Zn: mean 9.192 ± 7.357; min 4.171; max 25.42 mg/kg.

• Katsuwonus pelamis (skipjack tuna):

  • Al: mean 4.743 ± 0.450; min 4.161; max 5.039 mg/kg.
  • Cd: mean 0.014 ± 0.004; min 0.010; max 0.019 mg/kg.
  • Cr (total): mean 0.049 ± 0.011; min 0.034; max 0.056 mg/kg.
  • Cu: mean 1.207 ± 0.392; min 0.702; max 1.490 mg/kg.
  • Fe: mean 16.88 ± 7.124; min 7.705; max 21.97 mg/kg.
  • Li: mean 0.427 ± 0.080; min 0.324; max 0.483 mg/kg.
  • Pb: mean 0.006 ± 0.002; min 0.003; max 0.007 mg/kg.
  • Zn: mean 5.057 ± 0.486; min 4.430; max 5.376 mg/kg.

• Thunnus albacares (yellowfin tuna):

  • Al: mean 0.641 ± 0.261; min 0.283; max 0.959 mg/kg.
  • Cd: mean 0.009 ± 0.003; min 0.006; max 0.017 mg/kg.
  • Cr (total): mean 0.190 ± 0.118; min 0.065; max 0.360 mg/kg.
  • Cu: mean 0.485 ± 0.224; min 0.282; max 0.929 mg/kg.
  • Fe: mean 16.26 ± 8.157; min 6.330; max 29.94 mg/kg.
  • Li: mean 0.011 ± 0.005; min 0.006; max 0.020 mg/kg.
  • Pb: mean 0.012 ± 0.004; min 0.005; max 0.017 mg/kg.
  • Zn: mean 22.01 ± 17.20; min 3.920; max 50.86 mg/kg.

• Thunnus obesus (bigeye tuna):

  • Al: mean 9.361 ± 2.915; min 6.006; max 13.96 mg/kg.
  • Cd: mean 0.006 ± 0.003; min 0.004; max 0.014 mg/kg.
  • Cr (total): mean 0.127 ± 0.044; min 0.095; max 0.240 mg/kg.
  • Cu: mean 0.640 ± 0.148; min 0.453; max 0.866 mg/kg.
  • Fe: mean 11.99 ± 3.939; min 6.761; max 19.23 mg/kg.
  • Li: mean 1.180 ± 0.873; min 0.211; max 3.177 mg/kg.
  • Pb: mean 0.010 ± 0.004; min 0.005; max 0.018 mg/kg.
  • Zn: mean 5.159 ± 0.545; min 4.434; max 6.369 mg/kg.

• Thunnus thynnus (Atlantic bluefin tuna):

  • Al: mean 19.56 ± 11.33; min 6.265; max 44.23 mg/kg.
  • Cd: mean 0.051 ± 0.039; min 0.009; max 0.139 mg/kg.
  • Cr (total): mean 0.913 ± 1.263; min 0.209; max 5.396 mg/kg.
  • Cu: mean 1.526 ± 1.114; min 0.520; max 4.539 mg/kg.
  • Fe: mean 137.8 ± 100.9; min 21.24; max 323.4 mg/kg.
  • Li: mean 1.033 ± 0.890; min 0.000; max 3.449 mg/kg.
  • Pb: mean 0.280 ± 0.188; min 0.062; max 0.683 mg/kg.
  • Zn: mean 14.75 ± 12.02; min 1.904; max 44.47 mg/kg.

Mean total length per species (Section 3): A. solandri 105 ± 12 cm; K. pelamis 76 ± 0.13 cm; T. albacares 175 ± 19 cm; T. obesus 192 ± 20 cm; T. thynnus 235 ± 41 cm (biometric data reported for half of the T. thynnus specimens, since many were chosen by local fishermen).

Method detection limits (Table 1, mg/L) and emission wavelengths (nm): Al 0.004 (167.0 nm); Cd 0.0003 (226.5 nm); Cr 0.003 (267.7 nm); Cu 0.004 (327.3 nm); Fe 0.003 (259.9 nm); Li 0.005 (670.8 nm); Pb 0.0003 (220.3 nm); Zn 0.002 (206.2 nm). Limits of quantification (mg/L): Al 0.012; Cd 0.001; Cr 0.008; Cu 0.012; Fe 0.009; Li 0.013; Pb 0.001; Zn 0.007.

Risk assessment (Table 6; adult body weight assumed 70 kg; fish consumption set at 130 g/day, with three 250 g servings per week used as the AESAN reference scenario for the EDI/MoS calculation):

• Aluminium reference 1 mg/kg/week. EDI (mg) K. pelamis 0.5, T. obesus 1, A. solandri 0.05, T. albacares 0.5, T. thynnus 2.09. Margin of safety (MoS) K. pelamis 0.05, T. obesus 0.1, A. solandri 0.005, T. albacares 0.05, T. thynnus 0.21. Chronic daily intake dose (CDI, mg/kg/day) K. pelamis 0.34, T. obesus 0.67, A. solandri 0.03, T. albacares 0.046, T. thynnus 1.4 (the only species above the reference for Al).
• Cadmium reference 2.5 µg/kg/week. EDI (mg) K. pelamis 0.0014, T. obesus 0.0006, A. solandri 0.0007, T. albacares 0.001, T. thynnus 0.005. MoS K. pelamis 0.07, T. obesus 0.03, A. solandri 0.03, T. albacares 0.004, T. thynnus 0.27. CDI K. pelamis 0.2 × 10⁻⁴, T. obesus 0.1 × 10⁻⁴, A. solandri 0.1 × 10⁻⁴, T. albacares 0.15 × 10⁻⁴, T. thynnus 0.7 × 10⁻³ mg/kg/day.
• Lead reference 0.5 µg/kg/day. EDI (mg) K. pelamis 0.0006, T. obesus 0.001, A. solandri 0.001, T. albacares 0.001, T. thynnus 0.03. MoS K. pelamis 0.01, T. obesus 0.03, A. solandri 0.02, T. albacares 0.03, T. thynnus 0.85. CDI K. pelamis 0.25 × 10⁻⁴, T. obesus 0.21 × 10⁻⁴, A. solandri 0.2 × 10⁻⁴, T. albacares 0.25 × 10⁻⁴, T. thynnus 0.02 mg/kg/day.

Regulatory comparisons reported by the authors:

• The authors cite Regulation (CE) No 420/2011 as setting a 0.05 mg/kg fresh-weight cadmium limit for fish meat. Against that limit, T. thynnus mean Cd (0.051 mg/kg) is at the limit and 75% of T. thynnus specimens were reported as exceeding it; the other four species’ means were all below.
• The authors then cite “Directive 2006/66/EC” as establishing a 0.3 mg/kg total cadmium limit for tuna; against that limit, T. thynnus mean Cd (0.051 mg/kg) was below.
• The authors cite Regulation (EC) No 1881/2006 as setting a 0.30 mg/kg fresh-weight lead limit for fish meat. Against that limit, in Section 3 of the discussion the authors report “none of the species exceeded the maximum permissible concentration of 0.30 mg/kg,” while the abstract and conclusions report that “40% of the studied specimens of [T. thynnus] exceeded the legislated values for the concentration of Pb in oily fish meat.” Both statements can be reconciled by reading the discussion sentence as a species-mean comparison (T. thynnus mean Pb 0.280 < 0.30 mg/kg) and the abstract sentence as a per-specimen tally (40% of the 15 T. thynnus individuals exceeded 0.30 mg/kg; maximum 0.683 mg/kg). See verification notes.

Stable-isotope context for trophic interpretation (Table 3, drawn from external references, not measured in this study): δ¹³C (‰) A. solandri −16.71 ± 0.48, K. pelamis −17.6 ± 0.4, T. albacares −17.06 ± 0.34, T. obesus −17.6 to −16.5, T. thynnus −17.75. δ¹⁵N (‰) A. solandri 11.18 ± 1.04, K. pelamis 9.7 ± 1.5, T. albacares 10.46 ± 0.34, T. obesus 11.6 to 14.2, T. thynnus 14.5.

Methods (brief)

Seventy-five tuna specimens (Acanthocybium solandri, Katsuwonus pelamis, Thunnus albacares, Thunnus obesus, Thunnus thynnus; 15 of each) were caught by the Canarian fishing fleet in 2021. Total length was recorded for each specimen, and species identification was confirmed by marine fishery biologists of the Canary Islands.

Ten grams of muscle were taken from each specimen and homogenized. Samples were dried in an oven at 70 °C for 24 h, then incinerated in a muffle oven for 48 h at 450 ± 25 °C until white ash was obtained. When total mineralization was not achieved on the first pass (white or greyish-white ashes), 65% HNO₃ was added in a fume hood, the sample was evaporated on a heating plate at 70 to 90 °C, and reincineration at 450 ± 25 °C was performed until white ashes were obtained. Metal content was determined by inductively coupled plasma optical emission spectrometry (ICP-OES), with quality-control solutions analyzed every ten samples; precision was evaluated against the international standard reference materials DORM-1 and DORM-5 (National Research Council of Canada). All data are presented in mg/kg wet weight. The metals analyzed were Al, Cd, Cr, Cu, Fe, Li, Pb, and Zn (eight elements as listed in Table 1 and reported in Table 2; the abstract additionally lists Ni but Ni does not appear in Table 1 or Table 2 — see verification notes). The authors state that because little sample tissue was available, Hg and isotope analyses were deferred to later studies. Chromium was reported as total Cr without speciation into Cr(III) and Cr(VI).

Statistical analysis: a permutational multivariate analysis of variance (PERMANOVA) was performed with Euclidean distances using a unidirectional design with the fixed factor “species” (five levels). Principal coordinates analysis (PCoA) on square-root-transformed data was used to visualize multivariate separation, with 9999 permutations for pairwise comparisons and α = 0.05. Stable-isotope data (δ¹³C and δ¹⁵N) used in the trophic-transfer discussion (Table 3, Figure 3) were drawn from published studies of the same species in the Atlantic Ocean, not measured in this paper.

Risk assessment followed the AESAN (Spanish Agency for Food Safety and Nutrition) recommendations on fish consumption — three servings of 250 g per week for a 70 kg adult — and used the Acceptable Daily Intake formulation ADI = NOAEL/F, the Estimated Daily Intake formulation EDI = (C_metal × Cons) / Bw (with C_metal in µg/kg wet weight, Cons the day-to-day consumption in g/day, and Bw the body weight in kg), and the Margin of Safety MoS = EDI/ADI. The chronic daily intake dose was computed as CDI = (C × IR × EF × ED) / (BW × AT) with IR = 104.7 g/day, EF = 156 days/year (three times per week), ED = 30 years, BW = 70 kg, and AT = ED × 365 days/year. Mean daily fish consumption was set at 130 g/day. Fixed-ADI metals were Al, Cd, and Pb. The reference values reported in Table 6 are Al 1 mg/kg/week, Cd 2.5 µg/kg/week, and Pb 0.5 µg/kg/day.

The study was funded by the FoodE H2020 grant (Agreement 862663) and the Tuna Analysis Research Contract with the Government of the Canary Islands, Fishing General Direction (number A21100059); the authors declared no conflict of interest.

Implications

• Certification (HMTc): The paper contributes occurrence data for fresh marine predatory fish in the eastern Atlantic, with per-species, per-metal means, SDs, and ranges across five tuna species (n = 15 each). The Cd and Pb distributions for Thunnus thynnus muscle (mean 0.051 mg/kg Cd, mean 0.280 mg/kg Pb, max 0.683 mg/kg Pb) are the most pooling-relevant figures because the authors report 75% Cd-exceedance and 40% Pb-exceedance against EU fish-muscle limits in this species.
• Courses: Useful as a case study for QA/regulatory affairs teams on species-level biomagnification at the top of a pelagic food web, with a paired example of how a species’ size, age, and trophic position translate into category-defining metal loads (T. thynnus relative to the other four species) and into a per-specimen exceedance pattern (40% of individuals above the Pb limit, with the species mean below it) that a single-sample COA would not reveal.
• App: Adds Atlantic-Canary-Islands occurrence figures for tuna for Al, Cd, Cr, Cu, Fe, Li, Pb, and Zn (mercury not measured). Adds entries to fish and seafood at the marine predatory level.

Wiki pages this source may touch

• fish-marine-predatory — primary product surface; direct evidence on tuna species from the eastern Atlantic.
• fresh-fish — broader product context.
• seafood — broader product context.
• tuna — primary ingredient surface.
• fish — broader ingredient context.
• seafood — broader ingredient context.
• aluminum — Al occurrence in muscle of five tuna species.
• cadmium — Cd occurrence; per-species means and ranges; 75% T. thynnus Cd-exceedance against the 0.05 mg/kg limit the authors attribute to Regulation (CE) No 420/2011.
• chromium — total Cr occurrence (no Cr(VI) speciation).
• copper — Cu occurrence; the prose value “1526 ± 1114 mg/kg” for T. thynnus Cu on page 7 is a decimal-shift typo for the Table 2 value 1.526 ± 1.114 mg/kg (see verification notes).
• iron — Fe occurrence; T. thynnus mean 137.8 mg/kg ≈ 8 to 28× the other species.
• lithium — Li occurrence in tuna muscle, with T. thynnus and T. obesus markedly higher than the other species.
• lead — Pb occurrence; 40% of T. thynnus specimens above the 0.30 mg/kg limit the authors attribute to Regulation (EC) No 1881/2006.
• zinc — Zn occurrence.
• eu-1881-2006-contaminants-superseded — cited as the source of the 0.30 mg/kg fish-muscle Pb limit used for the exceedance tally.

Verification notes

• Paper-internal inconsistency on the metal panel: the abstract lists “Al, Cd, Cr, Cu, Fe, Li, Ni, Pb and Zn” as the metals determined by ICP-OES, but Table 1 (method LODs/LOQs) and Table 2 (results) list only eight metals (Al, Cd, Cr, Cu, Fe, Li, Pb, Zn) with no Ni row in either table. The metals frontmatter and the body of this source page follow Table 1/Table 2 (the actual measured set, eight metals); the abstract’s mention of Ni is treated as a manuscript error and is not propagated.
• Paper-internal inconsistency on T. thynnus Cu units: page 7 prose states “T. thynnus is also the species with the highest concentration of Cu, with 1526 ± 1114 mg/kg,” but Table 2 reports T. thynnus Cu as mean 1.526 ± 1.114 mg/kg. The Table 2 value is taken as authoritative (consistent with the per-species panel and with the maximum 4.539 mg/kg in Table 2); the prose figure is a decimal-shift typo.
• Apparent regulatory miscitation on cadmium: the discussion (page 10) cites “Directive 2006/66/EC” as establishing a 0.3 mg/kg total cadmium limit for tuna. Directive 2006/66/EC is the EU Batteries Directive and does not set a 0.3 mg/kg cadmium limit for tuna meat. The page reports the citation as the authors wrote it; the substantive Cd comparison the authors make against a 0.05 mg/kg fish-meat limit is consistent with Regulation (EC) No 1881/2006 as amended by Regulation (CE) No 420/2011, which is the contemporaneous EU framework for cadmium in fish at the time of the study. Slug eu-1881-2006-contaminants-superseded is included in the routing pointer for the Pb exceedance discussion; no slug is added for “Directive 2006/66/EC” because it is not the relevant instrument.
• Apparent paper-internal inconsistency on Pb exceedance: page 7 discussion reads “Regarding Pb, … none of the species exceeded the maximum permissible concentration of 0.30 mg/kg of fresh weight for fish meat”; the abstract and conclusions report that 40% of T. thynnus specimens exceeded 0.30 mg/kg. Reconciliation: T. thynnus species-mean Pb (0.280 mg/kg) is below 0.30; the 40% figure refers to a per-specimen tally, with the species maximum 0.683 mg/kg from Table 2 documenting that individual specimens are above the limit. Both readings are reported on the page.
• Mercury is not in the dataset: the authors explicitly note (page 3) that because little sample tissue was available, “the analysis of Hg and isotopes [was left] for later studies.” This source therefore does not contribute to mercury occurrence on the metal page for these species.
• Chromium is total Cr (no Cr(VI) speciation); Cr is used in the metals frontmatter, not Cr-VI.
• All values are wet-weight (mg/kg w.w.) per the authors’ Section 2.1; no dry-weight conversion is applied here.

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