Overview
This MDPI Biology paper measured nickel in three locally caught seafood types from Peninsular Malaysia — 19 commercial marine fish species from Setiu (Terengganu) on the east coast, the mangrove snail Cerithidea obtusa pooled from 17 west-coast mangrove sites, and the cockle Anadara granosa pooled from 12 west-coast intertidal sites — and compared the resulting human-health risk profile (estimated daily intake, target hazard quotient, and estimated weekly intake) to a 40-site green-lipped mussel Perna viridis dataset that the same group had previously published. Nickel was determined by air-acetylene flame atomic absorption spectrometry on nitric-acid digests of dried-and-ground tissue; DOLT-3 (dogfish liver) certified reference material was recovered at 88.8–119%. Wet-weight nickel (Ni) ranged 0.11–0.90 mg/kg in the fish muscle, 0.40–6.14 mg/kg in the snail total soft tissue, and 0.15–3.23 mg/kg in the cockle total soft tissue, with all three datasets falling well below the only Ni regulatory ceiling the authors could find (the US FDA molluscan-shellfish action level of 80 mg/kg wet weight). Target hazard quotients for nickel were <1.00 for average and high-level consumers across all three newly measured seafood types; only the high-level mussel consumers of the P. viridis dataset from the polluted Kampung Pasir Puteh sites had THQ values >1.00 in the cited comparison data.
Key numbers
All concentrations in mg/kg (Ni). DW = dry weight as analysed; WW = wet weight via the species-specific conversion factor (cockle 0.20; snail 0.24; fish factor varies per species, supplied in Table 1 of the supplementary materials). EDI in µg/kg-bw/day. THQ dimensionless. EWI = MWI (mean weekly intake) in mg/week per consumer for fish (0.70 kg/week average; 1.40 kg/week high-level) and mollusc (0.28 kg/week average; 0.56 kg/week high-level) intake rates. Risk-assessment basis: 62 kg adult Malaysian, oral reference dose (ORD) 20 µg/kg/day (US EPA), PTWI 91 µg/kg-bw/week (recalculated from EFSA TDI 13 µg/kg-bw/day) = 5642 µg/week (Table 1, p. 7 of 20).
| Dataset | N | DW range (mg/kg) | DW mean | WW range (mg/kg) | WW mean | EDI avg range (µg/kg/day) | EDI high range | THQ avg | THQ high | EWI avg (mg/week) | EWI high (mg/week) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Marine fish (19 species, Setiu) | 19 | 0.48–3.84 | 1.45 | 0.11–0.90 | 0.32 | 0.18–1.45 | 0.35–2.90 | 0.01–0.07 | 0.02–0.15 | 1.24–10.2 µg/wk (means in µg) | 2.48–20.3 µg/wk |
| Snail Cerithidea obtusa (17 sites) | 17 | 1.67–25.6 | 10.9 | 0.40–6.14 | 2.64 | 0.26–3.96 | 0.52–7.92 | 0.01–0.20 | 0.03–0.40 | 1.81–27.7 µg/wk | 3.61–55.46 µg/wk |
| Cockle Anadara granosa (12 sites) | 12 | 0.74–16.2 | 3.88 | 0.15–3.23 | 0.78 | 0.10–2.08 | 0.19–4.17 | 0.005–0.10 | 0.01–0.21 | 0.68–14.6 µg/wk | 1.35–29.2 µg/wk |
| Mussel Perna viridis (40 sites, cited from Yap et al. 2016) | 40 | 1.94–114 | 18.9 | 0.33–19.3 | 3.20 | 0.21–12.5 | 0.43–24.9 | 0.01–0.62 | 0.02–1.25 | 1.49–87.2 µg/wk | 2.98–174 µg/wk |
The EWI columns above are reported in the paper as µg/week per kg consumption fraction in Table 1; the body-text “mg/week” notation on p. 14 of 20 refers to per-consumer mean weekly intake (MWI) for the average-level (0.70 kg/week fish, 0.28 kg/week mollusc) and high-level (1.40 kg/week fish, 0.56 kg/week mollusc) consumption rates. The reported MWI ranges as percentages of the 5642 µg/week recalculated PTWI are:
- Fish: average-level 1.36–11.2%; high-level 2.73–22.3%.
- Snail C. obtusa: average-level 1.99–30.5%; high-level 3.97–60.9%.
- Cockle A. granosa: average-level 0.74–16.0%; high-level 1.49–32.1%.
- Mussel P. viridis (cited): average-level 1.64–95.8%; high-level 3.28–192% — only this cited mussel dataset exceeds the recalculated PTWI for some high-level consumers.
The amount of each seafood that a 62-kg adult would need to consume per week to reach the 5642 µg/week recalculated PTWI is reported as: 6.27–51.3 kg for Setiu fish, 0.92–14.1 kg for snails, 1.75–37.6 kg for cockles, and 0.29–17.0 kg for mussels (p. 14 of 20).
Highest and lowest Ni species in the fish dataset (p. 9 of 20): Atule maculatus highest (3.84 mg/kg DW) and Megalaspis cordyla lowest (0.48 mg/kg DW). Inter-species ordering by mean Ni was A. maculatus > T. lepturus > A. indica > N. hexodon > A. chacunda > others.
Regulatory comparator (p. 8 of 20): US FDA/CFSAN molluscan-shellfish action level for Ni = 80 mg/kg WW. All measured fish, snail, cockle, and mussel WW values are at least an order of magnitude below this ceiling.
Methods
Sample preparation: fish were weighed and length-measured at landing (10–20 g of dorsal muscle removed per fish); 20 snails (shell length 32.7–49.3 mm) per site and 20 cockles (shell length 23.6–33.9 mm) per site were pooled by total soft tissue. All samples were oven-dried at 60 °C for 72 h to constant weight, then ground with an agate pestle and mortar.
Digestion: 0.50 g of homogenized dry sample + 5.0 mL concentrated HNO3 (AnalaR grade, BDH 69%) in a hot-block digester at 40 °C for 1 h followed by 140 °C for 3 h. Digests were diluted with double-distilled water and filtered through Whatman No. 1 into acid-washed pillboxes.
Instrument: air-acetylene Flame Atomic Absorption Spectrometer (FAAS), Thermo Fisher Scientific ICE 3000 series AA (USA), Ni detection limit 0.010 mg/L.
QA-QC: certified reference material DOLT-3 (dogfish liver, National Research Council Canada) recovered 88.8–119%; all glassware was soaked overnight in 10% nitric acid before use; procedure blanks and sample triplicates were run for quality control.
Wet-weight conversion: species-specific DW→WW conversion factors were applied — 0.24 for C. obtusa and 0.20 for A. granosa — with the fish conversion factor reported per-species in Table 1 of the supplementary materials.
Health-risk assessment math:
- EDI = (Mc × CR)/bw, where Mc = metal concentration on WW basis (mg/kg), CR = consumption rate (g/person/day), bw = 62 kg adult Malaysian. CR values: fish 100 g/day (average), 200 g/day (high); mollusc 40 g/day (average), 80 g/day (high).
- THQ = EDI/ORD; ORD for Ni = 20 µg/kg-bw/day (US EPA regional screening level).
- EWI = EDI × 7 days.
- Recalculated PTWI for Ni: the paper notes EFSA has not established a PTWI for Ni; the authors derive PTWI = 91 µg/kg-bw/week from the EFSA TDI of 13 µg/kg-bw/day (13 × 7 = 91), giving 5642 µg/week for a 62-kg adult.
- Comparison against the FDA/CFSAN molluscan-shellfish action level of 80 mg/kg WW.
Speciation
No speciation. The paper reports total nickel only. The introduction notes that the +2 oxidation state (Ni²⁺) is the most common species in environmental and biological systems but does not separate oxidation states analytically.
Quality control
- CRM DOLT-3 recovery 88.8–119% — at the upper edge of typical acceptance bounds (75–125% is the common rule of thumb); not flagged as out-of-range but worth noting that the upper-end recoveries imply some matrix-driven enhancement.
- FAAS detection limit Ni 0.010 mg/L; per-sample LOD on WW basis is not stated as a single number because of the per-species conversion factors.
- Sample triplicates and procedure blanks run; no per-sample RSD reported in the paper text or in the Table 1 summary.
Implications
The paper records that for the three newly measured Peninsular Malaysian seafood types, Ni concentrations on a wet-weight basis are at least an order of magnitude below the only seafood-specific Ni regulatory ceiling the authors could identify (US FDA molluscan-shellfish action level of 80 mg/kg WW), and that the corresponding target hazard quotients are below 1.00 for both average and high-level consumers — i.e., no non-carcinogenic risk from Ni at the modelled Malaysian consumption rates. The only exceedance the paper documents is in the cited Perna viridis mussel dataset from polluted Kampung Pasir Puteh sites for high-level consumers (THQ up to 1.25); that exceedance is not from the newly measured data in this study but from a prior 40-site survey by the same group.
The per-species and per-site detail in the supplementary tables (Tables S4–S7, referenced but not present in the truncated PDF read here) is what makes the fish data potentially useful for any future per-species pooled-percentile work on marine non-predatory finfish; the supplementary materials should be retrieved separately if that synthesis is undertaken. The single-estuary fish design (Setiu, 19 species, August 2016 – February 2017, three replicates per species) is a constraint on inferring Peninsular Malaysian fish-as-marketed Ni; the snail and cockle datasets are more spatially distributed but pool across 3–4 sampling years.
This paper is also useful as a worked example of the EFSA-TDI-to-PTWI recalculation move (multiplying the daily TDI of 13 µg/kg-bw by 7 to get a weekly comparator of 91 µg/kg-bw/week) that other Ni-in-seafood risk assessments in the corpus apply differently; documenting this paper’s choice supports the regulatory-page work on regulations/efsa-nickel-tdi.
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