Witczak and colleagues bought 11 fish species from retail in Szczecin, Poland and measured 12 elements by ICP-AES, GF-AAS, and CV-AAS in muscle tissue. Six species were imported, primarily from China: Nile tilapia, panga, Alaska pollock, North-Pacific hake, yellowfin sole, and Pacific cod (Gadus macrocephalus). Five species were domestic: flounder, mackerel, rainbow trout, salmon, and bream. The study found that all species had total hazard quotients well below 1, indicating no acute non-carcinogenic risk from typical consumption. All imported fish had significantly more cadmium than the Polish domestic species.
Key numbers
Pacific cod (Gadus macrocephalus, imported from China, n=130 samples from 13 batches), muscle tissue, wet weight:
- Lead: Table 1, estimated 11 µg/kg (range 10 to 14) based on Table 1 continuation; Table 3 EDI row Pacific cod lead (Pb) = 0.005.
- Cadmium: 10 ± 6 µg/kg (range 5 to 18), Table 1 continuation.
- Total mercury: 31 ± 9 µg/kg (range 22 to 43), Table 1 continuation.
- Nickel: 90 ± 40 µg/kg (range 50 to 140), Table 1.
- Zinc: Table 1 shows the range 2.34 to 3.03 mg/kg (2,340 to 3,030 µg/kg).
- Cadmium percent of Tolerable Weekly Intake (TWI at 2.5 µg/kg body weight per week, EFSA): 1.39 ± 0.87% per 100 g portion (Table 4).
- Cadmium percent of Provisional Tolerable Monthly Intake (PTMI): 0.59 ± 0.37% (Table 4).
- Lead percent of BMDL0.1: 0.36 ± 0.06% (Table 4).
- Total Target Hazard Quotient (TTHQ) for Pacific cod was well below 1 (the highest TTHQ across all species was 0.169, for Nile tilapia) (Table 3, Figure 1).
Cross-species pattern: “in general, the levels of toxic elements decreased according to the following sequence: arsenic (As) > mercury (Hg) > cadmium (Cd) > Pb; however, the values of lead were slightly higher than those of cadmium in cod” (abstract). All imported species carried significantly more cadmium than domestic Polish species.
Methods (brief)
Muscle samples (1 g) were ground, mineralized in a CEM microwave oven with 65% nitric acid, filtered, and diluted to 25 g with deionized water. Zinc, nickel, iron, manganese, chromium, copper, aluminum, and lithium were measured by ICP-AES (Jobin Yvon JY-24). Arsenic was measured by ICP-AES with hydride generation. Cadmium and lead were measured by GF-AAS with Zeeman correction (Perkin Elmer 4110 ZL). Total mercury was measured by CV-AAS (Bacharach Coleman MAS-50). Three analytical replicates per sample. The MODAS-3 certified reference material was used for quality verification. Recovery ranged from 96.9% nickel (Ni) to 99.1% (Cu); LODs: Pb 0.8 µg/kg, Cd 0.31 µg/kg, Hg 1.6 µg/kg, As 0.3 µg/kg (Table 6). All measurements are wet weight of raw frozen muscle tissue.
Evidence fitness
Concentrations are for the specific commercial forms tested: frozen fillets as received in retail, covering 13 randomly selected batches of Pacific cod. The Pacific cod was imported from China (species Gadus macrocephalus). Results are not directly applicable to wild-caught Atlantic cod (Gadus morhua) or Mediterranean cod species. Arsenic was measured as total arsenic, not speciated; mercury was total mercury, not methylmercury. The column layout in Table 1 is complex in the published PDF (many species across two continuation tables) and some cross-species comparisons require care. Health risk metrics (EDI, THQ, TTHQ, TWI, BMDL) were computed assuming 100 g per day fish consumption and 70 kg body weight.
Limitations
Pacific cod sample scope is 13 batches of commercial imports, all from China; it does not represent global Pacific cod contamination profiles. The fish were purchased as frozen; thawing and processing history before purchase are unknown. Arsenic speciation is absent; in marine fish, organic arsenobetaine typically predominates but was not measured here. The batch-level design does not allow calculation of a population p95 for most analytes from published statistics.
Related evidence
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