Risk assessment of heavy metals in tuna from Japanese restaurants in the Republic of Korea

**Background:** The Republic of Korea has high per capita consumption of fishery products (69.9 kg in 2019), and tuna consumption has been increasing (from 2.76 g/day in 2005 to 5.32 g/day in 2019). Tuna, as a top predator with a long lifespan, accumulates high concentrations of heavy metals, particularly methylmercury (MeHg). Previous studies on heavy metals in Korean fishery products focused primarily on total mercury rather than MeHg, and none examined tuna from Japanese restaurants—the final point before consumption. This study aimed to conduct a risk assessment of MeHg, lead (Pb), cadmium (Cd), and arsenic (As) in tuna served at Japanese restaurants.

**Methods:** Thirty-one tuna samples (22 bigeye tuna, 9 bluefin tuna) were collected from Japanese restaurants across the Republic of Korea between January and April 2021. Samples were served as sashimi in refrigerated state, and only the cheek portion was analyzed. MeHg was analyzed using the MFDS Food Code 8 method with cold vapor atomic absorption spectrophotometry (Hydra-C analyzer). Pb, Cd, and As were analyzed using microwave digestion and inductively coupled plasma mass spectrometry (7900 ICP-MS). The limit of detection (LOD) values were 0.0024 μg/kg (MeHg), 0.0026 μg/kg (Pb), 0.0006 μg/kg (Cd), and 0.0078 μg/kg (As). Recovery rates ranged from 95.2% (MeHg) to 98.0% (As). Risk assessment was performed by calculating the %PTWI (provisional tolerable weekly intake) using JECFA standards: MeHg 1.6 μg/kg bw/week, Pb 25.0 μg/kg bw/week, Cd 7.0 μg/kg bw/week, As 15.0 μg/kg bw/week. Weekly tuna intake (7.35 g/week) and body weight (61.6 kg) were obtained from the 2019 Korea National Health and Nutrition Examination Survey.

**Key Results:** The geometric mean concentrations were: MeHg 0.56 ± 1.47 mg/kg (range: 0.26–1.08), Pb 33.95 ± 3.74 μg/kg (range: 2.70–262.03), Cd 14.25 ± 2.19 μg/kg (range: 2.43–41.86), and As 1.46 ± 1.89 mg/kg (range: 0.43–3.61). No samples exceeded the MRLs for Pb (0.5 mg/kg) or Cd (0.2 mg/kg), but 9.67% of samples exceeded the MeHg MRL of 1.0 mg/kg. The %PTWI values were: MeHg 4.2037, Pb 0.0162, Cd 0.0244, and As 1.1627. The %PTWI of MeHg varied substantially by age and sex: highest in men aged 19–29 years (10.6494), followed by men aged 30–49 years (7.2458) and women aged 19–29 years (4.8307). The lowest %PTWI was in women aged ≥65 years (0.2638). The extreme scenario calculation showed that consuming 174.84 g of tuna per week would yield a %PTWI of 100 for MeHg.

**Clinical Implications:** Although the mean %PTWI values for all heavy metals were within safe levels for the general Korean population, the finding that 9.7% of samples exceeded the MeHg MRL is concerning. The large variation in %PTWI by age and sex—with young adult men having values 40 times higher than elderly women—highlights the need for targeted risk communication. Since a single serving of tuna sashimi is typically 150–300 g, individuals who eat tuna more than once per week could exceed safe MeHg intake levels. The study notes that MeHg concentrations in this study were more than double those reported in previous Korean studies on wholesale-distributed tuna, suggesting that samples at the final consumption stage may have higher concentrations. The authors recommend improved monitoring by central and local governments, mandatory warning posters about MeHg toxicity, and further research on the dose-response relationship between tuna intake and blood MeHg concentrations. Limitations include the small sample size (n=31), inability to account for tuna habitat/size/age differences, and analysis of only the cheek portion.