Pacific bluefin tuna and southern bluefin tuna: mercury

Levels measured in Japanese government surveys and studies

Units are mg/kg (= ppm). Values are for the edible portion of fish on the market and appear to be wet weight (the sources do not say). Total mercury and methylmercury were not necessarily measured in the same samples. The MAFF rows (fiscal 2007–2010) give the median next to the mean.

How much to eat (official advice)

• The guidance applies to “women who are pregnant or may become pregnant” (MHLW, revised June 2010). Children, women who are breastfeeding, and adults other than pregnant women are not covered.
• Pacific bluefin tuna (hon-maguro): up to once a week (about 80 g/week).
• Southern bluefin tuna (indo-maguro): up to twice a week (about 160 g/week).
• One serving is calculated as about 80 g (one serving of sashimi, or one slice of fish). One piece of sushi or sashimi is about 15 g.
• If you eat two kinds of “up to once a week” fish in the same week, halve the amount of each. If you eat one “up to once a week” fish and one “up to twice a week” fish in the same week, also halve the amount of each.
• Even if you eat too much in one week, eating at one meal or over one week does not greatly change the mercury level in your body, and it is explained that you can simply eat less the following week.

Limits (Japan, international, EU)

Good to know

• The national precautions cover only women who are pregnant or may become pregnant. The Food Safety Commission of Japan (FSCJ) judged that “the fetus is the most susceptible”; children, women who are breastfeeding, and adults other than pregnant women are not covered. The MHLW also states clearly that it is not asking pregnant women to avoid fish high in mercury. → How much fish is OK during pregnancy?
• The provisional regulatory limit for fish and shellfish (total mercury 0.4 ppm) does not apply to tuna-type fish. The Pacific bluefin average (0.687) is above it, but the fish is outside the limit and instead has its own guidance amount for pregnant women. We found no official document explaining the reason for the exemption.
• The methylmercury in one serving (about 80 g), based on national averages, is about 42 μg for Pacific bluefin (0.525 ppm) and about 31 μg for southern bluefin (0.386 ppm). That is about 38% and 28% of the FSCJ’s tolerable weekly intake (2.0 μg/kg body weight per week; 111 μg per week for a 55.5 kg person) (Urayomi’s calculation).
• In the MAFF survey (fiscal 2007–2010, 120 samples each), average methylmercury was 0.60 in wild and 0.42 in farmed Pacific bluefin, and 0.69 in wild and 0.27 in farmed southern bluefin. Even within one species the variation between individual fish is large; in the MHLW compilation, one Pacific bluefin had total mercury as high as 6.1 ppm.
• The yardstick for “how much is OK” differs by about threefold between agencies. The tolerable weekly intake is 2.0 μg/kg body weight for the FSCJ (2005), 1.6 for JECFA (2003), and 1.3 for EFSA (2012); for the US EPA (2001) it is 0.7 when converted to a weekly figure. → Mercury page
• The FAO/WHO joint expert consultation (2010) is reported to have concluded that, in most of the situations it evaluated, women of childbearing age who eat fish lower the risk of poor neurodevelopment in their children compared with not eating fish. The MHLW likewise calls on people to avoid eating large amounts of fish high in mercury in a lopsided way, so as to keep the benefits of eating fish.
• The concentrations by fish species are from a compilation through fiscal 2008 (May 2010) and may differ from fish on the market today. The national guidance table also has not been revised since June 2010. A Food Safety Commission document (reprinting a literature review) summarizes that mercury levels do not differ by part of the fish. Cadmium is low in muscle: in the MAFF survey, Pacific bluefin was <0.01 (5 samples) and southern bluefin 0.03 (maximum 0.06, 5 samples).

Related explainers

• How Much Fish Is OK During Pregnancy? Guidance for Tuna, Canned Tuna, and Kinmedai, with Mercury Numbers
• Why Do Heavy Metal Standards Differ Between Japan and Other Countries? Japanese, Codex, and EU Standards and Tolerable Intakes Compared
• How Much Heavy Metal Do Japanese People Take In? Fifty Years of Lead, Cadmium, Mercury, and Arsenic Intake

Pages for each metal

• Mercury

Sources

• MHLW, “Notes on Eating Fish and Shellfish and Mercury for Pregnant Women” (revised June 2010)
• MHLW, “Notes on Eating Fish and Shellfish and Mercury for Pregnant Women,” Q&A
• MHLW, Document 2-4, “Survey Results on Mercury in Fish and Shellfish (Summary)” (May 2010)
• MAFF, “Data Collection of Survey Results on Hazardous Chemicals in Food (Fiscal 2003–2010)”
• MAFF, “Provisional Regulatory Limits for Mercury in Fish and Shellfish”
• FSCJ, Evaluation of the tolerable weekly intake of methylmercury (August 2005), document posted by the MHLW
• European Commission, Regulation (EU) 2022/617 (maximum levels for mercury in food)
• FAO/WHO joint expert consultation, report on the risks and benefits of fish consumption (2010)

Last checked 2026.10.03 (against the original government documents and papers, collected and cross-checked in Gemini Notebook).

Also in “Fish”

• Bigeye tuna
• Yellowfin tuna, albacore, and young Pacific bluefin
• Canned tuna
• Skipjack tuna
• Swordfish and striped marlin
• Splendid alfonsino
• Whales and dolphins
• Salmon
• Mackerel
• Sardines, horse mackerel, and Pacific saury