Heavy metals in food databaseShellfish, squid and crabChecked 2026.10.03
Scallop, oyster, abalone, and turban shell: cadmium, mercury
In shellfish such as scallops, oysters, abalone, and turban shells (sazae), cadmium tends to be much higher in the innards than in the flesh. In the MAFF fiscal 2010 survey (300 samples each), the scallop adductor muscle (kaibashira) averaged 0.45 ppm and the hepatopancreas (“uro”) averaged 33 ppm, and oyster flesh averaged 0.43 ppm. Mercury is low: 0.009 ppm in scallops and 0.007 ppm in oysters.
Levels measured in Japanese government surveys and studies
| Metal | Form / state | Mean | Range / max | Samples | Survey |
|---|---|---|---|---|---|
| Cadmium | Scallop, adductor muscle | 0.45 (median 0.32) | <0.03–1.6 | 300 samples | MAFF, fiscal 2010 |
| Cadmium | Scallop, hepatopancreas (“uro”) | 33 (median 31) | 7.3–68 | 300 samples | MAFF, fiscal 2010 |
| Cadmium | Scallop, gonad | 2.2 (median 2.1) | 0.59–6.0 | 300 samples | MAFF, fiscal 2010 |
| Cadmium | Pacific oyster (magaki), edible portion | 0.43 (median 0.29) | 0.15–1.3 | 300 samples | MAFF, fiscal 2010 |
| Cadmium | Scallop, edible portion | 0.12 | 0.01–0.51 | 57 samples | MAFF, fiscal 1997–2002 |
| Cadmium | Scallop, hepatopancreas (“uro”) | 5.80 | 1.30–16.00 | 72 samples | MAFF, fiscal 1997–2002 |
| Cadmium | Pacific oyster (magaki), edible portion | 0.30 | 0.10–0.68 | 45 samples | MAFF, fiscal 1997–2002 |
| Cadmium | Abalone, muscle | 0.04 | 0.02–0.07 | 15 samples | MAFF, fiscal 1997–2002 |
| Cadmium | Abalone, innards | 3.11 | 2.20–5.60 | 15 samples | MAFF, fiscal 1997–2002 |
| Cadmium | Turban shell (sazae), muscle | 0.05 | <0.01–0.10 | 15 samples | MAFF, fiscal 1997–2002 |
| Cadmium | Turban shell (sazae), innards | 4.65 | 1.20–9.50 | 15 samples | MAFF, fiscal 1997–2002 |
| Mercury | Scallop, total mercury | 0.009 | max 0.110 | 234 samples | MHLW, compiled through fiscal 2008 |
| Mercury | Oysters, total mercury | 0.007 | max 0.280 | 388 samples | MHLW, compiled through fiscal 2008 |
Units are mg/kg (= ppm). Cadmium is total cadmium and appears to be wet weight (the sources do not say). Mercury is total mercury. In the fiscal 2010 survey, “uro” is the scallop’s hepatopancreas; the scallop “edible portion” in fiscal 1997–2002 is everything except the shell and the “uro” (hepatopancreas), including parts other than the adductor muscle.
Limits (Japan, international, EU)
| Set by | Limit | Note |
|---|---|---|
| Japan (cadmium) | No cadmium limit for fish and shellfish | The cadmium standards under the Food Sanitation Act cover only rice (0.4 mg/kg or less in brown rice and polished rice) and mineral waters (0.003 mg/L). For foods other than rice, no standard is set because creating one would do little to reduce intake; the policy is to respond with measures at the production stage and surveys of actual levels (Consumer Affairs Agency). |
| Codex (cadmium) | Bivalve mollusks 2 mg/kg (excluding oysters and scallops) | Oysters and scallops are outside this value. |
| EU (cadmium) | Bivalve mollusks 1.0 mg/kg | The value from Regulation (EU) 2023/915. |
| Japan (mercury) | Total mercury 0.4 ppm, methylmercury 0.3 ppm (provisional regulatory limit for fish and shellfish) | A value notified by the Ministry of Health and Welfare in 1973 (Showa 48). Tuna-type fish, fish and shellfish from rivers (excluding lakes and marshes), deep-sea fish and shellfish, and others are exempt; other fish and shellfish are covered. |
| EU (mercury) | Fish and fishery products in general: 0.50 mg/kg | The value from Regulation 2022/617, carried over into Regulation (EU) 2023/915. Wet weight. Shellfish are on neither the 1.0 list nor the 0.30 list, so they appear to fall under the general category. |
Good to know
- The flesh (adductor muscle, muscle) tends to be lower than the innards. In the fiscal 2010 survey, the scallop adductor muscle averaged 0.45 ppm and the “uro” averaged 33 ppm (about 70 times). Abalone was 0.04 in muscle against 3.11 in innards, and turban shell was 0.05 in muscle against 4.65 in innards (fiscal 1997–2002).
- The Consumer Affairs Agency says that some innards of mollusks such as shellfish, squid, and octopus, and of crustaceans such as shrimp and crab, are high in cadmium, while explaining that these are foods eaten since long ago, that the possibility of harm in an ordinary diet is low, and to watch out for a lopsided diet of eating large amounts of the same food every day.
- Even for the same scallop, the values differ by survey. The fiscal 1997–2002 edible portion averaged 0.12 (57 samples) and the fiscal 2010 adductor muscle averaged 0.45 (300 samples); the “uro” was 5.80 and 33. The survey years, areas, and definitions of the parts differ, but the sources do not explain the reason.
- The oyster flesh (edible portion) averaged 0.43, with a maximum of 1.3, in the fiscal 2010 survey. Some samples are above the EU limit for bivalve mollusks (1.0), but Japan has no such limit, and the domestic survey was not judged against the EU standard. The median is 0.29.
- The Codex value for bivalve mollusks (2 mg/kg) excludes oysters and scallops. Japan has no cadmium limit for shellfish. → How Japan’s standards differ from other countries’
- Mercury is low: 0.009 ppm in scallops (234 samples), 0.007 ppm in oysters (388 samples), and 0.008 ppm in littleneck clams (asari; 254 samples). For arsenic, an old one-off report (1983, dry weight) found turban shell muscle at 15.0 total arsenic and 0.02 inorganic arsenic, and littleneck clams at 17.5 total and 0.05 inorganic. These are not wet-weight values.
- Japanese cadmium intake (2022) is 2.03 μg/kg body weight per week, about 29% of the FSCJ’s tolerable intake (7 per week) and about 81% of EFSA’s (2.5 per week). In a questionnaire across 14 regions of Japan, 24.8% of people said they eat shellfish “often.” → Cadmium page
Reducing it at home (shown in tests)
- The scallop adductor muscle and “uro” differ by about 70 times on average (0.45 and 33 ppm, fiscal 2010). In terms of concentration, not eating the innards such as the “uro,” or eating less of them, is what helps most. However, no public agency is saying “do not eat them.”
- We found no official test showing how much cooking reduces cadmium.
Related explainers
Pages for each metal
Sources
- MAFF, “Data Collection of Survey Results on Hazardous Chemicals in Food (Fiscal 2003–2010)”
- MAFF, “Survey Data on Cadmium in Domestic Agricultural, Livestock, and Fishery Products: Fish and Shellfish” (fiscal 1997–2002)
- Consumer Affairs Agency, Q&A on “Cadmium in Rice”
- FSCJ, Cadmium: Summary of the Food Health Impact Assessment
- MAFF, “International Standards for Cadmium in Food” (Codex)
- European Commission, Regulation (EU) 2023/915 (maximum levels for contaminants in food)
- MHLW, Document 2-4, “Survey Results on Mercury in Fish and Shellfish (Summary)” (May 2010)
- FSCJ, Document 3, “Findings on Inorganic Arsenic Exposure in Japanese People” (includes the 1983 report by Shinagawa et al.)
Last checked 2026.10.03 (against the original government documents and papers, collected and cross-checked in Gemini Notebook).
Heavy metals occur naturally in soil and the sea, and every food contains small amounts. This page lists facts from government surveys, limits and assessments and from published papers; it does not judge any food as good or bad. Where there is official advice — such as on eating fish during pregnancy — follow it.