Shim et al. 2004 — Mercury and fatty acids in canned tuna, salmon, and mackerel
This 2004 US study analyzed total mercury (tHg) and polyunsaturated fatty acids in canned tuna (n=240), salmon (n=16), and mackerel (n=16) purchased from stores in Lafayette, Indiana. Mercury was measured as total Hg by thermal decomposition amalgamation atomic absorption spectrophotometry (TDA/AAS); the paper does not speciate MeHg from inorganic Hg, but notes that up to 90% of Hg in fish is typically found as MeHg. Overall mean tHg was 188 ppb in tuna, 45 ppb in salmon, and 55 ppb in mackerel — all below the FDA action level of 1000 ppb. White/albacore tuna in water contained substantially higher tHg (mean 227–330 ppb) and higher EPA+DHA (mean ~902 mg/100 g) than light tuna in water (mean 54 ppb tHg; mean ~268 mg/100 g EPA+DHA), presenting a trade-off for childbearing-age women between omega-3 benefit and mercury risk.
Key numbers
Total Hg in canned fish (ppb, wet weight), by product type
| Sample | Type | tHg (ppb) |
|---|---|---|
| 1 (Starkist chunk light, water) | Light tuna | 52 |
| 2 (Polar chunk light, water) | Light tuna | 48 |
| 3 (Kroger chunk light, water) | Light tuna | 63 |
| 4 (Starkist chunk light, veg oil) | Light tuna | 174 |
| 5 (Chicken of the Sea chunk light, veg oil) | Light tuna | 191 |
| 6 (Kroger chunk light, soy oil) | Light tuna | 340 |
| 7 (Bumble Bee white albacore, water) | White/albacore tuna | 227 |
| 8 (Chicken of the Sea white albacore, water) | White/albacore tuna | 232 |
| 9 (Chicken of the Sea white albacore, water, pouch) | White/albacore tuna | 330 |
| 10 (Bumble Bee white albacore, soy oil) | White/albacore tuna | 220 |
| 11 (Chicken of the Sea pink salmon) | Salmon | 20 |
| 12 (Polar fancy pink salmon) | Salmon | 70 |
| 13 (Orleans jack mackerel) | Mackerel | 61 |
| 14 (Chicken of the Sea jack jurel mackerel) | Mackerel | 50 |
Each value is the grand mean of duplicate analyses of 3 lots with 4 composites each (tuna samples 1–10) or duplicate analyses of 4 composites (salmon and mackerel, samples 11–14). Limit of detection: 0.01 ng total Hg.
Summary by product category:
- Light tuna in water (samples 1–3): mean 54 ppb (range 48–63 ppb)
- Light tuna in vegetable oil (samples 4–5): mean 183 ppb (range 174–191 ppb) — ~3× higher than light tuna in water
- Light tuna in soy oil (sample 6): 340 ppb — highest among light tuna
- White/albacore tuna in water (samples 7–8): mean 229 ppb; pouch pack (sample 9): 330 ppb
- White/albacore tuna in soy oil (sample 10): 220 ppb
- Overall tuna mean (n=240): 188 ppb
- Salmon (n=16): mean 45 ppb (range 20–70 ppb)
- Mackerel (n=16): mean 55 ppb (range 50–61 ppb)
FDA action level for commercial fish: 1000 ppb. No sample exceeded this level.
EPA + DHA content by product type:
- Light tuna in water: mean ~268 mg/100 g wet tissue (DHA 181–300; EPA 32–39)
- White/albacore tuna in water: mean ~902 mg/100 g wet tissue (DHA 555–741; EPA 190–333) — highest EPA+DHA among tuna types
- Salmon: mean ~1,623 mg/100 g wet tissue (DHA 564–874; EPA 884–925)
- Mackerel: mean ~851 mg/100 g wet tissue (DHA 282–649; EPA 218–553)
Exposure estimate at current tuna consumption for a 60-kg woman:
- At 95th percentile consumption (20 g/d): all tuna products below USEPA RfD of 0.1 µg MeHg/kg bw/day
- At 99th percentile consumption (35 g/d): light tuna in oil and white/albacore tuna deliver 129–153% of RfD
- Safe mercury concentration in fish tissue at 8 oz/wk (32.43 g/d) intake: must be below 185 ppb to remain below RfD
Methods (brief)
Total mercury measured using Thermal Decomposition Gold Amalgamation Atomic Absorption Spectrophotometry (TDA/AAS, DMA-80 analyzer, Milestone Inc.), calibrated against NRCC certified reference materials Tort-2 (0.270 ppm Hg) and Dorm-2 (4.64 ppm Hg). Two calibration ranges used: 0–35 ng Hg (R²=0.9929) and 30–470 ng Hg (R²=0.9958). LOD: 0.01 ng total Hg. Composite samples were prepared by pooling and grinding the entire contents of 2 cans from each lot in a food processor. Fatty acids quantified by GC/FID (Varian 3900) using AOAC method 991.39 on lipids extracted by modified Folch method. SRM recovery for total fat: 95%. Standard deviation <±10% of mean for all mercury values (SD not shown). Mercury is reported as total Hg; no speciation of MeHg vs inorganic Hg performed, but authors note ~90% of Hg in fish is typically MeHg.
Implications
Certification: The substantial difference between light tuna in water (mean 54 ppb tHg) and white/albacore tuna in water (mean 227–330 ppb tHg) provides a concrete example of how product labeling and species selection, not just the “canned tuna” category, determine mercury exposure. Any HMT&C limit for canned tuna would need to distinguish albacore from light tuna to be meaningful. The 2004 FDA action level of 1000 ppb is not protective at high consumption levels; the authors calculate that 185 ppb would be the appropriate threshold at 8 oz/wk consumption for a 60-kg woman.
Courses: The mercury/omega-3 trade-off quantified here is a concrete teaching example: white/albacore tuna provides the highest EPA+DHA among tuna products but at ~4× the tHg of light tuna in water. Salmon and mackerel offer a better ratio (higher EPA+DHA at lower tHg).
App: Product-type-level tHg values (light tuna in water ~54 ppb, white/albacore tuna ~229 ppb, salmon ~45 ppb, mackerel ~55 ppb) are useful defaults for canned fish ingredient risk estimation; packing medium matters for tuna (soy oil or vegetable oil → higher tHg than water-packed).