Mediterranean Diet 101

Mercury Levels In Fish - Is Tuna Good For You

fish-stew-recipe-2-mFor ages, fish has been known as a healthy and highly recommended food. Environmental pollution is a global problem and many people wonder if fish is healthy and safe to eat.

Published: August 9, 2021.

Fish as food has many benefits - it is high in protein that has both high Protein BV and PDCAAS, fat content can be both high (good fats rich in omega-3 fatty acids) and low (again, rich in omega-3, but much higher protein-fats ratio), fish can be high in fat-soluble vitamins (vitamins A, D, E - especially in fatty fish species) and has many minerals.

Heavy (toxic) metals like mercury, thallium, lead, etc are present in every organism and usually, there is no mechanism for them to be expelled after being ingested. Organisms that are on the bottom of the food chain in the sea (and not only in the sea) have the lowest mercury levels, while predatory species can have rather high levels of mercury in the body (various organs, muscles included).

For example: heavy metals are found naturally in the environment, but they are also released into the environment as a kind of environmental pollution from man-made sources. In the seas and oceans, heavy metals settle on the bottom, where they are 'processed' by single cells organisms - bacteria. One of the most dangerous new compounds is - methyl mercury. Fish can absorb methyl mercury in two ways - by eating food that contains methyl mercury and from water that passes through their gills. When in the body, mercury binds to the proteins in the fish. Problem is that mercury and other heavy metals accumulate there during the time.

Long story short: single-cell organisms 'process' heavy metals (first concentration level), then they are eaten by larger plankton species (second concentration level). Plankton is eaten by small fish species like sardines, anchovies, smelts, etc (third concentration level). These smaller fishes are eaten by larger predatory species like various mackerel and similar fish species (fourth concentration level) and then come large fish species like various tuna species, marlins, large mackerels, etc (fifth concentration level). This is, of course, a simplification of very complex processes and interactions in nature, but it describes 'the big picture' :o)

US FDA (Food and Drug Administration) and NRDC (Natural Resources Defense Council) have released a list of fish species and the amount of mercury that they contain. This list and general recommendations change over time since mercury levels in fish - rise over time!

The following table gives recommended amounts of fish for pregnant and breastfeeding women and small children - what is safe for them, I guess it is safe for everybody else.

Highest Mercury Fish

AVOID Eating:

- Marlin
- Tilefish
- Swordfish
- Sharks
- King Mackerel
- Tuna (Bigeye, Ahi)

High Mercury Fish

Eat no more than three 6-oz (180g) servings per month:

- Sea Bass (Chilean)
- Bluefish
- Grouper
- Mackerel ( Spanish, Gulf)
- Tuna (canned, White Albacore, Yellow-fin)

Low Mercury Fish

Eat no more than six 6-oz (180g) servings per month:

- Bass (European, Striped, Black)
- Carp
- Cod (Alaskan)
- Croaker (White Pacific)
- Lobster
- Mahi Mahi
- Monkfish
- Perch (freshwater)
- Sablefish
- Skate
- Snapper
- Sea Trout
- Tuna (canned, chunk light; Skipjack)

Lowest Mercury Fish

Enjoy two 6-oz (180g) servings per week:

- Anchovies
- Butter-fish
- Catfish
- Crayfish
- Croaker
- Flounder
- Haddock
- Hake
- Herring
- Mackerel (N Atlantic, Chub)
- Mullet
- Oysters
- Perch (ocean)
- Plaice
- Salmon (Canned, Fresh)
- Sardines
- Scallops
- Shrimp
- Sole
- Squid (Calamari)
- Tilapia
- Trout (freshwater)
- Whitefish

As one can see, cheap sardines and similar species can be eaten (almost) freely. It is also important to note that some seas are richer with mercury (Far East Seas) and some have lower levels of mercury (Mediterranean Sea), although there are always local fluctuations.

Is Canned Tuna Healthy

Using the previous table and more data from FDA and NRDC, one can answer 'Is canned tuna healthy' question - Yes, canned tuna is healthy, but be careful what canned tuna fish you are eating, from what seas, and how often. Also, in many countries, canned fish manufacturers must write the amount of mercury in the canned fish - read labels.

For example, FDA's reports from 1990-2010, state that levels of mercury in swordfish:

- 0.995 PPM (parts per million) on average
- 0.539 PPM standard deviation
- 3.220 PPM maximum

This is statistics for 636 samples.

Statistics for mercury in canned tuna (light), reports from 1991 - 2010:

- 0.128 PPM on average
- 0.135 PPM standard deviation
- 0.889 PPM maximum

This is statistics for 551 samples.

Same statistic data for mercury in sardines, reports from 2002 - 2010:

- 0.013 PPM on average
- 0.015 PPM standard deviation
- 0.083 PPM maximum

This is statistics for 90 samples.

Anyway, amounts of heavy metals and other toxins vary on the fish species and where it was caught. The NRDC provides the following table as a general guideline on how much tuna can be eaten by small children and pregnant and nursing women:

Weight in Pounds

(one pound = 0.453 kg)

White Albacore Tuna Light Chunks
1 can/10 weeks
1 can/6 weeks
1 can/5 weeks
1 can/4 weeks
1 can/3 weeks
1 can/3 weeks
1 can/2 weeks
1 can/2 weeks
1 can/2 weeks
1 can/12 days
1 can/11 days
1 can/10 days
1 can/10 days
1 can/9 days
1 can/3 weeks
1 can/2 weeks
1 can/11 days
1 can/9 days
1 can/7 days
1 can/6 days
1 can/6 days
1 can/5 days
1 can/5 days
1 can/4 days
1 can/4 days
1 can/4 days
1 can/3 days
1 can/3 days

So, if you eat 250g of swordfish meat, on average, to consume same amount of mercury, you would have to eat around 2 kilograms of canned tuna (light) or 20 kilograms of sardines. Bone Appetite :o)

Not to mention farmed fish where toxin levels depend on where fish was farmed and where fish food came from. But that is another story ...

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