F ish is healthy, the word is out. It is easily digestible, sea fish also contains plenty of healthy fatty acids. But the fats also unsettle. Because some toxic substances such as dioxin accumulate in fatty tissue. Could in the healthy fish thus also a danger for the health of the fish gourmets be hidden? This question will be discussed by experts at the end of November in a workshop at the Berlin-Brandenburg Academy of Sciences and Humanities.
"You can never completely rule out health risks, of course," says Horst Karl, who is responsible for fish parasites and residues at the Max Rubner Institute (MRI) in Hamburg. The MRI is a federal institute for food research.
Fish: The greatest risk is incorrect positioning
For pangolins and seafood, however, the biggest problem today is not environmental toxins such as dioxins or the pathogens as they are present in the living animal. Horst Karl thinks much more about the path from the shopping cart to the dining table. "It’s the wrong storage that worries us the most."
Like many other foods, fish should be served as fresh as possible and stored only for a short time, preferably in a cool place. Microorganisms multiply at higher temperatures and longer storage times. "This also applies to smoked fish." For summer shopping, Karl advises, "In warm weather, schedule the fish purchase for the end of the shopping trip and quickly put the fish in the refrigerator afterward." In the meantime, the germs then have little time to multiply.
Apart from storage errors, illnesses after fish meals occur most frequently worldwide due to the toxin ciguatoxin. 10.000- to 50.000 times a year people are poisoned by them. Almost exclusively, this happens in warm regions because the toxin is produced by protozoa with the scientific name Gambierdiscus. They live on corals.
If fish graze the corals, they swallow the protozoa and accumulate the ciguatoxin. If a grouper, spiny dogfish, barracuda or other predatory fish catches one, it also stores the toxin. If this predatory fish then lands on the plate, the neurotoxin also affects humans.
Parasites and bacteria: Strict regulations for traders
Because a fish with ciguatoxin is no different in appearance or taste from uncontaminated animals, and cooking, freezing or marinating does not destroy the toxin, Australia and Florida have banned suspect fish such as barracuda from the menu entirely. However, since ciguatoxin only occurs in warm seas such as the Caribbean and the Pacific, from which hardly any edible fish is exported to Europe, it is mainly people in the tropics who are at risk – including tourists.
It is much easier to solve problems with parasites and bacteria. Nematodes, for example, are small threadworms that live in the digestive organs of certain fish, such as the herring worm or the cod worm. In humans, these parasites can cause inflammation with diarrhea and abdominal pain. Similar symptoms appear after infections with listeria. These are bacteria that are found almost everywhere in nature and can also get into fish on their way to consumers.
Horst Karl therefore lists a whole series of binding regulations for traders, processors and restaurants that mitigate such risks. For example, traders must screen fish meat to detect nematodes. If parasites do get through, there are two ways to deal with them – even in the household: heating above 60 degrees Celsius or freezing at minus 18 degrees for at least twelve hours. This reliably kills parasites and bacteria.
If you heat your fish well enough so that there are more than 60 degrees inside, too, you shouldn’t have any problems. For fish eaten raw, one rule applies: "For sushi, you should buy a week in advance and put the fish in the freezer until shortly before eating it," advises Horst Karl. Then nematodes and listeria no longer stand a chance.
Shrimp from aquacultures particularly affected
Even fish from aquaculture is not without problems
People around the world are eating more fish. The often comes from aquaculture. But even this breeding is not without problems. It often brings pollution – and still causes overfishing.
Unfortunately, chemical residues cannot be eliminated by cooking or freezing. Aquacultures in which shrimp are bred are particularly affected. Since the 1970s, they have been present in many tropical and subtropical seas. As demand increased, more and more shrimp were farmed in smaller and smaller tanks. Then infections often spread explosively.
Owners therefore used antibiotics and other animal medications. After 2000, substances such as chloramphenicol and nitrofurans, which can damage the bone marrow and genetic material of humans, were repeatedly detected in shrimps from these countries. "As a result, the EU set up a rapid alert system that can stop the flow of goods in just two hours," explains Horst Karl.
Import bans hit breeders hard and forced them to improve their methods. Since 2005, therefore, such residues have rarely been detected in shrimp imported into the EU. There have been fewer residues in farmed salmon anyway, because countries like Norway are doing a better job of their aquaculture and because the cold fjord water reduces the risk of infection. Shrimp or salmon caught in the wild are not treated with antibiotics anyway.
Dioxin levels in marine animals are falling worldwide
But other residues such as dioxins and other chlorine compounds could show up there. These substances are formed, for example, at high temperatures in waste incineration plants, but also in natural fires. In bodies of water, they are absorbed by plankton and then passed down the food chain. Organisms are slow to get rid of chlorine compounds such as dioxins, so they accumulate more and more, often reaching the highest concentrations in edible fish.
Since dioxins are very toxic, however, the strongest sources have now been plugged in large parts of the world. "Therefore, the concentrations of dioxins in fish are also decreasing," reports Olaf Papke of the Eurofins analytical laboratory in Hamburg, Germany. The company specializes in the detection of dioxins and other toxic chlorine compounds.
Reassuring result for fish gourmets
The EU limit for dioxins and similar substances is eight picograms (eight trillionths of a gram or eight billionths of a milligram) in one gram of fish muscle meat. "In fish from the North Atlantic, on the other hand, we measure only 0.3 to 0.4 picograms of dioxins," says Olaf Papke, citing a reassuring result for fish gourmets. However, the values in areas where particularly high levels of dioxins were released into the environment in the past are still significantly higher today.
This is how large quantities of these toxins were produced during the bleaching of paper. As a result, wastewater from the many paper mills used to carry large amounts of dioxin into the rivers that flow into the eastern Baltic Sea.
Since these toxins are very long-lived and the water there is hardly ever exchanged, the dioxin content in the fish of the eastern Baltic Sea is still far higher today, even though paper production has long since been converted. "We measure three to five picograms there in one gram of fish meat," says Papke. Values are significantly higher in fish from the vicinity of airfields where the dioxin-containing chemical Agent Orange was transferred during the Vietnam War. "There we measured up to 140 picograms of dioxins in fish muscle meat," explains Papke.
Fatty fish are particularly affected
Hands off eel and mackerel
The environmental organization Greenpeace has published a fish guidebook. Overfishing and fishing method are taken into account. Most popular food fish are caught too frequently or incorrectly.
Source: Die Welt
Because dioxins and other organic chlorine compounds accumulate primarily in fat, concentrations are higher in high-fat fish such as herring. The European eel, with around 30 percent fat, often exceeds the limits. Aquacultured eels, on the other hand, are fed with low-dioxin feed and contain much less toxin.
Olaf Papke also gives a cautious all-clear for heavy metals: "Since their emissions have been significantly reduced, mercury and lead in fish hardly cause any problems any more." Last but not least, the experts reassure about radioactivity after the Fukushima meltdown. The radiant substances carried in are extremely diluted in seawater when the currents carry them further.
So there is no need to worry about the Alaska pollock caught off the coast of Siberia and the fish sticks made from it. These regions are far away from the reactor disaster.
What dangerous toxins are in fish:
Heavy metals: Squid, cuttlefish and squid store cadmium in guts. Fish is the largest source of methylmercury in humans. Predatory fish such as swordfish and tuna contain large amounts of. Because of methylmercury, fish should be eaten only once or twice a week. Fish is the largest source of methylmercury in humans. Predatory fish such as swordfish and tuna contain large amounts. Because of methylmercury, fish should only be eaten once or twice a week.
Organic substances: Accumulate in fatty tissue. Fatty fish that is healthy in itself contains more of them. In the sea off Southeast Asia, dioxins can still originate from the defoliant Agent Orange (Vietnam War) – also in farmed fish from this region. However, the amounts are usually far below the recommended maximum amounts. Exceptions: Wild salmon, herring and cod liver from the eastern Baltic Sea contain more dioxin and PCBs. It is better to eat it infrequently. Exception 2: Wild eel from rivers with heavy industrial settlement, EU maximum levels are exceeded.