How healthy the Baltic Sea and its fish are

The view that the Baltic Sea is one of the most polluted seas in the world may sound implausible at first, especially for someone who has seen the oil fields of the North Sea, the trade ports of Hamburg, or the garbage-filled bays of Southeast Asia.

There are two reasons for that. Firstly, when speaking about pollution, people tend to lump together maritime traffic, urban sewage, and industrial pollution, as well as nutrient runoff from agriculture. While the former involve specific contaminants, nutrients are not toxic but impact the environment through indirect processes.

However, oxygen depletion in the waters, caused by excess nutrient loads, algal blooms and other stressors, contribute to increasing the impact of contamination from toxic substances and sources.

Secondly, the Baltic Sea is an inland sea, and the substances and problems that have once influenced the waters tend to persist. Even today, traces of the insecticide DDT can be found in the sediment layer of the Baltic Sea, regardless of the fact that the substance has been banned on these shores for dozens of years.

The author of this article, Randel Kreitsberg, on the Baltic Sea near Saarnaki island in Estonia. Image from a personal archive

Oil is to fish as alcohol is to humans

In my master’s thesis, I investigated the long-term effects of the 2006 oil spill in Nõva and Keibu bay, off the northwestern coast of Estonia. The effects of this relatively small spill, estimated at around 40 tons of heavy fuel oil, could be detected in the sediment layer and affected the fish even as long as a year and a half following the contamination.

Since fish can usually “process” and excrete the pollution from most oil spill incidents (fuels, oils, crude oil), it is possible to measure how their liver detoxifies their bodies and identify the measure of oxidative stress in the fish living in a certain environment.    

In the course of evolution, humans have adapted to alcohol consumption and have developed enzymes to reduce the toxic effect of alcohol in the body. The same analogy applies to oil and fish. Humans and fish are not so different, after all.

True, just as alcohol causes liver damage and a number of other health issues, fish suffer from the effects of oil and fuel oil. Chronic exposure may lead to major changes in the ecosystem.  

I like to think of myself as a fish doctor who performs health checks on water creatures. When people go to the doctor, they are not checked for the amount of harmful chemicals in their body, but whether they are healthy or not.

I do the same with fish. The environment and the Baltic Sea are contaminated by tens of thousands of toxic substances, and even a person walking down the street is exposed to tens and hundreds of toxins. It is all part of the environment and a stressor that every living organism, from amoeba to human, must deal with.

A visit to the doctor for a regular check-up may involve giving a blood and urine sample, and a a patient has his pulse, breathing, muscle strength, and other vitals checked. The health of fish can be similarly monitored and generalisations made about the surrounding environment based on their health indicators.

Me separating the internal organs of a fish for further analysis. Image from a personal archive

Are fish from the Baltic Sea safe to eat?

The toxic substances discussed here can be divided into two—those that the living organisms have been exposed to in the course of evolution, such as oil, and anthropogenic sources, which emerged in the environment a few years and decades ago, such as dioxins.

The defence mechanisms of living organisms are not very efficient in protecting against the latter—at times they are entirely inefficient. This is why dioxins, several man-made pesticides, plastic additives, and other modern-day substances are so harmful.

There is an ongoing race among the developers and producers of chemicals, on the one hand, and regulators and scientists, on the other. Many harmful effects from long-term use or exposure have a delayed response (consider, for example, the case of the notorious DDT, the famous discovery that was awarded the Nobel Prize but proved to be a scourge); also, it is unfeasible to test the mutual and reciprocal influences of all these tens of thousands of substances using scientific methods.

The fish of the Baltic Sea are living in this chemical cocktail, but so are humans. A justified question here is: should we be concerned? Or, to put it more simply: are fish from the Baltic Sea safe to eat?

A short answer would be yes, they are. In the course of my research I have confidently eaten what has been left of the fish after they have been caught and analysed for research purposes (since the tests are run mostly on the intestines, the flesh is left over). Also, as several research articles suggest, the beneficial substances in fish far outweigh the harmful ones.

Nothing goes wasted – fish fillets are perfect to eat. Image from a personal archive

Fish also get cancer

The other side of the coin is the health of these fish. The fact that a fish is good to eat does not mean that it is healthy itself. If a fish has developed liver cirrhosis from constant exposure to high doses of toxins, it is still good enough to make soup, but it is also a sign of danger, indicating the state of the environment.

Not all fish diseases are caused by contaminated water—like humans, fish also suffer from bacterial and virus infections, and also from various parasites, natural enemies, and the effects of the constant fight for survival.

One of the rather unexpected of these diseases, caused not only by genetic factors and lifestyle but also by environmental pollution, is cancer. The disease that involves uncontrollable cell growth is as old as multicellularity itself. For a hundred million years, animals have had to face some groups of cells that have “gone mad” and selfishly disrupt the functioning of the surrounding tissues and organs, possibly leading to the organism’s death.

Being exposed to strong stressors may result in an extremely rapid evolutionary adaptation, which may take place in the course of a few dozens of generations. Under the supervision of Tuul Sepp at the University of Tartu, we are currently working to formulate an equation entailing the contamination of the sea and tumour induction in fish, combined with evolutionary adaptation—namely, we wish to learn whether the fish of the Baltic and North Sea have developed some particularly clever intracellular mechanism against cancer after long-term exposure to contaminated seawater.

The one and only World Ocean

My father worked as a sailor on a trawler and, as a boy, I remember him bringing me all kinds of dried sea creatures from his ocean travels. There were sea urchins and sea stars, pufferfish and shark teeth, the bill of a swordfish and the fangs of a sea lion—treasures from faraway lands that triggered my interest in this mysterious underwater world.

Having now become familiar with subaquatic life in the seas of the world, I can see that even such vast and stable ecosystems, or, to be fair, for us it is the one and only maritime ecosystem—the World Ocean—are susceptible to human activity. The Baltic Sea is a young, constantly changing and evolving environment, and humans are part of the Baltic Sea ecosystem.

Sleeping in a tent by the Baltic Sea on the island of Vilsandi in Estonia. Image from a personal archive

If we move from the nearly freshwater eastern shores of the Baltic Sea towards the Danish straits, the sea life changes considerably with the increase in salinity: dolphins and sharks have been spotted in the Baltic Sea, even swordfish have accidentally ended up here, and the biodiversity of the Danish straits is already similar to that of the North Sea.

Having learned sea life for a couple of decades, I have only now begun to grasp the complexity of the system (which sounds like a cliché, but is true). I’m fond of these sandy, muddy Baltic shores, covered in reeds, stones and rocks, and also its greenish-yellowish-bluish-greyish waves—it is, after all, my Baltic Sea. 

Randel Kreitsberg is a Research Fellow in Ecotoxicology at the Institute of Ecology and Earth Sciences, University of Tartu.

A longer Estonian version of this article appeared first on ERR website.

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