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Scientists warn poison contamination in the Baltic Sea could affect German fisheries

Paul Krantz
Paul Krantz - [email protected]
Scientists warn poison contamination in the Baltic Sea could affect German fisheries
A fisherman takes his cutter out into the Baltic Sea to set his nets. Exacerbated thallium contamination in the Baltic would affect the local fishing industry as fish in the industry could become toxic. Photo: picture alliance/dpa | Jens Büttner

A team of researchers are sounding the alarm after confirming high levels of a toxic heavy metal in the Baltic Sea. Human activity, including proposed efforts to fix other environmental issues in the region could make the contamination worse.

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Scientists have warned that thallium levels in the Baltic Sea are significantly higher than previously thought.

A team of researchers from the American Woods Hole Oceanographic Institution (WHOI), confirmed that large parts of the Baltic Sea are already contaminated with the toxic heavy metal.

Their research, recently published in the Environmental Science & Technology journal, suggests that increased thallium levels in the Baltic Sea are a result of industrial activity in the region.

Thallium is considered the most toxic heavy metal for humans and animals. 

“Humans are releasing a lot of thallium into the Baltic Sea, and people should be made aware of that,” said Chadlin Ostrander, postdoctoral investigator in WHOI’s Department of Marine Chemistry and Geochemistry, in a summary of the research published by WHOI.

“If this continues…more thallium could accumulate. That would be of concern because of its toxicity,” he added.

Where does the thallium in the Baltic come from?

For now, thallium levels in Baltic seawater remain low. So you don’t need to cancel your trip to the Baltic Coast this summer.

That’s because most thallium in the Baltic is present in a layer of sulphide lying under the sand.

As long as thallium stays under the seabed in this form it remains harmless to marine life and humans, but construction work that disturbs the sea floor can release thallium isotopes into the water.

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sediment sampler on a boat

The sampling rosette is deployed from the deck of a boat into a deep basin of the Baltic Sea. (Photo: Colleen Hansel, ©Woods Hole Oceanographic Institution)

According to the research, between 20 and 60 percent of the toxic thallium that has entered the Baltic Sea in the last 80 years is due to human industry or shipping.

By analysing sediment core samples from the seafloor, the researchers determined that thallium enrichment picked up around the 1940s, suggesting its link to certain industrial activity.

“We predict, based on activities in the region, that the source of the thallium pollution is historic cement production in the region,” said senior scientist in WHOI’s Department of Marine Chemistry and Geochemistry, Colleen Hansel.

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“As cement production continues to rise globally, this research could serve to caution manufacturers about the need to mitigate potential downstream effects of cement kiln dust on surrounding aquatic and marine ecosystems.”

Human impacts are creating a toxic sea

Sune Nielsen, co-author of the study and adjunct scientist in WHOI’s Department of Geology & Geophysics suggests that thallium contamination may not be the most immediate concern for the Baltic Sea ecosystem.

“As a Danish national, I follow the bad news about the Baltic in the Danish media, and our finding just adds another dimension to the already poor conditions in the basin for marine life,” Nielsen said.

READ ALSO: Storm at Baltic beauty spot over Germany's gas plans

An influx of farm-fertilisers and sewage-treatment discharge into the sea has resulted in the Baltic being home to seven of ten of the world’s largest known marine “dead zones”. These occur when excess algae and bacterial growth, fuelled by pollution, use up too much oxygen in the water causing fish and marine life to die off.

But human efforts to revitalise these dead zones could exacerbate thallium contamination, the researchers warn.

Current proposals to reoxygenate dead zones consist of pumping oxygen into the sea, which the researchers say would disturb sediment layers and mix thallium into the seawater where it could be absorbed by fish and enter the food chain.

“There is no doubt in my mind that it adds to the urgency of needing to do something to bring the Baltic Sea back to a state where humans and marine life can co-exist naturally,” said Nielsen.

To be clear, despite the Baltic Sea being one of the most polluted areas in the world, fish from the region are still safe to eat.

Randel Kreitsberg, a marine scientist at the University of Tartu in Estonia puts it this way in a university blog article: "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...are fish from the Baltic Sea safe to eat? A short answer would be yes, they are."

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What is thallium?

Particularly toxic to mammals, thallium is a heavy metal which is not found freely in nature. 

It has previously been used in rat poisons and also as a lethal poison on people. For example, the Stasi used thallium to attempt to kill dissident Wolfgang Welsch in 1981 after he had successfully escaped East Germany.

READ ALSO: Why Germany will never forget the Stasi era of mass surveillance

A lethal dose of thallium for adults is around 800 milligrams, but it is easily absorbed by the body and hard to get rid of. So even small doses should be avoided.

Since 2006, the German Institute for Risk Assessment has advised that the daily intake of thallium should not exceed ten micrograms (millionth of a gram) per day. 

Commercially thallium is primarily used in the electronics industry, and to a lesser extent in the pharmaceutical and glass manufacturing industries.

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