Impact of Nord Stream explosions on marine animals
European environmental scientists conducted a pre-print study to evaluate the immediate effects of the Nord Stream pipelines’ sabotage on the marine ecosystem.
In addition to the widely reported release of over 100,000 tonnes of methane, the explosions that ruptured the gas pipelines in the Baltic Sea in September of last year also resulted in the resuspension of approximately 250,000 tonnes of heavily contaminated sediment, which received less media attention.
On September 26, 2022, the Nord Stream 1 and Nord Stream 2 gas pipelines, which transport gas from Russia to the European Union, were ruptured by unknown persons using four coordinated explosions in the exclusive economic zones of Denmark and Sweden.
To determine the impact of the explosions, the researchers used decades of sediment monitoring data from the Bornholm Basin, a busy shipping area, and hydrological models of sediment transport.
The blasts, each equivalent in power to the explosion of 500 kilograms of TNT, threw up a total of 250,000 tonnes of sediment, reaching depths of up to 30 metres below sea level.
The researchers analyzed the known concentrations of various contaminants in the sediment, including tributyltin (TBT), heavy metals, and chemical-warfare agents, to determine the toxicity of the sediment.
The team calculated a toxicity threshold for the sediment, determining that any more than 5.8 milligrams of sediment re-suspended per litre of seawater would be harmful to marine life.
The researchers found that the contaminants in the sediment, including lead and TBT, accounted for most of the toxicity, with lead and TBT alone responsible for 75% of the toxicity.
The sediment from the Nord Stream 1 blast breached the safety threshold for 15 days at depths of between 95 and 53 metres, while the Nord Stream 2 pipeline blast breached the threshold for 34 days at depths of between 78 and 42 metres.
Overall, the blasts contaminated 11 cubic kilometres of seawater for over a month.
Among the findings:
The explosions that caused damage to the Nord Stream gas pipelines led to the release of historically introduced pollutants into the deepest part of the Bornholm basin, with large volumes of water exceeding the environmental toxic threshold for up to 34 days.
The pollutants did not reach the surface of the sea or the surrounding shores. The primary cause of marine environmental risk was the resuspension of tributyltin (TBT), an endocrine disruptor used to protect ship hulls, and lead (Pb), which represented 75% of the total toxicity.
The Bornholm Basin is an important spawning and nursery ground for the Eastern Baltic cod (Gadus morhua) population. The rupture occurred at the end of the cod spawning season from March to September, and the resuspension of toxic sediments could have affected fishes, juvenile cods, and eggs in the area for over a month.
The long-term impacts on fish would most likely be endocrine disruption due to TBT exposure. Pb exposure could induce oxidative stress, affect biochemical and physiological functions, disrupt neurotransmitters, and cause neurotoxicity and disruptions to the immune system.
The contaminant load resulting from the resuspension of sediments by this event could add more pressure on already existing stressors, putting the Baltic cod stock under additional stress.
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