Explosions in the Nord Stream pipeline kicked up toxic sediments

The blasts, which blasted holes in Nord Stream’s underwater gas pipelines, ejected long-buried toxins in concentrations high enough to threaten marine life for more than a month, analysis of the site suggests.

Last September, a series of four explosions ruptured the Nord Stream 1 and 2 gas pipelines – which run from Russia to Germany – near the Danish island of Bornholm in the Baltic Sea, releasing more than 100,000 tons of methane into the sea and atmosphere. It’s unclear who was behind the blasts, but recent speculation points to a pro-Ukrainian group being responsible.

In addition to the dramatic sight of bubbles gushing out of the sea, the explosions also kicked up sediment from the sea floor and returned it to the water column. A team of environmental scientists led by Hans Sanderson from Aarhus University in Denmark feared the consequences could not be overlooked, especially considering the explosions took place near a historic dump for chemical warfare agents, including mustard and arsenic from the Second World War. They were trying to figure out how these chemicals might affect sea life.

explosive effect

Researchers used decades of monitoring data of the sediment in the busy shipping area of ​​the Bornholm Basin and hydrological models of sediment transport to determine the impact of the blasts, each estimated to be equivalent in magnitude to the blast of 500 kilograms of TNT. Their models showed that the blasts, which occurred at a depth of about 70 meters, kicked up a total of 250,000 tons of sediment that reached as far as 30 meters below sea level. Sanderson and his colleagues took known concentrations of various pollutants in the sediment, including the biocide tributyltin (TBT), heavy metals and chemical warfare agents, to see what was being stirred up.

They calculated how much of each pollutant would become bioavailable and calculated a toxicity threshold for the sediment. More than 5.8 milligrams of sediment resuspended per liter of seawater has been predicted to be harmful to marine life. The team found that the contaminants in the sediment, including lead and TBT — an endocrine disruptor used to protect ships’ hulls — accounted for most of the toxicity. Lead and TBT alone accounted for 75% of the toxicity.

The sediment thrown up by the Nord Stream 1 explosion contained pollutants that exceeded the safe limit for 15 days at depths between 95 and 53 meters. The Nord Stream 2 pipeline exceeded the threshold for 34 days at depths between 78 and 42 meters. In all, the blasts contaminated 11 cubic kilometers of seawater for more than a month. The work, which is peer-reviewed in a peer-reviewed journal, has been published as Preprint1.

“Impressive Modeling”

“It’s an impressive modeling exercise,” says Rodney Forster, a marine scientist at the University of Hull, UK. And the teams’ calculations on the spread of the sediment plume clearly show that the sediment did not reach the sea surface. “This explains why no visible plume of suspended matter can be seen on satellite images after the event, apart from the bubble plume,” adds Forster.

The impact of pollutants on marine life will not be known for months, if not years. But Sanderson is worried about some animals in the area. The area is a known spawning ground for cod. “There are high concentrations over a large area over a long period of time,” he says of the contaminated sediment. “It could potentially have a significant impact” on cod stocks. And the presence of TBT is “not good news for these organisms,” he says. The explosions occurred at the end of the cod spawning season and the eggs float to depths reached by the blown sediment. Sanderson speculates that the physical weight of the sediment could be another problem for the eggs, depressing them so that they no longer swim at the optimal depth to thrive before hatching.

Other animals that may be affected include the harbor porpoise, of which it is estimated that there are only 500 left in the Baltic Sea. The loss of even one would affect this population. The explosions may have damaged the porpoises’ hearing and thus their ability to communicate.

Sanderson says the team’s research shows that sediment levels need to be addressed alongside any activity that stirs up the seafloor – like installing pipelines or wind turbines or fishing. “The environmental impact of conflicts also needs to be addressed,” he adds.