Abandoned Offshore Pipelines Keep Shedding Microplastics into the North Sea

Decades after offshore oil and gas installations have been decommissioned, the subsea pipelines left in their wake may still be releasing microplastics into the sea.

A new study in the Journal of Hazardous Materials estimates that abandoned and deteriorating pipelines and umbilicals - including hoses and cables - on the United Kingdom continental shelf alone produce approximately 500 metric tonnes (~550 US tons) of microplastics annually.

"Our lowest release scenario is a similar order of magnitude to the annual releases of microplastics to the North Sea from UK rivers," the study's authors write.

"Our highest is considerably more than annual microbead releases from cosmetics prior to the UK ban."

Microplastics from UK continental shelf oil and gas infrastructure

Marine scientist Freija Mendrik of the University of Plymouth led the research. She says the results draw attention to a major but neglected source of microplastic contamination that could already be influencing marine organisms.

"Our research is the first to estimate the mass of plastics contained in oil and gas infrastructure in the UK continental shelf, with more than 120,000 [metric tons] of plastic potentially remaining in the marine environment after decommissioning," she explains.

"Our findings have relevance outside the oil and gas sector and for decommissioning decision-making all over the world, not just the UK."

Oil and gas extraction has taken place on the UK continental shelf since the 1960s, principally in the North Sea.

To compile a dataset of every known pipeline and umbilical installed there, Mendrik and her colleagues used records held by the North Sea Transition Authority.

Those records provided approximate details on the pipelines' dimensions, the quantity and types of plastic used in their construction and coatings, and whether they were likely to have been decommissioned in situ - left where they were - or recovered.

How abandoned pipelines degrade on the seabed

In general, large rigid pipelines remained on the seabed after associated infrastructure was removed. Certain pipes were coated with a polymer known as coal tar epoxy (CTE), before being covered by concrete weights.

Another category of pipeline has no concrete protection and instead uses a coating of fusion-bonded epoxy (FBE), another polymer.

The researchers then examined physical samples of these plastics from Shell UK Ltd pipelines and umbilicals. The equipment had remained on the seabed at the Brent oilfield, off the Shetland Islands, for 22 years before its recovery in 2024.

Scanning electron microscopy identified cracking and fragmentation in plastic sections directly exposed to the marine environment.

The damage suggested decades of abrasion from coarse sand and currents, as well as marks associated with creatures that had established themselves on the surfaces of the pipes.

Pipe sections enclosed in concrete generally showed less deterioration, although the passage of time had nevertheless affected those samples too.

Using all of the available evidence to build a series of models, the team calculated that these legacy plastics from oil and gas companies could release roughly 4.5 to 500 metric tons of microplastics into the UK North Sea each year, depending on environmental conditions.

Environmental risks of legacy oil and gas plastics

Additional analysis enabled the team to assess the significant environmental hazards posed by leaving an estimated 121,000 metric tons of plastic on the North Sea floor.

"Even under a best-case scenario for microplastic emissions, degradation of large rigid pipelines decommissioned in situ in the UK continental shelf could result in extensive additional harm [to marine life] to that already being caused by plastic debris from other sources," Mendrik and colleagues write.

Although the research considers one particular part of the UK continental shelf, decommissioned oil and gas developments worldwide have also left legacy plastics behind.

"Based on the knowledge that 55 percent of the UK inventory may not be recovered and over 97 percent of all pipelines decommissioned in the USA since the 1960s have been left on the seafloor then, under business as usual, the amount of plastics destined to remain in the marine environment is likely substantial," the researchers conclude.

Plastics are not the sole concern. For long periods after oil and gas infrastructure is decommissioned, heavy metals including mercury and other pollutants can continue leaching into the ocean, with effects on marine life that remain unknown.

"This has implications for management, legislation and litigation," says University of Plymouth marine biologist Richard Thompson.

"Contributions from the oil and gas sector are considerable and, going forward, decommissioning processes need to be properly considered prior to deployment."

The study was published in the Journal of Hazardous Materials.

This article was fact-checked and edited by Clare Watson. Although we take pride in our process, we are only human. If you notice an error, please let us know.