Almost exactly 48 years ago to the day, the 140m cargo ship Serra Branca sailed up the Tees estuary and docked at Seal Sands. Battered and bruised from a storm at sea a few days earlier, Teesside was chosen as the location to clean up the spill of its highly toxic cargo.

On 5th December 1974, 109 barrels of Aroclor - the brand name for a harmful chemical which is a PCB - were loaded onto a lorry at the Monsanto chemical factory in Newport in south Wales and driven to Liverpool’s docks to be loaded onto the Serra Branca.

PCBs, short for polychlorinated biphenyls, are a type of “forever chemical”. They aren’t soluble in water, which means that they accumulate as they go up the food chain.

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They also happen to be highly carcinogenic, and were widely used in industrial and consumer products like paints and as heat transfer fluids. Although their dangerous properties were confirmed in the 1960s their use continued before they were outlawed by most countries in the 70s.

In 1968 PCBs contaminated the food chain in Japan leading to more than 500 deaths and a national scandal.

Monsanto were sued in the early 2000s after a number of people came forward suffering from the long-lasting effects of the toxic chemicals that they produced.

Monsanto and its successor companies are reported to have paid out $820m in compensation to claims made relating to the harm caused by PCBs that they produced.

As part of the company’s long-running legal battles, internal documents from the time were made public and show that Monsanto knew about the harmful properties of PCBs in the 1950s, although they continued to produce them until 1977. When they discovered how harmful PCBs were, Monsanto created a ‘Pollution Abatement Plan’ to try to mitigate the effects of any incoming ecological disaster on their bottom line.

The Northern Echo: The former Monsanto site at Seal SandsThe former Monsanto site at Seal Sands (Image: Ineos)

One option that was suggested in the documents that were revealed decades later was to do nothing.

Monsanto decided to reveal the environmental harm of PCBs, although they now were able to control the narrative around how much information was known and when it would become known.

The Serra Branca left Liverpool on the 16th of January as it set a course for Glasgow, where it was due to collect more cargo before crossing the Atlantic to Brazil, however a storm the following night shook its hazardous cargo free within the hold, with 60 of the drums falling and suffering what Monsanto’s own assessment at the time described as “considerable damage”.

The polluted ship was redirected to Teesside, where Monsanto had another factory at Seal Sands, for the company to begin the clean up work.

In a decision that will infuriate locals to the area, the site on the north bank of the Tees is repeatedly referred to by Monsanto as their "Middlesbrough" site.

“The first problem arose,” it says in Monsanto’s report of the incident, “when the dockers walked off the scene, believing Aroclor to present a serious hazard to personnel.”

The Northern Echo: Monsanto's Seal Sands factory is now owned by Ineos.Monsanto's Seal Sands factory is now owned by Ineos. (Image: Google)

Smoggie dockers refused to handle the cargo for two days, and the manager of the Port Authority refused to let the hazardous material be removed from the ship until insurance could be provided to protect the workers.

After clearing the ship and sending the remainder of the undamaged cargo to Brazil, the salvaged PCBs were sent back to Newport by road to be disposed of. Much of the harmful waste from Monsanto’s Newport factory - the largest chemical factory in Europe at the time - was dumped in unlicensed landfill sites by a third party that they had contracted.

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Monsanto’s Seal Sands site eventually came into the ownership of chemical giant Ineos, who announced in 2020 that they would shut and demolish the site, leading to the loss of 60 jobs.

It’s generally accepted by scientists now that PCBs cause problems with the viability of young aquatic mammals, with research suggesting that high levels of PCBs in the food chain are killing killer whales before they reach maturity.

Dr Susan Wilson has spent three decades monitoring seal numbers in the Tees and has argued that the same is also true of seals.

The Northern Echo: Volunteer Sally Bunce is also concerned about the number of dead seals found along the coast near the Tees.Volunteer Sally Bunce is also concerned about the number of dead seals found along the coast near the Tees.

Written evidence submitted by Dr Wilson to the Parliamentary committee on the environment, which has set up a panel to investigate the die-off of crustaceans in the area over the last year or so, claims that after an increase in the number of seals breeding at the mouth of the Tees from 1997 until 2019 there has been a sudden decline.

In 2022 36 seal pups were born at Seal Sands, however 30 of them went on to die prematurely. Dr Wilson suggests “the possibility of their growth and health being compromised by contamination by PCBs”, although admits no sampling has been taken.

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It’s hoped that the imminent report into the recent deaths of wildlife in the Tees and off the coast will provide answers for fishermen, campaigners and residents along the coast for the unexplained deaths.