How 25,000 kilograms of ‘toxic’ tar was spilled in the Thames

Alex Haider had just returned from a swim when she first saw the tar. Nestled between bits of blackened seaweed floating on the water, you could almost miss it were it not for its gooey texture. At first, she paid it no mind, thinking it was just another piece of detritus: everything the sea rejects ends up in Southend. But there was something strange about what she spotted on 29 August. It was huge, black and, strangest of all, still warm to the touch. It also seemed to absorb anything it came into contact with, pulling in bits of plastic, rocks and seaweed. She decided to take it home for her husband Shah to look at.

Over the next few weeks, dozens of these tar blobs would start appearing on the 100-metre stretch of beach near the couple’s house. They collected each piece of the mysterious black tar they could find and took it home, and watched as it melted and absorbed the plastic bags they stored it in. “I was just thinking: Where is it from?”

Trying to answer that question would expose how 25 tonnes of “toxic” tar was spilled into the Thames in the capital’s main industrial port, and how the private body that was supposed to deal with it — the Port of London Authority (PLA) — kept the public in the dark. The Londoner has now discovered that the PLA underplayed its potentially “devastating” impact, as well as that FM Conway, the company responsible for the spill, may have misled authorities about its size. We’ve also discovered that over a hundred similar undisclosed petrochemical spills happened in the river in the last five years.

The secret spill

We’re driving to the beach along the “Golden Mile” of Southend, past fish and chip shops and the unlit fluorescent signs of amusement arcades, in Shah’s battered, sand-filled Hyundai. He’s middle-aged with glasses, greying hair and a beard, and is wearing cargo shorts despite the cold November weather. He’s also telling me about human excrement; specifically, the time he got doused in it.

It was October 2021, and while swimming in the sea by Southend, he and Alex were caught in the middle of an unannounced raw sewage release by Anglian Water. It was the moment that turned him and Alex into the campaigners they are now: the founders of a group called Southend Against Sewage.

But for all their campaigning, mysterious black tar was far outside of their remit. Their first thought, he says, was to call the Environment Agency (EA), the government’s main environmental regulator. The EA eventually told them they’d been informed of an incident by the Port of London Authority (PLA), and that it was being handled by the port’s contractors.

The PLA is a private body that manages the Thames from Teddington in west London to the estuary out east and oversees the capital’s major ports, which mostly sit between Dagenham and Gravesend. It is largely funded by dues paid by its members — the industrial users of the river and the PLA’s port facilities. In turn, it is supposed to use that money to “protect and enhance the environment”. That means that it takes the frontline in handling and preventing pollution incidents, only calling in the EA when something severe happens. In essence, it’s supposed to be a self-regulating system that keeps the Thames clean and profitable.

But across late August and early September, more tar started to appear on Southend’s beaches. The head of a local beach cleanup group, Win O'Sullivan, says she collected half a dozen pieces from a 20ft stretch of sea front in just one day. Suddenly, those initial promises that everything was under control began to feel hollow. As we walk along one of Southend’s desolate beaches, Shah tells me of how they started to get messages from friends and other campaigners about tar washing up as far away as Clacton or even in the Blackwater near Maldon.

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In an effort to find out what was going on, they posted about the issue on social media, until an email from an anonymous whistleblower entered their inbox. The spill was the “direct result of a valve failure on a tarmac silo in Dartford vicinity of the Thames in the last few weeks,” it read. “Port of London Authority are aware of the situation and claim to have recovered three-quarters of it, but it appears all very hush-hush.”

He got in touch with the PLA to ask what had gone on, and soon after he got a call from the organisation's head of corporate affairs. “They were completely shocked that we knew about it,” he recalls. “We told them what we know… And that’s when they admitted it.” Shah says he told the PLA they needed to issue a public statement. And so finally on 3 September, the PLA publicly acknowledged that over two weeks earlier, on 16 August, 25,000kg of bitumen had been spilled into the river at a dock in Gravesend. The site responsible for the spill was Imperial Wharf, a major silo for construction giant FM Conway. 

When I reach out to the PLA, they claim to have collected 20 tonnes of bitumen from the Thames since the incident, but say they’ve also been told by FM Conway that it’s collected nine tonnes itself — a total collection that was four tonnes more than the amount the company claimed it had spilled in the river. The “discrepancy”, as the PLA puts it, has raised the possibility that FM Conway may have underreported the spill’s size. Indeed, in the days after the spill, the company initially claimed it was just one to five tonnes of bitumen, before revising the figure up weeks later. When I put this, and other aspects of the story, to the construction firm, they declined to comment beyond acknowledging the incident occurred, citing the ongoing investigation.

Back at the beach in Southend, Alex and Shah are giving me an energetic demonstration of the first moment they spotted the tar on their local beach. That’s when we see it: a fresh clump of tar washed up on the sand, seven weeks after the spill happened.

‘It’s like our Serengeti’

Though the Thames doesn’t exactly have the cleanest reputation, tireless work by environmental campaigners over the past few decades means that it’s once again a thriving natural habitat. Nowhere is this more evident than the estuary: the southern bank from Gravesend is almost all wildlife reserves, and there are even colonies of sea horses, sharks and porpoises in the bay. Much of the area is a protected Site of Special Scientific Interest, and it’s one of the biggest mudflats in the UK, a type of habitat utterly vital to a swathe of different bird species.

“It’s like our Serengeti,” explains Alan Johnson, Kent and Essex area manager for the RSPB. He manages the RSPB wildlife sanctuary at Cliffe Pools, just a few miles upstream from the FM Conway site in Gravesend. Despite their proximity to the spill, he says he was not directly informed of it until several days later, after a contact in a local group forwarded on a message from the contractor leading the cleanup.

When I later contact the PLA for more information about spills in the Thames, they initially send a statement explaining what had happened in the bitumen spill, which suggests that all “local authorities were informed on day one”. But Southend council tells The Londoner they weren’t informed of the spill until 21 August, five days after it happened. Campaigners and locals like Shah fear that this lack of transparency, deliberate or not, hampered efforts to clean up the spill. The PLA claims that they informed just the nearest councils on day one, but the number it involved increased “from those closest to the spill to begin with, to a wider geographical area as bitumen was found further afield”.

Another point repeated in the PLA’s statements is that the bitumen was not dangerous and didn’t pose “any risk to public health”. But marine toxicologists spoken to by The Londoner were extremely worried about the dangers the chemicals in bitumen could pose to the area’s wildlife. Dr Tom Miller, senior lecturer in environmental sciences at Brunel University, told me that that bitumen contains an array of “toxic” pollutants. They cause deformities and damage to the hearts and lungs of fish, liver cancers and can have a devastating impact on invertebrates and algae. By affecting those vital feeder species, toxins can build up in the bodies of animals higher up on the food chain.

“They're saying it's harmless, but when something's in the water, it wears away and dissolves… You start to think: hang on, if that’s floating in the water, what's that giving off?,” Alex tells me over cups of tea in the couple’s kitchen. “It’s gradual, so you’re not gonna know straight away the impact it’s had on the wildlife…” she explains, trailing off into worried silence. Indeed, the problem with tracking the environmental impact of these kinds of spills is that it’s almost impossible to prove: for one it often takes a long time for the effects of chemical toxins to manifest, and, even then, short of capturing a bunch of protected animal species and testing the amount of chemicals in their blood en masse, there’s very little way to prove the exact cause of their exposure.

You’d assume that for all that spilled tar, it’d be easy to work out what actually caused it. But other than the tip off about “valve failure”, there’s no information about the spill itself. In a statement, FM Conway refused to tell me what had caused it, again citing the ongoing EA investigation.

Meanwhile, the Health and Safety Executive, the main government overseer of workplace maintenance and safety, said it was not only not involved with looking into the spill, but had no record of ever visiting the FM Conway site. When I pushed on how it is that they had never inspected a major bitumen terminal run by one of the UK’s biggest tarmac firms, they suddenly declared that they were investigating the incident and that as a result they couldn’t provide any information “at this time”.

But through our digging, we discovered that this was far from a one-off.

106 spills in five years

When we first heard about the bitumen spill in Gravesend, my first thought was to try and see if any similar incidents had happened in the past. But looking through the PLA’s website, we couldn’t find any evidence of other spills. This seemed strange, considering the PLA had its own specialist unit to deal with oil spills. Called Thames Oil Spill Clearance Associated (or TOSCA), it’s a 24/7 oil spill response unit with a large barge and two smaller response ships, all kitted out with dozens of pieces of specialist equipment. The unit is funded by TOSCA’s members, which include Shell, Esso, and an assortment of other petrochemical companies that use the capital’s industrial ports.

Using a little known piece of legislation called the Environmental Information Regulations, we were able to force the PLA to disclose how many spills there had been since 2014. In that time, the port has recorded some 177 petrochemical spills, 106 of which were in the last five years alone. That’s an average of almost two each month.

They stressed in that release that each of those spills (other than the bitumen) was tier one: the least serious form that can be controlled by “utilising local resources without assistance from other areas”. But when we pushed for more information on how they made those assessments — bear in mind the lowest severity incidents usually mean it’s unlikely that a regulator like the EA would get involved — their lawyers admitted they had “no formal, measurable criteria used to determine the tier level of an incident”. Instead the PLA teams made holistic assessments on a case-by-case basis.

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When I told this news to Shah and Alex, it shook them: the campaigners so used to pushing for accountability for sewage companies now had a whole new world to worry about. “When we see the boats going down [to the port], they're 2km or 3km out to sea. It feels like a different world,” says Shah. “Tar is one thing. That floats, you can see it. But what other petrochemicals are entering out into the sea that we're being told is under control?”

The whole situation poses some fundamental questions about how the PLA operates. The PLA is funded by the very companies whose spills it is supposed to stop, or escalate to the EA when bad ones happen. As a result, the port may have a vested interest in not creating too many problems for its members, lest they move their operations elsewhere. Those questions can also be posed by the EA, who seem fine with letting the port and its industrial users regulate themselves (even as the same model went disastrously wrong in the water sector, leading to a national crisis over sewage spills). We reached out to the regulator for this article, asking how many of the 121 spills in the Thames in the last five years they had been told about or looked into, but they refused to answer any of our questions, citing its ongoing investigation into the bitumen spill.

A spokesperson for the PLA stressed that its decision not to publicise the incident was based on advice by the local authorities who had “more direct relationships” with locals and that so far there “was no reported evidence of wildlife distress” from the spill. They added they were at the site within an hour and notified key agencies that day of the event, as well as an array of local councils. They stressed that they submit an annual return containing the total number of oil spills it logs to the coastguard each year, who can then choose to inform the EA. “We care deeply and act on our aims to improve the River Thames,” they went on. “Our response to this spill was quick, we recovered a very significant amount, and, crucially, helped to protect the local environment.”

After weeks of investigating, it still felt like there were more questions than answers. It's a feeling shared by the locals we speak to. “It's like Pandora's box. Once you open up one thing, there's something else, and then something else,” says Alex. “Where does this end?”