What do we still need to know about the Tyne nurdle spill?

On 19 July about 18 tonnes of plastic nurdles, consisting of about one billion tiny balls, spilled into the River Tyne after a crash between ships at the Port of Tyne.

It is believed to be the worst recorded incident of its type in Europe.

In the months since, teams of volunteers have joined in efforts to collect the microplastics that continue to wash up on north-east England's coast.

But several questions remain. So what do we know about the spill right now - and what are we still waiting to find out?

A wind turbine installation vessel called the Wind Orca collided with a container ship berthed at the Port of Tyne.

A gantry crane on the quayside collapsed and ended up lying across the ship.

Two containers on the BG Orange were full of nurdles. These are pre-production plastic pellets, about the size of a lentil, which are used as the raw material to manufacture nearly all everyday plastic goods.

About 18 tonnes of these pellets spilled into the water because of the crash.

This is still being investigated.

Northumbria Police said it was investigating the collision and so far, no-one has been arrested. The Marine Accident Investigation Branch is also investigating.

The Port of Tyne previously said it, along with others, had asked the International Maritime Organisation (IMO) to consider enforcing safer transportation methods for nurdles, something environmental groups have long called for.

By the end of September about 28% of the nurdles had been recovered, according to scientists.

But the Port of Tyne, the Environment Agency and the North East Mayoral Strategic Authority (MSA) said the numbers of nurdles washing up ashore had already "reduced significantly" by then and numbers were continuing to fall.

They said they believed the full recovery of the 18 tonnes was not achievable. When asked what percentage recovery rate would be considered a success, the bodies said they would measure success via various metrics including shoreline surveys.

The pellets from the spill have been found along the English coast from Northumberland to North Yorkshire.

On Friday the Danish Environment Protection Agency confirmed pellets found on the country's western coast had also likely originated from the Tyne spill.

Dr Matthew Perks at Newcastle University and his colleagues are monitoring the movement of the nurdles and examining how the pellets may deteriorate in water.

The team's modelling so far suggests about one in eight of the billion nurdles remain in the Tyne estuary and high river flows could flush these microplastics downstream in the autumn.

Perks said this was a crucial opportunity to collect the pellets.

Nevertheless he said it was unclear how far some of the nurdles could really travel.

"As time goes by, it becomes more difficult to pinpoint the areas where these nodules are likely to be," he said.

It is also unclear when the nurdles will start breaking down into nanoplastics. "That will change the way they behave," he said.

Long story short – we do not know yet.

Professor Bhavani Narayanaswamy at the Scottish Association for Marine Science said it could be months or years before we understood the full impact of the spill.

She said the nurdles could affect wildlife in various ways, including getting stuck in animal digestive tracts and adsorbing chemicals which then may be toxic to wildlife when ingested.

Prof Narayanaswamy said there was little research on the long-term impact of plastic pollution on animals compared with its immediate effects.

Dan Turner, who coordinates the North East England Beached Bird Survey, said the group had collected several dead birds along the coast which they would be testing for nurdles next month.

"It is quite possible that the seabirds have mistaken the plastic for fish eggs," he previously told the BBC.

Recovery is largely being paid for by insurers representing BG Orange, which was carrying the pellets, as well as local councils and the Port of Tyne.

Thousands of volunteers have also been involved in the clean-up.

Councils have been told to record their costs so they can seek compensation from the insurers of those ultimately found responsible.

The multi-agency group, consisting of the North East MSA, Port of Tyne and the EA, said the nurdle recovery programme was continuing but it had increasingly moved away from "large-scale clean-up activity" towards "targeted recovery and monitoring".

Environmental charity Fidra said it was unclear how long the clean-up would need to continue, considering the fact that nurdles could stay in water for years.

It said a long-term plan was required to tackle the pollution and the plans should be "adequately resourced" with responsibility clearly defined.

Volunteer Lou Shackleton said there was still a core group of individuals who gave up their spare time to monitor and recover nurdles on local beach.

She said the group needed all the help they could get.

"If you're happy to wrap up against the rain and the wind... come and join us," she said.

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