A toxic chemical which spilled into a canal in Walsall could be removed or neutralised within a week, an expert has claimed.

Sodium cyanide was one of three substances released into the canal after what the Environment Agency (EA) called a waste disposal incident at Anochrome Ltd.

Twelve miles of canals across the Black Country and Birmingham were cordoned off on Tuesday but the EA said on Wednesday the contamination zone was “smaller than expected”.

Dr Jonathan Paul, a senior lecturer in geosciences, said the situation would hopefully be resolved within a week.

Canal cyanide spill: Where is it and what are the dangers

Anochrome Ltd, which deals in surface coatings and sealing, said it “regrettably” released chemicals into the Walsall waterway in the early hours of Monday morning.

About 100 dead fish have been seen floating on the surface of the canal near Reservoir Place.

People have been urged not to go near a long section of the canal network from the middle of the borough to Birmingham and connected waterways in Wednesbury, Tipton and West Bromwich.

Speaking to BBC Radio WM, Dr Paul, a lecturer at Royal Holloway, University of London, said there were several strategies the EA could use to dilute or remove the toxic substance from the water.

“One of the cheaper solutions would be just to dilute the water, pump in a load of fresh water from somewhere else so the concentrations go down,” he said.

“There are other more active things they could do, they could run it through a filter to try and remove it.

“Or they could add certain chemicals to the water which would have the effect of taking the cyanide out of the water and making it a kind of scum on the surface which could be skimmed off and then disposed of safely.”

Sodium cyanide can cause seizures, vomiting and loss of consciousness.

Dr Paul said the EA would probably be rolling out these measures over a matter of days.

“Hopefully, touch wood, this situation will be resolved within a week,” he said.

“If there is a silver lining, it’s that cyanide breaks down naturally quite quickly over a course of days.”

The spillage has also affected people travelling on narrowboats, including Chris Smith and his family, who said they were trapped on the outskirts of Birmingham on a family holiday.

Mr Smith said they were unable to go home due to the closure of the canal and potentially might have to ask his employers for more time off.

Other people living on boats on the canal in the affected area were being made aware of the spill, the Canal and River Trust said.

Its chief executive, Richard Parry said: “It’s very serious, it’s very distressing, and it’s infuriating.

“The canals provide such benefits for people and for nature, they run through so many communities and to have a chemical of this toxicity released into the canal is very distressing.”

Mr Parry said initial tests of the canal showed the sodium cyanide had stayed largely at the area where it went into the canal, rather than spreading through the water.

“We’re hopeful once further testing is done, it may be possible at some point to reduce the affected area,” he added.

“But clearly the extent of the contamination in the area affected is going to be very severe.”

The EA said it believed three substances had leaked into the canal after the incident at Anochrome Limited.

They were sodium cyanide, sodium hydroxide, and possibly zinc.

Dr Paul said he suspected the firm was using the sodium cyanide to put surfaces on metals, describing it as “a very strong solvent like glue”.

He said sodium hydroxide, which is more commonly known as caustic soda, had the potential to make water “very alkaline” which would pose a risk to aquatic life while zinc would make water “very cloudy”.

“We have to appreciate this has happened in a canal network not a fast-flowing river,” he added.

“When you think of canals, the water doesn’t really go anywhere, and if it does move it moves at a very sluggish pace.

“So what the contaminants are doing is they’re essentially staying the in the same place [or] slowly diffusing in the water.”

Dr Alex Baker, an assistant professor of Chemistry at the University of Warwick, said there would be problems in the local ecosystem “for a fair while”.

He told the BBC: “If another predator comes along and eats the fish, that cyanide starts making its way up the food chain.

“We’re going to see cyanide in the soil as well so really it’s going to cause biological problems in the ecosystem for a fair while – not for humans, but definitely for small animals.”

Ducks, geese, and moorhens were spotted on or near the canal in the days after the spillage and a wide array of birds can be seen diving for fish across the Black Country canal network, with sightings including kingfishers and cormorants.

Speaking about similar cases of chemical spillages, Dr Baker said: “Romania had a serious problem [with sodium cyanide], far beyond what Birmingham is currently seeing, back in the 2000s.

“It took several weeks for it to fully move down into the sea.”

The spillage occurred in January 2000, when waste containing sodium cyanide flowed into the River Tisza, a tributary of the Danube, following a dam burst at a goldmine in Romania.

The accident killed about 80% of fish in the river and devastated local populations of birds and other animals.

• The chemical sodium cyanide is a white crystal-like solid with a faint almond odour
• It is used in industry for metal cleaning, plating and extraction
• When cyanide salts are swallowed they release cyanide in the body – they can also be absorbed through the skin
• Expose can cause symptoms including headaches, nausea, dizziness, loss of consciousness, seizures and vomiting
• It can be rapidly fatal if inhaled or ingested as it interferes with the body’s ability to use oxygen

Sodium cyanide dissolves in water and can have serious adverse health effects if people or pets come into direct contact with it, the council advised.

Anyone exposed to the water who felt unwell should seek medical advice through the NHS 111 service or phone 999 in an emergency, a spokesperson for the authority added.

People living on boats on the canal in the affected area were being made aware of the spill, the Canal and River Trust said.