Four former executives with a Finnish nickel mining company accused of contaminating lakes with uranium, cadmium and other toxic elements went on trial Tuesday charged with aggravated environmental damage.

Talvivaara Sotkamo, the bankrupt operator of the European Union's biggest nickel mine, is also named among the defendants in the highly-publicised case in Kainuu, east-central Finland.

The prosecutor asked the district court to seize 13.3 million euros ($14.6 million) in illegal profits from Talvivaara Sotkamo's estate and the four executives, according to court documents.

Situated around 500 kilometres (300 miles) north of Helsinki, the mine opened in 2008 amid expectations it would usher in a new era in nickel mining in Finland.

But the operation ended in environmental disaster and economic failure after toxic levels of nickel, cadmium, uranium, aluminium and zinc were detected in nearby lakes and rivers in 2012, and again in 2013 after waste water began to leak from the mine.

The company filed for bankruptcy at the end of 2014.

The case has generated huge interest in Finland, prompting the Kainuu court to hold the trial at a university campus because its courtroom is too small to accommodate the crowd.

The prosecutor is seeking suspended sentences and fines for the company's former chief executive, Pekka Pera, and three of his colleagues.

He also asked the court to impose a maximum fine of 850,000 euros ($932,000) on the bankrupt company for allegedly negligent procedures.

Both the company and executives pleaded not guilty.

Finland's largest daily Helsingin Sanomat cited unnamed sources as saying the defence would argue that "some environmental degradation" had been permitted by the authorities as it was part of mining.

The Finnish state has taken over the open-pit mine until a new ownership structure is decided on.

The mine is currently filled with water caused by a flooding problem that has to be resolved if operations are to resume.

The trial is expected to last around two months.

Damage claims from local landowners will be heard at a separate trial.