Fabio Riva, the son of steel tycoon Emilio Riva, was cuffed by border police as he arrived at Fiumicino airport yesterday after losing a battle in May against his extradition from London.
Riva, who had been wanted since 2012, is now expected to stand trial with about 50 other defendants in Taranto in the Puglia region of southern Italy, where the family's ageing Ilva plant is based.
The charges against them range from causing an environmental disaster and poisoning foodstuffs to corruption and abuse of office.
Riva's billionaire father had been placed under house arrest in 2012 but died last year.
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The site in Taranto, which provides work for around 16,000 people, has been under special administration since 2013 after the Rivas were accused of failing to prevent toxic emissions including carcinogenic particles from spewing out across the town.
The plant used to churn out an estimated nine million tonnes of steel per year - about a third of the country's total production.
Prosecutors in Taranto, who say the emissions have caused at least 400 deaths, expect the case to go to trial later this year.
Prime Minister Matteo Renzi has promised to clean up Ilva and sell it on. And despite the health fallout, locals cheer support for one of the few large-scale employers in the area, where the jobless rate stands at 20.6 per cent - well above the 12.7 per cent national average.