The waste left Albania in July 2024 in more than a hundred containers, bound for Thailand, which ended up rejecting the shipment.

Albanian customs documents indicated the shipment contained iron oxide, a legal export -- but the environmental group Basel Action Network (BAN) cited a whistleblower as saying it contained electric arc furnace dust, a toxic byproduct of steelmaking.

"Experts, in the presence of prosecutors, have been collecting samples from the impounded containers for a week" in the Albanian port of Durres, the prosecutor's office in the city told AFP on Friday.

"Everything is done according to a very rigorous protocol and under strict supervision," it said, adding that the samples would be sent to a laboratory in Italy.

The Durres prosecutors said they have opened an investigation into suspected smuggling and abuse of office in cooperation with the European Anti-Fraud Office.

It had requested several public institutions to make their laboratories and experts available for analyses as early as November 2024.

"It is difficult to understand why the prosecutors' office took so long to have the waste sampled and analysed," said BAN founder Jim Puckett, warning that the toxic material could have leaked or been tampered with.

"In any case, we can hope for an accurate result and progress on this case."

Environmental NGOs complain that industrial waste is often shipped by Western countries to be processed in Asia and Africa, in a global trade that they estimate may be worth up to $82 billion a year.