Nineteen individuals and three companies are currently under investigation on suspicion of trans-national waste trafficking and fraud in the operation active in Italy, Austria, Germany, Croatia, Serbia and Switzerland, Italy's carabinieri police said in a statement.

Twelve out of the 19 individuals were arrested and a plant in South Tyrol was seized following the four-year investigation. Contacted by AFP, police would not disclose the nationality of the suspects.

The alleged scheme -- which handed the two Italian companies involved "an illicit profit of hundreds of thousands of euros" -- involved turning ashes with illegal levels of pollutants into products such as barbeque briquettes, soil improvers, and additives for animal feed and for concrete, they said.

The investigation, which included telephone wiretaps, revealed a network of companies created to manage the entire supply chain, "from the production of the ashes to their distribution on the European market."

Plants in Croatia and Serbia produced briquettes from the toxic ashes, while sites in Germany and Austria used them for agricultural purposes.

The ashes were derived from pyro-gasification -- in which organic waste is heated to high temperatures in an oxygen-free atmosphere to transform it into gas -- and had concentrations of polycyclic aromatic hydrocarbons, or PAHs, above legal limits, said police.

PAHs in the air are associated with increased cancer incidence, according to the World Health Association.

The preliminary investigating judge in the court of Trento has also alleged unlawful conduct by officials within the provincial environmental agency of Bolzano, police said. That agency is tasked with inspections and verifications.

- Big profits -

The agency is alleged to have "played an essential role in supporting, shielding and facilitating the owners of the companies at the centre of the investigation," police wrote.

Not only did they fail to stop the trafficking of the toxic products, but they helped make the business appear legitimate, police alleged.

Agency employees did so by promoting favourable interpretations of regulations for the plants involved to politicians, delaying sanctions, and suggesting ways to circumvent prohibitions through administrative means, according to police.

They also allegedly exerted internal pressure on technicians tasked with carrying out investigations to avoid documents being sent to national authorities that would have confirmed that the ashes should have been correctly classified as waste.

"These public officials were not marginal figures; in fact, without their technical-institutional contribution -- capable, on paper, of transforming a toxic waste into a 'by-product' - the system could not have withstood national and European inspections and audits," wrote police.

The illegal profit achieved from the scheme stemmed from "the avoided cost of proper disposal of thousands of tons of ashes and from their sale as high-value products, as well as from the acquisition of CO2 quotas to be placed on the market."

During the course of the investigation police carried out inspections and seizures at various plants in South Tyrol, in Veneto and Lombardy, and in Austria, Croatia, and Germany.