Brazilian authorities are demanding that more than 1,400 tonnes of hazardous British waste found in three ports be returned to the UK.
The Brazilian environment agency, Ibama, says that international treaties have been violated.
An investigation into how and why the waste was sent to Brazil has been launched by the British government.
It has emerged that two companies named by Brazil as suspected exporters of the waste are owned by a Brazilian.
The waste, which included syringes, condoms, nappies and bags of blood, was found in about 90 shipping containers on three Brazilian docks in recent months.
The latest 25 containers found in a port near Sao Paulo were put on show for journalists on Friday.
'Not a rubbish dump'
The BBC's Gary Duffy said that inside them was everything from leftover food to cleaning products, creating a foul-smelling mess.
Among the rubbish were the names of many British supermarkets, and UK newspapers were also clearly identifiable.
Ibama officials say they want the waste sent back to the UK.
"We will ask for the repatriation of this garbage," said Roberto Messias, Ibama president.
"Clearly, Brazil is not a big rubbish dump of the world."
Reports in the UK media say the waste was sent from Felixstowe in eastern England to the port of Santos, near Sao Paulo, and two other ports in the southern state of Rio Grande do Sul.
The Brazilian companies that received the waste said they had been expecting recyclable plastic, The Times reported.
Ibama has named two British companies it suspects as being involved in the shipments.
The Brazilian director of those companies, who is based in England, told BBC Brazil that anything in the containers that was not plastic for recycling was the responsibility of his suppliers.
The British Embassy in Brazil said in a statement that it was investigating and would "not hesitate to act" if it was found that a UK company had violated the Basel Convention on the movement of hazardous waste.
Both the UK and Brazil are signatories of the treaty, which came into force in 1992.
UK Environment Secretary Hilary Benn told The Times he had ordered an investigation.
"If, having looked into this particular case, there are lessons that need to be learnt about enforcement, then we will do that," he said.
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