Julio Da Costa, 52, and Juliano Da Costa, 28, of Swindon, had originally pleaded not guilty to the offences and were due to stand trial in March, but the pair will now face sentencing following the change in plea.
They will be jointly sentenced alongside Edwards Waste Paper Ltd, its director Simon Edwards and sales manager Jonathan Coombes, who pleaded guilty to the same charges at a hearing at the Old Bailey in April (see letsrecycle.com).
Charges filed against Worldwide Biorecyclables Ltd, the company owned by the Da Costas, were earlier withdrawn by the court as the company had ceased trading.
The court confirmed that sentencing of the five will take place on March 5.
The prosecution followed a two-year investigation by the Environment Agencys National Enforcement Service into the export in 2009 of 89 containers containing around 15,000 tonnes of contaminated waste to Brazil, codenamed Operation Mound.
The shipment described as mixed plastics was rejected by the Brazilian authorities the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA) and the containers were repatriated to the port of Felixstowe in Suffolk.
Prosecutors argued that the men had breached terms of the Transfrontier Shipment of Waste Regulations 2007, after the containers were found to contain mixed waste including nappies, blood packs and syringes.
The case was widely covered by the national press when the alleged offences came to light, and caused some embarrassment for the UK internationally.
The maximum penalty for exporting waste illegally is an unlimited fine or up to two years in prison.