Fresh claims about overseas investing brothers Rafael and Federico Grozovsky

Mr Cunliffe claimed that the brothers were implicated in a toxic air pollution case at a sugar mill in 2007. Photo / Mark Mitchell

Argentine investors who were approved to buy a farm in New Zealand were allegedly investigated for a pollution incident which later led to fatalities, Labour MP David Cunliffe says.

Speaking under Parliamentary privilege, Mr Cunliffe made fresh claims about Argentine brothers Rafael and Federico Grozovsky, who were given approval to buy Onetai Station in Taranaki in 2014 for $6 million.

Mr Cunliffe claimed that the brothers were implicated in a toxic air pollution case at a sugar mill in 2007 that allegedly led to lung cancer and premature death among the victims.

The brothers' consent to buy Onetai Station is already being reviewed because of a separate incident, highlighted by Mr Cunliffe two weeks ago.

In a case which is ongoing, the two company directors were being investigated for a spill from a tannery which polluted a river in Buenos Aires in 2011.

Mr Cunliffe said that the new allegations showed that the Overseas Investment Office (OIO) oversight was "practically non-existent".

In the House today, he asked Land Information Minister Louise Upston whether the OIO knew of the 2007 incident when it approved the brothers' investment.

Ms Upston confirmed that the OIO was aware of the case and was investigating it.

"As I have stated in the House before, if there are any breaches of any conditions related to an application, there are options that the office can take."

Even if the Argentine investors were found not guilty in relation to the pollution spills, they could risk sanctions if they did not disclose them when applying to invest in New Zealand.

The Grozovsky brothers' company Ceol and Muir came into the spotlight last month after it was linked to Mossack Fonseca, the law firm at the centre of the Panama Papers.

An investigation into that link by the OIO found no evidence of wrong-doing, though the investigation was reopened following Mr Cunliffe's subsequent allegations.