At least 20 former detention centre staff have become seriously ill from mould exposure, including an Australian teacher who now has a cognitive disability.
Transfield may have misled a Senate inquiry over its efforts to fix a mould problem at the facility.
Transfield manager Derek Osborn gave evidence at a parliamentary hearing on May 19, 2015 and insisted the company had a "detailed process to remove" the mould on asylum seeker tents.
However, leaked internal emails obtained by AAP cast doubt over his evidence.
An email dated May 12, 2015 from Transfield site manager Andrew White said a team had made good progress on cleaning mould off the outside of tents in the family and single male accommodation areas.
However, the email warned cleaning the insides of tents had "quite a few complications".
Mr White was "looking at conducting a workshop... in the near future" to come up with a plan.
He said issues to consider included: "messaging" and "behavioural management team involvement".
A former detention centre youth worker told AAP asylum seekers had been consistently complaining about mould in their tents and management did not want to validate those concerns.
Dr Jones was barred from wearing safety protective gear, such as a plastic suit, googles and full face mask during his scientific testing on Nauru.
"I was prohibited from wearing personal protective equipment by Transfield due to what they thought was a foreseeable risk of inciting a riot," he told AAP.
"I myself became unwell after the inspections ... I had gastrointestinal problems and long-term sinus issues."
Dr Jones' report gave both a single men's tent and a family tent mould ratings of four (visible mould growth greater than 10sqm).
Broadspectrum insists it maintained a safe and healthy workplace for its employees while working at the detention centre until late October 2017.
The Home Affairs Department denied there had been any illnesses as a result of mould exposure at the Nauru detention centre.
However, Comcare said it received a complaint in 2016 from a worker employed by a contractor, who had been diagnosed with a respiratory condition after living at the Nauru detention centre.
Fibromyalgia, sarcoidosis, neurological symptoms, chronic pain, chest infections and persistent coughs, are among the medical problems some ex-staff have developed.
Mould exposure also exacerbated multiple asthma and sinusitis cases among asylum seekers, according to Doctors for Refugees.