The head of chemical giant Orica has told an inquiry NSW Environment Minister Robyn Parker refused to take his calls, reigniting calls for her sacking. Orica chief executive Graeme Liebelt told a parliamentary inquiry that he phoned Ms Parker three times after the August 8 chemical accident but only got as far as her chief of staff. Mr Liebelt said he had wanted to express his regret for the incident when he called on August 15, 16 and 17, and tell Ms Parker the company was taking the hexavalent chromium leak 'very seriously'. However, her chief of staff informed him Ms Parker 'was busy', the chemical company boss told the hearing in Sydney on Thursday. 'I called the chief of staff because I was at that time seeking to speak to the minister,' he told the inquiry. 'I had intended to say essentially three things - one is to express my regret for the incident, second is to say we were doing everything possible to respond to the incident in a responsible way, and to put these matters right. 'And then thirdly, to reinforce with the minister that we as a company take these matters very seriously, and we believe we have good standards in this area. 'I spoke to the chief of staff on a number of occasions and she explained to me that the minister was busy.' Ms Parker has been under fire over her handling of the August leak from the Kooragang Island plant, and the three day delay in notifying nearby Stockton residents of the accident. Last week she faced calls for her removal when she could not name Mr Liebelt as head of Orica, and admitted she had not spoken to anyone from the company after a separate ammonia leak from the plant. Mr Liebelt's comments were seized on by the state opposition, who repeated calls for Ms Parker's sacking. Labor leader John Robertson accused the environment minister of 'gross negligence' and 'staggering incompetence'. '(Premier) Barry O'Farrell needs to pick up the phone from India and sack Robyn Parker today for her negligence in the way she is dealing with this portfolio,' Mr Robertson told reporters. 'There is no excuse for this minister not taking a phone call from the managing director of Orica. This is absolute gross negligence, and this woman should be sacked.' But Ms Parker has defended her decision not to take the calls, saying it would have been inappropriate to speak to Mr Liebelt. 'By the time Orica called my office there was a review of the incident under way and that was the appropriate place for them to take any information,' Ms Parker said in a statement. 'Orica was too late in informing the community, too late in contacting authorities and too late in contacting the government. 'The time has come for Orica to stop shifting blame and become a good corporate citizen.' Ms Parker, Premier Barry O'Farrell and Health Minister Jillian Skinner will front the inquiry into the leak from the Kooragang Island plant on Monday.