While Apple is enjoying hot worldwide sales of its fashion electronics, its health and environmental responsibilities have come under fire in China.

Poisoned workers at one of Apple's supplier factories on the Chinese mainland have demanded a formal written apology from the Mac maker despite its recent acknowledgment of violations in its supply base. The workers also said that some of them have been asked to leave their jobs.

The California-based maker of iPods, iPhones and iPads acknowledged for the first time in the Apple Supplier Responsibility 2011 Progress Report on Tuesday that 137 workers at the Suzhou facility of Wintek, one of Apple's touch screen suppliers, had suffered adverse health effects following exposure to n-hexane, a chemical in cleaning agents used in some manufacturing processes.

It said the company considered this series of incidents to be "a core violation for worker endangerment" and required the factory to stop using the chemical while it improved its ventilation system.

"Since these changes, no new workers have suffered difficulties from chemical exposure," it said.

The company also said it required Wintek to work with a consultant to improve its environmental health and safety processes and management systems, and it is monitoring the implementation of these corrective actions and preventive measures. A complete reaudit of the facility will be conducted in 2011, it said.

The report said that all 137 affected workers had been treated successfully at Wintek's expense, and that most of them had returned to work at the same factory.

But Jia Jingchuan, a 27-year-old victim at the Suzhou factory, said the Apple acknowledgment meant nothing to victims like him and that their rights continued to be under threat.

"I got a call last week from the company asking me to leave. They promised to give me 140,000 yuan ($21,253) in compensation for my departure, but only on condition that I sign an exemption agreement, which means the company would not take any responsibility if my health worsened in the future," he said.

He added that as far as he knew at least eight victims had already left.

"I don't want to leave the factory ... What if my health worsened? How can I then afford future medical treatment on my own?" said a worried Jia.

The man also said that he still felt numb in his legs and hands nearly eight months after being discharged from hospital, and that he always felt tired after "very little physical exertion".

The mobile phones of Wintek Suzhou factory's executives were turned off when China Daily called on Thursday.

"A leading global company like Apple should see to the conduct of its suppliers and ensure that supplier workers receive fair and respectful treatment," Jia said.

"But what happened here is obviously a violation of its supplier code. Apple should give us a written apology for this."

Chronic worker dissatisfaction with management and wages at Wintek as well as the poison scandal erupted in violence in mid-January last year, when more than 2,000 employees gathered at the factory in Suzhou Industrial Park early one morning and smashed vehicles and factory facilities.

Since then Apple has been under pressure to address the conduct of its suppliers, especially over the poison scandal, but it gave no response before the release of its supplier report.

Apple also admitted in the report that another logo supplier had used n-hexane and it is working with the facility to speed up reform.