A month after a total of 23 workers at a lighting manufacturer in Foshan, Guangdong province, were diagnosed with mercury poisoning, the company and a provincial hospital were stepping up efforts to test more than 600 workers.

Hundreds of urine samples were sent to a Guangdong hospital for occupational diseases to determine if other workers have been poisoned with or exposed to mercury.

The samples came from workers from the Gaoming branch of the Foshan Electrical and Lighting Co Ltd, a Shenzhen-listed company. The 23 poisoned workers were working with fluorescent light bulbs, which contains elemental mercury.

According to the United States National Library of Medicine, elemental mercury is harmless if touched or swallowed but can cause considerable damage if breathed in as droplets in the air.

Victims can suffer from vomiting, difficulty in breathing and swollen, bleeding gums. If the exposure is high, there can be permanent lung or brain damage, even death.

In September, four workers at the company were poisoned. In November, 19 more were found to have mercury poisoning. The local government has established a special task force to help investigate how this happened.

Results from the first batch of urine samples would be released in a week, said a doctor from the outpatient department at the Guangdong provincial hospital of occupational diseases. He would only give his family name of Wu yesterday.

One of the workers, Peng Zhengjia, said he was diagnosed with a high level of mercury after he and three other workers arrived in a local hospital in the Pearl River Delta city to get a check-up in September.

Peng and the workers work with fluorescent lamps and he said there is plenty of contact with mercury.

"I have been suffering from bleeding gums, skin allergies, headache, shaky fingers and a loss of hair for the past two years," he said.

Peng, who has worked for the company since 2007, said he has told his employer of his condition and is planning to seek compensation.

Liao Huanguo, associate professor from Guangzhou-based Ji'nan University, attributed the growing number of occupational hazard cases to the poor awareness of migrant workers in safeguarding their legal rights and interest.

"Some of the employers have also ignored the legal interest of migrant workers to reap big profits," Liao told China Daily yesterday.

He urged relevant departments to further promote the country's labor laws and occupational prevention laws.

In another development, 33 workers from a metal and plastic company in Dongguan, Guangdong province, contracted a seizure-like condition that causes the arm to shake.

Six workers have thus far checked into a Guangdong provincial hospital in Guangzhou for treatment.

Li Sheng, one of the patients who has been a metal polisher at the company for seven years, said his lungs were found to have spots. All the victims are metal and plastic polishers, Li said.

Guangdong, which borders Hong Kong and Macao, is home to more than 31 million migrant workers.