Rubber chemicals have been made at the site since the 1930s
A chemical used to manufacture rubber may cause cancer in workers regularly exposed to it, according to a study of workers at a factory near Wrexham.
Researchers found that staff at the Flexsys plant who had come into contact with MBT were twice as likely to die of large intestine and bladder cancers.
They have called for more research in others groups of people exposed to MBT.
Flexsys said it was reviewing the study in order to decide if any further investigation was required.
Researchers at the University of Birmingham looked in particular for exposure to a chemical called 2-mercaptobenzothiazole, (MBT), which they say has been implicated in previous research as a possible carcinogen.
Their findings are to be printed in Occupational and Environmental Medicine, a monthly publication of the British Medical Journal.
They examined the death rates of employees who had worked at the plant for at least six months, between 1955 and 1984, as well as the diagnoses of cancer between 1971 and 2005.
Perhaps MBT should be handled with increased care as it may be a human carcinogen
University of Birmingham researchers
According to the research, 363 of the 2,160 employees had worked in a job that would have exposed them to MBT.
Many of those workers were first exposed to the chemical during the 1930s, 1940s, and 1950s, it said.
By the end of 2005, 222 of those employees had died, and 136 were traced who were still alive.
The findings - when compared to national statistics - show workers exposed to MBT were twice as likely to die of large intestine and bladder cancers.
They were also twice as likely to be diagnosed with bladder cancer, and four times as likely to be diagnosed with multiple myeloma (bone marrow cancer).
When compared with 1,797 workers who had not been exposed to MBT during their employment, the researchers said it emerged that the risks of cancer of the large intestine and multiple myeloma both increased significantly according to the amount of MBT exposure.
Higher cancer risk for staff
The report's authors have called for further research in other groups of people exposed to MBT to see if similar patterns emerge.
They warned: "In the meantime, perhaps MBT should be handled with increased care as it may be a human carcinogen."
The factory, known locally as the Ruabon Works, is one of the oldest industrial sites in the Wrexham area.
It has produced chemicals for the rubber industry since the 1930s, and Flexsys Rubber Chemicals Limited took over operations there in 1995, focusing on the manufacture of highly specialised chemicals for the international rubber industry.
In the early days, it was hard, with the chemicals, because you name the chemical, we were exposed to it
Tom Owen, former Flexys employee
In a statement, the company said: "The health and welfare of our employees is of primary importance to the company, and as such we are reviewing the study in order to identify what, if any, actions should be taken in terms of further investigation.
"MBT was produced at the Ruabon Plant from the 1930s until 2001 and it continues to be manufactured for Flexsys at one other location.
"For this product and all of the products we develop, manufacture, and market, the company employs great care to ensure that they do not pose undue risks to human health or the environment during all stages of their life cycles."
Tom Owen, 76, worked at the factory for 40 years, and was frequently exposed to MBT.
"I first started there in 1950. I worked on nearly every plant so there's nothing I've missed there," he said.
"In the early days, it was hard, with the chemicals, because you name the chemical, we were exposed to it."
Mr Owen retired in the early 1990s through ill health. He went on to develop bowel cancer.
"Some of my colleagues have had it too, " he said.
"I had operations for it but things didn't work out as they should do. I had to have a colostomy bag, but it wasn't working right. So they had to take the whole intestine out, and then my lungs collapsed.
"That went on for months - and I wouldn't wish it on my worst enemy."
Professor Tom Sorahan, who led the research, said the studies had taken place over a 15-year period.
"I understand the Flexsys plant no longer makes MBT but certainly it is made in other parts of the world and I think it's necessary for other countries and other industries to do similar studies to see if these findings are true or not," he told BBC Radio Wales.
Last year, Wrexham council's leader called for more information on sites used by the firm amid fears they could be contaminated.
Aled Roberts said he believed there were concerns over contamination at the main Cefn Mawr factory, as well as other sites in the Wrexham area.
He said the Environment Agency, council and Welsh Assembly Government should discuss how the clean the site.
At the time, he said: "Over the years chemicals apparently have been stored on the site and because of that the land in certain areas could be problematic."
The site is due to close by 2011 with the loss of 163 jobs after parent company Solutia Inc blamed competition from the Far East.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.