California's top occupational health doctor told a jury Tuesday that exposure to workplace chemicals caused two former IBM workers to develop cancer.

The testimony by Robert Harrison was the first time an expert witness has directly linked chemicals used at IBM's San Jose manufacturing plant to Alida Hernandez's breast cancer and James Moore's non-Hodgkin's lymphoma. Harrison is chief of the California Department of Health's occupational health surveillance and evaluation program.

Hernandez and Moore are alleging in Santa Clara County Superior Court that IBM knowingly exposed them to chemicals that made them ill and hid that information from them.

IBM argues that its clean rooms were safe and that the chemicals used there were not believed to be carcinogenic during the time of Moore's and Hernandez's employment.

Proposition 65

But Harrison testified that virtually all the chemicals cited in the case, including trichloroethylene, benzene and epichlorohydrin, are recognized as carcinogens either by California's Proposition 65 or scientific studies.

Proposition 65, also known as the Safe Drinking Water and Toxic Enforcement Act of 1986, requires the state to publish an annual list of chemicals known to cause cancer. Moore worked for IBM from 1966 to 1993 and Hernandez was employed from 1977 to 1991.

Harrison has served as chief medical consultant to the U.S. Occupational Safety and Health Administration since 1998 and currently sits on the state OSHA standards board.

He estimated that exposure to chemical solvents played a 70 percent to 80 percent role in causing Hernandez's breast cancer, in relationship to other factors like her age and the early onset of puberty. He discounted factors that IBM has cited, such as weight and hormone replacement therapy, saying they were nullified by other medical conditions.

In Moore's case, Harrison said solvents played an 80 percent to 90 percent role in his non-Hodgkin's lymphoma.

Harrison told the jury he based his opinion on a review of the plaintiffs' medical records and sworn statements they gave in pre-trial depositions. He said he also reviewed depositions given by other expert witnesses and by IBM doctors and nurses.

Harrison elaborated on the meaning of permissible exposure limits that govern how much chemicals an employee can safely be exposed to in the workplace. He said the limits were initially based on voluntary employer standards and only addressed the immediate effects of chemicals. ``They are not set to prevent workers from getting cancer years later,'' Harrison testified.

Substantial exposure

Although mathematical models that estimated Hernandez's exposure to toluene, acetone and xylene fell mostly within national guidelines, Harrison said they ``show that Ms. Hernandez was exposed to substantial quantities of these chemicals.''

During a brief cross-examination, IBM attorney Robert Weber established that exposure estimates were extrapolated from IBM measurements and were not actual measurements themselves. Weber will continue the cross-examination today.