Houston - Chemicals have replaced bacteria and viruses as the main threat to human health in western industrial nations, says toxicologist Rick Irvin.

"The major causes of death in the western world up until the 1950s were mainly diseases of microbial origin - influenza, pneumonia, tuberculosis, " says Irvin, toxicology professor at Texas A and M University.

"Through public health practices, immunization and nutrition, we've just about controlled those. The diseases we're beginning to see as the major causes of death in the latter part of this century and certainly into the 21st century are diseases of chemical origin, "Irvin said in an interview.

He said scientists now believe 70 to 90 per cent of all cancers, for example, are caused by exposure to chemicals. Heart disease, too, is essentially chemical in origin because it's caused by fatty foods and cigarette smoking, Irvin said.

"When you're talking about chemicals." Heart disease and cancer are responsible for more than 50 per cent of all deaths in western nations, Irvin said.

He said toxic chemicals may work singly or in combination with other chemicals to cause disease. In real life, people in industrial societies are exposed to many chemicals every day, Irvin said, "We're finding that with a lot of combinations, we get a toxic effect not previously known."
For example he said it has been found that diesel soot has as many as 100 chemicals in it, many of which combine to create the same carcinogens found in cigarettes.

Irvin believes the threat posed by toxic chemicals will grow because researchers are producing more and more new substances for industrial and scientific use. "There will be an explosion of new chemicals in the next 20 years, which will overwhelm governments ability to regulate their use.

"We're getting a lot more of what call high-tech chemicals - such as those used in the manufacturing of microelectronics - that have very specialized uses. We really don't know much about this group and its effects on humans.

"Irvin said people cannot avoid all chemicals, but they should use common sense to avoid excessive exposure to harmful ones. "For example, I don't smoke or drink and I don't take illegal drugs. I eat a high-protein, low-fat diet and I expect to live my threescore and 10 years.

"A person's genetic makeup influences his or her susceptibility to disease, but it appears that genes "modulate as opposed to determine" the amount of risk, Irvin said.

"Some people, because of their genes, are more likely to get diseases from chemicals than others, but their genes will not absolutely determine their fate." He also said that, while chemicals pose a threat to health, in some ways they are less insidious than bacteria and viruses. It is difficult to completely wipe out disease-carrying microbes because they can be transmitted to other humans, Irvin said.