(McClatchy-Tribune Information Services) -- In as little as three months, the brains of laboratory rats begin to change after being exposed to the air around congested Southern California freeways.

"The evidence we are clearly seeing is the molecular cascade that can lead to the development of cancer," said Dr. Keith L. Black, chairman of the department of neurosurgery at Cedars-Sinai Medical Center in Los Angeles.

Black is a world-class surgeon who pioneered research on ways to open the blood-brain barrier, enabling medicines to be used in the fight against brain cancer.

His war on brain tumors resulted in his being on the cover of a Time magazine special edition called "Heroes of Medicine," which was published 1997.

Black was scheduled to speak at Arrowhead Regional Medical Center in Colton on the topic of brain tumors and air pollution late last month, but the session was canceled.

For several years he has been involved in the study of ultrafine particles, including diesel soot and other combustion bi-products, that might increase brain cancer risks.

These particles, about 1/70th the diameter of a human hair, are able to lodge deep in human lungs and from there, enter the bloodstream and travel to the brain.

"The leading cause of cancer deaths in people less than 19 is brain cancer," Black said in a telephone interview earlier this week. "The young brain is more susceptible to environmental toxins that induce cancer."

"Of all the particulate matter, those coming from diesel appear to be the most worrisome," he said.

Some estimates suggest brain cancers and other tumors of children's nervous systems rose by more than 25 percent between 1973 and 1996.

"The young brain is more susceptible to environmental toxins that induce cancer," he said.

Additionally, an American Lung Association study has linked particulate pollution to lung cancer.

The fact that just three months of exposure to air from the Southland's snarled freeways caused precursors to cancer "has been a surprising finding for us," Black said.

"We are now beginning to look at more detailed studies, to try to understand the significance of the observations made," he said.

"One of the things we know about cancer is that it usually involves multiple factors," he said. "It is usually not one single hit," he said.

"We know cancer is a cascade" where 10 or more genes must be turned on to convert a normal cell into a cancerous one.

During Black's initial experiments with rats, two or three or occasionally four genes were activated in as little as three months.

Black said his research team at the Maxine Dunitz Neurosurgical Institute at Cedars-Sinai should have answers regarding the threat of these fine particles in three or four years.

If the case for the link to brain cancer is proven, then the information can be used by regulatory agencies to justify reduction of these fine particle emissions from cars and trucks, he said.

In the meantime, there isn't much people can do but perhaps avoid strenuous exercise near polluted areas, he said.

These tiny particles are too small to be filtered out by air conditioning systems, and too small even to be screened by N-95 face masks used by some people to protect themselves from the H1N1 influenza virus.

Copyright (C) 2009, San Bernardino County Sun, Calif.