Susan Lydon, a Bay Area author and journalist, never forgot the DDT fog trucks that rumbled through the Long Island, N.Y., neighborhood where she grew up.

She was her block's fastest youngster. The mist was cool. The trucks were slow. Lydon's speed allowed her to stay longer than any of her pals in that comforting, pesticide-laced mist the sprayers left in their wake.

Lydon died of breast cancer at age 61 in 2005, going to her deathbed certain those carefree runs decades ago sealed her fate.

Her concern, it appears now, was justified.

A breakthrough study of Oakland women suggests that exposure early in life to DDT significantly increases a woman's chances of developing breast cancer decades later, according to a new study published last week in the online edition of the journal Environmental Health Perspectives.

The findings bolster the controversial notion that exposure to low doses of hormonally active compounds at critical developmental stages -- in this case, as the breast is developing -- load the gun, so to speak, priming the body to develop cancer years later.

It also makes clear the final chapter of DDT's legacy is not yet written. The young girls most heavily exposed to the pesticide -- women born in the late 1950s and early 1960s, when use of the pesticide peaked in the United States -- have not yet reached 50, let alone the age of greatest breast cancer risk, typically sometime after menopause and about age 60.

The findings further suggest that society is destined to relearn the lesson of DDT many times over. Myriad synthetic chemicals in our environment interact with our bodies with unknown consequences. Government regulators have little power to take precautionary action against compounds that appear problematic.

Reports such as this, said Barbara Brenner, executive director of San Francisco-based Breast Cancer Action, show the fallacy of that approach.

"We have to start paying very close attention to what we put in our environment," she said. "This is an example of doing something to our environment where we did not understand the long-term consequences. I don't know how many times this story has to be told."

Researchers examined a unique database of about 15,000 Kaiser Permanente Health Plan members who participated in a longitudinal study tracking their health over decades.

Researchers with the Berkeley-based Public Health Institute selected 129 women within that study who developed breast cancer before age 50. They then analyzed their archived blood samples taken from 1959 to 1967, while they were much younger.

Every sample from a woman with cancer was matched as a control with a sample from a woman of the same age without cancer.

Researchers found that women who developed cancer later in life had far higher concentrations of DDT in their blood as youths.

More significantly, women who were 14 or older in 1945, when DDT first hit the market, saw no increased breast cancer rates, suggesting that exposure while the breast is developing is critical.

DDT, or dichloro diphenyl trichloroethane, was banned in the United States in 1972 amid concerns it was concentrating in the food chain and killing off bald eagles and other raptors.

But the report goes far beyond the pesticide. It indicts widely held ideas and common practices concerning minute amounts of chemicals ubiquitous in our environment.

"The work that needs to be done to identify whether there are environmental risk factors (with any particular compound) is very complicated," said Barbara Cohn, a senior researcher at the Health Institute and the report's lead author. "But it's very important. We need to look deeply at that."

The report suggests, for instance, that society is heading down the same path with atrazine, one of the world's most widely applied pesticides, said Breast Cancer Action's Brenner.

The most cutting-edge drugs in the fight against breast cancer are known as aromatase inhibitors. Post-menopausal women only produce estrogen in their adrenal glands, using the enzyme aromatase to convert the glands' androgen hormones to estrogen. Because estrogen stimulates some breast cancers, doctors attempt to curb cancer growth by blocking the body's production of aromatase.

Atrazine is an aromatase stimulator.

Despite this and other concerns about the pesticide's effect on wildlife, federal regulators say the science is too inconclusive to curb its use.

"We start using chemicals as if the only thing they're going to affect is the plant," Brenner said. "We have to start doing business a different way."

Reach Douglas Fischer at dfischer@angnewspapers.com or 510-208-6425.