Ever since a pair of Colorado researchers jolted the nation with a 1979 study that suggested power lines cause cancer, projects like San Diego Gas & Electric Co.'s proposed Sunrise Powerlink have sparked widespread alarm.

But almost three decades later, scientists have yet to show a clear link between the electromagnetic fields that transmission lines create and leukemia, brain cancer, breast cancer or other types of cancer, according to a wide array of state, national and world health agencies, and cancer prevention organizations.

Earlier this year, the California Public Utilities Commission affirmed a long list of previous reports in concluding: "At this time, we are unable to determine whether there is a significant scientifically verifiable relationship between EMF (electromagnetic field) exposure and negative health consequences."

In response, the regulatory agency decided in January to leave intact a 13-year-old policy that urges utilities to reduce exposure from new transmission lines -- spending 4 percent more than they otherwise would have -- but did not set specific exposure limits.

"You can't prove that the power lines are safe because you can never prove that anything is safe," said Charles F. Stevens, a professor at the Salk Institute in La Jolla and chairman of a National Research Council panel that investigated the matter in 2001. "But people have been trying for 30 years to establish a link, and so far they have been unable to."

While the mysterious nature of power lines and the general public's lack of knowledge about electricity tends to generate fear, the information gathered through hundreds of studies conducted around the world since that original Colorado study suggests there is little to be afraid of, Stevens said.

"The power line issue is something that is scary because everyone knows that electricity is very powerful," he said in an interview last week. "I think (power lines) are ugly and I don't want to be near one for that reason. But, personally, I wouldn't worry about it for health reasons."

Scientists' inability to establish a link, however, is small comfort to the hundreds of people who may wind up living next to giant wires and towers in Rancho Penasquitos, Ramona and Ranchita, if SDG&E gets the nod from the utilities commission to build its $1.4 billion project.

Sunrise Powerlink is a proposed 120-mile transmission line that would drape wires from metal structures as tall as 160 feet, in a meandering path from the Imperial County desert to Carmel Valley.

SDG&E officials say the line would deliver 1,000 megawatts of electricity to its 1.3 million customers in San Diego County and southern Orange County, increasing the region's current supply by about 25 percent. A megawatt is the standard measuring unit for electricity and generally is enough to keep the lights on in 750 to 1,000 homes.

Taking chances

While no clear link has been established, there is still reason for concern, said Donna Murdoch, spokeswoman for the citizen group Ramona Alliance Against Sunrise Powerlink. She lives on a street targeted for an underground section of line through the San Diego Country Estates.

"We don't want to be taking the chance of living next to (the line)," Murdoch said. "The route goes within 40 or 50 feet of homes, and it goes right through a park … I have a real hard time telling mothers holding babies that there is no problem."

Stephanie Donovan, spokeswoman for SDG&E, said concern is understandable.

But, Donovan said, "The world now has more information about EMFs than about any chemical that has been introduced, and yet there has been no consensus in the scientific community about the possibility of risk."

Donovan said that risk was not a factor in SDG&E's proposal to bury seven miles of wires underground through housing tracts in Ramona and Rancho Penasquitos. Donovan said the proposal aims to avoid condemning homes in Ramona, where there isn't enough room aboveground for a transmission line, and addressing both communities' concerns about having to look at wires.

While they say the risk is unproven, health agencies and organizations generally have refrained from declaring electromagnetic fields to be safe.

In a 1999 report, the National Institute of Environmental Health Sciences stated that the limited evidence of a connection between such fields and childhood leukemia cannot be dismissed out of hand.

And because of questions raised by some studies, the International Agency for Research on Cancer, a branch of the World Health Organization, classified electromagnetic fields as "possibly carcinogenic to humans" in October 2001. The lowest-risk of three categories of classes, the label means there is some limited evidence of cancer-causing potential but laboratory tests have failed to confirm that risk.

The "possibly carcinogenic" label puts electromagnetic fields in the same category as coffee, gasoline-engine exhaust and welding fumes.

The international agency's middle category is "probably carcinogenic to humans" and includes such things as diesel-engine exhaust and ultraviolet radiation. The upper category is "carcinogenic to humans." It includes asbestos, mustard gas and tobacco.

Studies come up short

Still, because of the inability to confirm the cancer threat, let alone measure a level of exposure that might trigger it, health and environmental agencies to date have not taken steps to control the strengths of such fields.

Steps to determine if such fields pose a serious danger were sparked initially by a landmark epidemiological study published by Nancy Wertheimer and Ed Leeper in 1979. The Colorado researchers, in surveying a list of 344 Denver-area children who died of leukemia between 1950 and 1973, found that a disproportionate number of the victims lived in homes behind power lines and transformers. They concluded the presence of the lines elevated the normal risk of contracting leukemia by two to three times.

According to a California Department of Health Services report, leukemia is a rare disease that normally afflicts four out of 100,000 children.

Reports by various agencies and scientists, however, suggest there were serious flaws with the Denver study. For starters, there was a possibility something else was to blame for the elevated incidence of leukemia, and that was not taken into account.

"People who live near power lines usually live in poorer neighborhoods, in older homes, on busy streets," Stevens said, suggesting living conditions and pollution could be factors.

Another flaw was that the study did not measure electromagnetic exposure, but instead estimated it by the type and size of nearby wires, experts say.

In the parade of studies to follow, other researchers sought to overcome the initial shortcomings. And one in Sweden that did measure strength of electromagnetic fields covered a much larger population base -- 500,000 people living within a football field's distance of power lines between 1960 and 1985. That study concluded the leukemia risk was four times normal.

However, neither the Sweden study nor others showed cancer risk rose as exposure to electromagnetic fields rose.

On a parallel track, laboratory scientists, in study after study, were unable to demonstrate that the exposure caused cancer in animals.

In a 1996 report, the American Cancer Society in Atlanta concluded that the lack of proof despite so many studies "leave one uncertain and rather doubtful that any real biological link exists between EMF exposure and carcinogenicity."

Cutting to the heart of the matter, the National Research Council panel stated that "there has been no case in which even tremendously high exposure to EMFs has been shown to affect the DNA of the cell, damage to which is believed to be essential for the initiation of cancer."

Contact staff writer Dave Downey at (760) 740-5442 or ddowney@nctimes.com.