For some years, environmentalists have been hoping scientists could come up with evidence to link environmental factors like chemical exposure or electromagnetic fields near power lines to incidences of breast cancer. But according to a recent article in the New York Times, they have failed to find such a smoking gun.  One major study involving more than 32,000 nurses found no evidence that DDT or PCBs increase breast cancer risk, while another Harvard study found no link to any chemical exposure whatsoever.  More recently, an $8 million study by the National Cancer Institute failed to link pesticides or exhaust fumes to breast cancer.  But environmentalists continue to look in this direction for the cause of this dreaded disease