A new study of English sole in Seattle's polluted Duwamish waterway suggests environmental contamination can damage animal and human DNA far more frequently than previously realized.
The DNA damage-detection method used by Donald Malins and Sandra Gunselman of the Pacific Northwest Research Foundation, with collaboration by the University of Washington, may also lead to a diagnostic tool to predict an individual's risk of developing cancer, Malins added.
"It's like a lottery," he explained. "You may have one chance in a thousand of getting a particular cancer or one in 10 million. The more damage to your DNA, the more it ups your chances of cancer."
DNA is the "instruction book" that governs a body's growth and repair. Too much change in the genetic code can increase the number of potential cancer-causing genes or decrease the number of cancer-suppressing genes.
The study was published today in the Proceedings of the National Academy of Science. Coming Jan. 15 from the same scientists is a related study showing a similar alarming level of atomic and molecular-scale DNA damage in the human female breast.
Malins is the scientist who in the 1980s first sounded the alarm about cancerous tumors in Puget Sound fish, fueling a cleanup effort.
In his new study, he harnessed two research tools, gas chromatography-mass spectrometry and infrared spectroscopy. That allowed him to examine alterations in fish DNA from pollutants at
the molecular and atomic level, instead of looking at entire genes.
What he found at so tiny a level was DNA modification he estimated as 100,000 times more frequent than previously suspected: as many as one in 15 DNA molecules in some fish appeared to have been altered.
"This is the highest degree of DNA damage ever seen in a living system," he said. "It is without precedent and quite unexpected."
When the two scientists compared Duwamish fish with English sole caught in clean water off Newport, Ore., they found damage at the molecular level of the Oregon fish was far lower: as much as 1,000 times lower.
And in a bit of good news, when they experimented with a small guppy called Medaka and moved it from polluted water to clean, they found its body capable of rapidly repairing the DNA damage back to a normal level.
"This means that if you are able to reduce the toxic threat, the normal repair mechanism will take over and repair the damage," Malins said.
Natural cancer-causing compounds in food, background radiation and other factors assault the body all the time, but damage is usually repaired before it can develop into cancer. Environmental scientists think human pollution can tip the scale in this constant war in favor of cancer, though predicting risk is a subject of fierce controversy.
Malins theorizes that as fish or human livers metabolize pollutants, they produce unusually high numbers of free radicals, or molecules with an unpaired electron in their outer orbit. These are unstable and thus apt to react with other molecules, possibly changing them.
The free radical idea is also somewhat controversial but is supported by a growing body of research. Also controversial is the idea that some vitamins such as A, C and E help "soak up" free radicals and render them harmless.
One disturbing finding is that English sole in the Duwamish that are just 1 to 2 years old are still exhibiting DNA damage, despite a decade of cleanup efforts.
Malins suspects fish are still being exposed to older polluted sediments, an idea the state Department of Ecology confirms. "Sediment cleanup is just beginning," said Joanne Polayes-When, who monitors the Seattle and Everett harbors.
The tested fish did not yet have cancerous tumors, which usually don't develop until the sole are 4 to 6 years old, Malins said.
Scientists at the private, nonprofit research foundation, funded partly from federal grants, think engineers could easily build a "black box" using the new techniques to monitor environmental pollution in animals.
A device for use on humans, however, would have to undergo stringent federal review that would likely take years before reaching a typical doctor's office, Malins said.