Dear EarthTalk: Should I fear radiation exposure associated with medical scans such as CT scans, mammograms and the like?
—Shelly Johansen, Fairbanks, AK
The short answer is
maybe. Critics of the health care industry postulate that our society's quickness to test for disease may in fact be causing more of it, especially in the case of medical scans. To wit, the radiation dose from a typical CT scan (short for computed tomography and commonly known as a "cat scan") is 600 times more powerful than the average chest x-ray.
A 2007 study by Dr. Amy Berrington de Gonzãlez of the National Cancer Institute projected that the 72 million CT scans conducted yearly in the U.S. (not including scans conducted after a cancer diagnosis or performed at the end of life) will likely cause some 29,000 cancers resulting in 15,000 deaths two to three decades later. Scans of the abdomen, pelvis, chest and head were deemed most likely to cause cancer, and patients aged 35 to 54 were more likely to develop cancer as a result of CT scans than other age group.
Another study found that, among Americans who received CT scans, upwards of 20 percent had a false positive after one scan and 33 percent after two, meaning that such patients were getting huge doses of radiation without cause. And about seven percent of those patients underwent unnecessary invasive medical procedures following their misleading scans. CT scans are much more common today than in earlier decades, exacerbating the potential damage from false positives and excessive radiation exposure.
"Physicians and their patients cannot be complacent about the hazards of radiation or we risk creating a public-health time bomb," says Dr. Rita Redberg, a cardiologist at University of California-San Francisco. "To avoid unnecessarily increasing cancer incidence in future years, every clinician must carefully assess the expected benefits of each CT scan and fully inform his or her patients of the known risks of radiation."
CT scans are not the only concern. Mammograms are now routine for women over 40 years old. But some studies suggest that these types of screenings may cause more cancers than they prevent. Because of this, the federally funded U.S. Preventive Services Task Force now recommends that women not otherwise considered high risk for breast cancer wait until age 50 to begin getting mammograms—and then to get them every two years instead of annually. However, the American Cancer Society argues that such restraint would result in women dying unnecessarily from delaying screenings.
Women with a family history of breast cancer may be at greatest risk. Researchers from the University Medical Center Groningen in the Netherlands found that five or more x-rays—or any exposure to radiation—before the age of 20 for "high risk" women increased the likelihood of developing breast cancer later by a factor of two and a half.
Individuals should ask tough questions of their physicians to determine if and how much screening is absolutely necessary to look for suspected abnormalities. Our knowledge of the risks of radiation-based screenings will only help us to make more informed decisions about our health.
Dear EarthTalk: What is happening with various programs initiated over the years in the U.S. to return to the wild certain animal species that had been endangered or threatened? And do environmentalists tend to be for or against such efforts?
—Susan Adams, Owl's Head, ME
From the standpoint of species and ecosystem health, limited attempts at predator reintroduction in the United States have for the most part proven very successful. The gray wolf, extirpated by hunters in the Yellowstone region some 90 years ago, is now thriving there in the wake of a controversial reintroduction program initiated in 1995, when the National Park Service released 31 gray wolves into the park's expansive backcountry. Today as many as 170 gray wolves roam the park and environs, while the elk population—which was denuding many iconic park landscapes in the absence of its chief predator—has fallen by half, in what many environmentalists see as a win-win scenario.
Other reintroduction efforts across the U.S. have also been successful. From the lynx in Colorado to the condor in California to the Black-footed ferret on the Plains, scientists are pleased with how well reintroduced species have taken to their new surroundings. As a result, many conservationists now view the reintroduction of iconic wildlife species as key to restoring otherwise degraded natural landscapes.
"When we kill off big cats, wolves and other wild hunters, we lose not only prominent species, but also the key ecological and evolutionary process of top-down regulation," says the non-profit Rewilding Institute, adding that the recovery of large native carnivores should be the heart of any conservation strategy in areas where such predators have disappeared. "Wolves, cougars, lynx, wolverines, grizzly and black bears, jaguars, sea otters and other top carnivores need to be restored throughout North America in ecologically effective densities in their natural ranges where suitable habitat remains or can be restored."
Not everyone is so bullish on wildlife reintroduction programs, despite their success. As for the Yellowstone wolf reintroduction, ranchers operating on private land outside park boundaries still complain about the threat of free-roaming wolves poaching their livestock. In response, the non-profit Defenders of Wildlife has implemented its Wolf Conservation Trust whereby donated funds are channeled toward paying ranchers fair market value for any stock lost to wolf predation. The group hopes the fund will "eliminate a major factor in political opposition to wolf recovery" by shifting the economic burden of wolf recovery from livestock producers to those who support wolf reintroduction.
Some environmental advocates also oppose wildlife reintroductions. One argument is that people have "played God" enough and should stop tinkering even more with wildlife and ecosystems, especially given that the overall long-term impact is always uncertain. And some animal advocates dislike such strategies from a humanitarian perspective: "Reintroduction programs subject wild animals to capturing and handling, which is always stressful for them, and may eventually put them in the line of fire of farmers who are already angry about predator-reintroduction programs," claims People for the Ethical Treatment of Animals (PETA), adding that, when predators are reintroduced to an area where they have long been absent, prey species tend to scatter and "their lives and behavior patterns are turned upside-down."
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