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Have synthetic chemicals given rise to more cancer?

Dear EarthTalk: How clear (or not) are the links between the rising incidents of cancers around the world and the prevalence of synthetic chemicals in modern society? — Alberto Buono, Lee, MAWith the World Health Organization hinting that cancer could unseat heart disease as the leading cause of death around the world, it’s no surprise that per capita cancer incidence is on the rise globally. In fact, cancer is the only major cause of death that has continued to rise since 1900. While it might depend on whom you ask, most researchers now agree that environmental factors—including exposure to chemicals and pollution—play a significant role today in determining who gets cancer and who doesn’t.A blue ribbon panel of cancer experts initially convened by President George W. Bush researched hundreds of studies and concluded in 2010 (in its 240-page report, “Reducing Environmental Cancer Risk: What We Can Do Now”) that our exposure to chemicals, pollution and radiation is to blame for the uptick in cancer deaths. “The American people — even before they are born — are bombarded continually with myriad combinations of these dangerous exposures,” the panel reported. “With the growing body of evidence linking environmental exposures to cancer, the public is becoming increasingly aware of the unacceptable burden of cancer resulting from environmental and occupational exposures that could have been prevented through appropriate national action.”The panel cited grim statistics about cancer’s march, noting that 41 percent of Americans will be diagnosed with cancer at some point in their lives, with 21 percent likely to die from it. Cancer researchers fear that our reliance on chemicals is the main culprit, as borne out by hundreds of studies.To wit, a 2000 study involving the examination of health records of more than 44,000 pairs of twins across Scandinavia found that “inherited genetic factors make a minor contribution” in causing most cancers but that “the environment has the principle role in causing sporadic cancer.” A 2010 UK study, whereby researchers investigated the level of chemical exposure of more than 1,100 women during their employment history, found that those study subjects who had been exposed to various industrial chemicals and airborne hydrocarbons were at least three times more likely to get breast cancer later on than women with little or no exposure in their backgrounds.Not everyone agrees. Writing in Forbes magazine, Henry I. Miller and Elizabeth Whelan of the industry-friendly American Council on Science and Health argue that the findings of the presidential panel are based on politics not science: “If the authors had only bothered to consult a standard textbook on cancer epidemiology, they would have learned that lifestyle factors such as smoking, obesity, excessive alcohol consumption and overexposure to sunlight—not chemicals in air, water and food—are the underlying causes of most preventable human cancers.”While few today would doubt the health risks of such personal lifestyle factors, the President’s cancer panel nevertheless concluded that “the burgeoning number and complexity of known or suspected environmental carcinogens compel us to act to protect public health,” and urged President Obama to use the power of his office to “remove the carcinogens and other toxins from our food, water and air that needlessly increase health care costs, cripple our nation’s productivity, and devastate American lives.”Dear EarthTalk: I heard that species of flora and fauna are dying at a growing rate globally. How is this calculated and which types of species are dwindling faster?— Colin GooderFranklin, N.C.Researchers believe that the rate of species loss currently underway is 100-1,000 times faster than what was normal (the so-called “background rate” of extinction) prior to human overpopulation and its negative environmental effects. But thanks to overhunting, deforestation, pollution, the spread of non-native species and now climate change, we are likely in the midst of the sixth mass extinction in the geologic history of the world. The previous mass extinction, 65 million years ago, wiped out the dinosaurs and other species; the previous one, 250 million years ago, killed off 90 percent of all species on the planet. While the current mass extinction might in reality not be that bad — only time will tell — eminent Harvard biologist E.O. Wilson predicts that the rate of species loss could top 10,000 times the background rate by 2030, and that fully half of the planet’s higher life forms could be gone within 100 years. This jibes with statistics from the non-profit International Union for the Conservation of Nature (IUCN)—keeper of the global “Red List” of endangered species—which currently considers 37.8 percent of the world’s already classified species to be threatened. Of course, this is far from the whole story, as biologists think that we have only classified 10 percent or less of the world’s total number of plant and animal species.Which types of species are being hit hardest? An analysis of IUCN statistics from 2008 found that of the world’s fauna (animals), invertebrates (animals without backbones, such as earthworms, shellfish and insects) were suffering the most, with 40.5 percent of those classified considered threatened. Next hardest hit were fish species, with 36.6 percent threatened, followed by reptiles at 30.5 percent and amphibians at 30.4 percent. Meanwhile, 20.8 percent of mammal species were threatened and 12.2 percent of birds. More shocking was the statistic that some 70.1 percent of plant species are at risk. However, a more recent (2010) study found that only 22 percent of the world’s classified plants are actually facing extinction. This finding has led analysts to question conservationists’ estimates in regard to animal species loss as well.In lieu of any direct way to measure the rate of species loss, conservationists have relied on reversing the so-called “species-area relationship,” whereby scientists tally the number of species in a given area and then estimate how quickly more show up or evolve as viable habitat increases (or decreases in the case of reversing the concept). But lately this method of tracking and predicting species losses has been criticized for generating overestimates. “The overestimates can be very substantial,” argues UCLA evolutionary biologist Stephen Hubbell, “...but we are not saying [extinction] does not exist.”However many species may be dying, it’s clear we are in the midst of another mass extinction, and if you believe 70 percent of biologists, unlike previous mass extinctions humanity is most likely the cause. Conservationists remain optimistic that we can marshal the resources to turn the tide—and we’ll need to if the planet is to remain habitable for our species, given our own dependencies on the world’s biodiversity. EarthTalk is written and edited by Roddy Scheer and Doug Moss.

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