Dear EarthTalk: Is there any proof linking human breast cancer to exposure to chemicals in the environment? Or do researchers think most cases of breast cancers are genetically inherited?
—Bettine Carroll, New York, NY
A groundbreaking research study coordinated by the non-profit Silent Spring Institute and recently published by the American Cancer Society found that synthetic chemicals have likely played a large role in the rising incidence of breast cancer throughout the world over the last half-century. The study identified 216 man-made chemicals—including those found in everyday products like pesticides, cosmetics, dyes, drugs and gasoline (and diesel exhaust)—that have been shown to cause breast cancer in animals. Researchers believe these substances, many of which "mimic" naturally occurring hormones once inside the body, are also to blame for the increasing prevalence of human breast cancer.
According to epidemiologist Devra Lee Davis of the University of Pittsburgh’s Graduate School of Public Health and one of the lead researchers on the new study, the more hormones cycling through a woman’s body during her lifetime, the more likely she is to develop breast cancer. Synthetic chemicals that mimic hormones magnify the risk, as the body doesn’t know the difference between its own real hormones and other introduced chemicals. Only one in 10 women who develop breast cancer inherits a defective gene from their parents, Davis adds, meaning that in 90 percent of breast cancer cases studied, external non-genetic agents (e.g. synthetic chemicals) contributed to the development of the cancer.
Another telling clue is the fact that the breast cancer risk of adopted children parallels the risk of the family they grew up in, not that of their biological family, as proven by analyzing medical records from Scandinavian countries that keep detailed registries following people from birth to death. "What we understand is that if cancer runs in your family it could be because your family had similar eating patterns, similar lifestyle patterns as well as lived in the same area," says Davis. "It’s really important that we take another look at
the kinds of chemicals that we are using everyday," she adds. "We think that there are alternatives that can be used."
The U.S. government has been reluctant to institute new restrictions on the production of highly profitable synthetic chemicals, but European regulators are taking the issue very seriously. The European Commission’s new Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) Program calls on chemical manufacturers selling anywhere in Europe to re-register and re-evaluate the potential health hazards—including cancer risks—of their products. Environmental and public health advocates hope that American chemical companies will follow that lead with chemicals sold here.
In the meantime, consumers can help prevent cancer by buying and eating organic foods, avoiding pesticides and other synthetic chemicals whenever possible, using non-plastic containers to reheat and store foods (some plastics are thoughts to leach cancer-causing chemicals into food when heated), and supporting government regulation and more research on synthetic chemicals and their effects.
Dear EarthTalk: What is the population status of Africa’s large mammals, such as elephants, lions, rhinos, and hippos? Are they all headed for extinction?
—Elias Corey, Seattle, WA
Overall, the variety and abundance of wildlife in Africa, as elsewhere around the world, is shrinking fast as human population grows and encroaches ever more on once wild and pristine landscapes. While illegal hunting (known in Africa as "poaching") still runs rampant despite government crackdowns, the spread of logging and agriculture contributes even more to the decline of many species of large mammals.
The population of the continent’s biggest mammal, the African elephant, has declined by more than 99 percent since the 1930s, when as many as 10 million of the great creatures roamed free there. At last count, biologists estimated that only about 600,000 elephants are left in all of Africa.
Elephant populations are thriving in areas of southern Africa, thanks to massive government conservation efforts, including a ban on the ivory trade as part of the 144-nation strong Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which limits trade in wild animals and their parts and accords varying degrees of protection to more than 33,000 species of plants and wildlife.
Africa’s hippopotamus population is also suffering, partly because of the very ban on ivory. Bullied out of the ivory trade, many African poachers have turned to hippo teeth, which measure as long as 24 inches and have become a valuable substitute for ivory. A 2003 census of the hippos of Virunga National Park in the African Republic of Congo, for example, found only 1,300 animals, down from an estimated 29,000 in a previous count three decades earlier. In neighboring Burundi, another recent census found that two thirds of that country’s hippo population—some 200 animals—had disappeared in just a five-year period.
As for rhinos, only 10,000 individuals exist around the world, down 85 percent since just 1970. Poaching has been the main culprit in the decimation of these animals, with a single pair of black rhino horns—coveted by Arabs in oil-rich Yemen who collect them as symbols of wealth and status—fetching as much as $50,000 on the black market. Of the two rhino species in Africa, the white rhino is faring slightly better and has rebounded from near extinction but isn’t quite in the clear yet. The black rhino, down to only about 2,500 animals, is still considered critically endangered, however. Where it once roamed across the entire African continent, the black rhino is barely hanging on in just a few East African countries.
Lions may be faring a little better, but not much. The nonprofit African Wildlife Foundation reports that the continent’s lion population has fallen off by half since the early 1950s when an estimated 40,000 "kings of the jungle" ruled. Besides contending with habitat loss to ever expanding human settlement, Africa’s lions have also had to deal with hunting and poisoning by livestock ranchers.
Although limited conservation efforts within Africa and internationally are helping some of these species remain barely viable, fighting extinction is an uphill battle, especially when expanding human population and sputtering economies force people to occupy previously wild lands and generate income by any means necessary. Individuals can help by donating money and time to organizations committed to saving these magnificent animals. With the extinction clock ticking fast, there’s no time to waste.