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Cancer: Belatedly, Environmental Causes Get their Due

Thursday, August 11, 2011

By Justine Chow and Feifei Li, EWG Research Assistants

In discussions of the causes of cancer, environmental exposures have long been the unloved stepchild.

But that's changing.

For decades, most cancer researchers focused on genetics, diet, smoking and aging populations as the chief culprits, all but dismissing other environmental factors. As recently as 2003, a World Health Organization report featured the conventional wisdom that only 1-to-4 percent of all cancers were due to pollution.

More cancer specialists and oncologists see environmental link
A new report by Duke University researchers highlights the dramatic shift since then among cancer specialists and practicing oncologists. In a paper being published in the September issue of the Journal of Oncology Practice, the Duke team reports on a survey of young oncologists it conducted at the 2010 Australia and Asia Pacific Clinical Oncology Research and Development Workshop.

The Duke researchers found that these specialists from low- to middle-income countries consider pollution and other environmental factors one of the three top reasons for the growing burden of cancer in their countries. Close to a third (32 percent) called environmental factors important contributors, contradicting the traditional reserve that cancer researchers and physicians felt about attributing cancer to environmental causes.

Even though air, water and soil pollution became a major concern during the 20th century, only recently has compelling evidence mounted that carcinogenic chemicals are taking a significant toll on human health. Case studies of water and soil contamination are finding cancer clusters and population-wide epidemiological trends that link pollution to increases in the overall cancer burden, especially in impoverished regions where exposures are often higher than in wealthier nations.

Long-term suspect: Pesticides
It's been 49 years since the publication of Rachel Carson's Silent Spring, which inspired wide public concern about environmental pollution by pesticides. However, the use of some especially problematic pesticides have still not been phased out.

Globally, pesticides have led to problems such as resistance, caused harm to wildlife and ecosystems and endangered the health of farmers and anyone else who comes in direct contact with them. Cancer was not the major concern at first, but in 1989 the World Health Organization reported that the use of herbicides such as 2,4-D had contributed to a 50 percent surge in non-Hodgkin's lymphoma in Americans over the previous 20 years.
Exposure levels were especially high in farming communities, especially in developing countries; sadly, those who dedicate their lives to producing food are most at risk for this deadly cancer.

Industrial air and water pollution
Power plants, oil refineries, vehicle and aircraft exhaust are the source of most air pollutants. This year, the latest national assessment of toxic air emissions by the Environmental Protection Agency reported that 80 of 177 common air pollutants have been linked to cancer. Among them, formaldehyde, benzene and polycyclic aromatic hydrocarbons (PAHs) are defined as the main cancer risk drivers.

Pollutants also routinely end up in water, contributing to cancer risk. There are many examples worldwide, including a telling episode in Crestwood, Ill., a village with an unusually high cancer rate where a well that fed into the water supply was contaminated with vinyl chloride from a dry cleaner for more than 20 years. The contamination was uncovered in 2009 and the link to cancer rates was established a year later.

Drinking contaminated water isn't the only risk. People can come into contact with water pollutants through bathing or showering or eating fish caught in contaminated water. In 2003, scientists at Hebrew University-Hadassah described in Environmental Medicine a cancer cluster among Israeli naval divers who had trained in a polluted waterway where they were exposed to industrial, ship and agricultural effluents.

Emerging contaminants: hidden chemicals in commercial products
Two classes of chemicals found in many consumer products - perfluorochemicals (PFCs) and polybrominated diphenyl ethers (PBDEs) - may pose a significant risk. Both have been found in the bodies of more than 95 percent of Americans. Research suggests that food, food packaging, carpets and dust are all primary routes of exposure.

Take, for example, the slick, oil- and water-resistant packaging coatings used for microwave popcorn and other pre-packaged fast foods. They likely contain significant levels of PFCs that migrate into the food and then into our bodies. Epidemiological studies of workers exposed to PFCs in chemical factories, as well as studies of laboratory animals, strongly suggest that this family of chemicals, and especially its most notorious member, perfluorooctanoic acid (PFOA), is linked to cancer.

A class of chemicals used as flame- and fire-retardants, known as PBDEs, also pose serious risks. In 2007, the EPA classified Deca-BDE as a possible human carcinogen. Although some PBDEs have been banned, Deca-BDE is still used around the world in electronic devices and couches. It might even be in your mattress. PBDEs readily leak into the environment from consumer products and can lead to other health and behavioral problems, especially in children, as well as cancer.

EWG welcomes the much-needed and long-overdue attention that cancer researchers worldwide are beginning to pay to the links between environmental pollution and cancer, even as public health workers continue to fight some of the well-established factors contributing to cancer incidence - smoking and diet.

Since most of the evidence for environmental contribution to cancer risk comes from epidemiological studies, differences in study populations and other possible confounding factors require careful scrutiny. Nevertheless, both scientists and the public are increasingly aware of the prevalence of environmental pollutants, helping to drive further toxicological research to fully understand the full range of health risks - including cancer - that these pollutants pose.

[A big thanks to Flickr CC and I2CPhotography for the car exhaust]

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