Subtle but potentially serious: health effects of low-level pesticide exposure

by Elizabeth Grossman

A new study has been added to the growing body of literature reporting on the potential health effects of low-level exposure to widely used pesticides. In this study, a pesticide (triflumizole, or TFZ) used on leafy greens, apples, cherries, strawberries, cucumbers, grapes, watermelons, and other food crops has been identified as an obesogen in mice. An obesogen is a chemical that promotes obesity by prompting the growth of more and larger fat cells, often doing so through prenatal exposure and setting the stage for metabolic disease later in life.

Since the identification of these effects in the past ten years or so, pesticides and other synthetic chemicals have come under increasing scrutiny for the role they may play in promoting childhood and adult obesity and related health effects. “An alarming recent trend is the increasing rate of obesity in very young children, even infants,” writes Bruce Blumberg, University of California Irvine professor of developmental and cell biology who led this new study of the fungicide called triflumizole (TFZ). “Since it is unlikely that infants are consuming more calories and exercising less than in the past, it is reasonable to hypothesize that the prenatal and/or early postnatal environment has recently changed.”

Blumberg and colleagues decided to study TFZ, which is also used on ornamental plants, because although it is widely used and not thought to be carcinogenic or particularly toxic, little is known about its developmental effects. Previous in vitro testing indicated that TMZ could activate the genetic receptor that regulates fat cell development, so the researchers wanted to learn if it would also produce these effects in vivo.

What they found was that at doses the researchers estimate are comparable to those people are likely to be exposed through food, TFZ prompted fat cell growth in mice exposed prenatally, while inhibiting growth of their bone cells. These effects occurred at doses that the scientists calculate to be about 400 times lower that the established threshold level below which no adverse health effects are expected to be observed. (These threshold levels are often called No Observable Adverse Effect Levels (NOAEL) and often used in regulatory safety standards, including those the US Environmental Protection Agency (EPA) sets for pesticides.)

After comparing the lowest exposures at which they found effects in mice to the EPA reference doses for TMZ, the researchers concluded that they “believe that effects will occur at likely human exposures, but one would need to measure actual exposures to be certain what the actual human body burdens are,” explained Bruce Blumberg via email. “No one is measuring exposure, but there is certainly both occupational exposure and exposure from consuming treated foods.”

In 2009, more than 56,000 pounds of triflumizole were used in California alone, on numerous labor-intensive food crops. So on its own, this study would be cause for concern. This study is, however, one of many reporting on subtle but potentially serious effects of exposure to pesticides at low levels, amounts comparable to those people encounter environmentally. Among these are the studies of organophosphate pesticides I reported on for The Pump Handle in September, which are increasingly being linked to adverse neurological impacts in children who were exposed prenatally. But many other biocides have also been identified as having potential adverse hormonal or developmental activity, typically at low exposure levels. Such evidence on atrazine, endosulfan, tributyl tin, vinclozolin, and those based on glyphosate has been summarized for Pesticide News by Gwynne Lyons of WWF-UK.

In a statement released November 1 responding to the ongoing debate over the environmental health repercussions of genetically modified crops, a group of prominent scientists that includes Bruce Blumberg cautioned that use of herbicide-resistant GMO crops has led to increasing herbicide use. The scientists wrote that “despite their widespread use, the human and wildlife toxicity of herbicides has not been well studied. Evidence suggests that at least some may induce detrimental health effects even at low exposure levels.”

This is problematic because testing used to set current safety standards for such chemicals often has not historically included low-dose effects. This means that what’s considered a safe level of exposure may be missing potentially important hormonal and developmental health impacts. That such effects may be absent from a regulatory toxicity review of a pesticide has both potential occupational and public health impacts. Long-term studies of children whose mothers were exposed to pesticides in their agricultural communities or through use of these substances in indoor pest control are beginning to show some of these impacts. The TMZ study is yet another indication that what is considered a safe exposure level of pesticide exposure – for agricultural workers, their families or for the food we eat – may merit another look.

Elizabeth Grossman is the author of Chasing Molecules: Poisonous Products, Human Health, and the Promise of Green Chemistry, High Tech Trash: Digital Devices, Hidden Toxics, and Human Health, and other books. Her work has appeared in a variety of publications including Scientific American, Salon, The Washington Post, The Nation, Mother Jones, Grist, and the Huffington Post. Chasing Molecules was chosen by Booklist as one of the Top 10 Science & Technology Books of 2009 and won a 2010 Gold Nautilus Award for investigative journalism.