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The Environmental Origins of Disease

Posted April 15, 2015

A Q&A with Nicole Deziel, Ph.D., M.H.S.


Nicole Deziel is an assistant professor at the Yale School of Public Health who studies how exposures to everyday environmental toxins affect human health. In particular, she wants to develop methods that accurately and precisely measure exposure to a host of chemicals that many people encounter and their homes and in their day-to-day lives. Deziel’s work focuses on several pollutants, including pesticides, organic pollutants and PAHs or polycyclic aromatic hydrocarbons that are found in oil and coal, tobacco smoke, and grilled meats. Her work also involves studying the content of vacuum cleaner bags, a great resource for gauging the array of chemical found inside homes.  Deziel joined the Yale faculty in 2014.

How important is one’s living area (home and environs) to their physical health?

ND: Our environment has a major impact on our health. The World Health Organization estimates that 25 percent of the global disease burden is due to environmental factors, such as contaminated drinking water or indoor/outdoor air pollution. In the United States we spend upwards of 90 percent of our time indoors. Many of the sources are in our homes, such as cleaners, pesticides, air fresheners, building materials, tobacco smoke and mold. Where we live can also have a major impact on our environmental exposures. Do we live near a major roadway? A farm where pesticides are applied? A waste incineration plant? Fracking wells? Pollutants can travel from these sources and penetrate homes. We come into contact with hundreds of toxic chemicals every day as we move through our environment. Exposure to any one of these compounds may be associated with a modest increased risk in an adverse health outcome, but because many exposures are ubiquitous, the affected population may be quite substantial.

What are some of the environmental health threats that you have studied?

ND: My work focuses on how to improve our approaches for measuring exposure to environmental pollutants. Accurate and precise exposure assessment can substantially enhance our ability to detect exposure-disease associations. In my work, I study several classes of pollutants, such as pesticides, persistent organic pollutants (chemicals that are so stable they will persist in the environment for years to come) and polycyclic aromatic hydrocarbons.

Are people generally aware of these hazards in their homes and living areas?

ND: We come into contact with hundreds of toxic chemicals every day as we move through our environment. People may not be aware that they are getting exposed to chemicals because they are “invisible” and the effects may not manifest for years to come. That being said, there is an increasing awareness among some segments of the public about the harmful effects of chemicals in consumer products. Public pressure often spurs companies to take action, such as the removal of bisphenol-A or BPA from water bottles.

You’ve incorporated vacuum bags full of dust and dirt into your research. Why do you do this and what do you find?

ND: I am a big fan of carpet dust. Dust is a reservoir for chemicals in the home and is an important source of chemical exposure for children. For example, pesticides are designed to break down outdoors, but resist degradation in carpet dust due to limited exposure to sunlight, microbial activity, moisture, and other factors. Pesticides may be present in carpet dust from drift from nearby treated fields, application in and around the home and garden or from tracking in on shoes or clothing. Non-dietary ingestion of dust has been estimated to contribute up to 40 percent of total pesticide exposure in children, depending on the pesticide, due to the high percentage of time children spend indoors and on the floor as well as their propensity to engage in hand-to-mouth activity. I have observed higher concentrations of pesticides in households reporting increased treatment of home and garden pests. I have also observed higher concentrations of dioxins and furans in the dust of homes located in close proximity to industrial facilities. Studies in agricultural areas have reported increased pesticide concentrations in house dust attributable to environmental sources such as take-home from farm work, agricultural drift and home use.

What threats do people living on farms face?

ND: Farm families may experience increased exposure to pesticides either from direct mixing and applying of pesticides, as well as “take-home” exposure from farm work, “drift” from nearby treated fields, residential pesticide use and dietary ingestion.

What are the health effects from this type and level of pesticide exposure?

ND: Recent meta-analyses support a link between self-reported residential pesticide exposure and increased risk of childhood leukemia. Other research demonstrates a link between pesticide exposure and other adverse health effects, such as decline in cognitive function in children.

On a smaller level, is it a good idea to use insect repellent or bug sprays inside the house?

ND: Pesticides are toxic by design—they are intended to kill or control living things, so minimizing their use is a good idea. I recommend practicing prevention—such as not leaving food scraps and crumbs, sealing entry points such as cracks or holes in walls and window screens.

All kinds of materials go into building a house. Are newer homes generally safer in terms of human health than older homes that used lead paint and other toxic substances?

ND: Older homes have higher levels of “legacy chemicals,” such as polychlorinated biphenyls, DDT and lead compared to newer homes. People can reduce exposure to these compounds by cleaning frequently to reduce dust, using wet cleaning methods over dry methods, like sweeping, which tend to resuspend dust. Also, following safe work practices when renovating. New building materials can also contain potentially harmful substances, such as volatile organic compounds in paints or flame retardants in insulation. One solution to pollution is dilution—so if you are doing painting or renovations, you can reduce exposure by ventilating your home (i.e., open a window!).

Discuss your long-term research goals. What do you want to accomplish?

ND: My long-term career goal is to become a leader in epidemiologic studies of environmental risk factors for cancer and other adverse health outcomes that incorporate novel exposure assessment methods. I want to develop accurate and precise methodologic tools to help us better understand links between environmental exposures and diseases. 

What has coming to the Yale School of Public Health been like?

ND: I love being a Yale professor. I love the intellectual freedom—the ability to pursue any idea that excites me. The members of the faculty have tremendous expertise and are passionate about their work. I think the smaller size of YSPH helps foster a collaborative, not competitive, environment. Working with students in and outside the classroom has been a real joy.

Source: Yale University

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