Wellness Chat is an EWG series bringing you the latest news on cancer prevention through discussions with experts in the field. Today’s guest: Nicole Deziel, Ph.D.
Nicole Deziel, Ph.D. in this lightly edited interview with EWG, she shares her thoughts on how household exposures can affect health.
EWG: Epidemiology is a little like detective work – searching for clues to disease trends and causes. One of the challenges is getting accurate measurements of what people are exposed to. That’s one of the focal areas of your research. What role does exposure assessment play in identifying the causes of disease?
DEZIEL: My work focuses on getting accurate, high quality measurements of what people are exposed to. If you don’t correctly identify who is exposed to low, medium and high levels of pollutants, you may substantially hinder your ability to detect a relationship between exposure to an environmental contaminant and a health problem, if one truly exists. Improving our methods for identifying who is exposed to harmful agents and at what levels can dramatically enhance our ability to understand the links between exposure and disease.
EWG: Why have you focused some of your research on indoor exposures?
DEZIEL: People can spend as much as 90 percent of their time indoors, and there are many potential sources of pollutants inside homes, schools and workplaces. For example, my collaborators and I have measured concentrations of pesticides in carpet dust. Dust is a reservoir for chemicals in the home and is an important source of pesticide exposure for children, due to the high percentage of time children spend on the floor as well as their propensity to engage in hand-to-mouth activity. In addition, pesticides that may degrade readily outdoors can persist in carpet dust inside homes due to limited sunlight, microbial activity, moisture and other factors.
EWG: You study flame retardants and their possible link to thyroid cancer. How are people exposed to these chemicals and why the concern for thyroid cancer in particular?
DEZIEL: Flame retardants are chemicals that are added to foam, furniture, upholstery, electronics and clothing to slow the spread of fire. One particular group of flame retardants, called polybrominated diphenyl ethers or PDBEs, are of particular concern because of their structural similarity to our naturally occurring thyroid hormones.
In 2000, a Swedish breast milk study prompted major public health concern about these chemicals. The study demonstrated an exponential increase in PBDEs, which are very fat-soluble and therefore tend to accumulate in human breast milk. The Swedish were forward-thinking and banked women’s breast milk beginning in the 1970s. At the time, there was very limited data on the human health effects of these compounds. This study raised awareness about these chemicals and spurred active research into their sources and potential adverse health effects.
We have since learned that when these chemicals enter the body, they can perturb our hormone systems. PBDEs are widespread in our homes, cars and offices. They’re also commonly found in the food supply, particularly in animal products and fatty foods, due to their widespread environmental contamination and tendency to be stored in fat. The two major routes of exposure are thought to be incidental ingestion of house dust and dietary ingestion. These compounds have been voluntarily phased out of use in the U.S., but they are extremely widespread and stable and therefore exposure will continue for years to come.
More than half a million people in the U.S. are living with thyroid cancer. Thyroid cancer rates are increasing faster than any other cancer and are three times higher in women than men. The causes are largely unknown. Thyroid cancer is rarely fatal. However, it often requires surgery and ongoing testing and treatment with radiation or chemotherapy, which may impact quality of life and is costly.
Increasing thyroid cancer rates are partially due to improvements in identifying and diagnosing cases. However, increased exposures to environmental pollutants such as PBDE flame retardants have been suggested to play a role.
PBDEs can mimic thyroid hormones and therefore disrupt thyroid gland function, potentially leading to cancer. Considering the widespread nature of exposure to these compounds, the recent rapid increase in thyroid cancer incidence and the largely unknown causes of this disease, my research project investigating exposure to PBDEs and risk of thyroid cancer could provide important insights for public health.
EWG: Any thoughts on the new flame retardant chemicals that are replacing PBDEs?
DEZIEL: While PBDE flame retardants have been phased out, replacement organophosphate flame retardants have increased in use since the 1990s.
For example, Firemaster 550®, a mixture of phosphorus-containing compounds including triphenyl phosphate, has gained popularity as an additive to polyurethane foam.
In the 1970s, Tris (1,3-dichloro-isopropyl) phosphate, or TDCPP, was restricted from use in children’s pajamas due to concerns about carcinogenicity. Tests linked TDCPP to tumors in the liver, kidney and testes of rodents. Despite this, it became a primary replacement for PBDEs in polyurethane foam. Recent studies from scientists around the globe have observed widespread concentrations in house dust samples.
Evidence for the potential hormone-disrupting properties of these compounds is mounting. There is an urgent need to better understand the exposures to these replacement compounds and the potential health effects.
EWG: In addition to flame retardants, are there any other “hot spots” of environmental exposure in the home? Any recommendations for how people, young and old, can reduce indoor exposures to potentially toxic substances?
DEZIEL: There are so many ways people can reduce their exposures to potentially harmful substances in their homes. Have a smoke-free home. Clean and vacuum often to reduce dust and allergens and other compounds. Seek alternatives to caustic household cleaners and avoid air fresheners and other scented products. Also, use gardening techniques that don’t involve pesticides and chemical fertilizers. These practices can limit a person’s exposure to potentially toxic substances, as well as their release into the environment.
EWG: You recently published a paper on the reproductive and developmental toxicity of chemicals involved in hydraulic fracturing, or fracking. People might be aware that fracking, the process of drilling for natural gas or oil by fracturing underground rocks to release it, could pollute groundwater. But what exactly are the exposures of concern?
DEZIEL: Hydraulic fracturing is a term used to describe the broader process of drilling and extracting natural gas from deep, tight formations that have only recently become accessible to us due to new drilling technologies. Extracting natural gas involves constructing a well site and drilling deep below the ground. This can be a noisy process with a lot of traffic and machinery that operates day and night.
The actual process of hydraulic fracturing involves injecting approximately 100 million liters of water and chemicals and sand a mile or more below ground under high pressure to create a network of cracks in the shale, facilitating oil and gas release. When the pressure is released, the gas flows up – as do briny water and natural contaminants such as metals and radioactive compounds. There are many potential risks from water contamination, air pollution, noise and stress. People could potentially be exposed to hundreds of possible pollutants, and it’s difficult to prioritize which ones to study.
In addition to potential environmental exposure to chemicals, the influx of workers into rural areas, known as population mixing, may be a relevant risk factor for childhood leukemia. Population increases have been previously documented with “booms” in resource extraction in other areas. The population- mixing hypothesis suggests that the introduction of new infectious agents, which could compromise the immune system, could increase risk of childhood leukemia. More research is urgently needed in this area to better understand the broad array of potential exposure and health risks.