Could heat make us more vulnerable to toxic chemicals?

As climate change increases heat waves around the globe, many of us are becoming more familiar with the associated health risks, such as heat-related illnesses, heart attacks and strokes. But could heat also increase our exposure to harmful chemicals in our environment? 

Cecilia Martindale, a MS student in the UW Department of Environmental & Occupational Health Sciences (DEOHS), recently received a Russell L. Castner Award to support her efforts to shed light on this question. She is characterizing how people’s exposure to glyphosate—the most widely used weed killer in the world, found in products like Roundup—varies with temperature using a large U.S. epidemiological data set.  

The chemical increases the risk of non-Hodgkin’s lymphoma by 41 percent, according to research by Martindale’s adviser, DEOHS Professor and Interim Chair Lianne Sheppard.  

“I’m interested in how climate change can impact toxic exposures in unexpected ways,” Martindale said. 

Why might heat increase exposures to herbicides? 

Previous research in outdoor workers has demonstrated a link between pesticide exposure and heat, but much less is known about how these coexposures might affect the general population. When it’s hotter, several factors may align to increase people’s glyphosate exposure. 

“If it's warmer early in the season, you're going to have more weeds,” Martindale explained, leading to greater application of herbicides like glyphosate. People might then ingest a higher dose of the chemicals that remain on some foods—particularly high levels are found in conventional oats, corn and soybeans.  

Because herbicides and pesticides are often volatile chemicals, they evaporate and are transported through the air more easily when it’s hot out. People also spend more time outdoors in warm seasons, increasing their exposure to these chemicals. What’s more, our bodies tend to absorb chemicals more readily through the skin when we’re sweating in the heat. 

How heat affects the body 

Martindale is collaborating with Sheppard and postdoctoral researcher Magali Blanco, who will join the DEOHS faculty in June, to analyze data from the National Health and Nutrition Examination Survey, including urinary glyphosate levels from about 7,000 adults and children across the United States. 

Because glyphosate lasts only about a day in the body, Martindale is comparing these levels with the local temperature a day before people provided samples. To get an accurate sense of how heat affects people’s bodies, she plans to use the wet bulb globe temperature, a physiologically relevant estimate of heat exposure, which incorporates humidity, sunlight and wind. 

The Castner funding will allow her to access data from a secure federal research center to link study participants’ locations with detailed historic weather data to make these estimates. 

“Whether or not we find a relationship with heat, we’ll learn a lot about how much glyphosate we have in our bodies in general,” she said. 

Breathing easier 

Before coming to DEOHS, Martindale worked as a clinical research coordinator in neurology in Salt Lake City. She noticed that study participants often had worse symptoms during periods of heat, wildfire smoke, or poor air quality because of atmospheric inversions in the valley.  

“That made me interested in environmental health generally,” she said, and motivated her to pursue her master’s in DEOHS.  

Martindale is now applying her interest in air quality and health through a research assistantship with DEOHS Assistant Professor Elena Austin. They are assessing indoor air quality and temperature in several rural schools across Washington state through a partnership with the Washington State Department of Health, which is providing HVAC systems to the schools. 

In some communities, “there might be more resistance to talking about climate change,” she said. “But people in general are really passionate about heat and air quality, because everyone wants to breathe clean air, and everyone can recognize when it's way too hot. It’s been very good to find those shared values.”