We often drive over roads and highways without thinking much about the smooth, black surface beneath us–at least not until we hit a pothole or rough patch. These crumbled, gritty spots of asphalt are caused by the erosion of asphalt binder. It turns out that this cementing material is a toxic glue that could be leaching into our water supply. While the results aren’t promising for the planet, they could encourage engineers to look for new and healthier pavement options. (1)
Could Asphalt Glue Be Toxic?
A study conducted by researchers from Florida State University aimed to examine the chemical behavior of asphalt binder. Ryan Rodgers is the director of the Future Fuels Institute at the MagLab, or National High Magnetic Field Laboratory. Since his career began, Rodgers has been studying the chemistry of petroleum and its effects on the world around it. While he and his team have published studies on the behavior of petroleum molecules, asphalt binder was the missing link in a well-examined chain.
“You see the brand new asphalt roads go down and they’re smooth as silk on top,” Rodgers told the MagLab’s fields magazine. “And then you look at one that’s 5 years, 10 years old, and you can see the [stone] aggregate. And you’re like, ‘Where the hell did all the cement go?'” To understand how asphalt’s toxic glue behaved, the research team needed to examine the molecular structure of this material. (2)
While an asphalt road includes crushed stones, sand, and gravel, the binder is what keeps it all together. Asphalt binder is a product of petroleum, crude oil that’s carbon-rich and took millennia to form between earth’s mantle below and massive rock and sediment above. After it’s pulled from reservoirs deep beneath the earth, petroleum is refined and distilled for a variety of uses. Asphalt binder is a by-product of this distillation process, a sticky black substance keeping the roads together. (3)
The Experiment Yields Results
Rodgers, already aware that soil and runoff neared asphalt roads contained carcinogenic substances, wanted to see how asphalt binder would react to water and light. Submerging a sample of the toxic glue in water, the team shined artificial sunlight over the glass slide. With a control sample kept in the dark, the results were what the researchers had theorized. Because of a process called photooxidation, the sunlight-bathed asphalt binder leached 25 times the amount of water-soluble organic compounds. Additionally, the compounds detected derive from petroleum and are generally considered toxic. (1)
Because the compounds were highly concentrated after sunlight exposure, the experiment proves that sunlight affects the asphalt binder molecules. This is easily translatable to paved roads, which bake in the sun and bathe in the rain day-in and day-out. “There are tens of thousands of elemental compositions,” Rodgers notes regarding the leached compounds. “Each one of those can have [hundreds of thousands of] different structures. So you’re just puking ungodly amounts of material that is aromatic. And it’s water-soluble, and it has every structure that you can possibly think of. So the idea that one of them is bad for you is probably pretty good.”
While the results may seem bleak, more research needs to be done by the team to determine the asphalt binder’s level of toxicity. The team hopes that their findings will provide the science to other researchers, industry leaders, and policymakers to identify and deal with toxic materials, however widely used. With 8.5 million miles of road in the United States alone, the results of this study will have resounding impacts across the globe. (2)
