Glue used to hold roads together can release toxins that may harm humans when exposed to sun and rain: Study
Researchers hope that engineers will use this information to find a better alternative during paving of roads
Our roads contain a compound that is likely to harm human health. When exposed to the sun or rain, it releases thousands of potentially dangerous toxins into the environment, a new study suggests. The compound called asphalt binders or cement is a black, sticky semi-solid substance that is produced during the petroleum refining process. They are used on paved roads to help seal ingredients such as stones, sand and gravel stick together. It is inexpensive and waterproof, making it an attractive adhesive.
But questions on the asphalt binder's impacts on the environment have lingered in the minds of the researchers from MagLab and Florida State University. They thought that the compound is unlikely to stay harmless. "How do silky smooth black roads turn into grey, rough roads? And where the heck did all the asphalt go?" questioned Ryan Rodgers, director of petroleum applications and the Future Fuels Institute at the MagLab.
Strengthening their suspicions were previous studies. Researchers have detected higher amounts of polycyclic aromatic hydrocarbons (PAHs) on the soils and runoff near paved roads. Though present naturally, these compounds are produced when coal, oil, gas, wood, garbage, and tobacco are burned. As for its health effects, it is cancer-inducing and may also cause cataracts, kidney and liver damage, and jaundice.
In this study, researchers wanted to understand if asphalt binders released the polycyclic aromatic hydrocarbons. So Rogers got hold of a jug of asphalt binder from a local paving company and sent it for analysis. The duo of Sydney Niles, a PhD candidate, and MagLab chemist Martha Chacón-Patiño, set up experiments to investigate more. For a week, the team simulated real life-conditions in their lab. They submerged a binder sample in water and exposed it to solar light. At different time points, they checked for the release of toxins in the water. “We had this road sample, and we projected fake sunlight on it in the presence of water,” explained Niles, lead author of the study. “Then we looked at the water, and we found that there are all these compounds that are derived from petroleum, and probably toxic. We also found that more compounds are leached over time.”
But what was driving the leaching? According to the team, solar energy was powering a reaction between water and the asphalt binder. The resulting products got into the water. To be sure if the sun was responsible, the team placed a sample of the asphalt binder and water in the dark. They found that sample exposed to the sun had 25 times more potential toxins in the water than the one placed without sunlight.
By the end of their analysis, they detected about 15,000 carbon-containing chemicals in the experiment that used sunlight. This could be worrisome, considering the harmful health effects of PHAs. However, researchers are not sure if these chemicals are toxic. “We have definitively shown that asphalt binder has the potential to generate water-soluble contaminants, but the impact and fate of these will be the subject of future research,” Rodgers said.
Moving forward, the team hopes for a future with safer roads. “Hopefully it’s a motivation for a solution,” Niles said. “I hope that engineers can use this information to find a better alternative, whether it’s a sealant you put on the asphalt to protect it or finding something else to use to pave roads.” The study is published in the journal Environmental Science & Technology.