When temperatures drop and roads get slick, rock salt is an important safety precaution used by individuals, businesses, and local and state governments to keep walkers, cyclists, and drivers safe. However, according to a new scientific review paper from a team of researchers at Virginia Tech and the University of Maryland, the human demand for salt comes at a cost to the environment.
Published in the journal Nature Reviews Earth & Environment with researchers Stanley Grant, Megan Rippy, and Shantanu Bhide from Virginia Tech’s Occoquan Watershed Monitoring Laboratory, findings revealed that human activities are making Earth’s air, soil and freshwater saltier, which could pose an existential threat if current trends continue.
“This is a slow-moving train wreck,” said Megan Rippy, assistant professor in civil and environmental engineering. “It’s playing out so slowly that it’s easy to overlook that our streams, lakes, and drinking water resources are becoming progressively saltier.”
Disrupting the natural salt cycle
Salts are compounds with positively charged cations and negatively charged anions, with some of the most abundant ones being calcium, magnesium, potassium, and sulfate ions. When dislodged in higher doses, these ions can cause environmental problems by impairing water supply for humans and wildlife. The study conducted at the Occoquan Watershed Monitoring Laboratory considered a variety of salt ions that are found underground and in surface water.
Although geologic and hydrologic processes bring salts to Earth’s surface over time, human activities such as mining and land development are rapidly accelerating the natural “salt cycle.” Agriculture, construction, water and road treatment, and other industrial activities can also intensify salinization, which harms biodiversity and makes drinking water unsafe in extreme cases. This research is establishing for the first time that humans affect the concentration and cycling of salt on a global, interconnected scale.
“Ecosystems are finely tuned to a certain level of salinity, and as that increases over time it can lead to big impacts, for example loss of important species, including fish. That applies to humans too. Too much salt in irrigation water can cause crops to fail, and salt in drinking water supplies has been linked to human health effects like preeclampsia. This is happening in the U.S. and around the world,” said Rippy.
Over the course of the study, Rippy, Grant, Bhide and University of Maryland researchers showed that human-caused salinization affected approximately 2.5 billion acres of soil around the world — an area about the size of the United States. Salt ions also increased in streams and rivers over the last 50 years, coinciding with an increase in the global use and production of salts.
Salt has even infiltrated the air. In some regions, lakes are drying up and sending plumes of saline dust into the atmosphere. In areas that experience snow, road salts can become aerosolized, creating sodium and chloride particulate matter, which lowers air quality and can be detrimental to wildlife and crops.
“One way that humans are upsetting the natural salt cycle is through our use of rock salt for deicing roads and parking lots in the winter,” said Bhide.
Finding new deicing methods
Stanley Grant, director of the Occoquan Watershed Monitoring Laboratory, said road salts have an outsized impact in the U.S., which churns out 44 billion pounds of the deicing agent each year. Road salts represented 44 percent of U.S. salt consumption from 2013-17, and they account for 13.9 percent of the total dissolved solids that enter streams across the country. This can cause a “substantial” concentration of salt in watersheds, according to the paper. To prevent U.S. waterways from being inundated with salt in the coming years, policies limiting road salts or encouraging alternatives can be beneficial, the researchers said. Washington, D.C., and several other U.S. cities have started treating frigid roads with beet juice, which has the same effect but contains significantly less salt.
“There’s a lot of interest in how we can change the way roads are maintained in the winter to reduce road salt use and its impacts on ecosystems and drinking water supplies,” said Bhide. “It’s a tricky issue, because deicing roads also reduces traffic accidents and saves lives.”
Salinization is also associated with “cascading” effects. For example, saline dust can accelerate the melting of snow, which can harm communities — particularly in the western United States — that rely on snow for water supplies. Because of their structure, salt ions can bind to contaminants in soils and sediments, forming “chemical cocktails” that circulate in the environment and have detrimental effects. These significant environmental and health implications are creating a need for a more sustainable approach to salt usage.
“History is littered with ancient civilizations that collapsed because they couldn’t balance their salt budget. I’m hoping this article will raise awareness and lead to action on this issue, so that history doesn’t repeat itself,” said Grant.
Chelsea Seeber for Virginia Tech
