The return of winter weather brings with it the scrape of plows and shovels and crunch of salt – the opening volleys of an annual struggle to keep roads and sidewalks safely navigable. But research in recent years has revealed that water quality has become collateral damage in our battle against the elements due to the use of salt and other deicing chemicals.
While snow and ice eventually melt, deicing agents can persist in the environment much longer. According to Amanda Carneiro Marques, PhD, an assistant professor in Drexel University’s College of Engineering whose research focuses on water quality monitoring and developing methods to trace the sources of water pollution, the extent of its persistence — and what it could mean for aquatic ecosystems and water treatment — is just now being fully understood.
Marques’ research has identified chemical markers for pollutants, such as deicing agents, that can be used to trace their journey from the surface of roads and sidewalks into nearby bodies of water, groundwater and reservoirs. Her efforts have supported local government agencies and conservation departments to develop strategies to avoid over-salting and to educate the public about the environmental impact of deicers.
She recently shared with the Drexel News Blog some of her insights from this work and what she believes can be done to address the challenge of keeping infrastructure safe in the winter, while also protecting our environment and freshwater sources.
We’ve been aware for quite some time that the chemicals used in road salt can have a detrimental effect on nearby water supplies and ecosystems. What are some of the short- and long-term effects that you’ve observed in your research?
Despite being very important for making travel conditions safer during the winter months, the application of deicing agents, such as road salts, can have extensive, negative environmental impacts. Salts have the potential to degrade water quality, aquatic ecosystems and infrastructure because they are soluble in water and difficult to remove.
Deicing agents — typically chloride or salts such as sodium chloride — dominate salt inputs to the environment. High application rates of winter deicers with chlorides can result in acute and chronic toxicity to aquatic organisms.
Excess sodium levels in reservoirs may compromise the health of individuals on sodium-restricted diets and cause harm to aquatic ecosystems. Furthermore, chloride ions have corrosivity potential, which can leach metals from water distribution infrastructure into the water and inhibit coagulation processes in water treatment plants — rendering the processes less effective and potentially allowing harmful chemicals to persist in drinking water.
Identifying the patterns of long-term salinization in water bodies across a region can support the development of effective alternatives to treat the area and minimize further water degradation. We know that salt can persist in the environment, depending on its physical characteristics, for quite a long time — from a few months to several years, or even as long as decades. So, to understand the extent of human health and environmental impact from deicing agents, we must consider the area over which they have been used, how long they have been applied and the environmental conditions and transport factors in the application area.
What are some of the general approaches that have been taken and considered thus far to help mitigate the problem?
There are a number of alternatives that have been explored. Educational programs and improvements on systems to evaluate weather and road conditions and support an efficient application of salt are some of the initiatives that have been implemented at the local level.
Other alternatives are strategies related to the identification of vulnerable areas — such as those where salt is more likely to be washed into a reservoir or drinking water supply — and the application of safe deicing agents at a rate adequate for that area. Pre-treatment options are also some alternatives that have been explored, such as application of brine — salt diluted in water — prior to snow events, which reduces the quantity of salt that needs to be applied after the event.
One of the difficulties in preventing pollution of waterways by runoff is pinpointing its exact source. How is your research approaching this challenge?
Since salt is largely spread on the surface, the approaches we are using focus on identifying the salt source and the major drivers for salinity levels and trends we have been observing in surface and ground water.
When salt hits the ground, there are several pathways that it might take in the environment. It can travel as surface runoff with precipitation and snowmelt events or infiltrate as the water seeps into the ground, reaching the soil and groundwater. The time and pathways that salt takes to travel influence the trends we are observing, thus why it is important to understand the entire process.
We use environmental tracers to understand the transport through surface to subsurface and we assess scenarios considering the effectiveness of mitigation strategies through modeling. One method uses the chemical ratios (chloride-bromide curves) in water samples as an indicator to identify the source of salt, which may come from anthropogenic activities, such as roads deicing, agriculture and sewage systems, among others; or from natural sources, like the chemical weathering of rocks.
We also analyze the land use and land coverage in the area, the types of systems and logistical planning guides for salt application, and other physical and climate factors that have the potential to influence the salt trends we’re observing in the environment.
These are all ways to try to understand the major contributing factors for salinity trends and propose mitigation strategies that would be more effective, given the particular characteristics of each area.
What are some of the limitations and challenges facing local municipalities as they work to keep infrastructure passable in the winter, while also striving to protect the environment?
A deicing agent works by lowering the freezing point of water, preventing ice from forming at its normal freezing point. Crucial for roadway and walkway safety during the winter months, chloride-based salts most commonly used are sodium chloride (most commonly applied), magnesium chloride and calcium chloride, among others.
The decision about the most adequate deicing agent to apply depends on the characteristics of the area, logistical planning — which can be related to cost — and effectiveness at different temperatures. For example, some chloride-based salts have the potential to produce less environmental impact than others, but they can be more expensive or not as effective for specific weather and road conditions.
Municipalities and conservation agencies and departments have been working on strategies to identify vulnerable areas for salt application and invest in training programs and other efforts to guarantee that the right amount is applied in the right place.
What is one recommendation you would make for an urban area that is trying to improve its winter weather management processes with respect to the environment?
The main takeaway is that because salt is persistent in the environment, real-time technology, environmental education and research are necessary to understand factors that can contribute to increasing salt trends in the environment and support an effective implementation of mitigation strategies to guarantee the quality of our freshwater resources.
Reporters interested in speaking with Carneiro Marques should contact Britt Faulstick, executive director, News & Media Relations, at 215-796-5161 or bef29@drexel.edu.
