Drops of Change: Fighting Against Freshwater Pollution in a Changing Climate

This post is part of a monthly series called “Drops of Change” by the North American Youth Parliament for Water (NAYPW), a chapter of the World Youth Parliament for Water (WYPW). For more information on the NAYPW, you can explore their website or contact NAYPW at outreachnaypw@gmail.com.

Written by Lauren Lawson, Anna O’Brien, Kennedy Bucci, and Rachel Giles, University of Toronto

Freshwater pollution threatens human quality of life and environmental integrity across the globe. From agricultural runoff to plastic pollution, contaminants plague our planet’s surface water and groundwater by degrading drinking water and destroying freshwater habitat which impacts human health. Differences in climate and policy drive geographically diverse freshwater pollution issues that often act in tandem as diverse suites of multi-stressors. Within North America, two large-scale freshwater pollution issues are plastic pollution, caused by extensive use of plastic and mismanagement of waste, and road salt pollution (salinization), caused by road-deicing salts. Plastic pollution is a constant issue for freshwater, while salinization worsens in colder months but persists to some degree through the summer via groundwater contamination. While each pollutant is often studied individually, more research is needed on their interactions as part of a multi-stressor framework. Furthermore, understanding how pollution will be altered in the face of climate change is crucial for resiliency planning for climate change adaptation. With increased and shifting drought, warming, and freeze-thaw patterns caused by climate change, freshwater is clearly under pressure from all sides; thus, we are fighting against the clock to mitigate freshwater systems under duress from multi-stressor pollution and a rapidly changing climate.

Plastic Pollution

Plastic consists of a wide range of synthetic and semi-synthetic materials that can be molded into solid objects. The first fully synthetic material, Bakelite, was invented in 1907 by Leo Baekeland, who also coined the term ‘plastic’. Mass production of plastic products began in the 1950s and plastic waste generation now far exceeds our management capabilities. Of the 6300 million metric tons of plastic waste generated as of 2015, we estimate only 9% was recycled, while 12% was incinerated and 80% accumulated in landfills or polluted the environment, with consequences for wildlife.

Aquatic animals can become entangled in large pieces of plastic debris, resulting in suffocation or starvation. Smaller plastics, known as microplastics, can act as a magnet for chemical contaminants, which can then be transferred into tissues of aquatic animals through ingestion. Ingestion rates are high; for example, Holland et al. (2016) reports 55% of bird species included in their Canadian study ingested plastic. Chemicals associated with microplastic pollution are often persistent, bioaccumulative, and toxic. Plastic particles can also cause a feeling of fullness in animals despite providing no nutrients as well as causing lacerations in animal digestive tracts.

Plastic Debris on the Lake Ontario Shoreline, Canada

Photo curtesy of Kennedy Bucci, University of Toronto

Plastic pollution can be improved through a variety of bottom up and top down strategies. From the bottom up, consumers can use their voices and buying power. Individuals can adjust their plastic use habits, participate in litter cleanups, or write to leaders expressing their concerns. Experts can collaborate to create solutions, including local recycling programs and new technologies reducing plastic pollution. From the top down, decision makers can create policies limiting, reducing, or restricting plastic production. For example, Environment and Climate Change Canada and Health Canada recently released a Science Assessment of Plastic Pollution, which recommends banning six plastic items by 2030: plastic bags, cutlery, straws, stir sticks, six-pack rings, and difficult to recycle plastics such as black plastic take-out containers. Youth leaders across the globe are mobilizing in the fight against plastic pollution, providing youth insight at national and international scales. There is no one-size-fits-all solution, but when bottom up efforts combine with top down approaches, we can better mitigate plastic pollution.

Road Salt

Some freshwater systems now record salinities approaching as high as seawater. While plastic is a constant input, road salt input is seasonal. About 30 million tonnes of road salt is used each year in North America, largely restricted to mountainous areas and temperate climates. While management has reduced road salt use from historic levels, application rates remain high and are of concern as freshwater salinization increasingly extends year-round.

Road salt use began in the mid-twentieth century, and includes various chlorides. Sodium chloride is the most common de-icer in “warmer” cold regions, like Southern Ontario, Canada, and is effective between -3.9 to -9.4 Celsius. At these temperatures, salt mixes with snow to create a brine that melts ice. In colder localities, calcium chloride is used as it is effective at temperatures as low as -31.6 Celsius. Salt enters aquatic systems through runoff and contaminated groundwater discharge. High salinities cause osmotic stress in organisms adapted to freshwater conditions as freshwater organisms; for example, fish have completely opposite forms of osmoregulation. Freshwater organisms are hyperosmotic (saltier than their habitat) and marine organisms are more isosmotic (similar saltiness to habitat). This difference in salinity tolerance can lead to dehydration of freshwater organisms in salty conditions. Road salt ultimately impacts a variety of freshwater aquatic organisms, as chloride ions interfere with signalling of biological messages and plant nutrient uptake.

Extensive road salt application on stairs not exposed directly to precipitation at a Transit stop in Toronto, Canada

Photo curtesy of Donald Jackson, University of Toronto

To reduce road salt use, decision makers must strike a balance between road-user safety and health of the environment. Some road salt alternatives include brining (mixing salt with water prior to application) and salt alternatives (e.g. beet juice, gravel). Brining is an effective alternative to solid road salts. However, some “natural” alternatives like beet juice may be more harmful to aquatic life than standard road salt. Additionally, while road salt is regulated on public roads, it remains unregulated in private areas, where owners tend to over-apply to avoid liability issues. Amount of road salt depends on the type of salt used and weather conditions, but it is suggested that if using rock salt one handful be used per square yard. If consumers better regulate road salt application, including on private land, contamination levels are likely to improve. 

How will a changing climate impact freshwater pollution?

On their own, plastic and salt can cause environmental stress. However, they also occur against a backdrop of global change including habitat destruction, biodiversity loss, and climate change. Warming moves organisms outside their optimal thermal temperatures, and changing precipitation timing and stochasticity (increased flood volumes, longer droughts) can disrupt organism life cycles. These can have interactive effects with pollution. Altered timing and intensity of hydrologic events will also alter timing of plastic or salt arrival into a stream or pond, bringing pollutants into contact with different species and developmental stages, which may be more or less sensitive to effects. The changing climate may also alter human behavior and plastic or salt inputs. For example, increasing freeze-thaw-freeze events may lead to increased use of road salt in the short term: melts will pulse salt into local aquatic systems, and a subsequent re-freeze will require the re-application of salt, increasing overall salt use. On the other hand, in the long-term road salt use may decrease due to warmer overall temperatures. Ultimately, while road salt and plastic pollution may seem like starkly different pollution issues, they are part of a multi-stressor framework. Diverse multi-stressors can impact freshwater organisms and freshwater resources, causing environmental degradation and human health impacts from multiple angles. With growing awareness of road salt and plastic pollution, we hope to see changing behaviors to reduce inputs of both, mitigating the effects of multiple stressors on freshwater. Increased investigation on the impacts of diverse multi-stressors will be crucial as understanding how pollutants interact and potentially amplify environmental stress is increasingly important in our rapidly changing world.

Looking forward

Road salt and plastic pollution are only two parts of the multi-headed beast of multi-stressors freshwater ecosystems face. While we should continue to increase our understanding of the effects of these stressors individually, the reality is that we can better predict future impacts to freshwater ecosystems by taking a multi-stessor approach. Ultimately, by amplifying youth voices and the youth drive for resiliency in the face of climate change, we are cautiously optimistic road salt and plastic pollution have the potential to be reduced within our generation’s lifetime.