Bronte Wells
Road runoff is a significant source of pollution, and its impact on the environment is an increasing concern. The road surface collects pollutants from various sources, including residue from petrol and oil, tyre wear, and vehicle emissions. When it rains or snow melts, these pollutants mix with water and are washed away from the road, entering the environment through outfalls and soakaways. This runoff water can contain harmful chemicals and particles, such as microplastics, heavy metals, pesticides, and road salts, which can have detrimental effects on aquatic life and ecosystems. With growing urbanization, it is crucial to identify effective mitigation measures to reduce the transport of these harmful constituents and minimize the negative impact of road runoff on the environment.
| Characteristics | Values |
|---|---|
| Polycyclic Aromatic Hydrocarbons (PAHs) | Tyre particles can kill species including coho salmon, brook and rainbow trout. PAHs are also found in exhaust fumes and fuel/oil spills. |
| Alkanes C20-C40 | Can be harmful to aquatic life. |
| Alkylphenols | Can be harmful to aquatic life. |
| Phthalates | Can be harmful to aquatic life. |
| Aldehydes | Can be harmful to aquatic life. |
| Phenolic Antioxidants | Can be harmful to aquatic life. |
| Metals | Zinc (Zn), copper (Cu), lead (Pb), nickel (Ni) and cadmium (Cd) are found in high concentrations in road runoff. |
| De-icing Salts | Can produce high sodium and chloride concentrations in ponds, lakes, and bays, causing unnecessary fish kills and changes to water chemistry. |
| Microplastics | Derived from tyre rubber, microplastics can be harmful to aquatic life. |
| Dust Suppressants | Can be toxic to fish. |
| Pesticides and Herbicides | Can be harmful to humans and aquatic life. |
| Fertilizers | Can contribute to algal blooms and excessive plant growth, and can lead to eutrophication. |
| Sediment | Can smother fish spawning and nursery areas. |
| Antifreeze | Can mix with rainwater and enter waterways. |
| Engine Oil | Can mix with rainwater and enter waterways. |
| Litter | Discarded plastic bags, cigarette butts, etc. can enter waterways. |
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What You'll Learn
Metal deposits, dirt, and dust
Metal deposits in road runoff come from several sources. Worn tires, engine parts, brake linings, rust, and car and truck exhaust all contribute to the presence of heavy metals in road runoff. In addition, platinum from catalytic converters can be found in road dust and dirt, particularly along highways and high-volume roads. These metal deposits can have toxic effects on aquatic life and potentially contaminate groundwater.
Dirt and dust in road runoff are also significant concerns. When land is cleared or disturbed during road construction, the rate of erosion increases, leading to sediment runoff. This sediment consists of soil particles that are washed away and transported to surface waters. The absence of vegetation leaves the soil exposed, making it more vulnerable to erosion and the formation of gullies. As a result, the sediment ends up in drainage ditches and storm inlets, eventually making its way into nearby streams and other water bodies.
The presence of dirt and dust in road runoff can have several adverse effects. For example, sediment can smother fish spawning areas and nursery areas, clog fish gills, and block sunlight from reaching aquatic plants. Additionally, dust suppressants used on unpaved roads can contribute to the toxicity of road runoff, posing risks to fish and other aquatic organisms.
Understanding the sources and impacts of metal deposits, dirt, and dust in road runoff is crucial for developing effective mitigation strategies. By recognizing the potential risks associated with these pollutants, we can implement measures to reduce their negative effects on the environment and protect our water bodies and the organisms that depend on them.
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Rubber and tyre particles
Tyres are a complex source of pollutants, emitting particles and compounds through atmospheric, aquatic, and terrestrial pathways. The production and use of tyres generate multiple heavy metals, plastics, polycyclic aromatic hydrocarbons (PAHs), and other compounds that can be toxic on their own or in combination. Tyre particles emitted during use are a major component of microplastics in urban runoff and are a unique and highly potent source of toxic substances.
TRWPs have been found to have negative impacts on the environment and pose risks to both environmental and human health. They are one of the main contributors to microplastic pollution, with the major amount of TRWPs consisting of coarser heterogeneous particles released onto road surfaces, soils, and aquatic ecosystems. The fine fraction of TRWPs (<50 µm) is easily transported by road runoff into receiving waters, while the main mass fraction consists of coarse particles (>100 µm).
The fate and effects of TRWPs in the environment are complex and not yet fully understood. While some studies have found that microplastics derived from tyre rubber did not harm sediment-dwelling organisms, other studies have reported negative effects on invertebrates and mussels. The transport of harmful constituents in road runoff and its impact on sensitive ecosystems is an area of ongoing research, with a focus on identifying effective mitigation measures.
Overall, rubber and tyre particles are a significant contributor to road runoff pollution, with potential environmental and human health risks that require comprehensive examination and effective management strategies.
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Anti-freeze, oil, and petrol
Antifreeze, oil, and petrol are among the most common types of pollutants found in road runoff. When it rains or snow melts, these contaminants are washed off roads, bridges, and other impermeable surfaces, flowing into drainage ditches, wetlands, waterways, and, eventually, larger water bodies like lakes, rivers, streams, and oceans.
Antifreeze, also known as coolant, is a vital car fluid that prevents engines from overheating in warm weather and freezing in cold weather. However, when antifreeze leaks or is improperly disposed of, it can end up on road surfaces and subsequently enter water bodies through runoff. Antifreeze is toxic to humans, animals, and the environment, posing a significant threat to aquatic life.
Oil is another prevalent pollutant in road runoff. Engine oil leaks from vehicles and is often improperly discarded, ending up on road surfaces. Additionally, oil spills can occur at fueling stations or when oil is discarded directly onto pavements or into storm sewers. Oil is particularly harmful as one gallon of used oil has the potential to contaminate one million gallons of water.
Petrol, or gasoline, is also a contributor to road runoff pollution. Spills and leaks from vehicles or fueling stations can result in petrol washing off roads during rain or snowmelt events. Petrol contains toxic chemicals that can contaminate water bodies and harm aquatic organisms.
The presence of these pollutants in road runoff has detrimental effects on the environment. They can interfere with the natural processes of aquatic life, such as photosynthesis, respiration, growth, and reproduction. Additionally, the accumulation of these pollutants in tissues and the food chain can further magnify their toxic impacts.
To mitigate the environmental impact of antifreeze, oil, and petrol pollution in road runoff, various measures can be implemented. These include adopting best management practices (BMPs), implementing pollution prevention and control programs, and improving the disposal and recycling of these substances. By addressing these sources of pollution and implementing effective solutions, we can reduce the harmful effects on our natural environment.
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Pesticides and fertilisers
Pesticides are particularly prone to runoff when they are applied to frozen soils, saturated soils, or when heavy rain follows soon after application. The solubility, adsorbency, and persistence of pesticides also play a role in their vulnerability to runoff. Highly soluble pesticides, for instance, are more likely to be carried by runoff water. Additionally, pesticides that do not strongly adsorb to soil particles are more likely to be washed off the treated site. Pesticides with slower degradation rates are more available to move with runoff water. Granular formulations have been found in runoff water more frequently than other formulations.
Fertilisers, when applied excessively or improperly, can be carried by rainwater from roads and rights-of-way. They contribute to algal blooms, excessive plant growth, and eutrophication in rivers, streams, lakes, and bays.
The impact of these pollutants on the environment and aquatic life is significant. Pesticides, for example, can adhere to sediment and be transported by wind and water, eventually settling on aquatic plants, rocks, and the bottoms of water bodies, impacting fish spawning areas and aquatic life.
To mitigate the effects of pesticides and fertilisers in road runoff, various control measures can be implemented during and after road construction. These include seeding and fertilising to promote vegetation growth, which helps to stabilise exposed surfaces and reduce erosion. Grassed swales, filter strips, and check dams are also effective in slowing down runoff water, allowing for the removal of pollutants.
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Microplastics and chemicals
Microplastics are a significant component of road runoff, with tire wear particles (TWP) being one of the major sources of microplastic pollution in the environment. TWP can enter water systems through road runoff, where tiny fragments from tires are left on road surfaces and subsequently washed into storm drains, eventually making their way into rivers and oceans. These particles have been detected in drinking water sources, including tap water and bottled water, with microplastic concentrations found to be highest in polyethylene terephthalate (PET) packaging.
In addition to TWP, road runoff can also contain other types of microplastics such as paint particles from buildings and road markings, as well as agricultural microplastics from films and containers used in farming. These microplastics can have various shapes, sizes, and plastic types, each with unique physical and chemical properties, and toxicological impacts. The small size of microplastics makes them difficult to regulate and removes them from most regulations, but it also makes them more easily ingested by wildlife, leading to blocked and damaged organs and the release of harmful chemicals into their bodies.
The presence of microplastics in road runoff is a global issue, with urban stormwater runoff containing high concentrations of microplastics that are transported to water bodies such as streams, rivers, lakes, reservoirs, estuaries, and oceans. This has been observed in studies conducted in various locations, including San Francisco Bay, Scotland, China, India, and Mexico. The concentrations of microplastics in urban runoff can range from 0 to 8580 particles/L, with stormwater runoff containing significantly higher concentrations of microplastics compared to wastewater treatment plant effluent.
Chemical pollutants are also present in road runoff, including total suspended solids, heavy metals, pesticides, industrial chemicals, and polycyclic aromatic hydrocarbons (PAHs). These chemicals can adhere to the surface of microplastics due to their hydrophobic nature, which makes them more likely to attach to the non-polar surfaces of plastic particles floating in water bodies. As a result, microplastics can concentrate these harmful chemicals, posing risks to aquatic organisms and ecosystems when ingested or absorbed by marine life. PCBs and PAHs, for example, can interfere with hormones in organisms, leading to reproductive disorders and impaired fertility. Long-term exposure to these contaminants has been linked to increased risks of various cancers in humans.
The assessment and management of microplastics and chemical pollutants in road runoff are crucial to protecting the environment and human health. Risk assessments have been conducted to evaluate the potential ecological risks associated with these pollutants, considering their abundance and chemical composition. Mitigation strategies such as rain gardens have been suggested to reduce the contribution of stormwater runoff to microplastic pollution in aquatic ecosystems. Additionally, public awareness and concerns about microplastic pollution have grown, highlighting the need for source prevention and stormwater management to address this global issue.
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Frequently asked questions
Pollutants found in road runoff include residue from petrol and oil, tyre particles, microplastics, de-icing salts, heavy metals, pesticides, and fertilizers.
During rain or snow melt, these pollutants are washed directly into ditches, wetlands, and waterways, or transported through stormwater systems to larger water bodies. They can harm aquatic organisms and have detrimental long-term effects on aquatic life.
On-site treatment plants for the elimination of polluted runoff are under consideration. The European Union is also pursuing legislation to reduce tyre particle pollution.
