Urban Storm Water: A Toxic Mix Of Pollutants

Urban storm water is a major carrier of pollutants, which has a detrimental impact on water quality and ecosystems. As rainwater falls on impervious surfaces such as roads, sidewalks, and parking lots, it accumulates a variety of pollutants, including fertilizers, soaps, detergents, oils, chemicals, and litter. These pollutants are then transported by stormwater into nearby waterways, causing harm to the environment and human health. The issue is challenging to manage as stormwater pollution comes from scattered, non-specific sources, and successful mitigation requires a comprehensive understanding of all contributing sources. Furthermore, with rapid urbanization and advancements in technology, new chemicals and substances are continuously being introduced into the environment, making it crucial to stay updated on stormwater pollution sources and their potential impacts.

Bacteria and microplastics

Bacteria in Urban Stormwater

The primary source of bacteria in urban stormwater is animal waste, which can come from domestic pets, wildlife, and livestock. Fecal coliform and Escherichia coli (E. coli) are the two main types of bacteria found in urban stormwater. These bacteria can indicate the presence of pathogens, which are difficult and expensive to test for directly. Fecal coliform and E. coli are more commonly found in heavily populated or farmed areas and can reach surface water through malfunctioning septic systems, manure spills, or runoff. Bacteria levels are also influenced by factors such as seasonality and land use, with higher levels typically found during the summer months and in areas with higher population densities.

Microplastics in Urban Stormwater

Microplastics are another significant pollutant in urban stormwater. Urban stormwater runoff has been identified as a major pathway for microplastics to enter aquatic ecosystems. These microplastics can come from various sources, including atmospheric deposition, effluent from wastewater treatment plants, and stormwater runoff itself. The concentrations of microplastics in urban stormwater vary, but they are often found in high quantities, with reported ranges from 0.3 to 24.6 particles/L and even higher in some cases. The specific morphology and size distributions of microplastics can also differ between rain events and baseflow, with smaller particles and higher concentrations typically found during rain.

The presence of bacteria and microplastics in urban stormwater has significant implications for environmental health and highlights the need for effective management strategies to minimize their impact on aquatic ecosystems.

Fertilizers, soaps, and detergents

Urban stormwater runoff can pick up and transport various pollutants as it makes its way through urban environments, which can have detrimental effects on the environment and human health. Fertilizers, soaps, and detergents are among the most common pollutants in stormwater runoff from urban areas. These substances can contaminate nearby waterways, leading to ecological and health issues.

Fertilizers are often used to promote plant growth and enhance the appearance of lawns and gardens. However, when excess fertilizer is applied or when it is not properly absorbed by the soil, it can be washed away by stormwater runoff. This contributes to nutrient pollution in water bodies, leading to excessive algae growth and the creation of oxygen-depleted "dead zones" where other organisms cannot survive.

Soaps and detergents are commonly used for cleaning purposes, but they can also become pollutants when they enter stormwater systems. These products often contain phosphates and other chemicals that can act as nutrients for algae, contributing to the same issue of eutrophication as fertilizer pollution. Additionally, soaps and detergents can reduce water quality by increasing the amount of suspended solids in the water, making it murky and reducing light penetration, which can negatively impact aquatic ecosystems.

To mitigate the impact of fertilizers, soaps, and detergents on stormwater pollution, individuals can take several measures. Homeowners can opt for organic or low-impact fertilizers and apply them sparingly, following recommended application rates. Using phosphate-free, biodegradable soaps and detergents can also reduce the impact on water quality. Properly storing and covering items that may contain these pollutants can help prevent them from being washed away during rain events.

In addition to individual actions, local governments and organizations can play a role in reducing the impact of fertilizers, soaps, and detergents on stormwater pollution. Educating the public about the environmental impacts of these substances and providing guidelines for their proper use and disposal can help create a collective sense of responsibility. Implementing regulations and standards for the use of fertilizers, soaps, and detergents in urban areas can also contribute to minimizing their impact on stormwater pollution.

Vehicular transportation

Stormwater transports a variety of contaminants to receiving waters, and its quality and quantity characteristics differ from those of domestic sewage. It is a significant contributor to pollution in many countries. Vehicular transportation, along with atmospheric deposition, has been identified as one of the major sources of urban stormwater pollution.

Secondly, the infrastructure associated with vehicular transportation can also contribute to stormwater pollution. Roads, parking lots, and other paved surfaces can become polluted by various substances, which are then washed away by stormwater runoff. For instance, roads may be contaminated with spilled fuels, oils, and other vehicle fluids, as well as de-icing salts and heavy metals from brake pads and tyres. These contaminants are then picked up by stormwater and transported to nearby water bodies, where they can have detrimental effects on aquatic ecosystems.

Furthermore, vehicular transportation can indirectly lead to pollution through atmospheric deposition. Vehicle emissions, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), can be deposited onto surfaces and subsequently washed away by stormwater. These emissions can also react with other compounds in the atmosphere to form secondary pollutants, such as ground-level ozone and fine particulate matter, which contribute to smog formation and adverse health effects.

Finally, the maintenance and operation of vehicles can generate waste streams that, if not properly managed, can contaminate stormwater. For example, washing vehicles can produce wastewater containing soaps, detergents, and other cleaning chemicals that, if discharged into stormwater drains, can contaminate water bodies. Similarly, the improper disposal of automotive batteries, oils, and other hazardous wastes can result in the leaching of toxic substances into stormwater runoff.

To mitigate vehicular transportation's impact on urban stormwater pollution, a range of measures can be implemented. These include regular vehicle maintenance to prevent fluid leaks and the implementation of best management practices during vehicle washing and maintenance activities. Additionally, the use of best practices in the transportation industry, such as proper waste disposal and spill cleanup procedures, can help reduce the contamination of stormwater by vehicular sources.

Atmospheric deposition

One study identified important traffic characteristics and climate factors, such as antecedent dry periods and rainfall characteristics, which impact the nature of wet and dry deposition of solids and heavy metals. This study found a correlation between Zinc (Zn) and traffic volume, while Lead (Pb), Cadmium (Cd), Nickel (Ni), and Copper (Cu) were linked to traffic congestion. As a result, reducing traffic congestion is more effective than reducing overall traffic volume for improving air quality, especially concerning Pb, Cd, Ni, and Cu levels.

The size of the particles involved in atmospheric deposition also varies between wet and dry deposition. Zn in dry deposition is associated with larger particle size fractions (>10 μm), whereas Pb, Cd, Ni, and Cu are linked to smaller particle size fractions (<10 μm). Wet deposition particles are generally smaller and can disperse over a more extensive area due to buoyancy forces. On the other hand, dry deposition particles are influenced by gravity and tend to have a more localized impact.

Additionally, the sources of particles in wet and dry deposition differ. Exhaust emissions are primarily associated with bulk (wet) deposition, while dry deposition particles often originate from vehicle component wear. Atmospheric deposition contributes to the contamination of urban stormwater with heavy metals and other pollutants, which can have detrimental effects on the environment and human health.

Litter

Improperly disposed waste products, or litter, are a major pollutant in urban stormwater. Litter can include items such as cigarette butts, cans, food wrappers, plastic bags, and paper. These items can have significant environmental and public health impacts. For example, litter can clog and damage sensitive tissues, such as fish gills, and smother organisms that live on or in the beds of lakes and streams.

Once litter enters stormwater systems, it can be carried to surface waters or infiltrate groundwater. This can lead to the contamination of these water sources, which are often used for drinking water, irrigation, and recreation. The impact of litter on water quality can be particularly severe during storm events, when the increased volume of water can carry more litter and other pollutants into water bodies.

To reduce the impact of litter on urban stormwater, it is important to properly dispose of waste products and to secure trash cans and other waste storage areas to prevent the wind from carrying trash away. Additionally, construction sites should ensure that all materials are properly secured, and communities should consider implementing anti-littering campaigns to raise awareness about the environmental and health impacts of littering.

Overall, litter is a significant pollutant in urban stormwater that can have far-reaching consequences for the environment and public health. By properly disposing of waste and taking steps to prevent litter from entering stormwater systems, we can help reduce the impact of this type of pollution on our water resources.

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