Stormwater Runoff Exposures

By Ean Peyton, Production Assistant

As cities become more developed, agricultural operations grow, and weather patterns intensify, stormwater pollution continues to become an important environmental concern. From heavy metals and pesticides, to sediment and nutrient loading, stormwater runoff is becoming more and more contaminated as time progresses. It typically drains into smaller streams and rivers where it builds up and is transported to larger bodies of water (lakes, bays, oceans). While the stormwater exposure list is growing, listed below are just a few of the main pollutants plaguing our waterways.


Sediment is probably the most abundant (and arguably the most severe) stormwater pollutant there is. We’ve all seen a stream, pond or lake right after a heavy rain turn into a murky, brown mess. Sediment can enter waterways through a few different ways. It can be picked up from construction zones or large areas with no vegetative cover and drained into nearby creeks and streams. It can also enter waterways through the destruction of streambeds. This is especially true for creeks and streams near heavily developed areas due to the large amount of runoff being forced into the watershed. In larger, developed areas, we typically see more impervious surfaces (those that are unable to absorb water such as asphalt and concrete) and because of this, runoff from larger areas is forced into smaller creeks and streams. These smaller creeks and streams cannot typically handle the stress of increased runoff and erode to compensate for the larger amounts of water. The eroded sediment can travel for miles before being deposited. According to the EPA, sediment pollution causes $16 billion in damage annually.

Sediment can have many serious ramifications in various watersheds. One of the most conspicuous effects sediment can have is the reduction in water clarity. While this may not seem to be too serious, reduced water clarity can cause more problems than just being unsightly. Reduced water clarity can inhibit aquatic plant growth by not allowing sunlight to penetrate through the water and in return, decrease food supply for organisms depending on those aquatic plants. Reduced water clarity also makes it rather difficult for aquatic organisms to see their prey, which can result in starvation during these prolonged times of poor visibility.

Sediment can also damage sensitive tissues in aquatic organisms and can even clog fish gills, resulting in reduced resistance to disease and lower growth rates. This coupled with the disruption of the food chain often causes massive declines in fish and other aquatic life populations. Sediment can also bury benthic (bed dwelling) organisms during heavy rain events under thick layers of silt. This typically leads to suffocation and can wipe out large populations in the benthos community.

In addition to land erosion and construction zones, there are other sources of sediment that can contaminate stormwater. Pavement and vehicle wear, the weathering of certain buildings and litter from organic materials such as leaves and grass clippings can all contribute to the collection of sediment in stormwater.


While there are many types of nutrients troubling waterways, the two main nutrients we consistently see problems from are nitrogen and phosphorous. Nitrogen can be found in three forms in our waterways: Nitrite (NO2-), Nitrate (NO3-) and Ammonium (NH4+). Phosphorus is typically only found in one form, which is Phosphate (PO43− ). The loading of these two nutrients into watersheds sparks a process known as eutrophication. Eutrophication is the excessive growth of algae and other aquatic plants due to the increase of nutrients present in bodies of water,. Large algal blooms are found in areas where heavy nutrient loading is taking place. When algal blooms start to grow, they typically block out light to organisms growing beneath and can make the water appear to be bright green. When these algal blooms die out, the decomposition process depletes these bodies of water of their dissolved oxygen, creating dead zones that are anoxic (completely devoid of dissolved oxygen). This is deadly to any organism dependent on the oxygen in the water to survive or on light to produce energy.

Sometimes, these algal blooms can be toxic. Brown tides, red tides and Pfiesteria (a single-celled organism that creates powerful toxins that are released into the water) can bloom due to the increased loading of nutrients in water bodies. According to study by NOAA, toxic algal blooms can create putrid odors, poisoned aquatic life, unsightly views and can damage recreational and commercial fisheries.

There are many sources from which nutrients can be picked up by stormwater. Sediment plays a large part in nutrient loading. Sediment locks in nutrients and can bond to nitrogen and phosphorus on a molecular level. When sediment rich in these nutrients are picked up by stormwater runoff, these nutrients are picked up as well. While these nutrients usually lock onto sediment, they are very soluble in water and can move farther than sediment that eventually settles out. Agricultural operations are a huge source of nutrient pollution in waterways due to the heavy use of nitrogen rich fertilizers and animal feed along with the abundance of animal waste. These nutrients are easily washed into nearby waterways, posing problems downstream. In more developed areas, sewer overflows and septic tank leaks can cause increased nutrient pollution that typically can be picked up by stormwater runoff.

Herbicides & Pesticides

Herbicides and pesticides are a lot like nutrients in that they can become attached to soil particles and/or easily dissolve in water. These toxic substances are incredibly poisonous to aquatic life and are frequently found in lethal levels. The biological effects that pesticides and herbicides have on aquatic life include hormonal imbalances, cancers, immune system impairment, cellular and DNA damage, eggshell thinning and even death. Some of these toxic agents can persist in the environment for long periods of time because of the delayed breakdown time. These agents also occur in the environment due to bioaccumulation. Essentially, as smaller, primary organisms are affected by pesticides/herbicides and are eaten by larger organisms, those larger organisms are also affected. This happens repeatedly with larger and larger organisms and eventually, we see a massive buildup of these toxins in organisms that are higher in the food chain. According to the EPA, in the US alone, over one billion tons of pesticides and herbicides are used each year and we consistently see aquatic population decline due to these agents. These toxins are carried by stormwater runoff from lawns that have been sprayed commercially or with do-it-yourself agents along with larger industrial, agricultural operations utilizing pesticides and herbicides for crop growth.

Heavy Metals, Oils and Detergents

Heavy metals are another pollutant that can persist in the environment due to bioaccumulation. Heavy metals that we typically see in polluted waters are mercury, lead and zinc, just to name a few. Most of these elements are poisonous to aquatic life and can cause neurological defects in many organisms. Most heavy metals are released into the environment and carried through stormwater from vehicle wear and leaks (oil, gasoline, antifreeze, etc.) along with sewer overflows and septic tank leaks. Detergents are also rather toxic to aquatic life and can be found in stormwater runoff. After heavy rain events, excess detergent found on the asphalt at car washes are washed into nearby waterways. While there are many detergents that are phosphate-free, there are still plenty of cleaners and detergents that contain phosphates, which can lead to eutrophication if carried into surrounding watersheds.

Stormwater runoff remains an important environmental concern across many industries, and businesses around the country are taking precautions to prevent losses. Some environmental policies will address these concerns, so it’s crucial to discuss runoff exposures with your clients. If you would like more information on stormwater runoff, please contact us.

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