We have known for years that rainwater can carry hazardous substances which affect the health of human and animal life. The classic example is acid rain. Burning coal and other fossil fuels produces sulfur dioxide (SO2), which various nitrogen oxides (NOx) catalyze into H2SO4, or sulfuric acid. The most commonly observed effects of sulfuric acid in human communities include peeling paint, corroded bridges, and erosion of public monuments. Once these materials begin to dissolve, they can then wash into our waterways. More directly, ecological health may suffer because of acidification of the water table, soil pH, or surface water.
Mercury was used in felting, and mercury poisoning is thought to be a potential origin for the phrase “mad as a hatter”
Other by-products of industrial processes, such as mercury vapor, are also capable of transmission via the water cycle. Similar to SO2, mercury vapor can bond to water vapor, and precipitates out during storm events. Unlike acid rain, the effects of mercury deposition from stormwater often have direct, immediate effects on human and environmental health. As dissolved mercury enters the water, it contaminates aquatic life, becoming concentrated in apex predator species, such as tuna. Pregnant women and children risk mercury poisoning when consuming this contaminated seafood. Mercury poisoning can cause, among other things, insanity.
But we have even larger stormwater problems. Beyond the obvious associations with atmospheric pollution, stormwater may be a vector for terrestrial pollutants. Specifically, we must account for the pollutants which cling to our city streets, our rooftops, our farm fields, and other trappings of industrial society. For example, when DDT commonly used, it would routinely wash off crops into streams and ascend the food chain to large fish. From there, it caused thinning of bird shells – notably, those of bald eagles and other river raptors. “Instead of eggs, heavily DDT-infested Brown Pelicans and Bald Eagles tend to find omelets in their nests, since the eggshells are unable to support the weight of the incubating bird.”
In Appalachian coal country, stormwater runoff from mine tailings has led to dangerously increased levels of selenium in local waterways. According to the EPA, “[t]oxic levels of selenium in water bodies have mostly been related to irrigation of western soils that are naturally high in selenium, ash pond discharges from coal-fired power plants using coal that has selenium in it, petroleum refinery effluents, and runoff or discharges from certain mining activities. 
An example of such mining activities is West Virginia mountaintop mining, where selenium-bearing overburden is exposed to weathering.”Selenium poisoning is perhaps most well-known for producing two-headed trout, though other wildlife deformities – “missing eyes, misshapen beaks, protruding brains,” and extra limbs have all been observed, as well.
In addition, stormwater runoff is largely responsible for massive algal blooms and subsequent hypoxic zones. Blue-green algae (aka “cyanobacteria”) “bloom formation seems to be linked to nutrient-rich water bodies (for example, water that contains a lot of phosphates from detergents and phosphate fertilizers).” The Chesapeake Bay deadzone and associated depletion of crab, oyster, and fish populations is largely the result of runoff from chicken farming operations, for example. Beyond inducing algal blooms, the pollution from agricultural runoff also significantly contributes to the decline of estuarine and lake fish stocks.
Algae bloom in the Chesapeake Bay
Cyanobacteria blooms also result in public health dangers, due to the wide variety of potent toxins such blooms produce. Prolonged exposure to such “cyanotoxins” can have numerous adverse effects on human and animal life. Mild sickness and skin irritation is the most common result of cyanobacterial exposure in humans. Though some studies have suggested a link between amyotrophic lateral sclerosis (ALS, a.k.a. Lou Gehrig’s Disease) and other neurodegenerative diseases to prolonged exposure, there is not yet scientific consensus on this point. What is clear is that ingesting algae-contaminated water can have serious adverse effects on animal life. The animal deaths (usually caused by damage to the liver or to the nervous system) that inevitably follow a bloom add their own hazards to public waterways, necessitating increased sanitation processing if such water is to be used for drinking.
The familiar rainbow sheen of urban stormwater.
In addition to the effects of industrial atmospheric pollution and pollution from mining and agricultural runoff, urban and industrial stormwater present their own complications. Many of the products used in, and byproducts of, industrial processes are known carcinogens. Urban and industrial stormwater also often contain heavy metals like arsenic, lead, and copper, which constitute well-known health hazards. Many of these chemicals are regulated under the Safe Drinking Water Act. However, we need look no further than the rainbow sheen from oil and gas for a particularly vivid example of stormwater acting as a vector for hazardous chemicals outside of the Safe Drinking Water Act’s purview. Notably, stormwater also flows through one of the Clean Water Act’s blind spots. In general, such non-point sources remain poorly controlled and under-regulated at this point. Knowing this, and presented with the evidence of runoff’s health impacts, we have a choice. We could move to incorporate health standards and data on human health impacts more completely and aggressively into our water quality statutes. Or we could accept the two-headed, deformed status quo as the best system possible under our current political reality. So, what’s it going to be?
