In this video excerpted from Big River, learn how farm runoff impacts water quality and human health. Tour the water treatment plant in Des Moines, Iowa, and learn how the water is filtered. Hear how high nitrate content in water can affect human health, causing such problems as blue baby syndrome, and understand why water treatment plants in agricultural regions need nitrate removal facilities because of the pollution from fertilizer runoff.
Fertilizers supply nutrients to help plant growth and are widely used in the agricultural industry to increase crop production. However, there are also negative impacts from fertilizer use. For example, fertilizers are rich with nitrogen, which is an essential element for growing plants, but runoff containing nitrogen compounds damages water quality. Farm runoff can pollute surface water and groundwater with high levels of nitrates (formed when nitrogen combines with oxygen), which can be harmful to people who drink the water. In particular, such pollution puts infants less than six months old at high risk for blue baby syndrome, caused by a blood disorder called methemoglobinemia.
Once consumed, nitrate can be converted to nitrite, which changes oxygen-carrying hemoglobin in the blood to methemoglobin. Unlike hemoglobin, methemoglobin does not bind to oxygen. This blocks the blood’s ability to deliver oxygen to cells throughout the body. In most people, there is an enzyme that converts methemoglobin back to hemoglobin, but infants have a low concentration of this enzyme and are susceptible to developing too high a level of methemoglobin in their blood. When that happens, the blood cannot carry sufficient oxygen. Signs and symptoms of methemoglobinemia include a blue coloration of the skin and mucous membranes, shortness of breath, fatigue, and dizziness. Acquired methemoglobinemia responds well to treatment, although severe cases can be fatal if not treated properly. Infants who drink contaminated water (likely mixed with powdered milk formula) are especially at risk. Individuals who have a deficiency of the enzyme, along with people who have low stomach acidity, are also vulnerable to this form of methemoglobinemia.
The Environmental Protection Agency (EPA) has set the maximum contaminant level (MCL) for nitrate to be 10 mg/L or 10 parts per million (ppm). Nitrate levels in municipal water supplies are regularly monitored to protect public health. However, private wells are easily contaminated by runoff. People who use well water should be aware of nitrate hazards and have the water tested, especially in agricultural regions. Studies have shown that a significant percentage of wells in agricultural watershed areas have nitrate concentrations that exceed the EPA’s maximum contaminant level. There are processes that can remove nitrate from water, making it safe to drink. Pregnant women and infants (and other at-risk people) should not consume well water that has high levels of nitrate unless it has been treated. In areas where nitrate concentrations are of particular concern, public water treatment plants may include nitrate removal facilities. For example, the public water supply of Des Moines, Iowa, comes from a river that flows through areas of intensive agriculture. As a result, the water has high nitrate content, and Des Moines operates the largest nitrate removal facility in the world.
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