Nitrogen is necessary for many biological processes and plays a particularly important role in photosynthesis, the process by which plants turn sunlight into edible carbohydrates. When people eat plants, or the flesh of animals that have eaten plants, they also ingest nitrogen, mainly in the form of nitrate, a compound formed when nitrogen combines naturally with oxygen.

Most of those nitrogen compounds pass through the digestive tract, which is why septic tanks and sewer systems are commonly responsible for contamination of water supplies. Nitrate can also make its way into water supplies from animal feedlots, dairies, industrial sites and farm fields.

From a human-health standpoint, small amounts of nitrate are not a problem. But when ingested in food or in water, nitrate can be converted into nitrite inside the body. And nitrite turns hemoglobin, the compound in blood that absorbs oxygen, into methemglobin, which does not.

In adults, enzymes in the body constantly convert methemglobin back to hemoglobin. But infants lack these enzymes until they are from 4 months to 6 months old. As a result, nitrate in their food or water, converted to nitrite internally, can quickly render their blood incapable of carrying oxygen. Adults also can be at risk if they consume food or water containing very high levels of nitrate, overwhelming the body's coping mechanism.

Oxygen-poor blood is blue, giving sufferers a decidedly cyanotic cast, and this is why infant nitrite poisoning is sometimes called "blue baby syndrome." Without quick treatment, such babies can die or suffer permanent brain damage. Fetuses also are at risk, so pregnant women are cautioned against drinking water with high nitrate levels.

The Environmental Protection Agency has estimated that as many as 52 percent of community water wells and 57 percent of domestic water wells in the United States are contaminated by nitrates. The U.S. Geological Survey estimates that up to 15 percent of wells in agricultural and urban areas have nitrate levels exceeding EPA standards.

According to the State Water Resources Control Board, Kern, Los Angeles and San Bernardino counties have the greatest number of public drinking water wells contaminated by nitrates.

John Krist