Nitrate contamination from fertilizer and manure

Nitrate Contamination from Fertilizer and Manure

Pesticides are not the only chemical input that may increase with intensifying agriculture. Nitrogen fertilizer is one of the most effective tools for increasing yields, and its use on a global basis grew more than fivefold from 1960 to 1990. It is still climbing today, although at a slower pace (83). Fertilizer consumption in developing countries is projected to double by 2020, with especially rapid growth in Africa and South Asia. (See Fertilizer Use is Climbing.)

Fertilizer Use is Climbing Estimated Growth in Fertilizer Use, 1960-2020 Source: Balu Bumb and Carlos Baanante, World Trends in Fertilizer Use and Projections to 2020, 2020 Brief No. 38 (International Food Policy Research Institute, Washington, D.C., 1996), Table 1.

This surge in fertilizer use has led to greater contamination of surface and groundwater with nitrates essentially dissolved nitrogen fertilizer that has not been taken up by plants. This contamination poses threats to both environmental quality and human health. Determining precisely how much and when to fertilize is not easy for farmers, and overfertilization is common. Excess nitrate is water soluble and easily washed through soil by rain or irrigation water, making nitrate contamination a widespread problem where nitrogen fertilizers are used with any frequency. Manure from intensive livestock operations is also a potent nitrate source. Although agricultural sources of nitrate predominate in most rural areas (84), nonagricultural sources such as septic systems and cesspools, and even nitrogen oxide particulates deposited by cars and power plants, all add to the burden.

Public health officials consider nitrate contamination a significant health risk based on both its wide distribution and its effects on infants. In young infants, exposure to high levels of nitrates can result in a disorder whereby the red blood cells cannot function properly, leading to insufficient oxygen or “blue-baby syndrome,” which can be fatal (85). In adults, high levels of nitrate exposure may increase the risk of contracting some cancers, although the extent of the risk is unclear (86).

Worldwide, the scale of nitrate contamination is undoubtedly quite large. Although no global assessment exists of how many areas exceed the WHO standard, individual country reports indicate that nitrate is one of the most common chemical contaminants found in drinking water. This finding is not surprising given the huge volume of nitrogen fertilizer used worldwide (87)(88)(89)(90). In the United States, for example, nitrate contamination is the nation’s most widespread groundwater pollution problem; in a national survey, 22 percent of wells in U.S. agricultural areas contained nitrate levels in excess of the federal limit (91). Nitrate is also a prime contaminant in Europe (92).

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