Adverse Effects


Agricultural pollution can have many adverse effects on organisms. For humans, the pollutants can travel through the soil and reach our drinking water, causing many different health problems. Nitrogen and Phosphorus from runoff can go through streams and get to concentrated areas, causing mass fish death. There are also heavy metals that can affect all forms of life.

Dead Zones

A dead zone is an area of water that has low levels of oxygen. The term comes from fishermen who fail to catch fish, shrimp, and crabs in areas with low oxygen concentrations. It is not an accurate term in the sense that the area has no life, since many organisms can survive in water with low oxygen levels, but this does kill a large number of the animals that live in those waters. The deaths of these animals is not caused only by the lack of oxygen. The sudden loss of food for other scavengers and predators causes more fatalities. For those who survive there may be other physiological effects, such as reduced growth. These organisms may have certain adaptations which allow them to survive in reduced oxygen areas.

Reduced oxygen levels in dead zones are caused by the decomposition of organic matter, usually in the form of phosphorus and nitrogen compounds. Much of this organic matter is a result of runoff from agricultural pollution. One of the largest dead zones in the world is in the Gulf of Mexico. This area gets as large as 21,000 km^2 in size. This dead zone is caused in large part by runoff going into the Mississippi River and draining into the Gulf. There are hundreds of other, smaller, dead zones around the world. The two largest dead zones are in the coastal areas of the Baltic Sea and the northwestern shelf of the Black Sea, which can be as large as 84,000 km^2 and 40,000 km^2 respectively.

Drinking Water

Increased nitrate levels in drinking water can affect human health. Elevated nitrate levels have been associated with cancer in the esophogus, stomach, colon, and bladder. There is some evidence that it may adversely affect pregnancy, resulting in spontaneous birth, stillbirth, premature birth, and birth defects. Other medical conditions that high nitrate levels may have links to are childhood obesity, thyroid disorders, increased blood pressure, and acute respiratory tract infections in children.

A particular example is methemoglobinemia. Increased nitrate levels, combined with other conditions, can cause this condition, which is sometimes called blue baby syndrome. In this disorder ingested nitrate inerferes with the oxygen-carrying abilities of a person's blood. People with this disorder may have shortness of breath, headaches, fatigue, dizziness, loss of consciousness, and their extremeties may turn a pale blue color. In severe cases methemoglobinemia may lead to coma and death.

Heavy Metals

There are often heavy metals used for agriculture in the form of fertilizers and manures. Some of these metals may travel through the soil into water. Concentrated amounts of these heavy metals are poisonous to many different organisms.

Gulf of Mexico Hypoxia, a.k.a. "The Dead Zone"
Workgroup Report: Drinking-Water Nitrate and Health—Recent Findings and Research Needs.