Fertilizer can be one of the most useful tools in agriculture, but it can also be destructive. Some of fertilizer's dangers may come from deliberate misuse, such as using the volatile products in fertilizer to produce bombs, but many harmful effects also come from those trying to use the product appropriately. Understanding the dangers is key to using fertilizer safely and effectively.
Excessive fertilization can do more damage to plants than none at all. Symptoms of excessive fertilization include brown leaf tips, leaves with an uncharacteristic yellow color between the veins, and wilted plants or slower growth. Disease and pests can also be a problem with excessive fertilization. Researchers with the University of California noted more infestations of pests in fruit trees with too much fertilizer because they developed more new shoots, which are more vulnerable to pests than more established shoots. Brown rot was also a problem. In the most extreme cases, the plant will die.
Fertilizers running off into water-based ecosystems is the most well-documented environmental harm. The increase of nitrogen in the water, which is not naturally present in such large amounts, encourages rampant growth of aquatic vegetation. Eventually, as these plants die, they deplete the oxygen in the water, causing problems for aquatic animal life. Overuse can even affect the ozone layer. A paper published by the University of Michigan noted that many scientists believe nitrogen oxides, a factor in ozone depletion at higher levels of the atmosphere, may be increasing due to the use of fertilizers.
Toxicity to Humans
Large amounts of some fertilizers can be hazardous to humans. One fertilizer that can be especially toxic to humans is known as anhydrous ammonia, a common industrial fertilizer. Ammonia spills can cause severe respiratory distress and even lead to evacuations of affected areas. In addition, some fertilizers are known to contain at least nine metals considered to be carcinogens, such as lead, and other metals, such as mercury, that are harmful in other ways, according to the California Public Interest Research Group.
Toxicity to Pets
Fertilizers can also harm pets and farm animals that may come into close contact with them. The ASPCA notes that cocoa bean mulch, a common fertilizer around the home, may keep some pests away and help provide nutrients for plant growth, but it attracts dogs and is harmful to them if they eat it. The toxic metals in some fertilizers, such as mercury, can also be harmful to pets.
Some fertilizers can actually be used in explosives. Ammonium nitrate, a common fertilizer, was the weapon used to blow up the federal building in Oklahoma City on April 19, 1995. Though harmless by itself, when mixed with fuel oil it becomes volatile.