Plant fertilizer can give gardens the necessary nutrients for proper growth. Unfortunately, fertilizers contain more than nutrients. Most fertilizers contain substances that are classified as heavy metals. These compounds affect plants in various ways and can add to the overall levels of metals found in one's soil.
Arsenic is a naturally occurring material that is toxic in large quantities to both humans and plants. Although it is found in some inorganic fertilizers and is limited by the Association of American Plant Food Control to 13 parts per million, arsenic serves no positive purpose in the nutrition of plants and animals. Many environmental groups fight for the complete removal of this substance from fertilizers before it can pollute sensitive ecosystems.
Cadmium is a component of phosphate found in many fertilizers. It is limited to 10 parts per million by the Association of American Plant Food Control and complete removal is considered an expensive and unnecessary process. There are few known side effects to cadmium and all of these occur rarely.
Cobalt sulfate is an additive in fertilizers that is meant to improve the feed value for livestock. The Association of American Plant Food Control limits cobalt to 136 parts per million. Farmers must be aware that cobalt sulfate is a carcinogen when inhaled by humans or animals.
A multitude of other heavy metals are found in common fertilizers. This list includes lead, selenium, mercury, zinc and nickel. Although some of these elements are necessary in continued plant nutrition, such as zinc, an overdose or misuse of fertilizer can lead to undesired environmental consequences.
Most manufacturers place warnings on their product urging parents from using fertilizers that contain heavy metals where children are present. Young children often place dirt in their mouths and are more susceptible to poisoning based on inhalation and skin contact. Adults should be exposed to the same minerals no more than a few times per year to avoid experiencing similar consequences.