Poisons and Toxins

Many poisonous chemicals are present naturally in the environment. For example, all of metals and other elements are widespread in the environment, but under some circumstances they may occur naturally in concentrations that are large enough to be poisonous to at least some organisms.

Examples of natural "pollution" can involve surface exposure of minerals containing large concentrations of toxic elements, such as copper, lead, selenium, or arsenic. For example, soils influenced by a mineral known as serpentine can have large concentrations of toxic nickel and cobalt, and can be poisonous to most plants.

In other cases, certain plants may selectively take up elements from their environment, to the degree that their foliage becomes acutely toxic to herbivorous animals. For example, soils in semi-arid regions of the western United States often contain selenium. This element can be bioaccumulated by certain species of legumes known as locoweeds (Astragalus spp.), to the degree that the plants become extremely poisonous to cattle and to other large animals that might eat their toxic foliage.

In some circumstances, the local environment can become naturally polluted by gases at toxic concentrations, poisoning plants and animals. This can happen in the vicinity of volcanoes, where vents known as fumaroles frequently emit toxic sulfur dioxide, which can poison and kill nearby plants. The sulfur dioxide can also dry-deposit to the nearby ground and surface water, causing a severe acidification, which results in soluble aluminum ions becoming toxic.

Other naturally occurring toxins are biochemicals that are synthesized by plants and animals, often as a deterrent to herbivores and predators, respectively. In fact, some of the most toxic chemicals known to science are biochemicals synthesized by organisms. One such example is tetrodotoxin, synthesized by the Japanese globe fish (Spheroides rubripes), and extremely toxic even if ingested in tiny amounts. Only slightly less toxic is saxitoxin, synthesized by species of marine phytoplankton, but accumulated by shellfish. When people eat these shellfish, a deadly syndrome known as paralytic shellfish poisoning results. There are numerous other examples of deadly biochemicals, such as snake and bee venoms, toxins produced by pathogenic microorganisms, and mushroom poisons.