Phytoremediation: Insuring Safe Selenium Levels
Selenium is a naturally occurring element found in soil. It becomes a problem when irrigation practices cause it to leach out of the soils in the western states. The selenium is deposited in the rivers, then accumulates until it reaches toxic levels. The high levels of selenium seriously affects the environment and agriculture downstream. However, with the use of phytoremediation, the possibility of safe selenium levels has never been closer.
Selenium is an essential trace element, number 34 on the periodic table, that is found naturally in the environment. It is distributed in most rocks, soils, water, and living organisms. There are places in the U.S., Australia, and China that do not have enough naturally occurring selenium. However, most areas of the world contain significant amounts of the element (Bentor).
Selenium is a micronutrient necessary for human and animal health. Supplements have been promoted as an aid in preventing many serious health problems, including cancer. It is thought to be an antioxidant that helps prevent damage done to cell tissues by free radicals. Selenium acts inside the cell to capture and destroy peroxides produced by the oxidation process of free radicals before they can alter the cell membrane (Coomer). However, there is a very small margin between the amount of selenium needed for optimal health and the amount that results in selenium toxicity in people. High levels of selenium can cause dizziness, irritability, fatigue, bronchitis, garlic breath odor, brittle nails and hair, and reduced hemoglobin levels (Canadian).
In livestock, excessive levels of selenium are one of the main agents of poisoning in the western United States. Two cattle diseases caused by high levels of selenium are alkali disease and blind staggers (Bauer). Alkali disease causes malformation in the hoofs, lameness, and hair loss. Blind staggers causes disorientation and circling (Selenium). Other effects of selenium toxicity include liver damage, kidney inflammation, excessive amounts of blood in body organs, ulcers in the gastro-intestinal tract and fetal resorption (Canadian).
Marco Polo documented one of the first recorded accounts of selenium poisoning. In his journal, he wrote about a strange disease that was affecting pack animals on the border of Western China near Tibet. After grazing on the plants there, the animal's hoofs started to fall off, a symptom of chronic selenosis (Bauer).
There is also speculation that selenium poisoning caused the delay of the calvary that was scheduled to reinforce General Custer at the Battle of the Little Bighorn in Montana. Relief troops reported that the delay was due to a "sickness" the horses developed while they were traveling through a seleniferous region. Orville Beath, a chemist at the University of Wyoming, also found historical accounts of early pioneers suffering from mysterious diseases while they were settling in areas...