Parathion

Parathion, or diethyl parathion, is an organophosphate compound. Like many other organophosphate insecticides, it is a very potent insecticide and acaricide. It was originally developed by IG Farben in the 1940s. It is highly toxic to non-target organisms. Its use is banned or restricted in many countries, and there are proposals to ban it from all use.

History
Parathion was developed by the German trust IG Farben in the 1940s. Dr. Gerhard Schrader was the inventor. After the war the Western allies seized the according patent and Parathion was thereafter marketed worldwide by different companies and under different brand names. The most common German brand was E605 (banned in Germany after 2002); this was not an E number (not a food additive). "E" stands for Entwicklungsnummer (German for "development number"), not for "European".

Properties
In its purest form, parathion consists of white crystals; however more commonly distributed forms take the form of a brown liquid which smells of rotting eggs or garlic. The insecticide is more or less stable, though it darkens when exposed to sunlight.

Applications
As a pesticide, parathion is generally applied by spraying, and often used on cotton, rice and fruit trees. The usual concentrations of ready-to-use solutions are 0.05 to 0.1%. The chemical is banned for use on many food crops.

Safety
Parathion is a cholinesterase inhibitor. It generally disrupts neural function by inhibiting the essential enzyme acetylcholinesterase. It is absorbed via skin, mucous membranes, and orally. Absorbed Parathion is rapidly metabolized to Paraoxon in which the sulfur atom is replaced by oxygen. Paraoxon exposure can result in headaches, convulsions, poor vision, vomiting, abdominal pain, severe diarrhea, unconsciousness, tremor, dyspnea and finally lung-edema as well as respiratory arrest.

Symptoms of poisoning are known to last for extended periods of time, sometimes months. The most common and very specific antidote is atropine in doses of up to 100 mg daily. Because atropine may also be toxic, it is now recommended to use small doses which are frequently repeated. If human poisoning is detected early and the treatment is prompt (antidote and artificial respiration), fatalities are infrequent. Insufficient respiration may lead to cerebral hypoxia and permanent brain damage. Additionally, peripheral neuropathy including paralysis is noticed as late sequelae after recovery from acute intoxication. Parathion has been extensively used for committing suicide and deliberately killing other persons. For the latter reason most formulations contain a blue dye providing warning.

Based on animal studies, Parathion is considered by the US EPA to be a possible human carcinogen. Studies show that Parathion is toxic to fetuses, but does not cause birth defects.

Parathion is very toxic to bees, fish, birds, and other forms of wildlife. Parathion can be replaced by many safer and less toxic alternatives (less toxic organophosphates, carbamates, or synthetic pyrethroids).

Protection against poisoning
To assure human protection the end user must wear protective gloves, clean protective clothing, and a respirator of the organic-vapour type when handling this material. He/she should bathe immediately after work. Industrial safety during the production process requires special ventilation and continuous measurement of air contamination in order not to exceed PEL levels as well as keeping personal hygiene. Frequent determination of workers' serum acetylcholinesterase activity is also helpful in regards of occupational safety, because the action of Parathion is cumulative. If an area of the body is contaminated with parathion, if possible, it should be removed immediately. Also, atropine may be used as a specific antidote.

Proposals to ban
According to the non-governmental organisation Pesticide Action Network, parathion is one of the most dangerous pesticides. This organization lists used. PAN lists Parathion also as 'bad actor chemical'. In the US alone more than 650 agricultural workers have been poisoned since 1966, of which 100 died. In underdeveloped countries many more people have suffered fatal and nonfatal intoxications. The World Health Organization, PAN and numerous environmental organisations propose a general and global ban. Its use is banned or restricted in 23 countries and its import is illegal in a total of 50 countries.