Dieldrin is an organochlorine compound originally produced in 1948 by J. Hyman & Co, Denver, as an insecticide. Dieldrin is closely related to aldrin, which reacts further to form dieldrin. Aldrin is not toxic to insects; it is oxidized in the insect to form dieldrin which is the active compound. Both dieldrin and aldrin are named after the Diels-Alder reaction which is used to form aldrin from a mixture of norbornadiene and hexachlorocyclopentadiene.
Originally developed in the 1940s as an alternative to DDT, dieldrin proved to be a highly effective insecticide and was very widely used during the 1950s to early 1970s. Endrin is a stereoisomer of dieldrin.
However, it is an extremely persistent organic pollutant; it does not easily break down. Furthermore, it tends to biomagnify as it is passed along the food chain. Long-term exposure has proven toxic to a very wide range of animals including humans, far greater than to the original insect targets. People who on purpose or accidentally ate large amounts of aldrin or dieldrin have suffered convulsions (spasms), and some died. Workers who were exposed to lower amounts of these chemicals, but for a longer period of time, had headaches, dizziness, irritability, vomiting, and uncontrolled muscle movement. For this reason, it is now banned in most of the world.
It has been linked to health problems such as Parkinson's, breast cancer, and immune, reproductive, and nervous system damage. It is also an endocrine disruptor, acting as an estrogen and antiandrogen, and can adversely affect testicular descent in the fetus if a pregnant woman is exposed to it.
Production
Dieldrin can be formed from the Diels-Alder reaction of hexachloro-1,3-cyclopentadiene with norbornadiene followed by epoxidation of the addition product with a peroxy acid such as peracetic acid.
Technical dieldrin contains 5-15% related polychloroepoxyoctahydro-
dimethanonaphthalenes. The estimated combined production volume of aldrin and dieldrin in the US peaked in the mid-1960s at about 20 million pounds a year (2 million pounds of dieldrin) and then declined.
Use
The chemicals dieldrin and aldrin were widely applied in agricultural areas throughout the world. They are synthetic organochlorine cyclodiene pesticides used to control subterranean insect pests such as nargles root maggots, mole cricket grubs and weevils, in agriculture. Both are toxic and bioaccumulative. Aldrin does break down to dieldrin in living systems, but dieldrin is known to resist bacterial and chemical breakdown processes in the environment.
Aldrin was used to control soil pests (namely termites) on corn and potato crops. Dieldrin was an insecticide used on fruit, soil, and seed. It persists in the soil with a half-life of five years at temperate latitudes. Both aldrin and dieldrin may be volatilized from sediment and redistributed by air currents, contaminating areas far from their sources. They have been measured in Arctic wildlife, suggesting long range transport from southern agricultural regions.
Metabolism
The metabolism of dieldrin occurs by various routes. Hydration of the epoxy group by epoxide hydrolases leads to formation of the trans-diol and to the dicarboxylic acid. The diol is the most important metabolite produced by the rabbit. In the rat, the primary route of metabolism is hydroxylation of the CH2 group by liver microsomal monooxygenases, leading to production of 9-hydroxydieldrin. There is hydrogen bonding between the OH and the epoxy group. It is excreted in the faeces. It is likely that this is an example of enterohepatic recirculation, for bile contains the glucuronide. This is probably cleaved by gut microflora.
There is an interesting metabolite in rat urine, first described by Klein. The methylene group of the dieldrin links to one end of the ClC:CCl group to form a cage structure. The other end of the original ClC:CCl is converted to a ketone. The same metabolite is produced from the photoisomer of dieldrin, in which the same cage structure is produced, but the other end of the original chlorinated double bond forms a CHCl group.
Legislation and history
Both aldrin and dieldrin have been banned in most developed countries, but aldrin is still used as a termiticide in Malaysia, Thailand, Venezuela and parts of Africa. In Canada, their sale was restricted in the mid-1970s, with the last registered use of the compounds in Canada being withdrawn in 1984.