Other Simple Organochlorines

An examination of several marine worms (Marenzellaria viridis, Polydora socialis, Scolelepsis squamata, Spiophanes bombyx, and Streblospio benedicti) has tentatively identified alkyl and alkenyl halides 100-105 (390). 

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The name of this insecticide is to many people synonymous with environmental pollution, and it is therefore an important example in this chapter but the story is not simple. DDT is an abbreviation for the chemical name of the insecticide dichloro-diphenyl-trichloroethane. It contains five chlorine atoms and is hence called an organochlorine compound. It was first made in 1874 but not found to be an insecticide until 1939 by Paul Muller. It was used extensively in the Second World War for the control of insects such as lice and mosquitoes, carriers of the diseases typhus and malaria. It was very effective in controlling these pests, and the diseases they carried, and undoubtedly thousands of soldiers lives were saved. Since then, the lives of millions of people throughout the world have also been saved by this insecticide both as a result of the reduction of these and other diseases and as a result of the improvement in crop yields which has reduced starvation. Indeed, in 1953 it was estimated that the use of DDT for malaria eradication had saved 50 million lives and averted more... 

In the peroxide formulation initiation, the organochlorine impurities that are present in commercial BisGMA accelerate the decomposition of the peroxides, a process that forms free radicals and reduces the stability and shelf life of the resin. In the a,b-diketone formulation, the organochlorine impurities complex with other additives in the formulation that are present to enhance free-radical formation. The presence of the impurities thus reduces the photoefficiency and negates the advantages of simple photoinitiated diketone curing. 

Some materials can be sterilized by y-irradiation ( Co source). In reality this treatment is mainly possible for material to be used for element determinations, as many compounds decay upon y-irradiation, e.g. tin compounds [63] or organochlorine pesticides [64]. Sterilization by pasteurization or similar methods or addition of chemical preservatives, e.g. butylated hydroxytoluene at 0.02% [65], are other alternatives. Stabilization by simple deep-freezing is also possible but induces difficulties in transport and storage. In addition, the material can only be used once as defreezing/refreezing may not lead to a homogeneous material. 

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