HHCs in Polymers and ByProducts

Kelthane, methoxychlor), cyclodienes (dieldrin, chlordanes, heptachlor, endrin, mirex, kepone), endosulfans, hexachlor-ocyclohexanes, ethylene dibromide, methyl chloride, Abate, and Chlorpyrifos are/have been most abundantly and indiscriminately used as residual insecticides and are/have been causing ecological and health problems. Cyclodienes were banned in the 1970s and Toxaphene and mirex in the 1980s. Only a few of these insecticides are allowed a restricted use because of their health and ecological effects. However, these (especially DDT) may still be used in developing countries (mosquito control in Africa) as well as in public health and military for control of arthropod vectors and body lice.

Chlorinated phenols (especially PCPs) were more commonly used in lumbar treatment. Bleaching of pulp with chlorine can produce chlorophenols, polychlori-nated dibenzodioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). Chlorophenols are acidic, water soluble, chemically reactive, but have limited persistence.

Chlorophenoxy herbicides are used to control broadleaf weeds (dicotyledons). These derivatives of phenoxyalkane carboxylic acids (2,4-D, 2,4,5-T, (4-chloro-2-methyl-phenoxy)acetic acid (MCPA), 2,4-DB) are water soluble as alkali salts and lipophilic as esters. These are readily biodegradable. These are of concern because of phytotoxicity, but mostly because of the serious ecological and health effects of their contaminant PCDDs, especially 2,3,7,8-tetrachlorodibenzo-/>-dioxin (TCDD).

PVC, one of the most versatile thermoplastics, accounts for 28% of the global annual chlorine consumption (19 million tons PVC). By-products, such as 1,1,2-trichloro-ethane, and gaseous and liquid wastes on incineration/ oxidation are sources of concern. PVC accounts for 150 000 tyr-1 of global production. Other end products using HHC include Neoprene or chlorobutyl rubber. Chlorohydrins are used in the production of propylene oxide to manufacture propylene oxide polymers. It is also used in synthesis of epichlorohydrin for resins and polymers, and specialty chemicals (alkanolamines). Other polymers include nylon-6, 6-hexamethylenediamine for carpeting, etc., and fluoropolymers (50 000 t yr- , globally), and Silicone (400 000 tyr-1, globally).

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