Halogen-containing pollutants

Interactions Between HALS and Acids Stabilized polymers can be exposed to acids from pollution or from degradation products of halogen containing compounds. Due to their chemical structure HALS can be basic (see Table 17.2) and form ammonium salts with acids. 

Catalytic Oxidization. A principal technology for control of exhaust gas pollutants is the catalyzed conversion of these substances into innocuous chemical species, such as water and carbon dioxide. This is typically a thermally activated process commonly called catalytic oxidation, and is a proven method for reducing VOC concentrations to the levels mandated by the CAAA (see Catalysis). Catalytic oxidation is also used for treatment of industrial exhausts containing halogenated compounds. 

Five compounds classified as priority pollutants contain an ether moiety and halogen atoms attached to the aryl and alkyl groups. Five pesticides are suspected to contain at least one compound from this class. B/i(2-chloroethyl) ether (BCEE) is used as a raw material in two pesticides BCEE itself functions as a fungicide or bactericide in certain applications. In the other three pesticides, the ethers are suspected to be present as raw material impurities. 

Fire-retardant coatings currently in use contain a number of ingredients that are either considered to be toxic heavy metals or on the hazardous air pollutants (HAPs) list. In addition, there is concern that the use of halogenated chemicals in these coatings and other products will be banned in the future. A recent paper contains the details of two reformulations programs. The first is a reformulation of a low VOC chlorinated alkyd coating and the second is a reformulation of a chlorinated emulsion system. Both programs successfully reduced the heavy metals and lowered the HAPs to an acceptable level (Dahm, 1996). 

Mutagenicity, Carcinogenicity, and Teratogenicity of Industrial Pollutants (ref. 15) contains summaries of teratogenicity information about industrial pollutants. Discussions of these pollutants are divided into four groups heavy metals, insecticides, monomers, and halogenated hydrocarbon solvents. 

Organohalides (Figure 1.17) exhibit a wide range of physical and chemical properties. These compounds consist of halogen-substituted hydrocarbon molecules, each of which contains at least one atom of F, Cl, Br, or I. They may be saturated (alkyl halides), unsaturated (alkenyl halides), or aromatic (aryl halides). The most widely manufactured organohalide compounds are chlorinated hydrocarbons, many of which are regarded as environmental pollutants or hazardous wastes. 

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