Pollution Problems

Industrial practices in plastic manufacture can lead to polluting effluents and the use of toxic intermediates, the exposure to which can be hazardous. Better industrial practices have led to minimizing exposure of plant workers to harmful fumes; for example, there have been problems in the past resulting from workers being exposed to toxic vinyl chloride vapor during the production of polyvinyl chloride. Much progress has been made in developing "green processes" that avoid the use of detrimental substances. For example, phosgene, a toxic "war gas," was formerly used in the manufacture of polycarbonates. New processes, now almost universally employed, eliminate its molecule the smallest division of a compound that still retains or exhibits all the properties of the substance

Cape fur seal lying on rock, dead of suffocation from a plastic wire wound around its neck, South Africa. (©Martin Harvey; Gallo Images/Corbis. Reproduced by permission.)

endocrine disruption disruption of hormone control systems in the body use. Also, the "just in time" approach to manufacture has been made possible by computer-controlled processes, whereby no significant amounts of intermediates are stored, but just generated as needed. In addition, efforts are ongoing to employ "friendly" processes involving enzyme-catalyzed low-temperature methods akin to biological reactions to replace more polluting high-temperature processes involving operations like distillation.

Spillage of plastic pellets that find their way into sewage systems, and eventually to the sea, has hurt wildlife that may mistake the pellets for food. Better "housekeeping" of plastic molding facilities is being enforced in an attempt to address this problem. Most plastics are relatively inert biologically, and they have been employed in medical devices such as prosthetics, artery replacements, and "soft" and interocular lenses. Problems with their use largely result from the presence of trace amounts of nonplastic components such as monomers and plasticizers. This has led to restrictions on the use of some plastics for food applications, but improved technology has led to a reduction in the content of such undesirable components. For example, the use of poly-acrylonitrile for beverage bottles was banned at one time because the traces of its monomer, acrylonitrile, were a possible carcinogen. However, current practices render it acceptable today. There has been concern about endocrine disruption from phthalate-containing plasticizers used for plastics such as polyvinyl chloride (PVC). The subject of this possible side effect is controver-

Cape fur seal lying on rock, dead of suffocation from a plastic wire wound around its neck, South Africa. (©Martin Harvey; Gallo Images/Corbis. Reproduced by permission.)

POST-CONSUMER PLASTIC WASTE, 2000

Polyurethane Foam

Total Thermoplastics

Total Thermosets

Sector source: Adapted from Oak Ridge National Laboratory.

sial, but caution in use is warranted pending further study. Plastics may also result in problems resulting from their improper use, and there is need of better education concerning limitations of use, for example, precautions that should be taken with items such as frying pan coatings and microwavable containers. When exposed to high temperatures, some plastics decompose or oxidize and produce low molecular weight products that may be toxic.

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