resistance to microbial attack, the destructive action of fungi and bacteria, is often ignored in the design of plastic materials many formulators consider polymers to be inert to the biological effects of environmental exposures. many workers have reported that synthetic polymers are not susceptible to microbial attack. however, there are two factors which alter the situation. the first is that the polymers are seldom used alone. they are combined with formulating ingredients, such as plasticizers, pigments, fillers and stabilizers; and they are used in multi-component constructions involving susceptible materials $em dash$ 90 cotton, paper, wood etc the second contributing factor is that the severity of microbial $left double quote$ attack $right double quote$ can range from complete functional failure, through embrittlement and cracking, to the stains, odors and defacement of surface growth. resistance to microorganisms can be improved by using non-migratory plasticizers and avoiding the most susceptible ones like adipates, azelates and high levels of epoxidized soybean oil. the biocides used in pvc to prevent the growth of microorganisms include organometallic compounds such as trialkyl tin oxides, arsenicals, and organic complexes of antimony or copper; some organic sulfur compounds are also used, as are quaternary ammonium compounds