PubMed1976
The complex problems of microbiological degradation of synthetic plastics and a fairly wide variety of 62 testing materials, belonging to 14 major groups of plastics, are described. Adaequate and reliable testing techniques had to be devised. Drawing on the experiences of H. Braun, 1930, and of Bushnell and Haas, 1941, as to the metabolism of bacteria and the utilization of certain hydrocarbons by microorganisms, and previous research work by A. Schwartz in Berlin, 1959-60, on microbial corrosion of plastics, methods of laboratory testing were developed. The bacteriological technique was based on selection of aerobic microorganisms, which were, by starvation, adapted to use the plastic materials as their only carbon source; foreign carbon sources had to be strictly eliminated; emphasis was laid on proper, double control cultures. The test organisms involved included P. aeruginosa and fluorescens strains, also a certain species of Candida, and mixtures of soil, sewage and garbage organisms grown on exposed plastic surfaces. By means of series of passages the selective adaptation and conservation of these organisms was continued up to 4 1/2 years. An anaerobic adaptation method for Desulfovibrio desulfuricans was developed and used successfully. After preliminary experimentation (Soil burial, sewage and garbage exposure tests) in the laboratory as well as in the open, a large scale Field testing programme under realistic and to some extent extreme conditions was implemented: Nine different plastic materials comprising eight plain high polymer plastics and for comparison one synthetic Cellulose derivate, together with glass control samples, were exposed in twelve different sewage, garbage, and soil media over a period of 3 months to 2 years, and subsequently examined. On the basis of the bacteriological results obtained from the adaptation series the test materials were classified into three categories, corresponding to the stimulation of bacterial growth: Group one, which allowed strong proliferation, included certain types of plasticized P.V.C. and Cellulose esters, as expected, and, as a new result, Polyurethane rubber; the latter showed clear signs of surface corrosion. Group two, which induced a clear but moderate growth, comprised a nylon trade type of Polyamide. Gruop three, allowing weak but still recognisable growth, included Formaldehyde pressure resing (Bakelite). This was surprising as it was thought that the formaldehyde and phenol components would exert a bacteriocidic or at least bacteriostatic effect. The results of the long and time consuming adaptation series with Pseudomonas aeruginosa were confirmed by the manometric dissimilation method of O. Warburg by means of the Braun/Melsungen apparatus. With this subtle but elegant procedure results and graphical recordings were obtained within hours and days...