mediate significance to microorganisms [Alexander ( 6 ) ] . Since the addition of the plastic materials in the soils might have increased the nitrogen demand, the slow degradation is to be expected. Probably, the degradation may be stimulated by supplemental nitrogen. This aspect will form a further area of study. Conclusions From the results of these tests it is concluded that fragments produced by the degradation of polyethylene and polypropylene in the presence of oxygen are biologically oxidized both in natural soil and in a n aqueous sewage sludge environment. The rate of degradation is much more rapid in sewage sludge than in soil, but these results indicate that if the degradation fragments are in the form of a fine powder, biodegradation should occur in approximately one year in natural soils. Fragments from degraded polystyrene appear to be more resistant to biodegradation.
Determination of the rates of such biodegradation will probably require the use of trace methods. Literature Cited (1) Guillet, J. E., in “Po1.vmers and Ecological Problems,” J.
Guillet, Ed., Plenum, New York, N.Y., 1973. (2) Coutts, J. R. H., J. Agr. Sci., 20,407 (1930). (3) Cole, J. O., Parks, C. R., Znd. Eng. Chem. (Anal. E d . ) , 8, 61 (1946). (4) Umbreit, W. W., Burris, R. H., Stauffer, J. F., “Manometric Techniques and Tissue Metabolism,” Burgess, Minneapolis, Minn., 1949. (5) Potts, J. E., Clendinning, R. A,, Ackart, W. B., Niegisch, W. D., in “Polymers and Ecological Problems,” J. Guillet, Ed., Plenum. New York. N.Y.. 1973. (6) Alexander; M., “Introduction to Soil Microbiology,” Wiley, New York, N.Y., 1961.
Received for reuiew December 10, 1973. Accepted May 24, 1974. This research was supported b y EcoPlastics Limited, Thornhill, Ont., Canada, and the National Research Council o f Canada.
Biodegradability of Photodegraded Polymers 11. Tracer Studies of Biooxidation of Ecolyte PS Polystyrene James E. Guillet,” Thomas W. Regulski, and T. Brian McAneney
Department of Chemistry, University of Toronto, Toronto, Canada
w The biological oxidation of a photodegraded polystyrene-vinyl ketone copolymer has been examined using a radioactive tracler technique. The evolution of radioactive carbon dioxide from the copolymer in both soil and an activated sewage sludge environment has been monitored. The results show that the photodegraded copolymer is considerably more biodegradable than the undegraded polymer. The rate of biodegradation observed is slow, but this is not unexpected in view of the known slow rates of biological degradation of lignin and other natural products containing aromatic residues. The tests show that the degraded polymerij are attacked by soil microorganisms a t measurable rates but the technique is not suitable for longer term tests due to a natural leveling off of bacterial activity in the closed systems used.
In Part I (page 919), it was demonstrated that degraded fragments of polyethylene and polypropylene were oxidized biological1 y by microorganisms in natural soil and sewage sludge to give carbon dioxide and water. However, using photodegraded polystyrene (Ecolyte P S ) resulted in no significant difference between the rate of COz production in the presence and absence of the plastic. It was concluded that In the case of polystyrene, the rate of oxidation was too slow to detect by this method. The present studies were carieied out to employ tracer methods to see if any biodegradation was occurring a t all under these conditions. Experimental Soil and Activated Sludge Samples. The samples used were the sample of garden soil and activated sludge described in Part I.
Polymers. Styrene aJ4C and styrene PJ4C were obtained from Mallinckrodt and diluted with purified styrene monomer. Copolymers were made using this diluted monomer with approximately 5% vinyl ketone by a bulk polymerization for 7 2 hr at 75°C using benzoyl peroxide as catalyst. The polymers were purified by dissolving in toluene and precipitation in methanol. This procedure was repeated three times and the polymer was then air dried for 24 hr a t room temperature. The residual monomer was assayed by gas chromatography and found to be less than 0.01% in both cases. Polymer properties are summarized in Table I. Photodegradation. The polymers were pressed into thin films approximately’0.20 mm thick and irradiated in a uv accelerometer. After irradiation the samples were slightly yellow and very brittle. The viscosity molecular weight was between 10,000 and 32,000 in each case. The polymers were then ground in a micromill to a particle size less than 200 mesh and stored in brown glass bottles before testing. The sample used in the sewage sludge
Table I. Analytical Data on Polymers Used polystyrene-a-I‘CSample A, 5% vinyl ketone
Yield Initial molecular weight, M, Irradiation time Molecular weight after irradiation, ~
40 g (40%)
795,300 188 h r (method 1) 158.9 h r (method 2) 32,200 (method 1) 15,000 (method 2)
polystyrene-,+ICSample 6 , 5% vinyl ketone
86 g (86%) 450,000
137 h r (method 2)
31,250 (method 2)
M,
Radioactivity 2.165 X 106 dis/min 1.752 X lo6 dis/min % residual monomer
