IN-SITU BIODEGRADATION OF POLY(3-HYDROXYBUTYRATE) AND POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE) IN NATURAL-WATERS

The biodegradation of samples of poly(3-hydroxybutyrate) (P(3HB)), pol y(3-hydroxybutyrate co-10%-3-hydroxyvalerate) (P(3HB-co-10%-3HV)). and poly(3-hydroxybutyrate-co-20%-3-hydroxyvalerate) (P(3HB-co-20%-3HV)) was investigated in situ in natural waters. The degradation was studie d by decrease in mass, molecular weight. and tensile strength. In two freshwater ponds the polymers were slowly degraded. After half a year of submersion the mass loss was less than 7%. After 358 days in a fres hwater canal, 34% mass loss was recorded for the homopolymer, and 77% for the P(3HB-co-10%-3-HV) samples, while the P(3HB-co-20%-3HV) sample s had completely disappeared. In seawater in the harbour of Zeebrugge, P(3HB) samples lost 31% of their initial mass, and the copolymers 49- 52%, within 270 days. In all of these environments, the degradation ra te was faster during the summer, when the temperature of the water was higher. No relevant changes in molecular weight could be detected, in dicating that the degradation took place only at the surface of the sa mples. The degradation resulted in considerable loss of tensile streng th of the copolymer samples. Ninety-two microorganisms, mainly bacteri a, able to degrade P(3HB) in polymer overlayer plates, were isolated a nd identified by fatty acid analysis. The isolates from one freshwater pond belonged mainly to the bacterial genus Acidovorax, while the mic roorganisms from the other freshwater pond belonged to various bacteri al genera, to Streptomyces, and to the mould genus Penicillium. Most o f the 31 bacterial isolates from seawater were identified as Alteromon as haloplanktis. The results demonstrate that P(3HB) and P(3HB-co-3HV) samples are effectively biodegradable in natural waters under real-li fe conditions and reveal the biodiversity of the microflora responsibl e for this biodegradation.