Nauendorf, Alice (2013) Interaction between marine benthic bacteria and plastic/compostable carrier bags : settlement, alternation, and declaration processes. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 81 pp.

Text M.Sc. 2013 Nauendorf, A.pdf - Reprinted Version Restricted to Registered users only Available under License German copyright act UrhG. Download (12MB) | Contact

Abstract

Plastic production and pollution have increased dramatically since the last 60 years. As plastic products are produced to be very resistant against biological degradation, they remain in the marine environment for decades and cause numerous harms to marine organisms. As alternative to plastic, compostable and bioplastic materials were developed. As bacteria are extremely abundant in the ocean, their potential contribution to biological degradation of plastic is of great interest. So far, to our knowledge, the settlement on plastic and its biological degradation by marine benthic bacteria is virtually unknown. The present study focuses on the settlement and biological degradation of aerobic and anaerobic benthic bacteria on a polyethylene (PE) and compostable carrier bag material. As the degradation process of plastic can be accelerated by UV-light, bags with and without prior exposure to UV-radiation were compared with regards to bacterial settlement under laboratory conditions. In a first experiment, slurries from natural oxic and anoxic sediments from Eckernfdrde Bay were incubated with pieces of PE and compostable bags. A second incubation experiment, using PE and compostable material, was carried out with pure cultures of Alcanivorax borkumensis, representative for the aerobic bacteria, and the anaerobic bacterium Desulfovibrio marinus. Analyses included epifluorescence microscopy for cell quantification on the bags and for the investigation of biological degradation weight-loss, scanning electron microscopy (SEM) and RAMAN spectroscopy. The experiment including slurries showed that cell densities were statistically significantly (F = 17.33, p = 0.0001) higher on compostable bags than on PE bags. Bags not exposed to UV-light had significantly (F = 37.613, p = <.0001) higher cell densities than UV-treated bags. Furthermore, aerobic bacteria settled in significantly (F = 106.127, p = <.0001) higher densities on the bags than anaerobic bacteria. Weightloss analyses, SEM images and Raman spectroscopy of both bag materials showed no signs of microbial degradation. In the second experiment, D. marinus settled in multilayer biofilms on both bag types while A. borkumensis showed considerably lower cell densities. Also after incubation with pure cultures biological degradation could not be observed. The compostable bags might have been higher colonized due to higher surface roughness and, assumingly, due to stronger physicochemical interactions between bag and cell surfaces. Anaerobic bacteria in the slurry experiment might have settled on bags in lower densities due to a lower metabolic rate than aerobic bacteria. UV -exposure of the bags did not accelerate bacterial settlement and biological degradation as the exposure duration might have been too short. D. marinus showed a fast biofilm formation, assumingly due to strong physicochemical interactions between bags and D. marinus, leading to a faster initial attachment. In conclusion, no biological degradation was observed in the two experiments. Even the, supposedly 100 % biodegradable, compostable bags did not show any sign of biodegradation. Also compostable bag material might therefore remain in the marine system for a long time, potentially causing similar harms as PE material. It can also be assumed that plastic debris will remain longer in anoxic marine environments than in oxic conditions due to slower bacterial activity.

Actions (login required)

View Item