Aerobic biodegradation of polyethylene glycols of different molecular weights in wastewater and seawater

In order to distinguish between aerobic biodegradation of synthetic polymers in fresh and seawater, polyethylene glycols (PEGs) were systematically and comparatively investigated in inocula from municipal wastewater and seawater aquarium filters for the first time. The molecular weight (MW) of the PEGs, (HO(CH2CH2O)nH, n = 3–1350) as representatives of water-soluble polymers, ranged from 250 to 57,800 Da. The biodegradation was observed by removal of dissolved organic carbon and carbon dioxide production by applying standardized ISO and OECD test methods. Specific analyses using liquid chromatography mass spectrometry (LC–MS) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) were performed. All PEGs selected were completely biodegradable in freshwater media within 65 d. PEGs with an MW up to 14,600 Da have a similar degradation pathway which is characterized by gradual splitting of C2-units off the chain resulting in formation of short-chain PEGs. In artificial seawater media, full biodegradation of PEGs up to 7400 Da required more time than in freshwater. PEGs with MW 10,300 and 14,600 Da were only partially degraded whereas PEGs with MW 26,600 and 57,800 Da were not degraded for a period of 135 d. The biodegradation pathway of PEG 250 and PEG 970 in seawater is similar to that for freshwater. For PEGs having an MW from 2000 to 10,300 Da, the degradation pathway in seawater differs from the pathway of the shorter PEGs.