Tossed at Sea: Plastic Degradation in Aquatic Environments

Aside from the aesthetic problem plastics in the ocean present, there is also great concern for the environmental impacts as well. Prior to 2009, the primary environmental concern regarding plastic hinged on the idea that plastic does not readily degrade and may take hundreds to thousands of years to do so. The reasoning behind this is that plastics are predominantly composed of hydrocarbons. Hydrocarbons, by their chemical nature, tend to be highly unreactive, especially the alkanes.
The idea of hydrocarbon stability in natural environments was challenged when Saido (2009) reported detectable amounts of styrene monomers, dimers, and trimers in ocean water and sand from beaches along the Japanese coastline. These molecules are not synthesized in nature but are the result of manmade products.
Reported here is the first evidence of a novel abiotic degradation process which has been observed between ocean water, UV light, and plastic polymers in controlled laboratory experiments. The production of small micro-particulates from parent plastic samples can be seen suspended in water by the un-aided eye in just days to weeks. All plastics studied (HDPE, PETE, and PC) display similar particulate production. After 18 months, the largest populations of micro particulates with a range of 5-60 microns have been found to exist between 5-10 microns.
Fourier Transform Infrared (FTIR) analysis of the initial and residual material over time shows oxidation of the polymers in laboratory studies with the formation of O-H, C=O, and C-O bonds. FTIR of plastics in field experiments exhibit similar patterns as well. Field samples appear to oxidize more readily as salinity increases. Given that the FTIR spectra are similar to what we see in the laboratory experiments, it is likely that small micron and sub-micron plastic particulates are entering the marine water column faster (days to weeks) than previously expected (decades to centuries). Small micro-plastics can cause entanglement and ingestion problems of microorganisms including planktonic species as are similarly observed in larger biota.