Plastic debris is a well known pollutant which is abundant worldwide, and affects all habitats. The threats of plastics in the marine environment vary from, ingestion by marine organisms, transporting bound organic pollutants such as polychlorinated biphenyls and entanglement.
Although most plastics are positively buoyant and are spread by wind, some sink below the surface and into the water column, or further into sediment.
Any surface in the marine environment will become colonised by microorganisms. Biofilm formation, leading to biofouling, develops through four discrete phases; adsorption of dissolved organic molecules, attachment of bacterial cells, attachment of unicellular eukaryotes and attachment of larvae and spores. Bacterial attachment is a well controlled, where attached cells produce extracellular polymers to create complex matrixes.
Understanding the mechanisms that determine the behaviour of plastic debris in the marine environment e.g/ buoyancy is essential for creating any possible evidence-based management programme. The investigators in this study aim to characterise early biofilm formation on plastic debris.
Plastic bags (20 x 28cm) were attached to weighted Perspex boards (22 x 26mm), and suspended 2m below the surface of the water in Queen Anne’s Battery (Plymouth, UK). Boards were sampled weekly for 3 weeks, between July and August 2010; mean water temperature was 16.2oC, salinity 33.3. Sampled boards were kept in seawater, and analysed within an hour of removal. Plastic was removed from the boards and cut into smaller squares (10 x 10cm); loosely attached material was washed off and the plastic was cut smaller again (1 x 2cm) which were used for all subsequent analyses.
A quantitative biofilm assay was used after modification of a previous protocol, and a quantitative hydrophobicity assay was also developed with modification of an existing protocol.
Biofilm formation was apparent on the submerged plastic after 1 week and significantly increased for the remaining duration. Coinciding with biofilm formation, the plastic surface became less hydrophobic during the investigation. The plastic started by floating on the surface of the water, in contact with the air, and subsequently sank each week until below the surface with signs of neutral buoyancy.
In this study, the plastic in week three after being cleaned to remove any biofouling behaved the same as the control plastic, floating at air-seawater interface, which agreed with previous research.
The number of heterotrophic bacteria that could be cultured, found on the plastic increased during the experiment from 1.4 x 104 cells cm-2 at week one to, 1.2 x 105 cells cm-2 at week three.
A large part in tackling what has become an international marine pollution problem is establishing a foundational understanding of the ways plastic debris behaves in the environment and the factors which influence this. Concordant changes in the physiochemical properties of plastic lie with the rapid development of microbial biofilms. Although plastic is readily colonised by bacteria, there is no evidence of potential plastic-degraders during early attachment.
Lobelle, D. & Cunliffe, M., 2011. Early microbial biofilm formation on marine plastic debris. Marine Pollution Bulletin. 62: 197-200.
1 comment:
This is a really interesting area of research because like you say it is a very prominent pollutant. Have you ever heard of the Great Pacific Garbage Patch? It is a shocking example of the way plastics can pollute our environments. Hopefully further research like the paper you have reviewed could help us to manage ecological problems like this.
I have done a quick google search and found that there is some research showing that biodegradation of plastic waste with selected microbial strains is becoming a more viable solution. Below is a review of some of the new advances in this field if you are interested.
Alex Sivan. (2011). New perspectives in plastic biodegradation. Current Opinion in Biotechnology. 22 (1), 422-426.
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