Case study: The RealRiskNano project

Bacteria glues plastic together: possible threat to sea life? The RealRiskNano project

RealRiskNano is a £1.1 million project funded by the Natural Environment Research Council (NERC) led by researchers from Heriot-Watt University, in collaboration with Plymouth University. Its aim is to investigate and improve understanding of the behaviour and effects of micro- and nano-plastics in the marine environment. Micro-plastics are defined as measuring 1 μm to 5 mm, and nano-plastics are defined as being <1 μm. The project also explored the attachment of toxic chemicals (e.g. polycyclic aromatic hydrocarbons (PAHs)) to the plastic particles, and whether these chemicals might then accumulate and cause toxicological effects in the tissues of marine organisms that ingest them.

In this study, the formation of polystyrene nano- and micro-plastic agglomerates was examined, using methods for generating artificial marine snow (organic material that forms particulates in the upper layers of the ocean), similar to that of Shanks & Edmondson (1989), and utilising natural seawater collected from the northeast Atlantic (Figure 1).

Figure 1: The potential for plastic particles to form agglomerates was investigated using a roller-bottle design similar to that of Shanks &amp; Edmondson (1989).

Bacteria glues plastic together: possible threat to sea life?

Through RealRiskNano, the microbiology team at Heriot-Watt University, led by Dr. Tony Gutierrez, used natural waters, collected from the Faroe-Shetland Channel and Firth of Forth, to understand the behaviour of these tiny plastic particles in marine waters. 

It was found that natural biopolymers, excreted by bacteria, can act as a “glue” in binding micro- and nano-plastics together so that they form polymer-plastic agglomerations in sea water (Summers, Henry & Gutierrez, 2018) (Figures 2a & b).

(a)

(b)

The biopolymers are common across all freshwater lakes and marine environments, but until now it was unknown what effects these sticky, glue-like materials had on the ubiquitous micro- and nano-plastics. The Heriot-Watt team found that, within minutes, the plastic particles grouped together with bacteria, algae and the biopolymers that these microorganisms produce. Unexpectedly, the glue-like biopolymer substances were observed to form the bulk of these plastic agglomerations when viewed under the microscope.

Staining the agglomerates with acridine orange revealed that they contained a community of associated microorganisms (Figure 3).

Figure 3: Nano- and micro-plastic agglomerates (green spheres) stained with the nucleic acid-specific stain acridine orange (orange dots showing bacterial cells) and observed under a fluorescence microscope. Plastic particles are: (a) = 20 μm, (b) = 1 μm and (c) = 50 nm plastic spheres; Scale bars, 5 μm. Images are composites of images from filters FITC and Rhodamin (ex 440 nm, em 510 nm and ex 546 nm, em 580 nm, respectively). ex = excitation wavelength; em = emission wavelength.

What are the impacts and next steps?

This natural process of packaging micro- and nano-plastics into “gluey” particles, and that become larger with time, raises concern as they are likely to be seen as a food source by small marine animals. It is unknown what the effects of any ingestion might be. This calls for future work to understand what impacts these micro- and nano-plastic agglomerates could have to organisms, from small invertebrates (incl. filter feeders) to humans.

Further information RealRiskNano project 

http://www.tony-gutierrez.com/portfolio-items/realrisknano-nanoplastics-...

https://epaquatic.org/realrisknano/

https://www.plymouth.ac.uk/research/marine-litter

Related media/press reports/related literature

Article featured by The Naked Scientist: “Microplastics bound up by bacteria”; Feb. 19, 2019: https://www.thenakedscientists.com/articles/science-news/microplastics-b...

Science interview podcast by The Naked Scientist for part of the show Periodic Table: 150 Au Years: “New wave of nanoplastics research”; Feb. 19, 2019; https://www.thenakedscientists.com/articles/interviews/new-wave-nanoplas...