WHY BIOFOULING CANNOT CONTRIBUTE TO THE VERTICAL TRANSPORT OF SMALL MICROPLASTIC

To explain the presence of buoyant microplastics like polyethylene and polypropylene in the deep-sea, the vertical transport by biofouling is one of the most referred mechanisms. Biofouling is thought to increase the density of microplastic particles to the point that they sink, but this has mostly been shown on microplastic particles of 1 mm or larger. Most microplastics in the ocean are smaller than 100 µm due to continuous fragmentation and microplastic particle abundance increases drastically with decreasing size. For a small buoyant microplastic particle to reach the deep-sea in a reasonable time, its excess density, the density difference between the particle and surrounding water, has to increase to the point that it can sink at around 10 m per day or faster. The composition of the biofilm and therefore its density as well as the thickness of the biofilm are important factors to gain the needed excess density. However, a biofilm matrix of only extracellular polymeric substances and bacteria has a lower density than seawater, in contrast to a biofilm including diatoms or large organisms like mussels or barnacles. And most marine biofilms seem to have a thickness of <15 µm on large surfaces. We argue that a small microplastic particle cannot host a biofilm community heavy and thick enough to induce an excess density large enough to enable rapid sinking or even sinking at all. Therefore, biofouling cannot be an efficient vertical transport mechanism for small microplastic.

Presentation Preference: Oral

Primary Presenter: Ina Benner, Memorial University of Newfoundland (ina.benner@gmail.com)

Authors:

Ina Benner, Memorial University of Newfoundland  (ibenner@mun.ca)

Uta Passow, Memorial University of Newfoundland  (uta.passow@mun.ca)