Interactions between microplastics and phytoplankton aggregates : Impact on their respective fates

Type Article
Date 2015-10
Language English
Author(s) Long Marc1, Moriceau Brivaela1, Gallinari Morgane1, Lambert Christophe1, Huvet ArnaudORCID2, Raffray Jean1, Soudant Philippe1
Affiliation(s) 1 : IUEM, UMR CNRS Ifremer IRD UBO 6539, Lab Sci Environm MARin LEMAR, F-29280 Plouzane, France.
2 : Ifremer, France
Source Marine Chemistry (0304-4203) (Elsevier Science Bv), 2015-10 , Vol. 175 , P. 39-46
DOI 10.1016/j.marchem.2015.04.003
WOS© Times Cited 155
Note Particles in aquatic environments: from invisible exopolymers to sinking aggregates
Keyword(s) Microplastic sink, Vertical export, Diatom and cryptophyte aggregates, Settling rate, Permeability
Abstract Plastic debris are resistant to degradation, and therefore tend to accumulate in marine environment. Nevertheless recent estimations of plastic concentrations at the surface of the ocean were lower than expected leading the communities to seek new sinks. Among the different processes suggested we chose to focus on the transport of microplastics from the surface to deeper layers of the ocean via phytoplankton aggregates that constitute most of the sinking flux. Interactions between microplastics and aggregates were studied by building a new device: the flow-through roller tank that mimics the behaviour of laboratory made aggregates sinking through a dense layer of microplastics. Three types of aggregates formed from two different algae species (the diatom Chaetoceros neogracile, the cryptophyte Rhodomonas salina and a mix) were used as model. With their frustule made of biogenic silica which is denser than the organic matter, diatom aggregates sunk faster than R. salina aggregates. Diatom aggregates were on average bigger and stickier while aggregates from R. salina were smaller and more fragile. With higher concentrations measured in R. salina aggregates, all model-aggregates incorporated and concentrated microplastics, substantially increasing the microplastic sinking rates from tenths to hundreds of metres per day. Our results clearly show that marine aggregates can be an efficient sink for microplastics by influencing their vertical distribution in the water column. Furthermore, despite the high plastic concentrations tested, our study opens new questions regarding the impact of plastics on sedimentation fluxes in oceans. As an effect of microplastic incorporation, the sinking rates of diatom aggregates strongly decreased meanwhile sinking rates of cryptophyte aggregates increased.
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