Plastic-associated harmful phytoplankton assemblages in coastal and off-shore habitats of the Mediterranean Sea

Plastics (macro, micro and nanoplastics) are durable and persistent pollutants that may alter
pelagic and coastal ecosystem functions. Plastics provide a durable substrate that can be
colonized by micro and macro-organisms. They support the growth of potential pathogens and
HAB species. Further, plastic debris has been considered to play a key role in the dispersal
also of biotoxins. The present study aimed to investigate harmful phytoplankton assemblages
that colonized numerous samples of micro and macro-plastics collected in the Mediterranean
Sea by qPCR assays, and to forecast toxin dispersal by quantifying toxin content onto plastic
debris. Further, the impact of polystyrene nanoparticles (PS NPs) to the HA diatom Skeletonema
marinoi was analyzed. All plastic samples were positive for the presence of Dinophyceae and
Bacillariophyceae communities and some plastic samples were colonized by toxic species of
dinoflagellate Alexandrium pacificum, Alexandrium minutum, Ostreopsis cf. ovata and diatom
Pseudo-nitzschia spp. Strains of A. pacificum isolated from plastic debris and analyzed by LCHRMS
produced PST (paralytic shellfish toxins). The levels of potential toxins on plastic samples
ranged from 101 to 102 ng cm-2. The interactions between HA diatom and plastic nanoparticles
demonstrated an increase of both extracellular and intracellular reactive oxygen species, and
significantly reduced colonies length using TEM and SEM techniques. Then, plastics can
negatively impact the ecological functioning of oceans. The potential risk of harmful microalgae
dispersal associated with plastic pollution was illustrated as well as for chemical compounds to
transfer through the trophic chain with implications for human health and marine ecosystem.