Mediterranean study identifies three most abundant microplastics

07 Mar 2019 --- Polyethylene (PE), polypropylene (PP) and polystyrene (PS) are the most abundant microplastics in the Mediterranean coastal waters, according to a new study published by the journal Marine Pollution Bulletin. The involved researchers also identified signs of plastic materials with marine origins for the first time – in particular, particles of ship painting – which were not studied in the Mediterranean basin until now.

The study describes the presence of different types of microplastics in the peninsular coastal Mediterranean, in particular along the coasts of Catalonia, the region of Murcia and Almeria in Spain. According to the results, other abundant types are nylon polymers, polyurethane (PUR), polyethylene terephthalate (PET), ethylene-vinyl acetate (EVA), polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS) and fluorocarbon polymer.

The research was conducted by the experts Miquel Canals, William de Haan and Anna Sànchez-Vidal of the Consolidated Research Group on Marine Geosciences of the Faculty of Earth Sciences at the University of Barcelona, Spain.

Diagnosis of the peninsular Mediterranean coast: Rounded, small and light microplastics
Cylinders and small spheres, polyester foam, filaments from fishing gears and many pieces of plastic from varied chemical compositions are among the materials found in Mediterranean coasts. The study analyzed about 2,500 samples of plastic materials taken from different oceanographic campaigns over a north-south axis in every area of study. In all studied areas, the most abundant materials are fragments of polyethylene (54.5 percent), polypropylene (16.5 percent) and polyester (9.7 percent) – the most produced thermoplastic polymer worldwide –which float in marine waters and are likely to come from the continent.

So far, none of the scientific studies could prove the permanence time of plastics in the sea before these deteriorate or are buried. According to the new study, the microplastics found in the Mediterranean coasts "are round-shaped, small, about a millimeter in diameter and light-weighted, which could suggest a state of advanced deterioration and therefore, a long permanence in the marine environment," de Haan notes.

The study identified places in the peninsular coasts which have maximum concentrations up to 500,000 microplastics per square kilometer – over the average of 100,000 mp/km2. “These results coincide with studies conducted in other regions of the Mediterranean, a marine ecosystem regarded as one of the biggest scuppers of floating microplastic worldwide", de Haan adds.

Microplastics in Catalan coasts: Extreme values in Tordera and Besòs
Along the Catalan coasts, the average concentration of microplastics is over 180,000 items per square kilometer. The most extreme levels have been found in the coasts of Tordera (500.000 mp/km2) and in Besòs (fins a 110.000 mp/km2), which are areas with a notable anthropic pressure due the high density of population, tourism, use of beaches and marine activities. The most abundant microplastics among those analyzed were polyethylene and most were translucent or transparent (65 percent).

In these coastal areas, the changes in intensity and the North Current – which moves simultaneously from north to south in the coast – and currents from the littoral are factors that may affect the distribution of microplastics in the sea. According to previous studies, the North Current could bring up to a billion plastic particles per day, weighing up to 86 tons.

Murcia and Almeria: Currents that come from the Atlantic and greenhouses
In the coastal waters of Murcia and Almeria, the variety of polymers is even higher – mainly nylon, polyurethane or polyethylene terephthalate – than the one in Catalan waters and the most predominant ones are dense microplastics which drown easily. Regarding colors, the most abundant ones are matt white (46 percent in Murcia and 54 percent in Almeria) and dark colors (20 percent and 12 percent respectively). In these coasts, marine dynamics – with the arrival of surface waters from the Strait of Gibraltar – could favor the emergence of microplastics coming from the Atlantic Ocean.

The state of the found microplastics could suggest a state of advanced degradation and long permanence in the marine environment - GRC Marine Geosciences - University of BarcelonaMoreover, there are extensions of cultivations in greenhouses, such as in Campo de Dalias in Almeria that generate uncontrolled dumpings of plastic in areas near the Almeria coast, with a maximum value of 130,000 mp/km2. In Murcia, the highest concentration is in Cartagena (140.000 mp/km2) but there are other places, such as the Mar Menor lagoon, that are affected by the impact of human activity.

The diversity of microplastics in the sea regarding composition and color, as well as differences in concentration, show different origins and volume depending on the analyzed area of the coast, according to the study authors.

What is the final destination of marine plastics?
Plastics do not always behave the same way and that is why it is hard to know generically their final destination in the marine environment. “Size and physical and chemical properties, as well as the conditions of the marine environment, determine the destination of microplastics in water,” says Sànchez-Vidal.

“Density of the plastic material is a determining factor regarding big fragments. When talking of a microplastic, dynamics are more complex. Also, the density of marine water varies due to several factors, namely temperature, salinity, geographical position and depth and it directly affects the buoyancy of the microplastics.”

The study describes for the first time the aggregate potential of microplastics to integrate into marine organics, formed by organic and mineral-derived particles. This interaction – described so far in the laboratory only – is a phenomenon that occurs naturally in the marine environment, as stated in the new study.

Therefore, 40 percent of the microplastics in quantity and 25 percent in mass can create these marine aggregates. This process could ease the drowning and accumulation of light microplastics in marine floors, an environment far from the only agent able to deteriorate them: the solar ultraviolet radiation.

“Around 66 percent of the microplastics we found in marine aggregates (polyethylene, polypropylene and expanded polystyrene) are low-density microplastics in the sea. This hypothesis could explain the presence of low-density microplastics in big marine depths worldwide, and why the abundance of plastics floating in the surface of the ocean is lower than expected,” Sanchez-Vidal explains.

Marine fauna, threatened by civilization’s plastic
Usually, plastics that float on the marine surface are eaten by marine organisms, which may think they are food. Even zooplankton is able to eat microplastics and throw them through fecal pellets. This is a known but largely unstudied area of marine ecosystems.

Also, apart from additives they contain, microplastics can bring toxic compounds to the trophic chain in marine waters (metals, organic pollutants and others). Transported by the marine currents, these plastic materials can become dispersal vehicles for invasive species and pathogenic organisms.