Plastic marine debris and persistent organic pollutants along the Portuguese coast: How much and how many?

Background/Question/Methods

Plastic pollution is now recognized as a global issue due to the general concern about the increasing amounts found in the oceans worldwide and the fact that plastic particles act as vectors of contamination with persistent bioacumulative and toxic (PBT) pollutants. The size of plastic fragments decreases in result of degradation, and microplastics (particles <5 mm) pose a potential risk to marine organisms as they mimic food items. Plastic may be introduced in the lower trophic levels and cause damage to the digestive tract and accumulation of PBT with unknown consequences for the marine ecosystems.

In order to understand the amount, size distribution of plastic particles < 10 mm and type of plastic in beaches of the Portuguese coast, samples of stranded litter were collected from accumulation areas at six beaches along the coast of Portugal, using 50x50 cm quadrats. Plastic debris were separated in 1 mm size classes (every mm from 1-10 mm,) counted and weighted. PBT (PCB, DDT and PAH) contents were determined in resin pellets (3-5 mm) sorted by colour (white, aged, coloured and black) using gas chromatography coupled mass spectrometry (GC-MS). Plastic polymers are identified using infrared spectroscopy (micro-FTIR).

Results/Conclusions

Distribution of microplastics is variable: the highest quantities were registered at Vieira de Leiria, draining from a plastic processors industrial area and at Sines a port infrastructure for container and cargo ships.  The weight of sampled plastic was ~0.33 kg (15858 items), 89 % being resin pellets of which the most abundant size classes were 3, 4 and 5 mm, (27.6, 46.6 and 39.0 % of total particles). Pellets were mostly polypropylene and polyethylene of the white (59.4 %) and aged classes (25.2 %). 70 % of the black pellets were found at Vieira de Leiria.

Black pellets presented higher concentration of PAH (12048 ng.g^-1) than the aged pellets (2248 ng.g^-1). However, aged pellets registered higher concentration of DDT (105.7 ng.g^-1) and PCB (187.2 ng.g^-1). The minimum values of POP were registered in Vieira de Leiria.

Despite the many factors that induce variability in the amount and contamination of beached plastic, results suggest that the plastic debris in this study are mainly from terrestrial origin, consistent with losses from industrial processiing and transfer from cargo ships.

This work was developed as part of an ongoing research project focused on studying microplastics along the Portuguese coast, and will further assess the harmful effets of transfer of PBT to marine invertebrates and fish.