In a research we conducted two years ago (and have been recently accepted in the Marine Pollution Bulletin), assessing larger microplastic (1-5 mm) abundance in the intertidal (ITZ) and supralittoral zone (SLZ) in four sandy beaches (Yuyos, Sombrillas, Agua Dulce and Pescadores) of Lima (Fig. 1), we found very strange results.
Fig. 1. Map showing the region and the sites selected in the coast of Lima. S1: Yuyos, S2:
Sombrillas, S3: Agua Dulce, and S4: Pescadores. Black squares above the high tide line indicate
the orientation of the transects from the supralittoral zone and below the transect from the
intertidal zone.
The microplastic (MP) concentrations varied considerably but, in general terms, our main issue was finding larger amounts of MPs in the ITZ in the two most polluted beaches (See Fig. 2 for a reference of the magnitude). Trying to explain why was hard. Superficial current did not make much influence as we assessed a very small area (the four beaches were very close to each other.
Fig. 2 Boxplot of the microplastic abundance (particles m-2) per beach and beach zone. SLZ:
Supralitoral zone, and ITZ: Intertidal zone
Reduced tidal action was observed in Yuyos and Pescadores, as they were highly influenced by artificial structures, like intertidal breakwaters. Aguilera et al. (2016) revealed that these structures promote retention and accumulation of human derived litter, including the entrapment of floating debris. This is one factor to understand the lack of washed up microplastics in this two beaches.
However, the extremely high abundance in Sombrillas and Agua Dulce may be do to something else. Something we should highlight is that the vast majority of the overall microplastics found in the four beaches were foams (78.3%), which is another very unusual result, as literature report fibers or fragments as the most common microplastics in sandy beaches. Also, the majority of the foams did not show weathering conditions, like coloring and degrade. We concluded that the high abundance of foams (determined PS after FTIR analysis) was due to the disposal of styrofoam materials (cups, plates, and other stuff) around the beach by beachgoers, provided by many local food businesses within Sombrillas and Agua Dulce. During the summer season, recreational beaches, like Sombrillas and Agua Dulce are overcrowded with people who make an inappropriate disposable of these materials or just bury them in the sand.
However, the extremely high abundance in Sombrillas and Agua Dulce may be do to something else. Something we should highlight is that the vast majority of the overall microplastics found in the four beaches were foams (78.3%), which is another very unusual result, as literature report fibers or fragments as the most common microplastics in sandy beaches. Also, the majority of the foams did not show weathering conditions, like coloring and degrade. We concluded that the high abundance of foams (determined PS after FTIR analysis) was due to the disposal of styrofoam materials (cups, plates, and other stuff) around the beach by beachgoers, provided by many local food businesses within Sombrillas and Agua Dulce. During the summer season, recreational beaches, like Sombrillas and Agua Dulce are overcrowded with people who make an inappropriate disposable of these materials or just bury them in the sand.
Our article is currently accepted but not yet published. Once it goes online, I will share it with whoever requests it on ResearchGate.
References
Aguilera MA, Broitman BR, Thiel M (2016) Artificial breakwaters as garbage bins: Structural
complexity enhances anthropogenic litter accumulation in marine intertidal habitats. Environ
Pollut 214:737-747. doi:10.1016/j.envpol.2016.04.058
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