1.5.1 Global Microplastic Concentration and Distribution
in Different Marine Ecosystems
The first study that reported the presence of microplastics in seawater was conducted
by Carpenter and Smith (1972). They estimated average microplastic concentrations
of 3500 items and 290 g per km
2 in the western Sargasso Sea. With this discovery,
the scientists tried to alert society about the problem of that contamination, but their
warning was ignored. At present, microplastics are much more abundant and
distributed all over the seas, oceans, and beaches, as revealed by numerous studies
over the last decade (Auta et al. 2017; Cole et al. 2011; Guo and Wang 2019; Hamid
et al. 2018; Hidalgo-Ruz et al. 2012; Kane and Clare 2019).
Microplastics have low density in general, which means that they can easily float
on the water surface or in the water column (Piperagkas et al. 2018). Microplastics
with density higher than that of seawater tend to sink down in sediments, where they
accumulate, while those with low density float on the sea surfaces (Alomar et al.
2016; Suaria and Aliani 2014). Density can change when microplastics are degraded
by the action of external agents or when biofouling caused by organisms occurs. In
addition, Eriksen et al. (2014) verified that the movement of microplastics is also
controlled by marine currents and oceanic gyres. According to that study, ocean
margins are zones of plastic migration, while subtropical gyres are areas of accumulation. Therefore, the distribution of microplastics in marine environments is
controlled by a wide range of causes.
In this section, the most important concentrations of microplastics present in the
literature over the last decade have been collected and selected. These data are
presented on maps of the continents of the world, in order to determine the geographical distribution of microplastics. Figure 1.12 represents the microplastic
abundance and distribution in Europe. This continent contains the largest contamination by microplastics, along with East Asia. The biggest concentrations of these
particles are present along the coast of Algarve (Portugal), in the lagoon of Venice,
and in the Rhine estuary (Frias et al. 2016; Vianello et al. 2013; Mani et al. 2015).
This can be due to the fact that microplastic particles tend to accumulate in areas
characterized by lower water movement, such as an estuary or a lagoon.
Other studies have reported high concentrations of microparticles in beaches, for
example, in Canary Islands, where more than 1600 items per m
2 in the beach of
Lambra were found (Herrera et al. 2018). The authors reached the conclusion that
debris accumulation depended mainly of coastline orientations and meteorological
conditions. In addition, the subtropical oceanic gyre affects the way in which the
currents vary from the coast to the open ocean during the year (Navarro-Pérez and
Barton 2001). The same occur to some remote areas where high amounts of
microplastics are recorded, i.e., Scapa Flow (UK), which accounted between
730 and 2300 items per kg of sediment, or Vik (Iceland), with 792 items per kg
(Blumenröder et al. 2017; Lots et al. 2017). This is mainly caused by the oceanic
currents. Other factors that can affect the pollution distribution are the salinity,
temperature, shape of the coast line, or coastal activities (Cincinelli et al. 2019).
20
V. Godoy et al.
in Different Marine Ecosystems
The first study that reported the presence of microplastics in seawater was conducted
by Carpenter and Smith (1972). They estimated average microplastic concentrations
of 3500 items and 290 g per km
2 in the western Sargasso Sea. With this discovery,
the scientists tried to alert society about the problem of that contamination, but their
warning was ignored. At present, microplastics are much more abundant and
distributed all over the seas, oceans, and beaches, as revealed by numerous studies
over the last decade (Auta et al. 2017; Cole et al. 2011; Guo and Wang 2019; Hamid
et al. 2018; Hidalgo-Ruz et al. 2012; Kane and Clare 2019).
Microplastics have low density in general, which means that they can easily float
on the water surface or in the water column (Piperagkas et al. 2018). Microplastics
with density higher than that of seawater tend to sink down in sediments, where they
accumulate, while those with low density float on the sea surfaces (Alomar et al.
2016; Suaria and Aliani 2014). Density can change when microplastics are degraded
by the action of external agents or when biofouling caused by organisms occurs. In
addition, Eriksen et al. (2014) verified that the movement of microplastics is also
controlled by marine currents and oceanic gyres. According to that study, ocean
margins are zones of plastic migration, while subtropical gyres are areas of accumulation. Therefore, the distribution of microplastics in marine environments is
controlled by a wide range of causes.
In this section, the most important concentrations of microplastics present in the
literature over the last decade have been collected and selected. These data are
presented on maps of the continents of the world, in order to determine the geographical distribution of microplastics. Figure 1.12 represents the microplastic
abundance and distribution in Europe. This continent contains the largest contamination by microplastics, along with East Asia. The biggest concentrations of these
particles are present along the coast of Algarve (Portugal), in the lagoon of Venice,
and in the Rhine estuary (Frias et al. 2016; Vianello et al. 2013; Mani et al. 2015).
This can be due to the fact that microplastic particles tend to accumulate in areas
characterized by lower water movement, such as an estuary or a lagoon.
Other studies have reported high concentrations of microparticles in beaches, for
example, in Canary Islands, where more than 1600 items per m
2 in the beach of
Lambra were found (Herrera et al. 2018). The authors reached the conclusion that
debris accumulation depended mainly of coastline orientations and meteorological
conditions. In addition, the subtropical oceanic gyre affects the way in which the
currents vary from the coast to the open ocean during the year (Navarro-Pérez and
Barton 2001). The same occur to some remote areas where high amounts of
microplastics are recorded, i.e., Scapa Flow (UK), which accounted between
730 and 2300 items per kg of sediment, or Vik (Iceland), with 792 items per kg
(Blumenröder et al. 2017; Lots et al. 2017). This is mainly caused by the oceanic
currents. Other factors that can affect the pollution distribution are the salinity,
temperature, shape of the coast line, or coastal activities (Cincinelli et al. 2019).
20
V. Godoy et al.