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The Risk of Exposure to Microplastics
When trying to assess the danger of MPs in the marine environment, various things have to be taken into consideration.
The risk to be exposed to MPs varies a lot with compartments, usually divided into water surface, water column and
sediments. Sediments are thought of as being the most
affected compartment, because they function as a sink for
MPs (Hidalgo-Ruz et al. 2012; Duis and Coors 2016). All
compartments considerably vary spatially and temporally
and distribution of MPs is, therefore, difficult to assess
(Chubarenko et al. 2016).
Risk of exposure is different for the different types of
polymers (buoyancy, fragmentation rate) and the habitat of
the organism (surface layer, water column, sediment)
(Andrady 2017). Polymers with low density tend to stay longer in the surface layer, possibly aggregating with phytoplankton in the euphotic zone (Long et al. 2017). They can
also be overgrown by microbes and other fouling organisms
and sink down in the water column together with MPs of
neutral buoyancy. Higher density polymers such as polyvinyl
chloride sink quickly and are readily available for benthic
filter feeders or deposit feeders such as bivalves and polychaetes (Avio et al. 2017).
The hazard that MP poses for organisms also varies
depending on the functional group such as the trophic level
of the organism. So far, mainly low trophic levels such as
filter feeders, deposit feeders and planktivorous fish have
been found to be contaminated with MPs, but recently MP
particles have also been detected in predatory pelagic fish
such as tuna (Romeo et al. 2015) and even filter feeding
mammals such as humpback whales (Besseling et al. 2015).
Studies have accumulated on examining fish guts for MPs
and have found evidence of MPs among multiple species and
life stages across different functional groups (Vendel et al.
2017). Transfer to higher trophic levels, such as fish preying
on zooplankton that has ingested MPs, has been hypothesized but no clear evidence has been found yet (Santana et al.
2017). So far, studies give contradictory results with some
claiming that MPs cascade to higher trophic levels (Setälä
et al. 2014) while others disagree or argue that they travel to
predators but do not persist in the gut (Santana et al. 2017).
Effects Due to the Specific Properties
of Microplastic Particles
All types of MPs are hypothesized to cause gut blockage or
a false sense of fullness, if not excreted within reasonable
time span (Gall and Thompson 2015). Most MPs are socalled secondary MPs resulting from fragmentation of larger
particles. Therefore, the shape of MPs can cause internal
ruptures and injuries. Most studies have been conducted with
primary MPs: spherical, highly defined microbeads not
reflecting the situation in the environment, as the most commonly found types are fragments and fibers. This calls for
the use of fragments or fibers in laboratory studies to enhance
significance of the obtained results.
The effects of MPs on an organism depend a lot on its
size. Seabirds often take up colorful plastic particles that fill
up their stomach and can be too large for gut passage (van
Franeker et al. 2011). Contrarily, very small particles
(1–400 nm) (GESAMP 2015), called nanoplastics if <100 nm
(Löder and Gerdts 2015), can potentially be implemented in
body cells after ingestion as they are small enough to pass
pores in membranes. Inside the cell, the particles can potentially disturb other tissues than the digestive system such as
the liver or lymph system (von Moos et al. 2012).
Impacts on biota can vary depending on the polymer type
of the encountered MPs. Some polymers such as silicone are
sturdier and break down slower under the influence of temperature and wave action than others due to their chemical
composition. They fragment slower and are also less likely to
leach pollutants as leaching of additives is dependent on surface area which increases with decreasing particle size
(Suhrhoff and Scholz-Böttcher 2016). Other polymers, however, are already toxic in themselves by leaching monomers
or oligomers such as polyvinyl chloride (PVC) or polystyrene (PS). These monomers have been shown to act as endocrine disruptors (Espinosa et al. 2016).
When MPs are introduced into the environment they are
free of microorganisms and have not yet been impacted by
waves or UV light. With time, MPs weather, pollutants
adsorb and leach, and microorganisms start growing on the
particles. These processes lead to changed characteristics of
the MPs. With growing or adhering organisms the buoyancy
changes and low density polymers start to sink and become
available for a different range of organisms. Furthermore,
biofilm-coated particles might not be recognizable anymore
as MPs or seem more palatable due to chemical cues emitted
from the microorganisms and are ingested with higher probability. Bacterial assemblages on MPs have also been found
to be different from other surfaces with yet unknown consequences (Kesy et al. 2016).
Considering all of the above, there are various things to be
accounted for when working with MP in the laboratory.
Glass containers or glass material should be used as much as
possible to reduce contamination sources. As this is only
possible to a certain extent, negative controls should also
account for plastic materials used within the experimental
set-up. To assess the effects of MPs in experiments, the concentrations have to be determined, to which the organisms
are exposed. Using spherical beads, this can be calculated
via diameter, density and mass of the spheres. Irregular beads
are more difficult to handle. Simple methods usually involve
counting chambers (Syberg et al. 2015), light microscopy
Microplastics in Aquatic Systems – Monitoring Methods and Biological Consequences
The Risk of Exposure to Microplastics
When trying to assess the danger of MPs in the marine environment, various things have to be taken into consideration.
The risk to be exposed to MPs varies a lot with compartments, usually divided into water surface, water column and
sediments. Sediments are thought of as being the most
affected compartment, because they function as a sink for
MPs (Hidalgo-Ruz et al. 2012; Duis and Coors 2016). All
compartments considerably vary spatially and temporally
and distribution of MPs is, therefore, difficult to assess
(Chubarenko et al. 2016).
Risk of exposure is different for the different types of
polymers (buoyancy, fragmentation rate) and the habitat of
the organism (surface layer, water column, sediment)
(Andrady 2017). Polymers with low density tend to stay longer in the surface layer, possibly aggregating with phytoplankton in the euphotic zone (Long et al. 2017). They can
also be overgrown by microbes and other fouling organisms
and sink down in the water column together with MPs of
neutral buoyancy. Higher density polymers such as polyvinyl
chloride sink quickly and are readily available for benthic
filter feeders or deposit feeders such as bivalves and polychaetes (Avio et al. 2017).
The hazard that MP poses for organisms also varies
depending on the functional group such as the trophic level
of the organism. So far, mainly low trophic levels such as
filter feeders, deposit feeders and planktivorous fish have
been found to be contaminated with MPs, but recently MP
particles have also been detected in predatory pelagic fish
such as tuna (Romeo et al. 2015) and even filter feeding
mammals such as humpback whales (Besseling et al. 2015).
Studies have accumulated on examining fish guts for MPs
and have found evidence of MPs among multiple species and
life stages across different functional groups (Vendel et al.
2017). Transfer to higher trophic levels, such as fish preying
on zooplankton that has ingested MPs, has been hypothesized but no clear evidence has been found yet (Santana et al.
2017). So far, studies give contradictory results with some
claiming that MPs cascade to higher trophic levels (Setälä
et al. 2014) while others disagree or argue that they travel to
predators but do not persist in the gut (Santana et al. 2017).
Effects Due to the Specific Properties
of Microplastic Particles
All types of MPs are hypothesized to cause gut blockage or
a false sense of fullness, if not excreted within reasonable
time span (Gall and Thompson 2015). Most MPs are socalled secondary MPs resulting from fragmentation of larger
particles. Therefore, the shape of MPs can cause internal
ruptures and injuries. Most studies have been conducted with
primary MPs: spherical, highly defined microbeads not
reflecting the situation in the environment, as the most commonly found types are fragments and fibers. This calls for
the use of fragments or fibers in laboratory studies to enhance
significance of the obtained results.
The effects of MPs on an organism depend a lot on its
size. Seabirds often take up colorful plastic particles that fill
up their stomach and can be too large for gut passage (van
Franeker et al. 2011). Contrarily, very small particles
(1–400 nm) (GESAMP 2015), called nanoplastics if <100 nm
(Löder and Gerdts 2015), can potentially be implemented in
body cells after ingestion as they are small enough to pass
pores in membranes. Inside the cell, the particles can potentially disturb other tissues than the digestive system such as
the liver or lymph system (von Moos et al. 2012).
Impacts on biota can vary depending on the polymer type
of the encountered MPs. Some polymers such as silicone are
sturdier and break down slower under the influence of temperature and wave action than others due to their chemical
composition. They fragment slower and are also less likely to
leach pollutants as leaching of additives is dependent on surface area which increases with decreasing particle size
(Suhrhoff and Scholz-Böttcher 2016). Other polymers, however, are already toxic in themselves by leaching monomers
or oligomers such as polyvinyl chloride (PVC) or polystyrene (PS). These monomers have been shown to act as endocrine disruptors (Espinosa et al. 2016).
When MPs are introduced into the environment they are
free of microorganisms and have not yet been impacted by
waves or UV light. With time, MPs weather, pollutants
adsorb and leach, and microorganisms start growing on the
particles. These processes lead to changed characteristics of
the MPs. With growing or adhering organisms the buoyancy
changes and low density polymers start to sink and become
available for a different range of organisms. Furthermore,
biofilm-coated particles might not be recognizable anymore
as MPs or seem more palatable due to chemical cues emitted
from the microorganisms and are ingested with higher probability. Bacterial assemblages on MPs have also been found
to be different from other surfaces with yet unknown consequences (Kesy et al. 2016).
Considering all of the above, there are various things to be
accounted for when working with MP in the laboratory.
Glass containers or glass material should be used as much as
possible to reduce contamination sources. As this is only
possible to a certain extent, negative controls should also
account for plastic materials used within the experimental
set-up. To assess the effects of MPs in experiments, the concentrations have to be determined, to which the organisms
are exposed. Using spherical beads, this can be calculated
via diameter, density and mass of the spheres. Irregular beads
are more difficult to handle. Simple methods usually involve
counting chambers (Syberg et al. 2015), light microscopy
Microplastics in Aquatic Systems – Monitoring Methods and Biological Consequences