190
(Nobre et al. 2015) and quantitative filtering of the water
samples. Other common methods are flow cytometer
(Sussarellu et al. 2016) and the use of a coulter counter
(Syberg et al. 2015). For characterization of the beads, FTIR
(Lusher et al. 2017), Raman spectroscopy and electron
microscopy (Murray and Cowie 2011) are the preferred
methods. The next step is to determine the presence of MPs
in the organism. This is usually achieved by dissecting to
check for presence in gut systems or histological analysis of
tissue samples (Farrell and Nelson 2013). Effects on the
organism can be directly determined via deformations of larvae. Potentially, MPs can induce epigenetic effects, e.g., in
copepods (Heindler et al. 2017). Epigenetics are usually
viewed as a quick and advantageous mechanism for an F1
generation to adapt to a stressor to which the F0 generation
was exposed. Microplastics can also cause a decrease in
reproduction (Heindler et al. 2017) and are therefore directly
affecting fitness. Sussarellu et al. (2016) also reported reductions in feeding activity, accumulation and inhibition of acetylcholinesterase activity in bivalves.
Microplastics as Vector for Pollutants
The effects of the combination of MPs with pollutants are
ambivalently discussed. First, it is important to differentiate
between pollutants adhering to plastics, which belong to the
group of persistent organic pollutants (POPs), originating
from the water, and between additives leaching from the MP
particles or emittance of monomers or oligomers from the
MPs themselves. The difference here is that pollutants that
adhere to plastics are usually already widespread in the environment, while pollutants associated with plastic have only
been around since the production of plastics, so roughly the
1950s (Hammer et al. 2012). Both groups of chemicals suggest a role of MPs as a vector to organisms. This is very
debatable for pollutants already present in the environment
as some argue that other pathways such as food and water are
several magnitudes higher than the intake via MPs, simply
due to the fact that MPs are still not that abundant in the
ocean and, therefore, bioaccumulation of this POPs is not
increased by MPs yet. Additionally, it is also discussed if
leaching additives from MPs are of major concern. Here, it is
important to differentiate between primary MPs and secondary MPs. Primary MPs are introduced already in the size
range of MPs whereas secondary MPs are often introduced
into the environment as macroplastics that fragment over
time into MPs. They weather over time and it remains an
open question how much additives are still present within
those fragments.
Heindler et al. (2017) revealed in a study on the toxicity
effects of polyethylene terephthalate (PET) and the common
plasticizer diethylhexyl phthalate (DEHP) that copepod nauplii are far more sensitive to exposure than adults. This
stresses the need for assessing the toxicity of MPs at different life stages and focusing on juveniles or larvae, which are
usually more sensitive to stressors than adults. Effects of
MPs on younger life-stages can have knock-on effects on
populations if for example mortality is significantly higher
and fewer individuals reach sexual maturity and reproduce.
Regarding laboratory methods, again, glassware should
be used where appropriate to make sure that no pollutant is
adhered to the experimental container and, therefore,
removed from the experiment. Toxin burdens can for example be assessed in different compartments (water, plastic, and
biota) via high throughput liquid chromatography (HPLC)
(Brennecke et al. 2015).
Conclusion
Although intensive research activities have already resolved
some methodological issues in MP research, there are still
some challenges, which need to be overcome before standardized operational protocols (SOPs) can be defined.
Sampling effort (spatial and temporal replication, as well as
sample volume) within a project is still limited by the high
demand for personnel and physical resources as well as the
long analysis time for MP samples. Thereby, an adequate
sampling design should be chosen to answer pre-defined
research questions as precisely as possible. It is obvious that
different research questions require the use of different methods, which in turn will hamper complete standardization of
methods. Nevertheless, a comprehensive and proper data
recording, as well as gathering additional information, e.g.,
environmental data, will contribute to high quality datasets.
In addition, the extraction of MPs from environmental
matrices is a crucial step, as inorganic and organic substances
concurrently sampled with the potential MPs, can interfere
with the subsequent analysis. Lately, many protocols have
been proposed to remove inorganic or organic materials from
samples. Thereby, developments were made to improve
extraction efficiency, while not affecting fragile MPs, i.e.,
applying high density solutions for density separation of
inorganic material or enzymatic purification of organic material. Finally, for a reliable identification of MPs a solely visible analysis is insufficient, and a chemical characterization
is highly recommended. Spectroscopic methods like Ramanor FTIR-spectroscopy are state-of-the-art, providing particle
related data (e.g., numbers, sizes) as well as thermal extraction methods like Pyr-GC-MS and TED-GC-MS, which provide mass related data and information about absorbed
pollutants or contained additives.
Both methods will provide relevant information for further studies on the effects of MPs on organisms. There is still
a huge lack of knowledge and besides evidence that MPs are
T. Hamm et al.
(Nobre et al. 2015) and quantitative filtering of the water
samples. Other common methods are flow cytometer
(Sussarellu et al. 2016) and the use of a coulter counter
(Syberg et al. 2015). For characterization of the beads, FTIR
(Lusher et al. 2017), Raman spectroscopy and electron
microscopy (Murray and Cowie 2011) are the preferred
methods. The next step is to determine the presence of MPs
in the organism. This is usually achieved by dissecting to
check for presence in gut systems or histological analysis of
tissue samples (Farrell and Nelson 2013). Effects on the
organism can be directly determined via deformations of larvae. Potentially, MPs can induce epigenetic effects, e.g., in
copepods (Heindler et al. 2017). Epigenetics are usually
viewed as a quick and advantageous mechanism for an F1
generation to adapt to a stressor to which the F0 generation
was exposed. Microplastics can also cause a decrease in
reproduction (Heindler et al. 2017) and are therefore directly
affecting fitness. Sussarellu et al. (2016) also reported reductions in feeding activity, accumulation and inhibition of acetylcholinesterase activity in bivalves.
Microplastics as Vector for Pollutants
The effects of the combination of MPs with pollutants are
ambivalently discussed. First, it is important to differentiate
between pollutants adhering to plastics, which belong to the
group of persistent organic pollutants (POPs), originating
from the water, and between additives leaching from the MP
particles or emittance of monomers or oligomers from the
MPs themselves. The difference here is that pollutants that
adhere to plastics are usually already widespread in the environment, while pollutants associated with plastic have only
been around since the production of plastics, so roughly the
1950s (Hammer et al. 2012). Both groups of chemicals suggest a role of MPs as a vector to organisms. This is very
debatable for pollutants already present in the environment
as some argue that other pathways such as food and water are
several magnitudes higher than the intake via MPs, simply
due to the fact that MPs are still not that abundant in the
ocean and, therefore, bioaccumulation of this POPs is not
increased by MPs yet. Additionally, it is also discussed if
leaching additives from MPs are of major concern. Here, it is
important to differentiate between primary MPs and secondary MPs. Primary MPs are introduced already in the size
range of MPs whereas secondary MPs are often introduced
into the environment as macroplastics that fragment over
time into MPs. They weather over time and it remains an
open question how much additives are still present within
those fragments.
Heindler et al. (2017) revealed in a study on the toxicity
effects of polyethylene terephthalate (PET) and the common
plasticizer diethylhexyl phthalate (DEHP) that copepod nauplii are far more sensitive to exposure than adults. This
stresses the need for assessing the toxicity of MPs at different life stages and focusing on juveniles or larvae, which are
usually more sensitive to stressors than adults. Effects of
MPs on younger life-stages can have knock-on effects on
populations if for example mortality is significantly higher
and fewer individuals reach sexual maturity and reproduce.
Regarding laboratory methods, again, glassware should
be used where appropriate to make sure that no pollutant is
adhered to the experimental container and, therefore,
removed from the experiment. Toxin burdens can for example be assessed in different compartments (water, plastic, and
biota) via high throughput liquid chromatography (HPLC)
(Brennecke et al. 2015).
Conclusion
Although intensive research activities have already resolved
some methodological issues in MP research, there are still
some challenges, which need to be overcome before standardized operational protocols (SOPs) can be defined.
Sampling effort (spatial and temporal replication, as well as
sample volume) within a project is still limited by the high
demand for personnel and physical resources as well as the
long analysis time for MP samples. Thereby, an adequate
sampling design should be chosen to answer pre-defined
research questions as precisely as possible. It is obvious that
different research questions require the use of different methods, which in turn will hamper complete standardization of
methods. Nevertheless, a comprehensive and proper data
recording, as well as gathering additional information, e.g.,
environmental data, will contribute to high quality datasets.
In addition, the extraction of MPs from environmental
matrices is a crucial step, as inorganic and organic substances
concurrently sampled with the potential MPs, can interfere
with the subsequent analysis. Lately, many protocols have
been proposed to remove inorganic or organic materials from
samples. Thereby, developments were made to improve
extraction efficiency, while not affecting fragile MPs, i.e.,
applying high density solutions for density separation of
inorganic material or enzymatic purification of organic material. Finally, for a reliable identification of MPs a solely visible analysis is insufficient, and a chemical characterization
is highly recommended. Spectroscopic methods like Ramanor FTIR-spectroscopy are state-of-the-art, providing particle
related data (e.g., numbers, sizes) as well as thermal extraction methods like Pyr-GC-MS and TED-GC-MS, which provide mass related data and information about absorbed
pollutants or contained additives.
Both methods will provide relevant information for further studies on the effects of MPs on organisms. There is still
a huge lack of knowledge and besides evidence that MPs are
T. Hamm et al.