this procedure underestimates the levels of plastics, as sampling is only centering on
the surface layer. Another point of interest is the quantity of sample, because some
works collected less than 500 g of sediments, whereas others can reach about
10 kilograms (Hidalgo-Ruz et al. 2012).
As a general rule, the sampling is performed with the following instruments: (1) a
sampling tool of a nonplastic material (usually a small spoon or shovel), (2) a frame
that specifies the sampling area, and (3) a container also of a nonplastic material in
which the collected sample is stored are required.
Biological Samples
The schemes for the biological sampling are diverse and strongly determined by the
organism that will be analyzed. Normally, zooplankton, fish species, or crustaceans
are getting by nets or traps. Also, smaller invertebrate organisms can be collected
directly by hand. Generally, the interest is in the digestive system, tract, or excretions
of the organism. Then, a dissection to release the intestinal content or the entire
digestive system is performed (Lusher et al. 2013).
1.3.2 Extraction and Purification of Microplastics
Density Separation
The flotation technique is the most used for the extraction of microplastics from
sediment samples. The objective is to take advantage of the difference in density
between the most common plastic polymers, which range from 0.28 to 1.47 gÁcm
À3 ,
and the sedimentary matrix, which has a density of approximately 2.55 gÁcm
À3 .
Particularly, a concentrated salt solution is prepared and put into contact with the
sediment sample. The solid-liquid mixture is agitated during a certain time and then
is left to decant. The plastic particles remain in suspension while grains of sand
decant. Afterward, the microplastics are recovered from the supernatant by filtration.
Despite being a cheap and environmentally friendly procedure, not all common
polymers are extracted using a concentrated salt solution. For example, high-density
polymers as polyvinyl chloride or polyethylene terephthalate (PET), among others,
end up settling with the sediment because the salt solution has a low density of
approximately 1.2 gÁcm
À3 . Therefore, high-density solutions are used to overcome
this drawback, for example, sodium iodine solution (1.8 gÁcm
À3 ), zinc chloride
solution (1.5–1.7 gÁcm
À3 ), or sodium polytungstate solution (1.4 gÁcm
À3 ) (Nuelle
et al. 2014; Imhof et al. 2012; Liebezeit and Dubaish 2012; Corcoran et al. 2009).
The flotation technique is adequate to extract high-size microplastics reaching
recoveries of 80–100% (Fries et al. 2013); however, microplastics with a particle
size lower than 500 μm are more difficult to extract. In this sense, consecutive
extraction stages are suggested to get better recoveries.
8
V. Godoy et al.
the surface layer. Another point of interest is the quantity of sample, because some
works collected less than 500 g of sediments, whereas others can reach about
10 kilograms (Hidalgo-Ruz et al. 2012).
As a general rule, the sampling is performed with the following instruments: (1) a
sampling tool of a nonplastic material (usually a small spoon or shovel), (2) a frame
that specifies the sampling area, and (3) a container also of a nonplastic material in
which the collected sample is stored are required.
Biological Samples
The schemes for the biological sampling are diverse and strongly determined by the
organism that will be analyzed. Normally, zooplankton, fish species, or crustaceans
are getting by nets or traps. Also, smaller invertebrate organisms can be collected
directly by hand. Generally, the interest is in the digestive system, tract, or excretions
of the organism. Then, a dissection to release the intestinal content or the entire
digestive system is performed (Lusher et al. 2013).
1.3.2 Extraction and Purification of Microplastics
Density Separation
The flotation technique is the most used for the extraction of microplastics from
sediment samples. The objective is to take advantage of the difference in density
between the most common plastic polymers, which range from 0.28 to 1.47 gÁcm
À3 ,
and the sedimentary matrix, which has a density of approximately 2.55 gÁcm
À3 .
Particularly, a concentrated salt solution is prepared and put into contact with the
sediment sample. The solid-liquid mixture is agitated during a certain time and then
is left to decant. The plastic particles remain in suspension while grains of sand
decant. Afterward, the microplastics are recovered from the supernatant by filtration.
Despite being a cheap and environmentally friendly procedure, not all common
polymers are extracted using a concentrated salt solution. For example, high-density
polymers as polyvinyl chloride or polyethylene terephthalate (PET), among others,
end up settling with the sediment because the salt solution has a low density of
approximately 1.2 gÁcm
À3 . Therefore, high-density solutions are used to overcome
this drawback, for example, sodium iodine solution (1.8 gÁcm
À3 ), zinc chloride
solution (1.5–1.7 gÁcm
À3 ), or sodium polytungstate solution (1.4 gÁcm
À3 ) (Nuelle
et al. 2014; Imhof et al. 2012; Liebezeit and Dubaish 2012; Corcoran et al. 2009).
The flotation technique is adequate to extract high-size microplastics reaching
recoveries of 80–100% (Fries et al. 2013); however, microplastics with a particle
size lower than 500 μm are more difficult to extract. In this sense, consecutive
extraction stages are suggested to get better recoveries.
8
V. Godoy et al.