Summary for Nov 24:
Density Separation materials:
NaI for a solution of density over 1.6g/ cm³ (60% weight/weight solution used by Nuelle et al., 2013)
Volumetric flask
Beakers
Filters
Filter funnel
Wash bottle
Distilled water
Need to decide size of flask, which will depend on sizes of sediment samples.
Density Separation method: (adapted from Nuelle et al., 2013)
After the sediment samples are taken from the benthic chamber and sliced at different depths, the
individual samples will be allowed to dry for 24 hours to remove some of the excess lower density
NaCl solution.
The plastic extraction method is performed after Nuelle et al. (2013), using the principle of flotation
of the microplastics in a higher density (1.8 g/cm3) solution of NaI. The sediment sample is added to
the volumetric flask (size will depend on the sediment sample size). The 60% weight/weight NaI
solution is filled to below the angle of the belly of the volumetric flask so that the sample could be
completely mixed by shaking. The flask will be shaken for 20 seconds and then filled with NaI
solution to the highest calibration mark. The flask is then shaken again for 10 seconds to ensure that
sediment on the surface due to surface tension and adhesion is limited. NaI solution is added to 1
cm below the rim of the flask. After settling for 10 minutes, the supernatant is poured into a beaker
(size depends on sample size) to below the angle of the belly of the flask. The procedure (shaking,
refilling, settling, and pouring) was replicated five times.
The supernatant in the beaker is then poured into a filter. The beaker was rinsed with distilled water
into the filtration unit. The plastic left on filter was air dried for later analysis.
Microplastic Grinding:
Grinding by hand with a file works well, but takes a very long time, not very fast (only had a very
small amount after 30 minutes) and had to stop because my hands hurt too much. Want to check
under microscope to check that the plastics are small enough.
Will use an automatic belt sander with a waste bag to catch the plastic. Different sandpaper grains
will be used to make differently sized microplastic.
Benthic Chamber method: (adapted from Huettel and Rusch, 2000)
In a benthic chamber, the penetration depth of different microplastics in sediment of selected grain
size similar to the sandy, well sorted sediment north of the East Frisian Islands in the North Sea will
be investigated. The chamber will be kept between 11°C and 12°C, similar to the average annual
bottom temperature off the German coast.
The benthic chamber method is adapted after Huettel & Rusch (2000). In the benthic chamber with
a diameter of 30 cm, sediments (amount depends on exact size of benthic chamber) are added
about 10 cm below the top of the chamber and a NaCl solution with a salinity of 34 is added. The
water is stirred by a rotating disk above the sediment. (also will need the specifications, speed of
disk, sizes of the chamber) Then microplastic is added to the chamber. After being left for 72 hours,
four sub-cores (will need diameter and length) are taken and sliced at 1 or 2 cm intervals.
Still need the specifications of the benthic chamber to determine the amount of sediment, water,
and microplastic. Also need the diameter and depth of the sub-core and how much space between
the top of the disk and water to the sediment surface.
North Sea environment:
Will keep the benthic chamber at 11-12°C and use water with a salinity of 34.
“Abstract: Annual average bottom water temperature was calculated for the period 2006 from
results of the TRIM model for the North Sea. Information on temporal and spatial variability in
temperature is important with respect to species distribution and habitat suitability modelling.”
Temperature measured at 1 m above the bottom
“Abstract: The salinity of the North Sea is influenced by the large volume of freshwater entering
from major European rivers. In coastal areas the salinity is typically between 32 and 34.5.”