Quality
Assurance and Quality Control. The objective of this research was to
extract MP debris (30 µm to 1 mm) from wrack line samples. Therefore,
the quality control used reflects the need to limit contamination within
that size range, which is mostly particulate in shape, rather than
smaller MP, including fibers, and nanoplastics. Briefly, quality control
procedures included washing and rinsing all glassware and utensils with
DI water before being muffled at 500˚C for 4 hours and then storing
covered to reduce airborne contamination.27 Laboratory
contamination of samples was assessed using four blank samples. The
materials from the blank samples consisted of an average of 12.8 ± 3.0
microfibers. Similar fibers were not found in the samples and therefore,
no corrections were done to the final results. Dyed Cotton laboratory
coats and gloves were worn at each step of the analysis. Analysis was
done in a laboratory in an air filtration system and all surfaces were
cleaned with DI water each time before use.
The percentage recoveries for the isolated MPs in POM were estimated
(Table S1) by mixing a proportion of the isolated MPs and POM in 1:5 and
repeated the whole extraction process using the binary solvent mixture
of ethanol and water (7:3) to recover the MPs. We used two approaches to
further evaluate our recovery method. First, we visually observed the
POM under the stereo microscope where 6 MP particles was the maximum
number found in only 1 of the twelve wrack line samples assessed (PL).
Second, 1 g each of the recovered POM was stained with methylene blue to
mask the fluorescence of organic matter and reduce interference. After
that, the POM was stained with Nile red and viewed under the
fluorescence microscope (Olympus CKX53 with Hamamatsu ORCA-Spark
431-3196, Japan). The fluorescent MPs were counted and estimated in
particle per gram (particle.g-1) of the POM (Figure
S3).