Page 9 - Shimadzu Journal vol.7 Issue1

Environmental Analysis

with samples, showed no contamination although the fibrous filter A subsample of fibres (n=15) spanning all trenches were analysed
membrane showed partly loose, clear fibres on some samples, hence by Fourier-Transform Infra-red Spectrophotometer (FTIR; IR
clear fibres were excluded from results. We did not find any white Tracer-100, Shimadzu, Japan) connected to an automatic infrared
fibres that may have been contamination from the white laboratory microscope (AIM-9000, Shimadzu, Japan) at the Shimadzu UK Ltd
coat worn during sample preparation. Laboratory Facility in Milton Keynes. Individual fibres were
manually removed and transferred to the surface of FTIR reflective
slides (Kevley Technologies, Ohio) (which provide a suitable
Fibre and fragment identification background for reflectance) or transferred to a Specac DC3
Under laminar flow amphipods were individually dissected to Diamond Cell and compressed for transmission measurements
remove the hindgut; defined as the body cavity posterior to Coxa (with background scans being taken through the diamond
4. The hindgut weight was recorded before samples were adjacent to the sample). The fibres presented in the results were
digested, following [54] , with 10% potassium hydroxide (KOH) analysed by transmission as this provided the most reliable results.
incubated over a 48h period at 40°C within a grade C fume vent. The fibre was observed using the wide field camera to identify
The volume of KOH used was at least three times greater than possible locations for further investigation and the measurements
individual gut weight [35] . KOH has been shown to be a suitable were made in transmittance or reflectance mode (50 scans over
solution to dissolve the guts of marine fauna, leaving the majority approx. 20 s) using the Wide-Band MCT (mercury cadmium
of microplastics unaffected [56] . telluride) detector. For each fibre, three points were scanned and
After digestion samples were left to cool before being filtered the results were compared to those in the Shimadzu materials
through Whatman No. 541 filter paper. Filters were then library for matches or closest similarity. Some of the fibres which
transferred onto a petri dish for stereomicroscopic analysis (Nikon showed unusual structure were scanned in several places to reveal
ocular 40x, Intralux 4000-1). The observed microparticles (those more about their chemical composition.
particles which had not been digested) abundance was recorded
and categorised by colour and shape (e.g. Fig. 3) [57, 58] . The Results
samples were then wrapped in muffled tin foil and transferred to
a photolab where representative digital images were taken Microparticles of man-made synthetic or semi-synthetic fibres and
(Cannon EOS 1300D DSLR) to provide visual information on colour fragments were found in the hindgut of amphipods at all nine sites
and differences in shape across the nine sites. (Fig. 4a). The percentage frequency of ingestion varied between
50-100% of amphipods from a given site; the lowest being the New
Hebrides Trench (50%) and the highest the Mariana Trench (100%).
Of the 90 individual amphipods examined, 65 individuals (~72%)
contained at least one microfiber or fragment. The mean and
standard error (SE) of the number of items ingested per individual of
all amphipods sampled in all trenches was 1.34 ± 1.1 (range: 1 to 8
items per individual). The New Hebrides Trench amphipods
contained the lowest mean number of microparticles (0.9 ± 0.4) and
the Marina Trench had the highest (3.3 ± 0.7) (Fig. 4b). There was
no relationship between the number of microparticles and depth in
the Kermadec Trench amphipods (Kruskal Wallis χ = 0.23, df = 3, p
2
= 0.97).
A total of 122 ingested microparticles were identified and were
categorised into fibres and fragments (Fig. 4c). Fibres were found
within every trench and appeared in 84% of amphipods whereas
the occurrence of fragments was lower and appeared in only 16%
of amphipods. No fragments were found in the New Hebrides
Trench amphipods.
Using a crude colour-based categorisation the most prevalent items
ingested were blue fibres (66%) with all amphipods sampled from
the Marina Trench containing at least one of these. The next most
prevalent items ingested were blue fragments (16%) followed by
black fibres (13%), red fibres (4%), pink fragments (<1%) and
purple fibres (<1%). However, the FTIR analysis revealed that these
fibre and fragment groupings did not correspond to a single
material type but rather a variety of materials (Table 2). Six of the 15
items analysed using FTIR were semi-synthetic cellulosic fibres, rayon
and lyocell, the natural fibre ramie that are used in products such as
textiles. The rest included synthetic polymers such as Nylon,
polyethylene (PE), polyamide (PA), or unidentified polyvinyls closely
resembling polyvinyl alcohol (PVAL) or polyvinylchloride (PVC) and
with most including an inorganic filler material. One fibre found in
the Peru-Chile Trench at 7050m was clearly a polyethylene coated
strand of polyester. None of the 15 subsamples were found to be
naturally occurring.

Fig. 3 A selection of microfibre examples found within amphipod hindgut
samples from 10,890m in the Mariana Trench.

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