Page 9 - Shimadzu Journal vol.7 Issue1
P. 9

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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