The contents of all upper GITs and
separately a subsample of 20 intestines (10 from fledglings and 10
from older birds) were transferred into glass beakers and a 10% solution
of potassium hydroxide (KOH) was added to digest soft organic tissue.39 (link),40 (link) KOH was chosen for its efficiency to digest organic matter while
preserving the mass, morphology, and the chemical integrity of many
plastic polymers, even when heated up to 40 °C and shaken to
200 or 300 rpm, as evidenced by several studies.41 (link)−43 (link) In this study,
the beakers were kept on a low-profile shaker (IKA HS 501 digital,
Staufen, Germany) at 100 rpm for at least 2 days (max 3 days) to enhance
the digestion process, at room temperature. Thereafter, the mixtures
of KOH solution and GIT content were filtered through a stainless-steel
sieve (mesh size: 20 μm) and then vacuum-filtered through a
filtering membrane (cellulose acetate filter, pore size 5 μm,
Sartorius Stedim Biotech, Göttingen). The extracted particles
were visually sorted, and only the plastic-like particles were further
analyzed by spectroscopy. Particles from natural origin, e.g., squid
beaks, exoskeleton of crustaceans, and other prey items that remained
after KOH digestion as well as stones, etc., were not analyzed by
FTIR spectroscopy, but thoroughly checked for hidden plastic particles.
Filter papers were kept and can be used in future microplastic studies.
separately a subsample of 20 intestines (10 from fledglings and 10
from older birds) were transferred into glass beakers and a 10% solution
of potassium hydroxide (KOH) was added to digest soft organic tissue.39 (link),40 (link) KOH was chosen for its efficiency to digest organic matter while
preserving the mass, morphology, and the chemical integrity of many
plastic polymers, even when heated up to 40 °C and shaken to
200 or 300 rpm, as evidenced by several studies.41 (link)−43 (link) In this study,
the beakers were kept on a low-profile shaker (IKA HS 501 digital,
Staufen, Germany) at 100 rpm for at least 2 days (max 3 days) to enhance
the digestion process, at room temperature. Thereafter, the mixtures
of KOH solution and GIT content were filtered through a stainless-steel
sieve (mesh size: 20 μm) and then vacuum-filtered through a
filtering membrane (cellulose acetate filter, pore size 5 μm,
Sartorius Stedim Biotech, Göttingen). The extracted particles
were visually sorted, and only the plastic-like particles were further
analyzed by spectroscopy. Particles from natural origin, e.g., squid
beaks, exoskeleton of crustaceans, and other prey items that remained
after KOH digestion as well as stones, etc., were not analyzed by
FTIR spectroscopy, but thoroughly checked for hidden plastic particles.
Filter papers were kept and can be used in future microplastic studies.
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