Publication Date:
2018-11-12
Description:
The global annual production of plastics increased 20-fold in the last five decades, reaching about 335
million tons in 2016. Concomitantly, environmental pollution by plastic litter became a rising issue.
Plastics easily escape from landfills into the surrounding environment and rivers, which discharge huge
quantities of litter into the oceans. Plastic debris spoil the coastlines or accumulate in subtropical
oceanic gyres. Marine plastic litter can have adverse effects on marine vertebrates and invertebrates.
Larger items, such as lost fishing nets are particularly hazardous because many marine species may
become entangled and immobilized. Limited predator avoidance, starvation or drowning may be the
consequences. Plastics are hardly biodegradable but subject to mechanical degradation by wave action
and UV-radiation. Progressive fragmentation of larger plastic items generates smaller fragments,
finally yielding micro- or even nanoparticles. Upon ingestion, smallest plastic fragments may enter
organs and even penetrate into cells where they may cause imbalances of the cells homeostasis.
In the present study, the ingestion of microplastics by marine invertebrates, the possible transfer into
cells of the digestive tract, and the cellular effects in the midgut gland were studied. The Atlantic ditch
shrimp (Palaemon varians) served as model species. It inhabits coastal regions, estuaries, and brackish
water systems, which are strongest exposed to anthropogenic pollution. The shrimps received fluorescent
polystyrene microbeads of 0.1, 2.1, and 9.9 μm in diameter as food. Uptake of the microbeads
into the digestive organs and, particularly, into the midgut gland was analysed by fluorescent
microscopy of cryostat sections of the digestive tract. Activities of antioxidant enzymes were measured
to verify cellular stress responses. Amplification of NADPH-oxidase transcripts served as indicator for
the presence of a cellular defence system capable of generating reactive oxygen species.
The smallest particles penetrated into the midgut gland while the largest particles retained in the
stomach. An increase in the cellular defence mechanism against oxidative stress was verified by the
activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). Formation of reactive
oxygen species (ROS) indicated NADPH oxidase activity, a superoxide (O2-) generating enzyme. The
expression of NADPH oxidase in the midgut gland of P. varians was verified by PCR-amplification.
The midgut gland of P. varians showed an intense cellular reaction after exposure to microplastics. The
rapid increase of the anti-oxidative enzymes, particularly SOD, indicates a significant liberation of
reactive oxygen species, presumably as an immune reaction of the NADPH-oxidase system. Oxidative
stress, in turn, can have adverse effects on various cell structures and cell functions by affecting membranes, proteins, or DNA. Finally, it causes a toxicological impact on organs and the whole organisms.
Future studies should address the direct effects of increased oxidative stress in terms of toxicity, i.e.
by the occurrence of lipid peroxidation. Also the destination of particles inside the organisms, may help
identify corresponding mechanisms that lead to oxidative stress and contribute to the big picture of
microplastics in the environment.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Thesis
,
notRev
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