Publication: Environmental Pollution (Journal
of environmental science)
Title: Trophic transfer of microplastics from mysids to fish greatly exceeds direct ingestion from the water column
HASEGAWA Takaaki (Graduate School of
Environmental Science, Hokkaido University)
NAKAOKA Masahiro (Field Science Center for
Northern Biosphere, Hokkaido University)
Available online 9 January 2021
・Discovered that carnivorous fish take in
large amounts of microplastics from their prey.
・Microplastics that accumulate in fish are smaller due
to those subdivided by prey species.
・Pointed out that microplastics can have a
serious impact on marine ecosystems through the food chain.
HASEGAWA Takaaki, a master course student
at the Graduate School of Environmental Science, Hokkaido University, and NAKAOKA
Masahiro, a professor at the Field Science Center for Northern Biosphere, same
university, have revealed that the amount of microplastics taken up by fish
from seawater is much higher through prey organisms than through direct intake
from the water.
As marine pollution from plastic debris
continues to increase worldwide, there is particular concern about the impact
of microplastics on marine organisms. Fish take up microplastics not only
directly from seawater but also indirectly by feeding on prey, but the relative
importance of the two pathways has been unclear. In this study, we examined the
importance of the prey-mediated pathway in the uptake of microplastics by fish
using the carnivorous fish, Myoxocephalus brandti, and its prey, the
mysids, Neomysis spp.
The results showed that the amount of
microplastics ingested by M. brandti through the feeding of
microplastic-containing mysids was 3 to 11 times greater than that ingested
directly from the water. In addition, microplastics taken up by the fish via
prey were smaller in size than those taken up directly, because microplastics
are broken down into smaller particles during the process of mysid uptake. It
has been pointed out that microplastics can migrate into body tissues and cause
adverse effects. Plastics also contain toxic chemicals, which may also affect
higher consumers by concentrating through the food chain. Further research on
these effects is expected.
The result of this study was published in journalEnvironmental Pollution released on 9 January 2021.
Microplastic (MPs) uptake experiment design
(left) and experimental results. The fish took up a larger number of
microplastics via their prey, the mysids.
Marine pollution by plastic litter is
increasing around the world, and it is predicted that by 2050 the amount of
plastic litter in the world's oceans will be greater than that of fish. In
particular, it has been reported that "microplastics" with a particle
size of 5 mm or smaller are taken up by all living organisms, and there is
concern about their impact on ecosystems. Marine animals are known to take up
microplastics not only directly from seawater, but also by feeding on small
prey that carry microplastics in their bodies, but no studies have examined the
relative importance of these two pathways. Some marine organisms, such as
crustaceans, also break down microplastics through feeding and digestion, so
microplastics taken up through prey are expected to be even smaller than those
taken up directly from the water.
In this study, we used the carnivorous fish
Myoxocephalus brandti and its prey, the small crustacean mysids Neomysis
spp. to examine (1) the importance of the indirect pathway via prey in fish
ingestion of microplastics and (2) variation of microplastic particle size by
indirect pathway (Fig. 1).
Fig. 1 A fish M. brandti (left) and
mysid (right) used in the experiment. The body lengths of the fish and mysid
are about 8 cm and 1 cm, respectively.
Breeding experiments were conducted at the
Akkeshi Coastal Research Station of the Field Science Center for Northern
Biosphere, Hokkaido University, using mysids and shimofuri sculpin (hereafter
referred to as “sculpin”) collected from Lake Akkeshi in eastern Hokkaido.
Fluorescent polyethylene particles with a particle diameter of 30 μm were used
as microplastics. Direct ingestion of microplastics from the water was examined
by rearing sculpin in tanks containing two different concentrations (200 and
2000 μg/L) of microplastics in seawater (water group). On the other hand,
uptake of microplastics through indirect pathways via prey was investigated by
feeding mysids (Fig. 2) exposed to microplastics at the same concentration
conditions to sculpin in tanks without microplastics (mysid group). The amount
and particle size of microplastics accumulated in the digestive tract of
sculpin in each group were quantified and compared among treatment groups.
Fig. 2 Mysid with microplastics
(fluorescent beads) incorporated. The portion of the stomach where the
fluorescent beads were incorporated is indicated by a white circle.
Sculpin in the mysid group took in 8 to 11
times more microplastics by number and 3 to 5 times more by mass than those in
the water group. The microplastics were finely granulated during the process of
uptake by mysids, and as a result, the microplastics taken up by sculpins in
the mysid group were smaller in particle size than those in the water group.
This indicates that the indirect pathway via prey organisms is more important
than the direct pathway from the water for the uptake of microplastics by fish.
Expectations for the future
This research has revealed that
microplastics are transferred through the food chain to animals at higher
levels in the marine ecosystem. Microplastics not only have a negative effect
on animal feeding and digestion activities, but also, when finer particles are
produced, they migrate from the digestive tract to the body tissues and have
adverse effects. It has also been suggested that plastics contain a variety of
toxic chemicals*1 that may also affect higher consumers by concentrating
through the food chain. We are currently conducting an experiment to
investigate the accumulation of various chemical substances in body of sculpins
by feeding mysid that contain microplastics containing toxic chemicals to
sculpins. Through this experiment, we hope to clarify the overall picture of
the impact of microplastics on marine ecosystems through the food chain.
*1 Toxic chemicals: Plastic, a petroleum
product, adsorbs POPs (persistent organic pollutants) such as PCBs and PAHs due
to its chemical affinity, and also contains various chemical additives such as
brominated flame retardants and UV absorbers. In animals, including humans,
these chemical substances are known to cause various adverse effects when they
accumulate in high concentrations in the body.