The data presented here, and that of other medical studies
with rodents and humans, indicate that fragments of
microplastic may translocate from the gut cavity to the blood
stream in a wide range of organisms. To establish the extent
to which this occurs in natural populations, and to identify
any adverse effects, it will be necessary to further refine
techniques to quantify small plastic fragments. For example,
current methods to identify plastic debris using Fourier
transform infrared spectroscopy only permit particles of
plasticdownto approximately 20 μminsize to be conclusively
identified (3), but it is entirely feasible that plastic particles
are now present in the environment at the much smaller
nanometer scale.more smaller particles. Further research is required to test
these predictions and to determine the upper and lower size
boundaries for ingestion and translocation of plastic debris
in other organisms. The greater accumulation of smaller
particles suggests that as an item of plastic degrades, the
potential for it to accumulate and translocate within the
tissues of the organism increases. Other physical properties
of plastic particlesmayalso affect ingestion and translocation;
medical studies using humans and rodents indicate that both
the shape and charge of the particles are likely to play an
important role in translocation (42). The composition of
microplastic debris in the marine habitats varies in shape
(e.g., fibers, spheres, irregular fragments) and polymer type
(e.g., polystyrene, polyethylene, polyester), and as an article
of plastic debris degrades it will decrease in size, and
monomercontent and its surface properties will also change.
For example, medical studies with human white blood cells
have shown that the styrene content of polystyrene microspheres
strongly influences their ability to be phagocytised
(43). Further research is therefore needed to investigate the
factors influencing ingestion and translocation of microplastic
in a wider range of organisms.
The ingestion and translocation of polystyrene microspheres
by mussels did not cause any measurable changes
in the oxidative status of hemolymph, the viability and
phagocytic activity of hemocytes, or filter feeding activity