Wright S.L, Thompson R.C, Galloway T.S (2013). “The physical impacts of microplastics on marine organisms: A review”, Environmental Pollution. 178: 483-492.
This paper is a collective review and analysis of peer-reviewed journals, focusing on the detailed examination of microplastics and their transmission through the marine ecosystem via biological, ecological, physical transfers. This includes the primary ingestion of macro/micro plastics and the trophic level transference due to predation of contaminated organisms. It includes a methodical examination using multiple references from different scientific bodies that expands and correlates the data allowing a more global overview. A simplified diagram (Fig.1) is included to amalgamate the potential pathways for microplastics transmission described in the text and visualise the tabulated data. However, the table lacks consistency in the units which makes comparisons difficult as the concentration values differ, if the writers converted the information into the same format it would be clearer for analysis.
The review’s section 2 focuses on the factors that affect the bioavailability of microplastics including: size, density, abundance, and colour. Primarily, it suggests that due to the small size of the particles, accidental or mistaken consumption occurs in different trophic levels; from plankton to large filter feeder cetaceans directly or indirectly (by means of polluted plankton) eating microplastics. The density of plastic particles also affects the location of the particulates in the water column causing a variation in what plastic material is ingested at different depths. Hence, those living in the euphotic layer will be polluted with different materials than organisms at deeper depths because there is a different in buoyancy due to the kgm-3. The abundance and colour of microplastics also affects the probability of ingestion as evidence from experiments suggests that organisms will ingest polymers of similar colours to their prey, and those that are fully opaque over those that are translucent indicating predator selectivity.
Section 3 expands on the biological interactions in the food web and the effect of weather/seasonal movements in the ocean. Due to the seasonal movement of particulates when there is a degradation in the pycnocline divides, microplastics can enter the benthic system allowing a transfer of pollution into deeper depths. This indicates that suspension feeders and detritivores, as well as epibenthic and endobenthic dwellers, will incorporate the microplastics into the substratum increasing the concentration in the lower depths of the water column.
The final Section details how microplastics physical impact the ecosystem and organisms in the food-web, lots of data has been collected on the affects on marine vertebrates as noticeable effects can be seen: blockages in digestive tracts, abrasions, and poisoning, all resulting in the starvation and deterioration of the individual. Furthermore, ingestion, directly or indirectly, can affect the reproductive cycle and reproductive success of species due to the absorption of toxins from the breakdown of polymers to monomers. This can affect the enzymes, muscles, and cell membranes of organisms, which increases in higher trophic levels due the accumulative effect of the food pyramid.
To conclude, this paper address key issues that are affecting the health of our ecosystem in a clear and decisive manner, allowing the reader to follow the content without confusion. The language used is accessible and the tables format is clear, bar the lack of unit consistency, while the diagram integrates all given data to allow visualisation for the reader.
Benthic – sediment layer at the bottom of the water column.
Bioturbation – disturbance of sedimentary deposits by organisms e.g the reworking and mixture of the sediments layers on the benthos.
Defouling – unaccumulation of microorganisms, plants, algae, or animals on wetted surfaces, becoming separated and disassociated.
Detritivores – feeds on detritus (dead matter from organic material).
Euphotic layer – layer of the ocean where light reaches, and photosynthesis can occur.
Flocculation – molecules come out of suspension and clump together to form small clustered masses.
Macroplastics – larger molecules of polymers that break up to form microplastics or are ingested by vertebrates.
(Primary) microplastics – manufactured to be microscopic e.g. microbeads in beauty products made of polyethylene.
(Secondary) microplastics – fragmented microplastic polymers that break up due to degradation from UV, chemical reactions or catalysis.
Pycnocline – oceanic layer stratification influenced by density (which is caused by temperature and salinity).