More knowledge of small plastic particles in the marine environment is needed
NEWS | 2015-10-08
It is well documented that microscopically small plastic particles occur in most parts of the marine environment. But what effects do these plastic particles have on plankton and the ecosystems in which they live? EviEM has looked for evidence in the scientific literature.
Small plastic particles occur widely
Large amounts of plastic waste have ended up in the seas as a direct consequence of the use of plastics in society. Estimates have shown that between 4.8 and 12.7 million metric tons of plastic waste was introduced to the marine environment from a total of 192 coastal nations in one single year (2010). Microplastics (often defined as plastic particles smaller than 5 mm) occur both as primary particles (already small when manufactured) and as secondary particles (fragments of larger objects). In recent decades the relative abundance of secondary particles (in relation to primary particles) in the world’s seas has increased. Microplastics have even been detected in the sea sediment at a depth of up to 5,000 metres.
The concentrations measured in sea water depend greatly on the size of particles studied. It can therefore be difficult to compare studies using different means of sampling. In Swedish coastal waters, 150-2,400 particles per cubic metre have been collected in a net with mesh size 0.08mm, up to 100,000 times more than caught with a mesh size of 0.45mm (o.01-0.14 particles per cubic metre). In the Atlantic and the Pacific Ocean the number of microplastic particles (of a size between 0.28-0.505 mm) caught in coastal water or open sea has varied between 0 and 32.8 per cubic metre.
Lack of knowledge of the effects of microplastics
Microplastic particles can have biological effects due to their physical characteristics or due to a release of chemical substances. Marine animals can mistake the particles for food, which can lead to undernourishment or starvation, and the particles can block or in other ways disturb important organs. Chemical substances released from the particles can either be part of the plastic material itself (so called additives) or consist of pre-existing contaminants in the sea that subsequently adhered to the surfaces of the plastic particles.
Both field studies and laboratory studies have confirmed that small organisms may eat or in other ways ingest microplastic particles, and that the plastic particles can spread from lower to higher levels in a trophic chain. Biological effects of microplastics have, however, only been studied in the laboratory, often using particle concentrations considerably higher than those found in the marine environment. It is therefore difficult to judge how representative these studies are. Furthermore, the studies have often made use of round particles or particles with an even surface, but it is possible that angular and/or sharp particles can have greater effects or similar effects at lower concentrations.
EviEM´s Evidence Overviews provide surveys of current environmental issues
An EviEM Evidence Overview gives a general view of the state of knowledge of a certain environmental issue. It is based on a limited literature search and so does not claim to be comprehensive. One of its purposes is to investigate if there is enough material to undertake a systematic review of the topic, and if there is reason to do so.