This Subject Update outlines the harm that plastic is causing to the marine environment and to humans.
It is not just the ubiquity of plastic waste that is pushing individuals, communities and governments to take action. It is also the potential harm that plastics can cause both to marine life and humans. This question of the harm caused by plastics is emotive. Images of plastics found in the stomachs of albatross chicks on Midway Island by the photographer Chris Jordan bring home how thoughtlessness is affecting life on our planet. Likewise, the footage of a dead whale calf from Blue Planet II brought the issue of marine plastic pollution into millions of homes.
Plastic can cause harm to marine life and humans in three ways. Physical harm can be caused when animals become entangled in plastics and when animals eat plastic. Chemical harm can occur due to the toxic nature of the chemical additives associated with the manufacturing of plastics. Biological harm can occur as microorganisms such as viruses and bacteria ‘hitch-hike’ on plastic particles, taking them to new environments or speeding their spread.
Some of the reporting of the potential harm caused by plastic can be misleading. It is important to respect the specificity of language used by the science community. ‘Mays’ and ‘coulds’ are used for a reason. There is much we know about the harm caused by plastics and much we do not know or is currently being studied. Over-exaggeration or over-statement of the harm caused by plastic may seem useful in the short-term to bounce people into action, but in the long-term exaggeration can lead to a lack of trust, and compound inertia.
It is also useful to reflect on whether we need to know everything before taking action. The scale of the plastics issue is such that we can choose to take action now. Scientists are finding plastic in every area of the ocean that they are looking, from the Arctic sea ice (Peeken et al., 2018) to the deepest parts of the ocean (Jamieson et al., 2019). The amount of plastic being produced is astonishing, with 8.3 billion tonnes produced since 1950, and more plastic produced in the decade from 2005, than the whole of the 20th century. The projections are that this rate of production will continue to soar to an annual production of 1.8 billion tonnes by 2050.
In addition, the growing body of evidence is such that we can adopt the precautionary principle. This means that until we can show that plastic pollution is causing no harm, we should do as much as possible to limit its potential impact on marine and human health.
Entanglement in plastic kills a range of marine life, including seals, turtles and sharks
Strong evidence observed in marine environment, with entanglement shown to have caused death in 344 marine species. Extent currently measured using computer modelling and accuracy being improved using citizen science reporting and apps. Some media overstatement of the number of deaths caused by entanglement should not detract from the seriousness of the issue.
Eating large pieces of plastic leads to starvation, gut blockage and death
Strong evidence base in the marine environment. Studies have shown a strong correlation between macroplastic ingestion and mortality in seabirds and turtles.
Eating microplastics leads to malnutrition and lacerations
While it is hard to observe ingestion and the impact of microplastics in the marine environment, there is strong evidence from several laboratory studies, e.g. copepods and lugworms, that show adverse impact of plastics on growth, reproduction and lipid stores. These have a predicted knock-on impact on population growth and ecological functions of individual species.
Eating nanoplastics causes cellular damage
While hard to observe in the marine environment, with techniques not yet available to study nanoplastics directly in the open ocean, there is evidence of uptake and damage noted in a laboratory study.
Chemicals involved in plastic production harm marine life
Strong evidence of persistent organic pollutants previously used in plastic production continuing to accumulate, magnify and cause harm in the marine food web. This is backed up by strong evidence from laboratory studies that underline harm caused by toxic chemicals such as PCBs and PBDEs.
Plastics concentrate uptake of toxins by marine life
There is a need to investigate whether toxins concentrated on plastic particles are more harmful than the other ways that these chemicals are transferred to marine life. There is some evidence from laboratory studies demonstrating that this could take place under the right conditions.
Invasive species are more effectively transferred by plastics
There is evidence for the spread of non-native species and harmful algal blooms, but no follow-on research estimating the magnitude of the harm contributed by plastics in these cases. Evidence from experimental work on algal cysts complements environmental observations.
Microorganisms are more effectively transferred by plastics
Good evidence for plastic affecting the prevalence and spread of coral disease, with a need to investigate further, especially in area of aquaculture.