Many marine animals ingest plastics
Globally, marine animals are exposed to plastic particles that are ingested at all levels of the food web; from zooplankton, mussels and worms to fish, birds and marine mammals. Animals ingest plastics by mistaking them for food and eating them or taking them up through their gills.
Experiments have shown that microplastics can also be transported upwards in the food web from one species to another, for example, from mussels to shore crabs. It is likely that microplastics are also transferred between species higher up in the food web. Predatory fish and seals can ingest microplastic particles both via water intake and their prey.
Impaired reproduction and food intake
To date, most experimental studies aimed to establish whether microplastic particles are harmful have been carried out using higher concentrations than those found in the marine environment.
In such experiments, it has been shown that high concentrations of microplastics impair zooplankton survival, food intake, and reproduction. But harmful effects have also been observed in experiments using lower concentrations, that are more similar to concentrations found in the marine environment:
- Oysters’ reproductive ability was severely impaired after ingesting microplastics, and their progeny had poor chances of survival.
- Langoustines exposed to microplastic fibres over eight months lost weight and were in poor nutritional condition.
- Fish accumulated microplastics in the liver, gills and gut, and exhibited toxic effects in the liver.
The zooplankton Daphnia with ingested microplastics.
This gives cause for concern of harmful effects of microplastics on marine organisms. More studies are needed on how different kinds and shapes of microplastics affect different species, and in lower concentrations.
Additionally, there is a lack of knowledge to establish links between the impact and exposure of microplastics at population levels, because a negative impact is often caused by a combination of different environmental factors.
Hazardous substances leach from plastic to animals
Plastic is manufactured by combining many tiny building-blocks, so-called monomers, to form a long chain called a polymer. In many cases, various chemicals and additives such as stabilisers, flame retardants, and softening agents, are added to give the plastic desired properties.
The manufacturing process is never perfect, which means that free monomers and unbound additives can leach from plastic and into the water or air, or directly into the body of animals that ingest the plastic. The substances in the plastic can also leach out during degradation in the environment.
Examples of hazardous substances in microplastics are the endocrine-disruptive additive bisphenol A (BPA) and various phthalates, which are used to soften plastic.
Another example of harmful substances often used in plastics, especially in electronics, is brominated flame retardants, which are toxic, highly persistent, and accumulate in organisms.
Field studies indicate that hazardous substances in plastics can be released and accumulate in marine animals. For example, concentrations of flame retardants in South Atlantic lanternfish increased with increasing concentrations of plastic debris in the water. In the case of albatross chicks, a link has been reported between the amount of plastic debris in their stomachs and their poor state of health.
The endocrine-disruptive substance nonylphenol, an additive in plastics, has also been found in yellowtail kingfish in areas of the Pacific Ocean with the largest concentrations of plastic debris. Nonylphenol does not normally spread far from its source, and its presence in fish in remote areas is a sign that nonylphenol has been transported there with plastics.
Hazardous substances via plastics – a concern?
Microplastics can attract fat-soluble and hazardous substances in the marine environment. The properties of plastics mean that they are able to bind and contain concentrations of environmental pollutants up to a million times higher than that of seawater.
According to the EU list of priority pollutants, 61% of environmental pollutants on and in plastic debris in the oceans are classified as hazardous, because they cause genetic damage and can be carcinogenic or endocrine disruptive.
Research shows that environmental pollutants are generally more easily released from plastics when in the digestive tracts of animals rather than in seawater. This increases the risk of transfer of hazardous substances for animals that ingest plastic.
In addition, pollutants are more easily released from plastics in the stomach of warm-blooded animals, such as birds or mammals, compared with fish and crustaceans. However, other studies indicate that in most marine habitats the contribution of hazardous substances from microplastics is minor compared to what animals take up through their food, water, and sediment.
But these studies could potentially underestimate the risk associated with plastics ingestion by not taking into account that truly tiny microplastic particles can translocate from the digestive system to cells, tissue, and blood, where they remain for a prolonged time. In such cases, animals would be exposed to hazardous substances for a longer time than if the particles only pass through the stomach and intestine.
Further studies are needed to understand the significance of both additives and environmental toxins on and in plastics ingested by marine organisms compared to the uptake of these substances via food, water and sediment.
The concentration determines the impact …
The animals worst affected by microplastics are probably those exposed to the highest concentrations. Exposure depends on where animals live, how they search for food, and how long the plastic remains in their bodies.
A considerable challenge for research is that we do not yet know the quantities of microplastics in the marine environment. Studies measuring concentrations in the marine environment have mainly collected plastic particles ranging in size from a third of a millimetre up to five millimetres and larger.
But there is reason to believe that higher concentrations of microplastics would be found in the marine environment should the particles collected be smaller than those commonly collected today. For example, a study using a filter for catching particles as small as 0.01 millimetres found concentrations of microplastics to be a thousand to a hundred thousand times higher than the concentrations measured using a filter for catching particles no smaller than 0.3 millimetres in size.
We know that global production of plastics is increasing exponentially and that plastics are found today in all corners of the world’s oceans.
… and the concentration is increasing.
At the same time, we know that global production of plastics is increasing exponentially and that plastics are found today in all corners of the world’s oceans. It is estimated that between 4.8 and 12.7 million tons of plastic debris end up in the world’s oceans every year. It is likely that most of these plastics will break down over time into microplastic.