How ocean plastic pollution is finding its way back to our dinner tables

With awareness growing of the amount of plastic littering our seas, Libby Peake investigates what happens when the material enters the food web, eventually finding its way to our dinner tables. 

Plastic soup

Earlier this year, 13 adolescent male sperm whales – the largest toothed predators on the planet, which can weigh up to 57,000 kilogrammes (kg) and normally live about 70 years – beached themselves on Germany’s North Sea shore. Five more, thought to be from the same pod, also washed up on the Lincolnshire and Norfolk coastline. All of the animals were found to contain pieces of plastic in their stomach and intestines, including a 70-centimetre engine cover, a 13-metre fishing net and the remains of a plastic bucket. While researchers say that the plastic was unlikely to have caused the whales to beach themselves, the findings are undoubtedly disturbing, and just one of several incidents that have been drawing attention to the problem of plastics in the ocean in recent months.

Indeed, in January of this year – around the time that the sperm whales were washing up on our shores – the Ellen MacArthur Foundation, in partnership with the World Economic Forum, released a report that claimed that there would be more plastic in the ocean than fish by 2050 if we do not change the way we produce, consume and manage plastic (the methodology for this claim, however, was called into question as, to reach the estimate, it extrapolated data from just one area – San Francisco Bay). In any case, according to the report, ‘The New Plastics Economy’, at least eight million tonnes of plastics leak into the ocean every year, equivalent ‘to dumping the contents of one garbage truck into the ocean every minute’. The cumulative impact of this leakage means that there are already more than 150 million tonnes of plastics in the ocean today.

This research follows on from an equally disturbing report produced last year by the Commonwealth Scientific and Industrial Research Organisation in Australia, Imperial College London and the University of New South Wales, the devastating conclusion of which is evident in the title: ‘Threat of plastic pollution to seabirds is global, pervasive and increasing’. According to the report, an estimated 90 per cent of seabirds (compared to less than five per cent in 1960) have ingested plastic, often mistaking it for fish or fish eggs. And, unlike with the sperm whales, plastic can be directly linked to seabird mortality in many cases. When birds ingest plastic, it can cause fatal gut blockages, and there are plenty of distressing images of juvenile albatrosses, for instance, that have died with stomachs full of plastic that they were fed by their parents (adult albatrosses can regurgitate plastics, while the young cannot). It is likely that things like bottle tops and potentially sharp shards of hard plastic injure or kill the birds by puncturing their stomachs or making them feel full when they are, in fact, starving.

But it’s not just birds and whales that are affected and, increasingly, it’s not only the large bits of ingested or entangling plastic that are causing worry – scientists are starting to look at the impacts of microplastics (and the chemicals that adhere to them, more of which in a moment). Microplastics are less than five millimetres in diameter and can either enter the water as microbeads – tiny particles of plastic that slip through wastewater treatment systems, but are still added to cosmetic products like face and body wash and toothpaste (though countries are increasingly banning them and companies are increasingly phasing them out) – or that break away from larger bits of debris. Plastic, as is well documented, doesn’t biodegrade for hundreds of years at least, but it does photodegrade, meaning that as it’s exposed to the sun’s UV rays (helped along by waves and currents), it breaks down into ever-smaller pieces. These tiny pieces, along with the plastics that enter the water as microbeads, can then be ingested by creatures throughout the food web.

The majority of plastic in the marine environment, in fact, isn’t only small, it’s microscopic, meaning that it’s less than one millimetre in diameter, with plenty of evidence that it will further break down to become ‘nanoplastic’, 1,000 times smaller than an algal cell. These tiny plastics can be absorbed by organisms from plankton on up, and there are concerns that such material could be absorbed in animal tissue, bioaccumulating as it moves up the food chain. It’s early days in terms of research, but the initial picture is looking ominous.

Speaking to the BBC ahead of the introduction of the single-use plastic bag tax in England, Tamara Galloway, Professor of Ecotoxicology at Exeter University, said: “The estimate has been that [people eating an average amount of seafood] might consume 11,000 tiny pieces of plastic over the course of a year. And obviously the challenge for us is to work out: does that cause any harm? Is it unpleasant? Is it something that we don’t particularly want to do? But is it causing us significant harm compared to other sorts of chemicals? We don’t know that yet.” 

What Galloway does know, based on a series of experiments with different marine species, is that different organisms – zooplankton, lugworms, and mussels (as well as plenty of others) – can all ingest the small plastic particles that are becoming ever more numerous in the ocean environment. Delivering an address in 2015 to the Association for the Sciences of Limnology and Oceanography (ASLO), Galloway said that particles can also transfer from one species to another higher up the marine food web, as was shown in an experiment conducted with filter-feeding mussels and an omnivorous scavenger, the common shore crab.

Galloway explains: “The next experiment we conducted sought to determine if the trophic transfer of plastic could be occurring – could they pass from organisms lower down the food web into others? And the organism we decided to study was... the common shore crab. This is an omnivorous scavenger on the floor of the ocean, and it frequently feeds on mussels. So, what we did was we allowed mussels to ingest plastic from the water, and then we used those mussels and fed them to crabs. And then we traced what happened to the plastic particles that the crabs had ingested along with their mussels. And... up to 14 days later, the tissues of the crabs still contained large numbers of microplastic particles... [Plastic particles] were present in the faecal pellets, they were being expelled actively from the body. And then what we then did was we traced back through the body of the crab using bioimaging techniques to determine where they might still be located.” This bioimaging, of the sort used in medical research, showed that the bits of polystyrene were wedged in the crab’s guts and “stuck all over the surface of the gills”, “14 days after an initial feed of plastic particles to another organism”. 

Galloway concludes: “This proves that microplastic particles are present in the ocean and that they are bioavailable to different marine organisms. But it doesn’t necessarily tell us what harm those plastics might be doing”, which is a key question researchers are starting to investigate. For her part, Galloway has shown that the presence of PVC in sediment where lugworms feed significantly reduces their feeding activities, even at concentrations as low as five per cent. Indeed, that experiment showed that lugworms, which are “a key prey animal for wading birds and fish”, grown in sediment spiked with PVC of a similar size to sediment particles reduced feeding to such an extent that the lugworms had 40 per cent lower energy reserves after four weeks of exposure.

And while the idea that plastics could potentially be decreasing the number of calories available down at the bottom of the food web is certainly cause for concern, a potentially more significant problem isn’t the effect of the plastic itself. Instead, it’s the persistent organic pollutants that are also present in the ocean and that, because they are hydrophobic, attach themselves to the surface of plastic. Such chemicals include compounds like DDT and polycylic aromatic hydrocarbons (PAHs), which are both carcinogenic and endocrine disruptors, meaning they can disrupt the body’s hormonal system, potentially resulting in cancerous tumours, birth defects, or other developmental disorders.

Our cover artist Bonnie Monteleone explains how such substances enter the marine environment: “Anything that winds up in the air is going to wind up potentially in the water, and through runoff it ends up in our oceans, so that’s one way that fertilisers that we spray on crops winds up there. And PAHs are caused from the combustion engines. So, when we use fuels, we are creating this chemical compound, and then that chemical compound ends up in the atmosphere and then eventually ends up in the ocean... These are manmade chemicals that are just like the plastics – there’s nothing in nature that can actually break them down over a very long period of time.”

Moreover, evidence is mounting that these chemicals can transfer from the plastic to the animals rather than passing through them and back out to the ocean. Monteleone explains some research she’s involved with at the University of North Carolina Wilmington (UNCW): “We looked at these particular chemicals that attach themselves to the plastic, and then we were able to prove that those chemicals will leach off or remove from the plastics and into the gastrointestinal fluids of sea turtles. So, we now know that it’s not that those chemicals stay on the plastics and they can just be defecated – those chemicals will transfer into the blood stream. So, again, this is very preliminary... but the evidence is pointing to the fact that, most probably, those chemicals are getting into our blood through the foods that we eat, especially fish.”

Researchers at the University of California, Davis, and San Diego State University, meanwhile, have measured the bioaccumulation of chemicals and adverse health effects from plastic ingestion in fish. In a paper published in Scientific Reports, ‘Ingested plastic transfers hazardous chemicals to fish and induces hepatic stress’, they describe an experiment in which they exposed Japanese madaka, a widely used model fish, to three different diets: a negative control, a virgin-plastic diet (containing 10 per cent virgin LDPE pre-production plastic) and a marine-plastic diet (containing 10 per cent LDPE that had been deployed in an urban bay, where it had accumulated chemicals like PAHs, PCBs (polychlorinated biphenyls) and PBDEs (polybrominated diphenyls, a flame-retardant added to plastics)). The paper concludes ‘that fish, exposed to a mixture of polyethylene with chemical pollutants sorbed from the marine environment, bioaccumulate these chemical pollutants and suffer liver toxicity and pathology’, adding: ‘Fish fed virgin polyethylene fragments also show signs of stress, although less severe than fish fed marine polyethylene fragments.’

Researchers at the University of California, Davis (and elsewhere, no doubt) are also now conducting much-needed research to determine what happens as bioaccumulated plastic and associated toxins move up the marine food web (with concentrations potentially being magnified in the process), but Monteleone, for one, isn’t taking any chances and has stopped eating fish, telling me: “We should definitely probably minimise the amount of fish that we’re eating – absolutely”.

In the meantime, as awareness of the problem grows, there are plenty of organisations that are coming up with ideas to stem the tide of plastics reaching the ocean. While quick to point out (and perhaps overstate) the benefits that plastics offer society, plastic manufacturers are increasingly at least acknowledging the urgent need to find solutions to the problem. More than 60 companies in 34 countries have signed up to the ‘Declaration of the Global Plastics Associations for Solutions on Marine Litter’, which commits them to a number of rather vague promises, including: working in public-private partnerships to prevent marine debris; working with the scientific community to understand the origins, impacts, and solutions to marine litter; promoting enforcement of existing laws to prevent marine litter and spread knowledge about efficient waste management systems; enhancing opportunities to recover plastic for recycling and energy recovery; and stewarding the distribution of pellets and products to customers to prevent product loss. As of the last progress report (2014), the plastic industry claims more than 185 marine litter projects have been planned, or are underway or completed around the globe, from beach clean-ups to educational campaigns and research into the extent and impacts caused by marine debris.

The clamour to address the problem will only become louder as awareness grows, and to that end, some high-profile educational campaigns have attempted to capture the public’s imagination and demand solutions, from David de Rothschild’s expedition on the Plastiki, a catamaran made from 12,500 reclaimed plastic bottles that crossed the Pacific in 2010, to efforts by dedicated groups including 5 Gyres and Project Kaisei. Another recent effort at education comes in the form of a feature-length documentary, A Plastic Ocean, currently seeking distribution, in which ‘an international team of adventurers, researchers, and world-saving heroes’ seeks to bring ‘to light the consequences of our global disposable lifestyle’ and ‘document the global effects of plastic pollution – and introduce workable technology and policy solutions that can, if implemented in time, change things for the better’.

Many scientists contend that we can’t really do much about the plastic already in the ocean, and should focus on prevention, but the Ocean Cleanup, a foundation founded by 21-year-old Dutch student Boyan Slat (see Resource 78), is attempting to capture some of the plastics already polluting our waters. This summer, the foundation intends to launch a trial 100 metre-long barrier designed to trap plastic bags, bottles and other litter in the North Sea, 23 kilometres off the coast of the Netherlands. The launch represents an initial test, which will be followed by the launch of a 2,000 metre-long capture system off the coast of Tsushima Island in Japan early next year, and, if all goes to plan, by a 62-mile-long V-shaped barrier array in the North Pacific Gyre (home to the so-called Great Pacific Garbage Patch) in 2020. Feasibility studies indicate that the floating dam – which works by using the ocean currents to push plastic towards a network of floating booms with impermeable ‘skirts’ that concentrate debris to a central point – could passively ensnare up to 80 per cent of plastics that encounter it. 

Even if it works, though, this barrier cannot capture microplastics, let alone nanoplastics that are becoming ever more ubiquitous in the water. If there’s ever going to be a solution to that, it will have to be of a completely different sort. The bioplastics industry has highlighted that bioplastics, while certainly not offering ‘a license to litter’, could potentially help mitigate the problem of ‘unavoidable’ marine litter in future, although this will require more testing and standardisation to ensure that such material biodegrades in marine conditions (as opposed to just in industrial composting conditions), as well as testing to determine if the biodegradation of bioplastic in the sea results in any ecotoxicological effects. Already, however, Italian bioplastic producer Novamont has conducted laboratory research into its third-generation Mater-Bi bioplastic, which determined that, while products made from the material will not disappear immediately if they reach the sea, fragments that end up in the coastal area between the beach and the sea bed will degrade by 90 per cent in less than a year. The resulting report, ‘Marine Biodegradation of Third Generation Mater-Bi’, suggests ‘these materials can be suitable to manufacture plastic items with a high risk of dispersion in the sea (such as fishing equipment)’.

This article was taken from Issue 84

And as for the plastic already in the sea, slight hope, at least, might be found in recently-released research from scientists at the Kyoto Institute of Technology and Keio University in Japan. ‘A bacterium that degrades and assimilates poly(ethylene terephthalate)’, published in the journal Science in March, documents the discovery of a species of bacteria, Ideonella sakaiensis 201-F6, which is able to use PET as its main energy and carbon source, in samples of sediment, soil and wastewater collected near a plastic bottle recycling plant. While this particular bacterium is not suitable for use in the ocean, some scientists, including Professor of Microbiology at Swinburne University Enzo Palombo, have suggested that the quick evolution of land-based microbes to digest plastics could be matched by marine counterparts. Speaking to the Guardian, Palombo said: “I would not be surprised if samples of ocean plastics contained microbes that are happily growing on this material and could be isolated in the same manner.”

Before getting too excited about the prospect of mitigating ocean plastic with such bacteria, though, know that, as well as discovering the bacterium, the researchers also determined that it would take six weeks to break down a thin film of PET, and only if the temperature remained at a stable 30 degrees Celsius. Others in the scientific community have also warned that plastic could be less toxic in its whole, unhydrolysed form, as breaking it down could release toxic additives into the ocean.

One thing’s for certain, though, if such bacteria are found to exist in the ocean, they’ll have a gargantuan task in trying to get through the 150 million tonnes of plastic already in our seas. Let’s not add to their meal. 


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