Marine Plastics: A Global Threat

Coastal Protection Core Journal, Coastal Protection Core, Scarborough, Queensland, Australia
Hailed as the wonder material of the 20th century, plastics have become an ever-present and indispensable part of our lives. Unfortunately, their resilience and universality have also made them a major threat to marine ecosystems, impacting hundreds of species and millions of animals all over the world. Entanglement and ingestion of plastic debris cause horrific injuries to animals, often resulting in permanent disfigurement or death. Despite current clean-up efforts, far more needs to be done to help minimize this impact.


Marine plastics shaping up to be one of the widest ranging and most insidious environmental threats of the future. Their convenience, resilience and chemistry are the key drivers of this threat and the further we investigate this issue, the more severe it becomes. But before we delve to deeply into the ramifications of marine plastic pollution, its worth reviewing what we’re actually up against.


The first synthetic polymer was created in 1869 by John Wesley Hyatt in an effort to replace the ivory needed for, oddly enough, billiard balls. In 1907 Leo Baekeland created the first truly synthetic plastic (Bakelite) and had it marketed very successfully as ‘the material of a thousand uses. Chemical companies began rapidly developing new forms of plastic, but it wasn’t until WW2 that things really took off. Nylon was invented to replace the silk used in parachutes, plexiglass replaced actual glass and plastic production increased un the US alone by 300%. The post war consumer boom of the 1950s was the first time plastics became truly universal, appearing in homes and businesses all over the world as never before (CHF 2017).

In the 1960s an awareness of our impact on the environment led to the realisation that plastic may not be our greatest achievement. Plastic pollution was beginning to make itself known around the world, primarily through marine debris. This concern grew during the 1970s and 80s as rubbish dumps began to fill rapidly and litter became more prominent.

The issue of course is that for the first time, humans had developed a product with no natural form of recycling. Whereas metals oxidise, timber and plant fibres rot and glass and pottery can be crushed into inert sand, plastic remains chemically unchanged. This resilience leads to plastic persisting in the environment, accumulating wherever humans or natural forces direct it.

Types and Sources
In terms of their chemistry, plastics are all based on long polymer chains. Simple versions of these exist naturally (e.g. cellulose) but over 90% of all plastics are derived from fossil fuels, and account for about 6% of global oil use (Australian Government, 2016). There are many variations on the basic polymer building block making plastics difficult to categorize chemically. The 7 SPI resin codes listed on many hard plastics are a recycling code (hence the number being contained in a recycling symbol) and do not define every type of plastic.

The uses of plastics are almost innumerable, though some broad categories do stand out and highlight why plastic has become such an issue. 26% of all plastic is used in packaging- material designed for immediate disposal. In 2013, this share of the market equated to 78 million tonnes and a value of US$260 billion. From this point, packaging manufacturing was projected to double in the following 15 years and reach an estimated 318 million tonnes by 2050.

In a waste context however, plastic is not typically defined by its use, but either by its origin of entry into the environment or its size. Using these approaches, it becomes marginally easier to identify focus points to prevent plastic from entering the environment, and strategies for cleaning up, respectively.

Point of origin analyses are challenging given the universality of plastic, particularly with consumer products. Once in the environment, clues such as labels and markings gradually wear off, making sources harder to identify the longer the plastic has been adrift. Its also a method that only works on floating plastics, or those caught in strong enough currents to bring them to shore. Shoreline studies have consistently shown however that areas near urban centers have consistently higher levels of debris, particularly ‘new’ material, and that around 80% of all marine plastic has a land based origin (Australian Government, 2016).

Studies of the size of the individual pieces of plastic are more focused on tracking the dynamics and spread of plastic debris once it is in the oceans. These are the studies that give us estimates of the sheer scale of the debris problem, and the specific issues it may be causing in the environment. Scales vary between studies, but in general there are 2 main sizes of plastics; macroplastics (>5mm) and microplastics (<5mm). Given the variability within these categories the remainder of this review will focus on macroplastics, while microplastics will be covered in a following article.

Most plastic pieces begin as macroplastics and, as the most obvious pieces of litter are the pieces focused on primarily by research and clean up initiatives. This category includes a wide variety of commercial, industrial and consumer products, from bottle tops to pallet wrap and lost fishing gear (both commercial and recreational). The World Economic Forum (2016) described the problem graphically as follows;

“Each year, at least 8 million tonnes of plastics leak into the ocean—which is equivalent to dumping the contents of one garbage truck into the ocean every minute. If no action is taken, this is expected to increase to two per minute by 2030 and four per minute by 2050.”

Data collected by both Clean Up Australia and the Tangaroa Blue Foundation from cleanups indicates that about 40% of waste collected in Australian cleanups can be attributed to beverage rubbish, even outstripping cigarette butts in terms of items collected (Australian Government, 2016). Data from the Georges River Combined Councils Committee (NSW) indicated that between 25000 and 50000 plastic bottles were removed from the Georges river annually. Could this be indicative of every urbanized river?

Lost fishing gear too contributes both a high volume and a high impact debris load to our oceans too. Commercial nets and longlines no longer under the control of fishermen continue ‘ghost fishing’, causing damage over a large area. Some of the highest collection figures for ghost fishing gear recovery come from the Gulf of Carpentaria, where nets have been recorded at up to 3 tonnes per kilometre. Recreational fishing too contributes kilometres of nylon and braid fishing line, hard and soft plastic lures, floats and bait bags, much of it accidentally when lines become snagged and snap off. This anchored debris may not be able to travel long distances, but it does present a high density, persistent threat to wildlife in the areas it accumulates.

Once in the ocean, depending on their density, plastics either sink to the bottom or float on the surface and depending on the local hydraulics, can be carried a considerable distance. Either route means plastics are gradually broken into physically smaller pieces due to abrasion against rocks and sand and/or solar radiation. Unlike natural products like glass or metal however, this breakdown only occurs in a physical sense; the polymers that make up the plastic are very resistant to chemical change, especially in an environment as stable as the ocean. It is during this process that they pose the greatest risk to marine life, by either entanglement or ingestion.


Arguably the most visually shocking impact of marine plastic on wildlife, entanglement is known to impact at least 143 species of animals around the world. Typically large, mobile animals such as fish, sharks, seabirds, dugongs turtles, crocodiles (Fig. 1), dolphins, whales are the most affected, but even smaller animals like crabs have been shown to suffer from entanglement. These animals often suffer horrific injuries including amputations and infections, as well as a significantly increased risk of drowning, starvation, smothering and increased predation. Discarded fishing gear is notorious for causing these kinds of impacts; from 9000 analysed ghost nets in the Gulf of Carpentaria, it was estimated that 15000 turtles had been entangled, though this figure may be much higher. The Australian Seabird Rescue noted that on the east coast of Australia, 20% of pelicans are injured by fishing line, often resulting in euthanasia due to the severity of the injuries inflicted.

Figure 1: Even top predators such as crocodiles are victims of entanglement. Source Jackie Castellaine, Aurukun Community Council


Less graphic than entangled animals, wildlife suffering from plastic ingestion is likely to be far more widespread than it appears on face value. Over 200 species of marine animals have been proven to ingest plastic polymers- though given the scale of plastic debris, this figure is likely to be far higher. Plastics are mistaken for specific food items; seabirds tend to target small hard plastic pieces that may resemble krill, small fish or other edible plankton, whereas turtles most commonly ingest soft plastics, like bags, balloons and wrappers, as these represent their jellyfish prey. Other species may eat the plastic as it has epiphytic growths on it with some nutritional value. Filter feeders, such as baleen whales and manta rays are particularly at risk because of the volume of water they filter and the tendency for aggregations of their prey to form around floating structure or current lines, which also tend to concentrate debris.

Once ingested plastics can accumulate in the gut, forming a physical barrier and limiting the animals ability to feed. Alternatively, they can also cause internal damage, as sharp corners puncture the gut from the inside out. Both effects can rapidly lead to infection, starvation and death. Seabirds (particularly shearwaters) are known for bringing plastic fragments back to feed their chicks, leading to significant mortalities in seabird colonies across the world.

According to Dr Heidi Auman:
“98% of Laysan albatross chicks (Fig. 2) from Midway Atoll National Wildlife Refuge contained marine plastic debris in their stomachs. Most of this could be measured in multiple handfuls and included: shards of unidentified plastic, bottle caps, Styrofoam, beads, fishing line, buttons, chequers, disposable cigarette lighters (up to six per bird), toys, PVC pipe and other PVC fragments, golf tees, dish washing gloves, highlighter pens, medical waste and light sticks. Non-plastic items included neoprene O-rings, rubber pieces, and a lightbulb. Naturally killed chicks had significantly greater masses of plastic and had significantly lighter body masses and lower fat indices than injured but otherwise healthy chicks.”

Figure 2: Laysan Albatross chick carcass showing gut cavity with plastic debris, including plastic shards, bottle tops and a disposable lighter. Source Chris Jordan, Smithsonian Institute Ocean Portal, 2016
In addition to blockages and internal injuries, plastics can also affect the buoyancy of an animal, particularly sea turtles. The blockages lead to gas buildup from digestive processes, causing animals to float uncontrollably. This exposes them to starvation, increased predation and boat strike. It is estimated that at least 50% of the worlds turtle population have ingested plastic in some form.

Concluding Thoughts

Plastic debris is an insidious, wide reaching and deadly problem facing every one of us. The volume of plastic that has already been released into the oceans means that even if we stopped releasing plastic today, the effects will continue for years at least. What is also clear is that failure to act will grossly compound a problem that we already know exists, which is nothing short of catastrophic negligence.

So, what can we do? At a consumer level, it is a matter of choice- don’t buy or use plastic. Obviously, this cold turkey approach is unfeasible given how intrinsically we have woven plastic products into our lives, hence the famous waste management slogan ‘Reduce, reuse, recycle’. The recent addition of ‘refuse’ has been critical in a number of public campaigns to cut back on items as simple as coffee cups, drinking straws and plastic bags. For the unavoidable items, reuse and recycling are the two alternatives to keep plastic within the economy and out of the ocean.

Management level decision making has a vital role to play, both in terms of legislative control of plastic use (and misuse) and to targeting priority areas and resources for cleanup campaigns. By coordinating with not-for-profit and community organizations, these actions have already captured significant volumes of plastic.
What is clear is that more effort is needed across the board to address this issue, and that every piece counts.


1.World Economic Forum. 2016. The New Plastics Economy: Rethinking the future of plastics, online at, Accessed on 28/7/17
2.Australian Government. 2016. ‘Toxic tide: the threat of marine plastic’. Australian Standing Senate Committee on Environment and Comunications. Commonwealth of Australia. 2016. Online at . Accessed on 27/7/17
3.CHF. 2017. ‘The History and Future of Plastics’. Chemical Heritage Foundation. Philadelphia. Online at . Accessed on 28/7/17

One Reply to “Marine Plastics: A Global Threat”

  1. Come on Australia. Lets beat this plastic snowball effect. Find more waysto avoid plastic use and to find more innovative ways to use plastic waste for things like road pavements, building products, fuel sources. Avoid using pkastic shopping bags, plastic drinking straws and coffee cups. Use refillable cups and reusable straws and take your own reusable shopping bags to the supermarket. If we all try a bit harder we can beat this thing and start to repair the damage before it’s too late.

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