How plastic ends up in the sea and what we can do to prevent it
From rivers to the ocean: how does plastic end up in the sea?
Every year an ever-greater amount of plastic floods our oceans, causing incalculable damage to marine ecosystems. Faced with this crisis we must urgently ask ourselves: how does it get there? What real impact does it have on nature? And above all, what actions can we take as citizens, businesses and governments to curb this problem? We analyse these issues below.
Plastics are the most-collected waste by the NGO Ocean Conservancy in their annual clean-up visits to beaches and coastal areas. Since 1986, it has mobilised thousands of volunteers worldwide and according to the report The Beach and Beyond 2021, which sums up their activities in the Top 10 rubbish items recognising that for the first time in 30 years the top 10 most-commonly found items found in clean-ups are all plastic objects such as cigarette butts, packaging and disposable straws, which can take 500 years to decompose.
How and why does plastic end up in the ocean?
Pollution and plastic in the ocean almost always starts with our rubbish bins. Every year huge quantities of plastic continue to enter the sea, while global production continues to grow, having reached 430 million tonnes by 2024. The vast majority of plastic waste ends up being incinerated or scattered across landfill sites and the most unlikely corners of the planet, such as the Challenger chasm on the seabed.
Most of this abandoned waste ends up in the ocean, where waves and wind break it down into tiny fragments known as microplastics. These less than 5 mm particles get sucked into ocean whirlpools forming huge floating islands of plastic such as the Great Pacific Garbage Patch, the largest in the world measuring 1.6 million km2 and weighing 80,000 tonnes.
If these polymers are discarded thousands of miles away, how do they end up floating in the oceans? The New Zealand oceanographer Laurent Lebreton suggests in his research published in scientific journal Nature, in 2017 and 2019, that rivers, especially the largest and most polluted ones, are the main factors responsible for plastic being carried to the seas — according to his estimate, between 1.1 and 2.4 million tonnes every year —.
Lebreton also includes people's behaviour on the beaches, as well as fishing practices, farming and maritime transport as among other causes responsible for plastic in the sea. Unsurprisingly, waste originating from boats is responsible for almost half of the pollution found to date in the North Pacific Garbage Patch, as shown in a recent study published by Nature magazine. Wastewater, wind, rain and floods also carry plastic from the land into the oceans, especially single-use plastics — bags, straws, cotton buds or wrappers — which, being lightweight, are easily carried on the wind to the coast or find their way to the river network before reaching the sea.
From consumption to the ocean: the journey plastic takes
The plastic we use every day follows an invisible journey, one that we rarely give a second thought to. It is derived from fossil fuels, becomes short-lived products and, when not managed properly, can end up in rivers and oceans.
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Production and consumption
The cycle begins with the extraction of oil and gas, which are transformed into plastic resins to manufacture packaging, bags, bottles and a vast array of everyday products.
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Short-lived use, particularly in disposable packaging
A large proportion of these plastics is used for single-use bottles or products that are utilised for minutes or hours but remain in the environment for decades. Their lightness and low cost have led to their widespread use in everyday life, from food wrappers to disposable bags and cutlery.
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Inadequate management or littering
At the end of their useful life many plastics are not recycled and are discarded into the environment, ending up in landfill, on urban land or simply left lying around.
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Transport by wind, rain, drains and rivers
Once in the environment, wind and rain carry plastic waste into drains, streams and rivers, which act as "motorways" to the sea.
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Reaching the sea
Most of this discarded waste eventually ends up in seas and oceans, where it accumulates on coastlines, on the seabed and in large areas of floating litter. Once there, it affects ecosystems and marine wildlife.
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Fragmentation into microplastics and nanoplastics
In the ocean, plastic does not biodegrade but breaks down into increasingly smaller fragments due to the effects of the sun, waves and water, creating microplastics and nanoplastics. These tiny fragments disperse through water, sediment and even the air, making them much more difficult to remove and leading to their presence in drinking water, food and the bodies of numerous species, including humans.
Consequences of ocean plastic
Disasters such as ecosystem degradation and the exposure of flora and fauna to chemicals – more than a million animals die each year after mistaking plastic for food – are just some of the consequences of plastic in rivers and seas. Furthermore, our health could also suffer as a result of this polymer, as we ingest it through table salt and other foods. The UN Environment Programme (UNEP) estimates the cost of this ecological disaster at around $13 billion dollars a year. Below we explain in detail other impacts caused by the presence of this material in our oceans:
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Impact on marine wildlife
Many marine species ingest plastic, mistaking it for food, which leads to digestive blockages, malnutrition, poisoning and even death. What’s more, many animals, such as turtles and seals, become entangled in nets, ropes and other debris, suffering from suffocation, strangulation, injuries and infections that impair their ability to swim and feed.
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Impact on ecosystems
Corals, mangroves and seagrasses are suffocated by plastic waste, which prevents them from receiving oxygen and light, thereby affecting their development.
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Economic impact
According to the UN, the costs associated with plastic pollution in tourism, fisheries, aquaculture and other activities, such as clean-up operations, are estimated at between $6 and $19 billion. Furthermore, it is projected that by 2040 the annual financial risk to businesses could be around $100 billion if governments require them to cover the costs of waste management for the expected volumes.
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Potential impact on human health
Humans are also vulnerable to plastic pollution in water sources, which, according to the UN, could cause hormonal changes, developmental disorders, reproductive abnormalities and cancer. Humans can ingest plastic through seafood, drinks and even table salt, but it can also penetrate the skin and microplastics can be inhaled when suspended in the air.
Main river routes through which plastic enters the ocean
Various studies have identified a group of major rivers, mainly in Asia and Africa, as the main waterways through which plastic enters the ocean. However, according to the Aquae Foundation this is very difficult to measure as much of this plastic ends up degrading on contact with water, sunlight and bacteria, turning into microplastics that are very difficult to track. Despite this, some rivers have high levels of pollution:
1. Yangtze River (Asia):
This river in China is the longest on the Asian continent and discharges 330 million kilos of rubbish into the sea every year.
2. Ganges River (Asia):
This river, which is sacred to Hinduism, carries 120 million kilos of plastic waste into the sea every year after flowing through India and Bangladesh.
3. The Xi, Dong and Zhujiang rivers (Asia):
The Zhujiang River and its two tributaries (the Dong and Xi) rank third, discharging 106 million kilos of plastic annually.
4. Cross River (Africa):
This coastal river, which flows through Cameroon and Nigeria, carries more than 40 million kilos of plastic into the sea each year.
5. Brantas River (Asia):
This Indonesian river is the longest in East Java and discharges 38 million kilograms of plastic into the sea every year.
Source: Nature.
Yangtze River
Ganges River
Zhujiang River
How much plastic goes into the sea?
According to 2026 data from the United Nations (UN), 11 million tonnes of plastic enter the ocean every year and by 2040 this figure is estimated to reach 37 million tonnes – the equivalent of dumping a lorryload of rubbish into the ocean every minute. The World Economic Forum (WEF) goes further and predicts that, at this rate, by 2050 there could be more tonnes of plastic than fish in the oceans. Most of the plastic dumped into the sea comes from Asia, specifically from countries such as China, Indonesia, the Philippines and Vietnam – the top four on a list compiled by Jambeck's team.
Solutions to curb the flow of plastic into the sea
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Citizens
Reducing the use of single-use plastics (bags, bottles, cutlery or straws) and replacing them with reusable alternatives is one of the most direct ways to reduce the amount of waste that may end up in rivers and seas. Furthermore, actions such as recycling and taking part in beach clean-ups help to slow down the flow of plastic into the ocean and reduce the amount of litter present.
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Businesses
One of the key actions is the adoption of the circular economy at all levels of the company. This involves reviewing processes throughout the entire life cycle of a product or service, from its conception to its end of life. Once this review has been carried out, principles such as eco-design can be applied; in other words, during the product design phase, a decision is made to use recyclable and reusable materials that are easy to dismantle, thereby minimising the generation of plastic waste.
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Governments
Governments and international organisations are passing laws and regulations to limit single-use plastics, improve waste management, promote separate collection and strengthen extended producer responsibility. For example, from 1 January 2024 the European Union has banned the sale of single-use plastic products where sustainable alternatives are readily available and affordable. This includes cotton buds, cutlery, plates and straws.
What can you do?
As citizens we can help reduce plastic waste pollution in the environment through simple everyday practices such as these:
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Choose reusable containers over disposable ones
Replace plastic Tupperware with glass or steel containers.
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Avoid leaving rubbish on beaches, in rivers, in parks or on the streets
Littering with plastic waste contributes to the degradation of ecosystems and the death of many animals.
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Sort your packaging correctly
Place plastic items in the correct bins so they can be reused.
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Reduce your consumption of over-packaged products
Choosing products with fewer layers of plastic (for example loose fruit rather than trays and cling film) directly reduces the amount of waste you generate.
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Take part in beach or riverside clean-ups
Organised clean-ups along coastlines and rivers remove waste before the water carries it out to sea. As well as their direct impact these activities raise awareness of the problem and encourage changes in behaviour within the region.
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Check cosmetics and products that may contain microplastics
Some personal care products and detergents contain plastic particles or synthetic polymers that can end up in the water after use.
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Wash synthetic clothes using suitable programmes or filters where possible
Garments made from polyester, acrylic and other synthetic fibres release plastic microfibres with every wash, which can end up in rivers and seas. Using gentle, short wash cycles, washing bags or specific filters and washing less frequently reduces the amount of microplastics that are shed and end up in wastewater.
Iberdrola's role in combating marine pollution
Plastic pollution in the oceans is a global issue that requires joint action by individuals, businesses and governments to develop strategies to reduce the damage to our ecosystems. For this reason, the Iberdrola Group is seeking to minimise greenhouse gas emissions and achieve carbon neutrality through various initiatives, ranging from our 2030 Biodiversity Plan – where we aim to contribute through a conservation-focused approach (preventing, reducing, restoring and offsetting impacts) – to processes such as electrification and decarbonisation, with the aim of reducing the use of fossil fuels and moving towards a more sustainable economy.
These strategies include measures to mitigate plastic pollution in the oceans through projects such as East Anglia One, where we are promoting the installation of two floating containers designed to collect plastic and some of the oils, detergents or fuels floating in the vicinity of Lowestoft harbour. Another particularly important project is New England Wind, where protocols are in place to minimise the impact of underwater noise on marine wildlife – particularly mammals and turtles – in order to safeguard their welfare.
As well as carrying out sustainable projects, we also focus on finding innovative solutions to continue preserving our ecosystems through the PERSEO start-up programme, an open innovation programme with start-ups designed to develop technologies and business models to enhance the company's sustainability.