Plastic Rivers: Just 10 Streams Carry 95 Percent Of Plastic Into Oceans

Every minute, another truckload’s worth of plastic trash ends up in the ocean, amounting to 8 million tons every year.1 That plastic is ending up in sea turtle and whale stomachs, strangling seabirds and, perhaps even worse, being broken down into microplastics that are consumed by fish and plankton — with unknown consequences.

How to clean up the swirling garbage patches in the world’s oceans is a daunting question. At least one organization, The Ocean Cleanup, is tackling it from a practical standpoint, using a passive trash-collecting system that they estimate may remove half the plastic from the Great Pacific Garbage Patch (which covers 1.6 million square kilometers (nearly 618,000 square miles) of the Pacific Ocean’s surface) in just five years.

Another option is to tackle the garbage at its source, a task that may be more achievable than it seems because 95 percent of the riverborne plastic flowing into the ocean comes from just 10 rivers.2

10 Rivers Carry Almost All Plastic Into The Ocean

Researchers from the Helmholtz Center for Environmental Research in Leipzig, Germany, looked at the concentration of plastic in 57 rivers throughout the world.

Data on both microplastics (particles less than 5 millimeters (mm), such as microfibers and microbeads) and macroplastics (particles greater than 5 mm, such as plastic bags and bottles) were analyzed, with researchers multiplying the concentrations of plastic in the river with water discharge to figure out how much plastic (by weight) was entering the oceans.

“They then fed these data into a model that compared them with the estimated weight of plastic litter generated per person per day along each river,” Scientific American reported.3 The study authors added, “A substantial fraction of marine plastic debris originates from land-based sources and rivers potentially act as a major transport pathway for all sizes of plastic debris.”4

Their analysis revealed that large rivers with dense populations along their shores delivered a disproportionate amount of mismanaged plastic waste into the ocean. “The 10 top-ranked rivers transport 88 to 95 percent of the global load into the sea,” the researchers concluded.5

Eight of the rivers (the Yangtze, Yellow, Hai, Pearl, Amur, Mekong, Indus and Ganges Delta) are found in Asia while two (the Niger and Nile) are in Africa. The worst polluter of the bunch, by far, is the Yangtze, located in China, which releases 1.5 million tons of plastic waste into the Yellow Sea annually (more than is released by the other nine rivers combined6).

Together, the 10 rivers are responsible for dumping 0.47 to 2.75 million tons of plastic into the world’s oceans every year.7 The silver lining to the finding, if there is one, is that better waste-management practices targeting these 10 rivers could have a major effect in curbing the amount of plastic flowing into the ocean.

The Top-Polluting Rivers Are Located In Asia, With The Yangtze River Topping The List

A similar study published in 2017 in Nature Communications created a global model of plastic inputs from rivers into oceans, based on waste management, population density and hydrological information.8 The model estimated that between 1.15 and 2.41 million tons of plastic waste enter the ocean every year from rivers, with 74 percent of the emissions occurring between May and October.

The researchers, from The Ocean Cleanup, also found that rivers account for a hefty share of ocean plastic, in this case revealing that the 20 top-polluting rivers, most of them located in Asia, accounted for 67 percent of the global total of river plastic emissions into the ocean.

Again, the Yangtze River in China, which is the third-longest river in the world, earned the dubious moniker of top polluter. The Ocean Cleanup researchers stated:9

“Most of this river plastic input is coming from Asia, which emphasizes the need to focus on monitoring and mitigation efforts in Asian countries with rapid economic development and poor waste management … there is very little data to document these assumptions and thoroughly verify the validity of our model.

Yet, the relatively high concentrations of ocean plastic found at the surface of the North Pacific Ocean where buoyant plastics originating from Asia can accumulate, suggest that our assumptions are plausible.”

Fisheries, fishing vessels and other ships contribute less than 20 percent of plastic debris in the oceans. The rest, more than 80 percent, starts off on land. Once in the ocean, it’s known that nearly 700 species (and probably many more) are negatively impacted by such debris.

According to environmental advocacy group Ocean Conservancy, some plastic products persist for so long, even in salty ocean water, that they’ll still be recognizable after 400 years.10

In the U.S., one of the top waste-generating countries, littering is a major issue, especially in the form of single-use plastics, like soda bottles, drinking straws and potato chip bags. In much of Asia and Africa, however, plastic debris ends up in rivers due to lack of proper disposal and handling of general waste as well as that from landfills and industry.

Efforts To Curb Plastic Pollution Should Target Freshwater Environments

Rivers, being a major source of transport of plastic into oceans, should be a major focus of cleanup and prevention efforts, not only to curb the transport but also because, as Martin Wagner, an associate professor at the Norwegian University of Science and Technology’s (NTNU) department of biology, “Rivers are wonderful and complex ecosystems in themselves.”11

In a book on the topic titled Freshwater Microplastics: Emerging Environmental Contaminants? Wagner points out that there are more than 5,300 grades of synthetic polymers, each with different physicochemical properties. As such, each is likely to exert very unique effects once in the environment.

“In light of this, treating microplastics as a single pollutant does not make sense,” he writes. The book continues:12

“Due to the chemical makeup of plastic materials, receiving environments are potentially exposed to a mixture of micro- and nano-sized particles, leached additives and subsequent degradation products, which will become bioavailable for a range of biota.

The ingestion of MPs [microplastics] by aquatic organisms has been demonstrated, but the long-term effects of continuous exposures are less well understood.”

Further, much of the study on plastics in the environment has centered on the ocean, while little is known about plastics in freshwater systems. As of the book’s writing, less than 4 percent of publications referred to plastics in freshwater, “reflecting the idea that streams, rivers and lakes are mere transport routes transferring plastics to the oceans similar to a sewer … this is too simplistic,” the books preface notes.13

Wagner believes that focusing on removing plastic from the ocean is a shortsighted solution because in order to stop it in the long run, it has to be traced back to its source, which in most cases is land and the rivers that transport it. “We have to go to the source of the problem to stop it, and the source is on land,” he said in an NTNU news release, adding:14

“We also don’t know how much plastic there is in rivers and lakes. This is crucial knowledge to be able to identify and understand the most important sources of plastic litter — which in turn is essential to find effective solutions to the problem … Plastics break down into microplastics.

We know very little about the impact of microplastics on ecosystems, whether we’re talking about freshwater or oceans … Long-term experiments and new methods are needed to find out how microplastics affect nature — and us.”

Majority Of Fish In Freshwater Environments May Contain Plastic

What little research that has been done on plastics in freshwater environments is not reassuring. In one such study, 83 percent of the fish had plastic debris in their gut, mostly microplastics, particularly microfibers.15

The fish appeared to consume more microplastics near urbanized sections of the river and when fish ate a lot of the plastics, they appeared to eat a less diverse variety of other food items. Microfibers have also been found in most water samples collected from the Hudson River,16 and studies show concentrations of fibers tend to be particularly high in beach sediment near wastewater treatment plants.17

So, ironically, the practice of recycling plastic bottles into clothing items, which is done by certain outdoor companies as a way to reduce waste, may ultimately end up being environmentally destructive, as microfibers from clothing are released during washing.

These microscopic plastic fibers soak up toxins like a sponge, concentrating PCBs, flame retardant chemicals, pesticides and anything else found in the water. It could be that the longer the particles stay inside the fish, the more chemicals may leach into its body. So the microfibers may be harming marine life via two mechanisms: physical blockage and chemical poisoning.

One solution to the microfiber pollution problem would be to install filters in washing machines — similar to lint traps in dryers — that could catch the fibers prior to their being released with the wastewater. Special coatings may also help to stop the loss of microfibers during washing, but the apparel industry has been slow to respond in taking steps to stop microfiber pollution.18

Doing Your Part To Curb Plastic Pollution

Efforts to improve waste management in Asia are urgently needed to help curb plastic pollution, but you can also make a dent in the waste by using less plastic in your daily life, especially in the case of single-use disposable items like straws, bottles, bags and cutlery.

Data obtained by The Guardian suggests 1 million plastic bottles are purchased every minute worldwide. Worse still, this is expected to increase by 20 percent by 2021 and reach more than half a trillion sold every year by 2020.19

Fewer than half of the plastic bottles purchased in 2016 were recycled, and only 7 percent were made into new bottles,20 which means the rest end up in landfills or marine environments. Don’t underestimate the impact even one person can have by making simple tweaks to their routine.

Will you really miss that plastic straw with your water? Do you really need a throwaway bag to carry home one or two items from the store? It’s time to rethink our throwaway society and choose reusable over single-use whenever possible (and it’s usually possible).

Following are some of the most straightforward steps you can take to cut down on plastics usage in your life. Share them with a friend or two and the positive impacts will only continue to be magnified:

  • Use reusable shopping bags for groceries
  • Take your own leftovers container to restaurants
  • Bring your own mug for coffee, and bring drinking water from home in glass water bottles instead of buying bottled water
  • Request no plastic wrap on your newspaper and dry cleaning
  • Store foods in glass containers or mason jars rather than plastic containers and plastic freezer bags
  • Avoid disposable utensils and straws and buy foods in bulk when you can
  • Opt for nondisposable razors, washable feminine hygiene products for women, cloth diapers, handkerchiefs instead of paper tissues, rags in lieu of paper towels, and infant toys made of wood rather than plastic
  • Avoid processed foods (which are stored in plastic bags with chemicals). Buy fresh produce instead, and forgo the plastic bags

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Sources and References
1, 2, 6 Big Think August 10, 2018
3, 7 Scientific American February 1, 2018
4, 5 Environ. Sci. Technol. 51, 21, 12246-12253
8 Nat Commun. 2017 Jun 7;8:15611.
9 June 8, 2017
10 Ocean Conservancy, Stemming the Tide
11, 14 Gemini April 2018
12, 13 Freshwater Microplastics: Emerging Environmental Contaminants?
15 Environ Pollut. 2017 Feb;221:218-226.
16 Washington Post October 30, 2016
17 Outside June 20, 2016
18 The Guardian May 13, 2017
19, 20 The Guardian June 28, 2017