About 88 to 95 percent of marine plastic waste is estimated to come from 10 rivers in Asia and Africa, according to a study by German researchers. And one of those rivers, the Mekong, is facing an increasing pollution crisis caused by plastic bags and bottles near its mouth in southern Vietnam.


Plastic bags hang from the branches of mangrove trees lining a tributary of the Mekong River in the southern Vietnamese province of Soc Trang on Aug. 23, 2018. (Mainichi)

The research team at the Helmholtz Centre for Environmental Research in Leipzig in eastern Germany made the estimate in a thesis published in the Environmental Science and Technology journal in October last year. The rivers have become polluters due to improper treatment of plastic waste on the ground. As approximately 2 billion people live in emerging and developing countries along the rivers' basins, emergency measures to stop the pollution are required.

The researchers carried out the analysis using open-source data such as plastic waste samples taken from rivers across the globe and the volumes of water flowing from those rivers into the oceans. Their study showed that the Yangtze River in China transports the largest amount of plastic waste, followed by the Indus River flowing through India and Pakistan, the Yellow and Hai rivers in China and the Nile going through northeast African countries.

Eight of the 10 most polluting rivers are in Asia, indicating that Asian countries are the main conduits of plastic waste dumped into the sea. Of the 240 water samples taken in 57 rivers, 98.5 percent contained microplastic pieces five millimeters or less in diameter. Plastic pieces larger than that were contained in 55 percent of the samples

Bigger rivers tend to have a higher density of plastic waste, and those 10 major rivers polluting the sea stood out for their contributions to environmental degradation. According to the researchers at the German institute, rivers worldwide move between 470,000 and 2.75 million metric tons of plastic into the oceans annually, and plastic waste continues to threaten marine organisms for decades and centuries as plastic does not naturally break down, and continues to float at the mercy of the oceans' currents.

Dr. Christian Schmidt of the research team points out that an effective countermeasure to stop marine plastic waste is to reduce its inflow into rivers. "In the first place, a waste management system is needed in the most polluting countries. Waste should be removed from the streets and rivers," Dr. Schmidt said by email. This approach, he added, "does not sound exciting or innovative, but it will likely be most effective."

Many of the Asian rivers transporting plastic waste flow through China. Late last year, China stopped importing plastic waste citing the need to protect the domestic environment after years of accepting nearly half the world's plastic refuse as a resource. There is no data showing how much plastic waste imported by China has leaked into the environment, and the impact of Beijing's about-face on the marine environment worldwide is still unclear.

Said Schmidt: "It has a big impact on global plastic material flows. Suddenly, the domestic waste management of high income countries has to deal with way more waste than before. Hopefully, this will be a positive incentive for action on waste reduction and increased recycling rates."

What appeared to be colorful jellyfish in blue, yellow and orange were hanging from the branches of mangrove trees covering the Mekong Delta in Tran De of Soc Trang province in southern Vietnam. They were actually plastic bags coming from the Mekong, the mighty 4,300-kilometer-long river that originates in the high mountains of Tibet, flows through six countries in Indochina, and splits into multiple smaller rivers before meeting the South China Sea.

Truong Van Hau, 46, a local fisherman catching shellfish using a dragnet, let this reporter ride his boat to see the waters in the delta. No plastic waste such as bottles was visible on the surface, but when Hau pulled up his dragnet near the mouth of the river, plastic bags and containers emerged among fallen leaves.

Hau's usual fishing ground, which was unreachable on this day because of high waves, has more waste, he explained. "Waste flows into the area because of the currents. When I catch one to two kilos of shellfish, I also get three to four kilos of trash (comprising leaves and plastic)." Having been a shellfish fisherman for nine years, the amount of plastic waste "is on the rise," said a worried Hau.

 

From his fishing boat, a woman was visible on a nearby shore. She dumped waste in a plastic bag, and splashed water on the floating bag to move it away from shore. Large volumes of dumped plastic bags among coconut shells could be seen on the ground here and there along the coast. At a nearby port, a sanitation worker was dumping waste into the river, but they were collecting one thing: plastic bottles. "We pick them up because 1 kilo of these earns 3,000 dong (about 14 yen)," they said.

Countries in Southeast Asia like Vietnam have a high demand for plastic products, which play a greater role in daily life than in other parts of the world. Bags are used to carry food bought at roadside stalls, and drinks in plastic bottles come with plastic straws. In 2015, Indonesia, the Philippines, Thailand and Vietnam were named by Ocean Conservancy, a Washington-based group calling for the protection of the marine environment, as major sources of marine plastic waste, besides China.

WWF Vietnam, the local branch of the international environmental protection group, acknowledged that Vietnam is Southeast Asia's "hotspot" of marine litter. The main reason for this, a representative explained, is "the increasing use of plastic packaging while the development of waste management systems lags behind."

Groups such as WWF Vietnam have developed a water stewardship program involving stakeholders and governmental organizations for better water management and reduction of water pollution in some parts of the Mekong Delta. Waste management improvements include better collection and separation, using trash for compost or for recycling to generate an income. Communicating this concept to local residents is part of the program, according to WWF Vietnam.

Establishing a proper waste collection system and changing people's thinking are two major hurdles to plastic litter prevention, and both of these goals remain a distant dream in Southeast Asian countries.

(Japanese original by Kosuke Hatta, Brussels Bureau, and Shinichi Nishiwaki, Bangkok Bureau)