Revealed: The rivers and countries most to blame for plastic pollution in the oceans

Scientists in Europe think they've worked out which countries' rivers put the most plastic into the ocean - and there are some surprising entries on the list. 

About 8 million tonnes of mismanaged plastic waste (MPW) a year ends up in the ocean, according to the International Union for Conservation of Nature, threatening not just marine life but getting into the food system and exacerbating climate change. 

Up to 2.7 million of that enters the ocean via rivers, new research suggests, taking plastics from inland areas and dumping them into the ocean. The vast majority of that - about 80 percent - comes from just 1656 of them, "small urban rivers among the most polluting". 

According to scientists in the Netherlands and Germany, the world's most polluting river when it comes to plastic is the Pasig River in the Philippines, which runs through the capital of Manila. Only 25km long, its dubious honour comes courtesy of its short length. 

"Our results indicate that countries with a relatively small land surface area compared to the length of their coastline and with high precipitation rates are more likely to emit ocean plastics," the study, published this week in journal Science, said. 

"Particularly, for areas in the Caribbean such as the Dominican Republic and tropical archipelagos such as Indonesia or the Philippines, this results in a higher ratio of discarded plastic waste leaking into the ocean."

The Philippines is also the world's worst emitter of plastic waste via rivers, the research found, accounting for nearly a third of the 1656 worst rivers. 

Second was India, followed by Malaysia, China, Indonesia, Myanmar, Brazil, Vietnam, Bangladesh and Thailand. 

It was previously believed China's Yangtze River was the worst - but it came 64th in their rankings. 

"The Yangtze catchment is one of the biggest river basins with a very high total amount of MPW generation. However, the distance from MPW generation to the river and to the ocean is considerable as well. 

"Therefore, according to our model, only a relatively small fraction of MPW reaches the Yangtze River and even a smaller fraction subsequently reaches the ocean."

The Pasig has long been polluted thanks to overcrowding, industrialisation and the presence of various tributaries feeding into it. There have been efforts in recent years to clean it up. 

It's estimated only 0.6 percent of China's MPW reaches the ocean, while 9 percent of much smaller Malaysia's does. 

The research was based on visual observations of plastic, so doesn't account for tiny microplastics, invisible to the naked eye. IT's estimated around 60 percent of all plastic ever created has been discarded. 

"Work on the origin and fate of plastic pollution in aquatic environments suggests that land-based plastics are one of the main sources of marine plastic pollution, either by direct emission from coastal zones or by transport through rivers."

They estimated between 1.2 and 4 percent of all discarded plastic finds its way to the ocean in just one year.

A similar study four years ago found just 10 rivers were responsible for most of the plastic pollution, with the Yangtze at the top. The scientists behind the latest study say they've now got a lot more data, proving the problem is much more widespread than the 2017 study suggested. 

In 2019, researchers in Canada said it's likely the average person consumes hundreds of pieces of microplastics every day, even more if they drink from plastic bottles. It's not clear yet what the long-term impacts will be. 

Other countries whose rivers are contributing to ocean plastic pollution are Nigeria, Turkey, Cameroon, Sri Lanka, Guatemala, Haiti, Dominican Republic, Venezuela, Tanzania and Algeria.