Plastics science

It is fair to say that in recent years no two scientific papers have attracted more public attention and mainstream media headlines than the following: ‘Indonesia is the second Largest Marine Polluter in the World’; and ‘Ten Rivers contribute 93 per cent of Ocean Plastics’.

Those headlines, with many other variations, have been doing the rounds; are quoted, re-quoted, misquoted, extracted, cut and pasted into other articles and used as 90-second simplistic click-bait insta-news memegram videos designed both to shock and horrify millennials who have no time to read an article or sit down and watch an entire episode of David Attenborough’s Blue Planet or Al Gore’s An Inconvenient Truth without checking their Facebook.


Indonesia, the world’s second largest ocean polluter

This originates from a paper, Plastic waste inputs from land into the ocean, by a team from University of Georgia’s College of Engineering, led by associate professor Jenna Jambeck and first published in the February 2015 issue of the US journal Science.

It claims that Indonesia is the world’s second largest ocean polluter, after China (see Figure 1).

This has been quoted and used widely; by (among others) the United Nations Environmental Programme, World Economic Forum and the mainstream media, and the data have generally been accepted as being accurate by all and sundry, even by the Indonesian government.

Interestingly, one rarely reads about China’s rating as Top Gun in the global pollution table or, for that matter, Philippines (#3), Vietnam (#4) or Thailand (#6), possibly because the governments of these countries largely ignored the report, while Indonesian NGOs and government felt shamed and so embraced it. Possibly, feeling that since the report came from the US, the data must be accurate and not the result of estimates and assumptions fed into a supercomputer model. The US ranks at number 20, while a footnote to the table places the EU at number 18.

The article in Science, which kicked-off the global outrage, estimated that 2.5 billion tonnes of municipal solid waste was generated in 2010 by 6.4bn people living in 192 coastal countries. Plastics waste is predicted to have roughly tracked plastics resin production to more than 270 million tonnes in 2010.

The researchers then built a framework and calculated the amount of mismanaged plastics waste. They said: “Our framework was designed to compute, from the best-available data, an order-of-magnitude estimate of the amount of mismanaged plastics waste potentially entering the ocean worldwide.

“It is also a useful tool to evaluate the factors determining the largest sources of mismanaged plastics waste. The amount of mismanaged plastics waste generated by the coastal population of a single country ranges from 1.1 million tonnes to 8.8 million tonnes per year, with the top 20 countries’ mismanaged plastics waste encompassing 83 per cent of the total in 2010.

“Total annual waste generation is mostly a function of population size, with the top waste-producing countries having some of the largest coastal populations.”

For each of 192 coastal countries with at least 100 permanent residents that border the Atlantic, Pacific, and Indian oceans and the Mediterranean and Black seas, the framework included: The mass of waste generated per capita annually; the percentage of waste that is plastics; and the percentage of plastics waste that is mismanaged and, therefore, has the potential to enter the ocean as marine debris.

By applying a range of conversion rates from mismanaged waste – itself an estimate ‘from best-available data’ – to marine debris, the computer model estimated the mass of plastics waste entering the ocean from each country in 2010, then factored in population growth data to project the increase in mass to 2025, and thereby predicted growth in the percentage of waste that is plastics – et voila!

Of course, this was an exercise in computer modelling (see Plastics in Packaging, January 2019), in which no actual field tests were conducted, and it wasn’t until two years after the publication of her report that Jenna Jambeck visited Indonesia.

During Jambeck’s visit to Jakarta, the Indonesian Plastics Industry Association (INAPLAS) made a valiant attempt to dispute the data. Average plastics consumption per capita, including virgin and recyclate, is only 22.54kg or 0.057 kg/PPD, which is much lower than neighbours Singapore, Malaysia, and Thailand, which are all in excess of 60kg/capita.

INAPLAS pointed out that Jambeck’s total plastics waste generation rate of 0.057kg/PPD was grossly inflated from the reality of 0.018kg/PPD – leading to Jambeck’s volume of marine litter expelled by Indonesia being in the range of 0.48-1.29 million tonnes per year, while INAPLAS calculated just 0.17 million tonnes per year of non-managed litter (see Figure 2).




But by that time the damage was done, and Indonesia had been firmly branded as a global polluter. Today there isn’t an educated Indonesian who is not aware of this somewhat shameful label.


Plastics rivers

In February 2018, the US Journal Scientific American published an article called Stemming the Plastic Tide: 10 Rivers Contribute Most of the Plastic in the Oceans, by Prachi Patel, which claimed that: “Our seas are choking on plastic. A staggering eight million metric tons wind up in oceans every year and unravelling exactly how it gets there is critical.”

Patel was reviewing a report by Christian Schmidt, a hydrogeologist at the Helmholtz Center for Environmental Research in Leipzig, Germany, published in November 2017 in Environmental Science & Technology magazine.

The ten rivers that carry 93 per cent of that trash are the Yangtze, Yellow, Hai, Pearl, Amur, Mekong, Indus and Ganges Delta in Asia, and the Niger and Nile in Africa.

The Leipzig methodology was to take published data on the plastics concentration in 57 rivers of various sizes around the world. These measurements included bottles and bags, as well as microscopic fibres and beads. The researchers multiplied these concentrations by the rivers’ water discharge to calculate the total weight of plastics flowing into the sea. They then fed this data into a model that compared it with the estimated weight of plastics litter generated per person per day along each river.

So, this is another piece of groundbreaking desk-research and computer modelling.

And it is false, according to the Norwegian organisation Grid-Arendal, which was established in 1989 to support environmentally sustainable development by working with UN Environment.

Grid-Arendal pointed out that: “Plastics gets into the ocean in many ways. It is dumped directly or is blown in by the wind. It comes from ships and lost fishing gear. It is also carried by rivers. One estimate of total plastics input to the oceans from all sources is around eight million tonnes per year and about 80 per cent is attributed to land-based sources. However, it’s not possible at this stage to accurately verify these figures.

“In a recent study of the amount of plastic litter transported by 57 river systems, ten rivers were estimated to be responsible for 90 per cent of it. In other words, 90 per cent of the plastic coming from rivers is from these ten. It does not mean that 90 per cent of all plastic in the ocean is coming from these ten rivers.”


Back to Indonesia

A basic command of geography will alert our Grown Up Readers to the simple fact that not one of these rivers (Yangtze, Yellow, Hai, Pearl, Amur, Mekong, Indus and Ganges Delta in Asia, and the Niger and Nile in Africa) are anywhere near Indonesia, and a quick Google of tide and monsoon systems suggest that, with the exception of the Mekong, none of the outflow would be likely to reach Indonesia.

So how can both the Jambeck and the Schmidt reports be correct? They appear to contradict each other, which is a point I put to Jenna Jambeck in an open social media group.

She replied: “There is only a small overlap in the studies. The rivers go very far inland, so the waste is coming down them great distances [according to the paper shown here]. It only shows rivers entering the ocean, not all coastline, so their 90 per cent estimate is only for river input, not all input [why it is less than our paper].

“If there are no major rivers entering the ocean in a country that show up in their method, then it won’t be on the list of top rivers. But river input is just one conduit to the ocean. Waste is also just dropped on the coast or washes in from rain on land (run-off, storm-water), or rivers near the coast.

“Our paper took a 50km buffer of coastlines for every country that has a coastline for the estimate of plastic waste available to enter the ocean. So, it was more than rivers, but all waste generated along the coast. In our case, islands had a high potential for input.

“The rivers paper just did rivers, so they left out areas that we did (although I think they did the same countries). The overlap in our studies would be at the 50km mark – so where the rivers meet the ocean and 50km inland only. So, you can’t directly add their number and ours – but they would be somewhat additive (minus that buffer). And there isn’t any contradiction on why they both cannot be correct.

“It is very clear in our paper the methods, results and limitations of the study. I think it is important that everyone read it before critiquing it. All along, my message has been about not pointing fingers. But we do know where waste management infrastructure is lacking and that estimate came from that. Data was used that had been reported by each country’s government to the World Bank – or estimated with a statistically significant model (see the paper). The paper was peer-reviewed and has been read and commented on by many people.”

Let’s be clear about these reports. They are not the Sir David Attenborough scientific expeditions going into the jungle to get cuddled by gorillas, they are computer models using data drawn from previously published sources or, to quote Jenna Jambeck: “While we did a sensitivity analysis on the data, we found the top 20 did not really change. And if data was lacking, then what this did was motivate people to collect more correct data – solid waste data is often not very extensive – but this paper has made people want to collect more and better data that is so badly needed.”