River sediments and air are major sinks and transporters for microplastics, according to a study done on the Ganges River in India and Bangladesh.
The study, which is published in Science of the Total Environment, has found that sediment along the Ganges houses about 57 microplastics per kilogram, while 41 microplastics per square metre settle out of the air and every 20 litres of water contains one microplastic particle.
“This research is groundbreaking, and we need to make the findings understandable for the key stakeholders, including policy makers,” says co-author Dr Gawsia Wahidunnessa Chowdhury, from the University of Dhaka in Bangladesh.
In total, the researchers have estimated that the Ganges and its tributaries deposit 1-3 billion microplastics into the Bay of Bengal every day.
In this study, they found that rayon (a synthetic fibre made from cellulose) was the most common type of microplastic at each site, ranging from 54-82% of the samples found.
Blue was the most common microplastic colour, representing 48-79% of the microplastics found at each site.
“This research based on primary field data has provided clear insight on the levels of microplastics in different environmental matrices of River Ganges and that several major river systems of the world have reported comparatively higher microplastics than the Ganges,” says co-author Dr Anju Baroth, a scientist at the Wildlife Institute of India.
“This study could be used to further mature the theory on major sinks and sources of microplastics in major river systems of the world.”
The researchers collected water, sediment and air samples from 10 different sites along the Ganges: 3 in Bangladesh and 7 in India.
They found that fibres from cloth were the most common type of microplastic, representing 95%-99% of the microplastics in samples.
“Our research shows that clothing is the major source of microplastics in the air, water and sediment of this vast river system, enabling us to work with partners and policy makers to seek locally appropriate solutions,” says co-author Professor Heather Koldewey, from the Zoological Society of London, UK.
“These can be informed and supported by the brilliant scientists from Bangladesh and India who were key members of the team involved in this paper.”
Microplastics increased further downriver, and were also higher in proximity to big population centres.
Lead author Dr Imogen Napper, a research fellow at the University of Plymouth, UK, says that researchers have known that rivers are a major source of microplastics for some time.
“However, there has always been uncertainty about the sheer amounts being transported, and whether they represent long-term sinks,” says Napper.
“This study goes some way to unravelling that mystery, and revealing the true scale of microplastic contamination that our river systems can represent.”