A study by researchers at Tokyo Metropolitan University has traced how microplastics from polymer-coated fertilisers (PCF) end up deposited on beaches and in the sea, contributing to the so-called ‘missing plastics’ phenomenon in marine pollution.
As the study, which was published in the Marine Pollution Bulletin journal found, around 0.2% of PCF deposits are washed into rivers and end up at Japan’s coastline, however where there are canals connecting fields to the sea, this rises to 28%.
Use of polymer-coated fertilisers
Polymer-coated fertilisers contain a thin layer of plastic to release nutrients slowly, making them last longer. They are used extensively in rice cultivation in Japan and China, as well as in the production of wheat, corn, and other crops in the US, UK and Western Europe.
As previous studies have found, between 50% and 90% of plastic debris found on beaches in Japan is derived from PCFs, however, until now, the process by which said materials made their way from land to sea was not well understood.
Conducting the research
The team of researchers, led by Professor Masayuki Kawahigashi and Dr. Dolgormaa Munkhbat, analysed PCF deposits across 147 sites on 17 beaches in Japan, in various different environments.
At beaches close to river mouths, they found that less than 0.2% of the polymer-coated fertiliser used in surrounding fields was deposited on beaches – more than three quarters (77%) of the fertiliser capsules remained in the fields, while 22.8% was estimated to be transported out to sea.
At the same time, beaches situated close to near direct drainage channels from agricultural land displayed much higher deposition, with up to 28% of PCF-derived microplastics washing back onto shore.
‘The team concluded that waves and tidal action help them wash back onto land, making beaches a temporary sink for microplastics,’ the study found. ‘Given that most PCFs lost from fields end up in rivers, the majority of these plastic capsules end up going “missing”.’
The research team said that their research represents a ‘key first step’ in tracing how PCFs contribute to the global challenge of missing plastics. Read more here.
