Several studies have been published recently which highlight the accumulation of plastic in riverbed sediment and an underestimation of the volumes flowing into rivers.  The first states that ‘hundreds of millions of microplastic particles could be flowing into UK rivers, hidden in raw sewage’. It goes on to say that ‘recently, there was public anger over revelations that Thames Water, a UK utilities company, released 2 billion litres of raw sewage into the River Thames in just two days. This is on the back of Southern Water’s record £90 million fine for thousands of illegal raw sewage discharges over several years. However, these stories do not report on the amount of microplastics that would have also been released within these discharges as that data is not routinely collected.

Applying an example of the average numbers of microplastics found in a litre of effluent to the amount released in the Thames case could equate to about 500 million microplastic particles entering the River Thames. This is happening all over the UK, with raw sewage being deposited along many British coastlines and rivers.

This is an enormous number of microplastic particles that the public is not aware of. And if the numbers are underestimated, the relevant action to tackle this pollution may not be taken. Microplastics can cause harm to aquatic life in many ways. Ingestion can cause blockages in organisms that can ultimately lead to a reduction of vital nutrients or death. They can also affect the growth of crops if they leach into the soil.’ The paper can be read here.

Another study published in Science Advances stated that ‘researchers modelled the journey of microplastics released in wastewater treatment plant effluent into rivers of different sizes and flow speeds, focusing on the smallest microplastic fragments — less than 100 microns across, or the width of a single human hair. The study found that in slow-flowing stream headwaters — often located in remote, biodiverse regions — microplastics accumulated quicker and stayed longer than in faster flowing stretches of river. Further information can be read here.