An unseen stream of plastic rubbish flowing along the bed of the river Thames and out into the North Sea will have far-reaching effects on marine life, a new report indicates.

 

Scientists from the Natural History Museum and Royal Holloway, University of London, collected rubbish over a three-month period at the end of 2012 from seven locations along the river bed of the upper Thames estuary, between Crossness and Broadness Point.

 

The team netted 8,490 items including plastic cigarette packaging, food wrapping and cups that may have been blown or washed into the river down storm drains. More than 20% of waste was made up of sanitary products such as pads and plastic backing strips, which had most likely been flushed straight down the toilet. The full extent of the unseen waste could be far worse, the study warned, as plastic bags and other large items may have escaped the small nets used in the study.

 

The two most contaminated sites were in the vicinity of sewage treatment works at Crossness and Littlebrook, the report found, and could indicate that plants were not filtering out larger waste, or were letting sewage overflow when heavy rains created extra waste.

 

The report said the data represented only a snapshot, and as such it was difficult to estimate the volume of litter that was actually entering the North Sea this way. But scientists said the figures highlighted an underestimated problem.

 

The report also warned that larger pieces of plastic are being continuously rolled backwards and forwards by the estuary's tidal movements and broken down into smaller and smaller "microplastic" fragments that are easily digested by birds, fish and smaller species such as crabs.

 

The findings are the latest evidence that plastic pollution is having as big an impact on freshwater environments as the seas.