Three new studies from postgraduate students Alex McGoran, Katharine Rowley and Katherine McCoy, all from the Department of Biological Sciences at Royal Holloway, paint a picture of a River Thames that is far more polluted than would appear at first sight.
While each of the three each studied a separate aspect, taken together, the findings were grim.
Alex McGoran showed that two resident estuarine species of crab - the native shore crab and the invasive Chinese mitten crab - are ingesting microplastics, which could reduce the urge to feed and leave the animals, with less energy for growth and reproduction. She found that their stomachs were filled with tangles of fibres, fragments of microplastics from sanitary pads, balloons, elastic bands and carrier bags.
“Tangles of plastic were particularly prevalent in the invasive Chinese mitten crab and we still don’t fully understand the reason for this. We propose that when crabs moult - shedding their exoskeleton to grow)- that plastic is trapped in the discarded gut lining”, she says.
Katharine Rowley focussed on the quantification of microplastics in the River Thames water column. Her study found that 93.5% of microplastics in the water column were most likely formed from the fragmentation of larger plastic items, with food packaging thought to be a significant source for these plastics.
Globally, in comparison to published estimates of microplastic contamination in marine and freshwater environments, the River Thames contains very high levels of this pollutant - more than the rivers in Europe and the US - which could be due to the fact that a large portion of the river is tidal, she said. She estimated that on peak ebb tides, 94 thousand microplastics flow down the River Thames per second in some areas. Water column microplastics were 24.8 per m3 at Putney and 14.2 per m3 at Greenwich – ‘outfalls where raw sewage is known to be released into the catchment during periods of rainfall’, she reported.
A third study, from Katherine McCoy in collaboration with river clean-up charity, Thames21, looked at “flushable” and “non-flushable” wet wipes as a source of plastic pollution in the River Thames and the environmental impacts they have on the invasive Asian clam. Wet wipes found in sewage effluent are deposited in large numbers on the foreshore on the south bank, just upstream from Hammersmith Bridge, creating massive wet wipe reefs.
Clams adjacent to the wet wipe reefs were found to contain synthetic polymers,
“These products are often described as flushable, but they have been known to block sewage pipes by contributing to fatbergs and have now been seen to cause environmental disruption on the foreshores of the river Thames. Our study shows that stricter regulations are needed for the labelling and disposal of these products,” she noted. “There is great scope to further research the impacts of microplastics and indeed microfibres on Thames organisms.”
Professor Dave Morritt from the Department of Biological Sciences at Royal Holloway, said: “Taken together these studies show how many different types of plastic, from microplastics in the water through to larger items of debris physically altering the foreshore, can potentially affect a wide range of organisms in the River Thames.”
The Natural History Museum and the Zoological Society of London also collaborated on the three studies. As Paul Clark, who works in the Life Sciences Department at the museum said in response to these latest findings: “I was born in London and as a child I remember the Thames as a heavily polluted river which led to the decline of its fish populations. When the Government ordered a clean-up of the catchment the River returned back to life. What our students have shown in this collaboration is that although the Thames is certainly cleaner with regards to some chemical pollutants, e.g. heavy metals, the River is severely polluted with plastic. And once again our wildlife is threatened.”