Toxic chemicals that were dumped in Britain’s rivers in previous decades are making it harder for them to recover, according to a study published in the journal Water Research.
Scientists from Cardiff University, the University of Exeter, and the Centre for Ecology and Hydrology looked at rivers in the South Wales valleys as during the 1970s over 70% were classified as grossly polluted due to a combination of poor sewage treatment, colliery waste and industrial discharge.
Since then, industry has declined, deep mining has ceased and sewage treatment has improved to the point that clean water species such as salmon and otters have returned to rivers such as the Taff.
Yet the study found that Welsh rivers in urban locations still have damaged food chains and fewer species of invertebrates in comparison to more rural rivers.
According to the researchers, these effects might be explained by the higher concentrations of former industrial pollutants such as PCBs (Polychlorinated Biphenyls) and flame-retardant chemicals (PBDEs) that persist in these rivers despite being phased out.
Professor Charles Tyler, from the University of Exeter’s School of Biosciences, added: ‘These apparent effects of what we call “legacy” pollutants – PCBs, flame retardants, organochlorine pesticides and other complex organic chemicals that have now been largely discontinued from production and use – are yet another reminder that we continue to live with problems caused by toxic chemicals from past decades.
‘These chemicals still occur widely in rivers, lakes and seas in Britain and beyond, and still affect a wide range of animals.’
Professor Steve Ormerod of Cardiff University’s School of Biosciences and Water Research Institute added: ‘Urban river ecosystems in Britain have been on an improving trajectory since at least 1990, but there is still a way to go before we can say that they’ve wholly recovered from well over a century of industrial and urban degradation.
‘The slow degradation of some pollutants means that we may have to wait a long time before these chemicals disappear. Perhaps one of the lessons is that we should avoid ecosystem damage in the first place rather than try to solve problems after they occur.’
In March, scientists from Lancaster University said that the UK may be underestimating how poor the water quality is in its streams and rivers.