Europe’s rivers are awash with organic chemicals that can kill or subtly harm aquatic life, according to the most extensive survey yet of pollution in the continent’s major river basins.

Toxicologists contacted by New Scientist welcomed the study, but point out that the researchers may have exaggerated the risks by choosing to define relatively low levels of chemicals as harmful. Such small concentrations might well affect animal populations, but by themselves would probably not be enough to cause a population to collapse.

Ralf Schäfer of the University of Koblenz-Landau in Landau, Germany, and colleagues analysed water quality data from over 4000 monitoring sites and measured concentrations of 223 different organic chemicals.

They discovered that at 14 per cent of sites, the concentrations of chemicals could potentially be lethal. The map below illustrates this. The colours indicate the fraction of sites in each river basin that exceed the lethal risk threshold.


What’s more, 42 per cent of the sites may have subtler problems. The concentrations of organic chemicals were not immediately lethal, but could cause longer-term damage, such as impacts on breeding or increased vulnerability to disease.

All previous studies had focused on much smaller areas, such as individual streams. “The most important message from our study is that chemical pollution is a large-scale, not just local problem,” says Schäfer.

The risk appears to be highest in central European and French rivers, especially those that empty into the North Sea from the Netherlands and Belgium. UK aquatic life also faces chronic risks.

Pesticides pose by far the greatest risk to fish and invertebrates, with weedkillers having the biggest impact on algae.

Journal reference: PNAS, DOI: 10.1073/pnas.1321082111