Roach. Photo credit: Charles Tyler

A long shadow cast by our chemical past

The production of many insecticides such as DDT has now been banned in Europe and most of the rest of the world. However, high traces of these chemicals can still be found in fish today near where production sites used to be.

A study published last month in the journal Chemosphere that looks at fish in 13 rivers across the Thames and Anglian area has shown that these chemicals can still be found in wildlife living in UK rivers, long after they are no longer being produced.

Dr Patrick Hamilton was part of the team with the Centre for Ecology and Hydrology (CEH) looking at how the concentrations of DDT in fish varied across England. DDT was an early insecticide and its discovery earned its inventor Paul Müller the Nobel Prize for medicine and physiology in 1948 for its seemingly endless applications for crop protection and combating insect-borne disease. However, its long persistence in the environment started to show effects and was linked to declines in birds of prey around the world. The accumulation of DDT up the food chain was causing egg shell thinning to the point where eggs could break as they were laid.

DDT is rarely detected in waters. However, it can persist in sediments acting as a source for future release.  For example, in Germany and Italy, the dredging of sediments near sites which hadn’t produced DDT for 10 years caused the release of this buried DDT back into the overlying water. A similar story was found by Hamilton and researchers from the Centre for Ecology and  Hydrology for roach from the Wheathampstead site on the river Lee.  The elevated DDT concentrations found in the fish were likely to be linked to the nearby chemical production site, even though production of pesticides on the site had stopped in 1982. In addition, previous work by the group, using genetic profiling had found that large weirs restricted migration of this fish population, in effect trapping them in the area. This is likely to also have contributed to these high concentrations in fish.

Fortunately, no obvious adverse effects were apparent for the individual fish they sourced from this area. One reason for this could be that the fish in this area have adapted to cope with the high DDT concentrations over time. However, the authors do not rule out possible implications for other wildlife in the area. The authors reviewed recent similar studies across Europe and found that this is not the only case where local historical industry has left a legacy of high DDT levels in fish. Not only this, but all of the roach sampled at the Wheathampstead site had concentrations of DDT above levels considered safe fish eating birds. This study brings another example to the table of the long legacy of historical pollution in our waterways and sets the wider context for the continuing persistence of DDT across European waters.

The full text can be read on the Science Direct website.

Written by Richard Cross, Biosciences Pressgang

Date: 13 September 2016

Read more University News