Science - June 10, 2004

Chlorinated pesticides more dangerous than previously thought

Chlorinated pesticides, poisonous substances that were thought to be strongly bound to soils, leach out quite easily into water, and therefore also into the food chain. Experiments by the sub-department of Environmental Technology at Wageningen University have shown this to be the case.

Heavy rainfall or floods are especially likely to lead to poisonous chlorine compounds being released into the water and then the food chain, according to research leader Dr Tim Grotenhuis and his colleagues. “The problem is that the concentration of the substances increases, the higher they reach in the food chain.” The chlorinated pesticides belong to the group known as persistent organic pollutants (POPs). A large number of these are forbidden by the United Nations organisation for the environment, UNEP.

Grotenhuis points to the dangers particularly in heavily industrialised areas such as the Rotterdam port area and the Ruhr in Germany. Especially where pesticides factories are located, chlorinated pesticides are found in the soil. For a long time it has not been known whether these industrial areas should be considered a sink or a source of chlorinated pesticides. Grotenhuis and his colleagues now think that they are more likely to be a source than a sink, an underground storage area.

In the experiments turbulent conditions such as flooding were simulated, and shown to lead to heavy leaching of chlorine compounds into the water, of up to ninety percent. The simulated conditions are not that unrealistic either; pesticides and other toxic substances are known to be found in large quantities in soil in river beds, flood plains and other low lying areas that are periodically inundated.

Hugo Bouter