Science - May 18, 2006

Shrimps dazed by medicines

Tiny organisms in the Dutch waterways are probably being numbed by traces of medicines in the water. Researchers in Wageningen have come to this conclusion after doing experiments with the freshwater shrimp Gammarus pulex. ‘Something is not right, but we are not quite sure what,’ says Dr Marieke de Lange who works at the Aquatic Ecology Group and Alterra. ‘We are concerned.’

Medicines that are not broken down by sewage treatment make their way into the living environment. As a result, a litre of water in a river like the Dommel contains some tens to a few hundreds of nanograms of medicines, such as the painkiller ibuprofen, the anti-depressant Prozac or carbamazepine, a medicine for epilepsy.

An article will appear soon in Aquatic Toxicology in which the Wageningen researchers publish their findings. It is the first time that the effects of low concentrations of medicines on the behaviour of invertebrates have been studied. More specifically, they have looked at the behaviour of freshwater shrimps. ‘Gammarus pulex plays a key role in the food chain,’ says De Lange. ‘The shrimp helps to decompose organic material because it eats leaves. It is also a prey for fish.’

The effect of the anti-epileptic medicine carbamazepine was not statistically significant, but with even just a few tens of nanograms of ibuprofen and Prozac per litre of water, the freshwater shrimps became less mobile. The Wageningen scientists are not sure how this happens. ‘Perhaps the medicines reduce the working of the muscles,’ speculates De Lange. ‘That is what the literature suggests, at least, but we have not yet looked into this. We think the effect may have consequences for the food web. Less active water shrimps are easier for fish to catch.’

As far as De Lange is concerned, the findings merit further research. ‘We live in a society where people live longer and use more medicines. The amount of medicines released into the environment is likely to increase. That’s why we want to know exactly what’s going on.’/ WK