A wide range of chemicals such as the ones used in agriculture and by industry may leach into the surficial aquatic environment and underground water resources. The resulting chemical pollution can affect aquatic ecosystems by damaging fauna and its habitats, thus reducing biodiversity.

Moreover, pollutants may accumulate in the food chain and harm living organisms. Humans can also be exposed to chemical pollutants by eating contaminated fish or seafood, drinking polluted water or through recreational activities.

Currently, little knowledge exists regarding the mobility and biodegradability of pollutants in soil, sediments and water and their transport throughout the environmental compartments such as soil, groundwater, sediments and surface waters.

In the context of the EU-funded project AquaTerra 1 , a team of European researchers has investigated the load and concentration as well as the degradation of selected pollutants in these compartments, in order to improve understanding of their behaviour and fate.

To date, they collected more than 1,700 samples of soil, sediments and water in 5 EU river basins (Ebro, Elbe, Danube, Meuse and Brévilles) over three years and measured the content of persistent organic pollutants (POPs). Results show that: * Deposition rates of atmospheric polyaromatic hydrocarbons range from 50 to 600 ng/m2 per day excluding the winter period), and vary between the river basins studied.

* Despite being banned for agricultural use for 5 years, pesticides, such as atrazine, are still found in spring and groundwaters at quantities between 0.9% and 2.8% of the annually applied amount before the ban.

* Hotspots showed concentrations of ß -hexachlorocyclohexane (HCH) that are 1,000 times higher when compared to upper catchment sediments. Nevertheless these high concentrations are diluted when mixing with sediments further downstream.

* Selected herbicides contained in the collected samples are partially degraded by micro-organisms during laboratory experiments.

The authors concluded that variations in deposition rates of atmospheric pollutants between river basins may be locally controlled for example by controlling industrial sites. On flood plains, they found that enhanced sediment transport can lead to a dilution of some pollutants within the river basin floodplains. Furthermore, they observed degradation of some pollutants in laboratory experiments, which indicates that microbial degradation of herbicides also potentially occurs in soils. However, they also observed some pesticides remain in soils for long time periods and are not degraded or if so, very slowly.

Overall, this work highlights some important features of the behaviour of POPs in the environment, especially their deposition, mobility and persistence within the environment. These findings provide enhanced information to help us understand the way river basins response to pollution and may become useful in the context of river basin management policies. Contact: Johannes.barth@uni-tuebingen.de