By mistake, the natural turbidity of rivers caused by suspended matter is often taken for pollution. True pollution of suspended matter occurs by adsorption of pollutants to suspended particles. Dissolved or adsorbed to particles the pollutants get into the Rhine via the atmosphere, runoff, leaching and erosion. Furthermore, older, polluted sediments are remobilised by dredging and transported further downstream.
A large share of the total amount of organic and inorganic substances transported with suspended matter consists of pollutants transported together with suspended matter.
In 2009, the ICPR drafted a Sediment Management Plan aimed at reducing the pollutant load of suspended matter and thus of sediments.
The HCB (hexachlorobenzene) contents mainly originate from a chemical plant near Rheinfelden, which has been shut down and in which this substance occurred as by-product. Even though this persistent organic pollutant has been forbidden in the Rhine bordering states for a long time, it is still detected in suspended matter, sediments and fish. This mainly applies to the Upper Rhine. HCB contents fall from the Upper Rhine (Weil am Rhein) to the German-Dutch border at Bimmen-Lobith.
Lead (Pb) reaches the Rhine via exhaust fumes from cars and the atmosphere, as it is a tetraethyllead component which used to be an antiknock additive in petrol. Due to its toxicity tetraethyllead was replaced in the beginning of the 1990s. The lead contents of suspended matter have continuously fallen ever since. Substances input via the atmosphere, such as lead, accumulate in suspended matter downstream.