At the ICPR monitoring station Koblenz (Rhine-km 590.3) the load of hexachlorobenzene (HCB) on suspended solids has been measured for several years. In addition, sediments from impoundments on the Upper Rhine were analysed for HCB. The results show that the HCB load on suspended solids in the river Rhine has decreased to nearly half the initial value between 1985 and 1991. The still relatively high HCB concentrations amounting in average to 40 µg/kg on the suspended solids sampled at Koblenz can only be explained by recalling that sediments in the impoundments and in other contaminated sites of the Upper Rhine constitute a historic HCB storage, which contributes to the HCB load on suspended solids through remobilization during flood events.

With regard to future trend monitoring activities for HCB in suspended solids, a minimum sampling interval of 14 days is recommended.

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