Box 7 I Geochemical characteristics of river and floodplain sediments in Europe

Work carried out by FOREGS (Forum of European Geological Surveys) shows that sediments from streams and floodplains of numerous rivers in various parts of Europe have been severely contaminated by heavy metals in waste from mining and other human activities over several centuries. For example, parts of the Innerste River floodplain in Germany, which is now used for agriculture, contain up to 2 per cent lead and several grams per tonne (ppm) of cadmium and mercury in the upper 50 cm as a result of mining in the Harz mountains. Such floodplains constitute chemical threats that may be triggered by future catastrophic floods or through the action of acid rain. Downstream, harmful effects on ecological systems may cross political borders and eventually reach the sea. This type of pollution needs to be surveyed in order to quantify the extent of the problem, evaluate health effects and develop plans for mitigation and abatement strategies. FOREGS has developed methods comprising chemical analyses of regionally distributed samples of pre- and post-industrial deposits of floodplain sediments, which facilitate an appraisal of the pollution against a varying natural geochemical background. Examples of the type of data that could be obtained by such geochemical mapping are given in Figure 7.7.