International conference on heavy metals in the environment

Mercury contamination of waters and soils is an environmental problem of increasing concern throughout the Amazon River baxin. In order to better understand the sources of Hg in a major tributary to the Amazon, a monthly time series spanning an entire hydrological cycle has been measured for two rivers of the Upper Madeira drainage basin. At both gauging stations, we observe a hydrological control on the temporal variability of the dissolved and the total mercury (THg) concentrations: they increase in phase with increasing discharge and we observe the highest THg concentrations at the peak stage. Mercury associated with particles represents more than 90% of the TH g in high-water period, and tends to decrease only slowly with falling river stage. This suggests that weathering processes are still active during this last stage. One of the principal factors controlling the distribution of Hg in Andean waters is apparently the process of soil erosion. (Résumé d'auteur