Mercury contamination in the Madeira River, Amazon: Hg inputs to the environment

The potential contamination of Amazon rivers by Hg used in gold-mining activity has recently worried various local and international environmental authorities. Some attempts have been made to quantify the problem, however logistic difficulties and lack of reliable information have led to some misinformation. In 1986 three Brazilian research groups at the Universities of Rondonia, Niteroi, and Rio de Janeiro started a joint project on the Madeira River to quantify Hg contamination in the area. This note presents the first estimate of Hg inputs to the regional environment, describes the evolution of the problem, and discusses its eventual impact on the local biota and human population. The Madeira River is located in the southwestern Amazon basin and drains a watershed covered mostly by tropical rain forests. Most gold-mining occurs in the Madeira River itself along 300 km from Porto Velho, capital of the State of Rondonia, along the Bolivian border, to the town of Guaraja Mirim.