Mercury in Negro River, Amazonas, Brazil - Preliminary study of exposure indicators in fish and human populations

Abstract

This was a pilot study accomplished in two populations of the Negro River: São Gabriel da Cachoeira, located in the border between Brazil, Colombia, and Peru (middle Negro River); and Barcelos (lower Negro River), close to the city ofManaus. Fish samples were collected in both locations. In addition, using a random protocol, hair samples were collected from the population of both communities to evaluate their mercury exposure. The Hg analysis was accomplished by atomic absorption spectrometry, using a Mercury Analyzer HG 3500. In São Gabriel da Cachoeira, measurements performed in 140 fish samples of nine carnivorous species resulted in a mean Hg concentration ofO.453 Ilg/g (0.039 -3.921 Ilg/g), and in 76 fish samples of two non-carnivorous species resulted in a mean Hg concentration of 0.102 Ilg/g (0.003 -0.552 Ilg/g). In the same location, measurements of 157 hair samples resulted in a mean Hg concentration of 13.025 Ilg/g (0.303 -83.116 Ilg/g). In Barcelos, measurements performed in 126 fish samples of eight camivorous species resulted in a mean Hg concentration of 0.459 Ilg/g (0.062 -1.930 Ilg/g), and in 147 fish samples of six noncarnivorous species resulted in a mean Hg concentration ofO.097 Ilg/g (0.018 -0.184 Ilg/g). In Barcelos, measurements of242 hair samples showed mean Hg concentrationQf9.671 Ilg/g (0.0719 -52.049 Ilg/g). There are gold mining activities in the upper Negro River, in Colombia, and the Hg levels show a gradient beginning in São Gabriel da Cachoeira and decreasing towards Barcelos. The results of the present work suggest that the riverside communities of the Negro River have been exposed to mercury through fish consumption for a long time once the mercury presence seems to be natural in the area. However, the population living in the area under the impact of gold mining activity possesses a segment of older people that was less affected by Hg exposure in more recent decades. Further studies are necessary to detennine the risks ofHg exposure for the population ofNegro River basin.