Spatio‐temporal geochemistry of mercury in waters of the Tapajós and Amazon rivers, Brazil

Abstract

Spatial and temporal variations of mercury (Hg) concentrations were monitored in the surface waters from the lower portion of the Tapajós River, the Arapiuns River, its principal tributary, and the Amazon River at its confluence with the Tapajós. In the rivers, Hg concentrations in the water column are governed by the concentration of suspended particles. Hg in the filtered water showed very little seasonal variation with low concentrations in the lower Tapajós (Ͻ1.8 ng L Ϫ1), Arapiuns (Ͻ0.8 ng L Ϫ1 ), and Amazon (Ͻ2.8 ng L Ϫ1). Concentrations of fine particulate Hg (0.6-29.7 ng L Ϫ1 ) represent 40%-90% of the total volumetric concentration of Hg. In relation to their oxyhydroxide contents, suspended particles are not richer in Hg than nearby soils where oxyhydroxides control the accumulation of Hg. The study shows that the dominant stock of Hg in the aquatic ecosystems of this region is derived from erosion of natural soils in the catchment rather than from anthropogenic pollution. The input of natural Hg coming from soils into the aquatic ecosystems may have increased over historical levels in the region. This increase of total Hg in aquatic ecosystems could potentially account for high levels of methylmercury recently reported in fish and humans in the lower Tapajós River area, but the link between the different processes that promote high levels of methylmercury exposure for the human community remains to be proved.Numerous recent studies (Bidone et al. 1997; Lebel et al. 1997;Malm et al. 1997) have documented exceedingly elevated levels of mercury in fish of the Tapajós River, one of the principal tributaries of the Amazon River. Exposure to methylmercury (MeHg) through fish consumption by the 1 Present address: IRD-Bolivia, CP 9214, La Paz, Bolivia (roulet@cict.fr). AcknowledgementsThe project would never have seen the light of day without the collaboration of Aldo Queiroz Gomes, coordinator of the Santarém campus and Cristovan Waverly Diniz, rector of the Universidade Federal do Pará (UFPa). We would also like to thank Louise Cournoyer, Gerson da Costa de Oliveira, Jean Lebel, Pierre Pichet, Everaldo Portella, Isabelle Rheault, Sewbert Rodrigues Jati, Gil Serique, Delaine Sampaio da Silva, Persio Scavone de Andrade, Nicolas Soumis, Silmara Sousa de Morales, Carlos-José Sousa Passos, Sophie Tran, and Ronilson Vasconcelos Barbosa for their assistance in the field and the laboratory. The analytical methods used for Hg were developed by Professor P. Pichet for the laboratory of the Chaire de Recherche en Environnement H-Q/CRSNG/UQAM.

LIOFILIZACIÓN DE PULPA DE Myrciaria dubia HBK MC VAUGH, CAMU CAMU

“…Concentraciones de mercurio menores a las del río Nanay han sido encontrados también en el río Amazonas, en territorio brasileño (Roulet et al 2001b). En estos ríos de agua blanca las mayores concentraciones de mercurio se encuentran en las partículas en suspensión (Roulet et al 2001b).…”

“…Concentraciones de mercurio menores a las del río Nanay han sido encontrados también en el río Amazonas, en territorio brasileño (Roulet et al 2001b). En estos ríos de agua blanca las mayores concentraciones de mercurio se encuentran en las partículas en suspensión (Roulet et al 2001b). En el río Madre de Dios, estas partículas en suspensión compuestas mayormente de arena, arcilla y limo proporcionan al agua una coloración marrón y escasa transparencia de la columna de agua de alrededor de 16 a 24 cm (IIAP-CTAR Madre de Dios 2000).…”

“…El mercurio, metal muy tóxico para el ambiente y la salud de las poblaciones humanas, es objeto de estudio en varios lugares de la cuenca del río Amazonas (Veiga 1997a;1997b;Lodenius y Malm 1998;Maurice-Bourgoin et al 1999;Roulet et al 1999;2000b, 2001a2001b;Carmouze et al 2001).…”

Effects of Small-Scale Gold Mining Tailings on the Underwater Light Field in the Tapajós River Basin, Brazilian Amazon

“…Chlorophyll-a (chl-a) concentrations vary from 5.0 to 25.1 µg·L −1 [26,27], and cyanobacteria blooms related to urban-derived diffuse nutrient input at the margins of the Tapajós mouth (Santarém) have been reported [28]. In this section of the river, total suspended sediments (TSS) are composed primarily of fine matter discharged from upstream [29][30][31] reaching concentrations up to 4.1 mg·L −1 during rising and receding water levels [32]. In the Tapajós, for example Costa et al [32] observed, on average, lower a cdom absorption (a cdom (440) = 3.2 m −1 ) than values measured in black water rivers of the Amazon (8.6 m −1 ).…”

Mercury in soils and sediments from gold mining liabilities in Southern Amazonia

“…Furthermore, this liability is only a small contribution to the amount released by the Spanish and Portuguese, during over 200 years of gold and silver mining during the colonial times in South America 8 . On the other hand, there are now evidences that Amazonian soils should present naturally elevated and widespread concentrations of mercury [9][10][11][12] . These naturally elevated concentrations reflect on mercury contents of fishes, which are living in areas distant from any anthropogenic source of the metal 13,14 .…”