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This exploratory study aimed to examine the relationship between fish eating habits, human mercury levels, and mercury levels in fish in three communities of the Napo River Valley, Ecuadorian Andean Amazon, a region without gold mining but with significant deforestation and volcanic soils with naturally high mercury levels. By recognizing the politicoeconomic factors which cause deforestation, the cultural factors which influence diet, and the biogeochemical factors which contribute to mercury levels, this study employs an ecosystem approach. Interviews on diet were conducted, hair samples from 99 individuals were collected, and samples of commonly eaten fish were taken. Samples were analyzed using cold vapor atomic fluorescence spectrometry (CVAFS). Two rural communities were found to have higher fish consumption and hair mercury levels (8.71 lg/g and 5.32 lg/g) as compared to an urban community (1.87 lg/g). A sequential analysis of hair established mercury levels by month. No seasonal tendencies were noted. Piscivorous fish (0.36 lg/g) were found to be more contaminated in mercury than herbivorous fish (0.05 lg/g). The study shows that sociocultural factors are important in determining mercury exposure. The two village communities consume different species of fish with different frequencies, leading to differential exposure and mercury concentrations in hair samples. The levels of mercury in these two villages were similar to those found in Brazil where neurobehavioral tests showed a correlation between these relatively low levels of mercury and decreased psychomotor capacities. These findings are concerning and should be followed by further studies on the multiple factors that affect the health status of these exposed communities.

Small-scale gold mining in Portovelo-Zaruma, Southern Equador, performed by mercury amalgamation and cyanidation, yields 9-10 t of gold/annum, resulting in annual releases of around 0.65 t of inorganic mercury and 6000 t of sodium cyanide in the local river system. The release of sediments, cyanide, mercury, and other metals present in the ore such as lead, manganese and arsenic significantly reduces biodiversity downstream the processing plants and enriches metals in bottom sediments and biota. However, methylmercury concentrations in sediments downstream the mining area were recently found to be one order of magnitude lower than upstream or in small tributaries. In this study we investigated cyanide, bacterial activity in water and sediment and mercury methylation potentials in sediments along the Puyango river watershed, measured respectively by in-situ spectrophotometry and incubation with (3)H-leucine and (203)Hg(2+). Free cyanide was undetectable (<1 μg·L(-1)) upstream mining activities, reached 280 μg·L(-1) a few km downstream the processing plants area and was still detectable about 100 km downstream. At stations with detectable free cyanide in unfiltered water, 50% of it was dissolved and 50% associated to suspended particles. Bacterial activity and mercury methylation in sediment showed a similar spatial pattern, inverse to the one found for free cyanide in water, i.e. with significant values in pristine upstream sampling points (respectively 6.4 to 22 μgC·mg wet weight(-1)·h(-1) and 1.2 to 19% of total (203) Hg·gdry weight(-1)·day(-1)) and undetectable downstream the processing plants, returning to upstream values only in the most distant downstream stations. The data suggest that free cyanide oxidation was slower than would be expected from the high water turbulence, resulting in a long-range inhibition of bacterial activity and hence mercury methylation. The important mercury fluxes resultant from mining activities raise concerns about its biomethylation in coastal areas where many mangrove areas have been converted to shrimp farming.

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The Puyango River Basin covers approximately an area of 4400 km 2 , it is located in Southern of Ecuador, with Calera and Amarillo rivers as tributaries. In this region, one of the main activities is small scale gold and silver mining. Currently there are 110 processing plants on the bank of Calera and Amarillo rivers, causing a significant degradation of natural resources. A seasonal comparison of metal concentrations in surface water, sediments and particulate matter from the Puyango River and its effluents is made. It was done a differentiation between natural contaminations with the anthropogenic one generated by mining activity. Samples were taken during dry season (2004) and rainy season (2006), and analyzed physicochemical parameters, anions and cations and the concentrations of heavy metals. The results show a clear influence of gold mining in Puyango River contamination, starting with its tributaries, Calera and Amarillo rivers, which have the highest concentrations of heavy metals from the basin, corresponding with the location of the mineral processing plants.