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Total mercury (T-Hg) and methylmercury (MeHg) concentrations have been measured in the muscle tissue of 16 fish species consumed in the Mojana region of Colombia. T-Hg analysis was performed by cold-vapor atomic-absorption spectroscopy (CV-ASS) and MeHg analysis by gas chromatography with electron-capture detection. Higher T-Hg and MeHg concentrations were detected in carnivorous species (T-Hg = 0.371 +/- 0.172 (microg g(-1) fresh wt, MeHg = 0.346 +/- 0.171 microg g(-1) fresh wt) than in non-carnivorous fish (T-Hg = 0.155 +/- 0.108 microg g(-1) fresh wt, MeHg = 0.146 +/- 0.102 microg g(-1) fresh wt). In the different species mercury was present almost completely as the methylated form, with percentages between 80.5 and 98.1% (mean 92.0 +/- 3.4%). In 13.5% of fish-tissue samples T-Hg concentrations exceeded the maximum level recommended by the World Health Organization for human consumption (Hg = 0.5 microg g(-1) fresh wt). Although mean T-Hg concentrations in all fish samples (0.269 +/- 0.181 microg g(-1) fresh wt) did not exceed this limit, risk assessment suggested that the consumption of 0.12 kg fish day(-1) could increase the risk of mercury poisoning of the inhabitants of this region.

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Mercury (Hg) used in gold amalgamation is a major source of contamination in developing countries. Water, sediments, plankton, fish, and human samples from Grande Marsh, a Hg-polluted marsh located in the south of Bolívar, municipality of Montecristo, Colombia, were collected during both the rainy and the dry seasons (2003-2006), at three different sampling sites, and analyzed for total Hg (T-Hg) content. Water, sediment, seston, phytoplankton, and zooplankton T-Hg concentrations were 0.33 +/- 0.03 microg/L, 0.71 +/- 0.03, 1.20 +/- 0.06, 0.52 +/- 0.03, and 0.94 +/- 0.05 microg/g dry weight (wt), respectively. T-Hg levels in these compartments were highly pair-correlated (p < 0.05), and for all of them, except sediments, greater values were found during the dry season. Significant differences were observed for T-Hg concentrations in fish according to their trophic position. Average highest T-Hg values were found in carnivorous species such as Caquetaia kraussi (1.09 +/- 0.17 microg/g fresh wt), Hoplias malabaricus (0.58 +/- 0.05 microg/g fresh wt), and Plagioscion surinamensis (0.53 +/- 0.07 microg/g fresh wt), whereas the lowest were detected in noncarnivorous species such as Prochilodus magdalenae (0.157 +/- 0.01 microg/g fresh wt). In those fish species where seasonal comparisons were possible, specimens captured during the dry season had greater T-Hg levels in muscle. Although the T-Hg mean level for all fish samples (0.407 +/- 0.360 microg/g fresh wt) did not exceed the recommended limit ingestion level, risk assessment based on the hazard index suggested that a fish intake of 0.12 kg per day (a small carnivorous specimen) could increase the potential health effects related to Hg exposure in the local human population, whose hair T-Hg median value was 4.7 microg/g, and presented a low but significant correlation with fish consumption (r = 0.250, p = 0.016). In short, Hg pollution from gold mining around Grande Marsh has permeated the food web, and currently levels in fish represent a serious concern for human health.

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