Keywords: water pollution, mercury concentration, bottom sediment, bioavailability, Mexico, neutron activation analysis, heavy metals, dams, water column, water quality, water reservoirs
Distribution of mercury in the water and bottom sediment of the J.A. Alzate Dam, Mexico
In this paper, mercury concentration in the soluble, particulate and total fractions of water and in the sediment from the Jose Antonio Alzate Dam in the State of Mexico was evaluated using neutron activation analysis in order to determine the bioavailability and distribution of this metal. Sampling was carried out on three separate seasons – cold dry season, hot dry season and rainy season – such that, at least one complete hydrological cycle in the dam was covered. Results show that mercury constitutes a significant problem in the dam. Concentration in the water column is higher than the maximum acceptable level (10 ng/L) as established by national environment criteria and is present at considerable levels in the bottom sediments (up to 500 µg/kg). In the water, mercury presents a seasonal variation, where the highest concentrations are found during the dry period and the lowest concentrations at the end of the rainy season due to dilution of the metal in water. Sediment concentration of mercury shows evidence of self-cleaning mechanisms in the dam in which, principally through processes of sedimentation, part of the metal is removed from the water column, improving the outflow water quality.