IWRA Proceedings

AbstractLake Izabal located at northwest of Guatemala has an extension of 717 km2 and mean depth of 11.6 m. The basin has a population of approximately 320000 living in towns that have not wastewater treatment services. The Lake has overcame significant deterioration during the last three decades, because of deforestation, intensive agriculture and cattle, mining and lack of wastewater treatment. Lake Izabal represents a source of food and water for different purposes for the human population. The uses of water and the high biological diversity levels found in protected areas in the basin, have increased the concern on environmental pollution and water monitoring. The basin geology is characterized by showing ophiolites at north of Lake Izabal and carbonate-hosted deposits located at the west of the lake. Sediments were collected in October 2004, using an Ekman dredge in six locations in Lake Izabal and dried at 60°C; Total metals were determined by Atomic Absorption Spectrophotometry (AAS), after digestion with HNO3/HF (5:4), evaporation to dryness, and dissolution in 0.1 N HCl. The metal available fraction was determined by sucesive digestion with H2O2 and 0.3 N HCl, filtration and measurement by AAS. High levels of Pb were found (highest value in the Lake center, 49.3 mg/Kg). A partial explanation for the high concentrations is suggested from a geological basis, since Pb -Zn carbonate-hosted deposits are located 100 km at west of the lake. The discharges of untreated wastewater to Polochic River could also be responsible for inputs of lead. Zinc showed the highest total mean concentration (101.9 mg/Kg) in the Lake center and the highest available concentration in El Estor (80.9 mg/Kg). The sediments at south and east showed lower concentrations for this metal. Nickel mining during seventies and early eighties is considered to have increased the levels of metals near the ore. Thus El Estor which is the site nearest to the mining facilities and to the most populated town, showed the highest total and available mean concentrations of nickel (1648.2 mg/Kg and 1114.6 mg/Kg, respectively) and chromium (1923.8 mg/Kg and 205.6 mg/Kg, respectively). These values are significantly higher than concentrations found in the other sampling sites, as for example, sediments at the Lake center and San Marcos River showed total nickel concentrations of 333.6 mg/Kg and 43.4 mg/Kg, respectively. Available fractions of lead, nickel and zinc were high regarding the total concentration. Instead, chromium and cadmium showed a lower available concentration fraction in almost all the samples. The results are useful as the baseline for toxic metals in sediments of Lake Izabal and for making decisions regarding the aquatic environment management, since recent concessions for nickel extraction are starting to operate in the basin.