Armando Ramírez

Heavy metals and organic carbon in sediments from the Tuy River basin, Venezuela.

The Tuy River basin, located in north-central Venezuela with an annual average temperature of 27°C and precipitation of 140 cm, was selected to conduct a geochemical study of bottom sediments, with the object of establishing the natural and human influences in the abundance and distribution of Fe, Mn, Cr, Co, Cu, Ni, Pb, Zn and organic carbon. The basin is lithologically divided into two sub-basins, north and south. The north sub-basin drains a iow-grade metasedimentary terrain with a population density of 800 persons km−2 and approximateiy 600 industrial sites, while the south sub-basin in underlain by metavolcanic and ultramafic rocks, with a population density of less than 10 persons km−2.Stream bottom sediment samples (150) were collected during the years of 1979–1986 in 16 unpolluted sites and 13 polluted sites. The sediments were air dried at room temperature and sieved through a 120 stainless steel mesh (125 μm). Samples of grain size smaller than 125 μm were analysed, the heavy metals being determined by atomic absorption spectrometry and the organic carbon (Corg) by dry combustion.The higher concentrations of heavy metals and organic carbon found in the pristine areas were in the south sub-basin, especially in those areas with higher annual precipitation and tropical forest. This indicated that the metavolcanic and ultramafic rocks yield higher concentrations of heavy metals than the metasedimentary rocks. It was also noted that the higher concentrations of Cr and Ni are associated with the ultramafic rocks. The results obtained from the sediment samples collected in the polluted sites showed that the elements Pb, Zn and Corg are enriched up to 4 times as a result of ail the human activities taking place in the basin. Organic carbon is an excellent indicator of domestic wastewater, Pb and Zn are good indicators of the automotive traffic and industrial effluents. The concentrations of each heavy metal did not show any significant correlation with grain size fractions; however, the concentration of organic carbon did show a negative correlation with grain size. The lithological, climatic and vegetation influence in the abundance of heavy metals and organic carbon in stream sediments clearly indicates the necessity of establishing background levels for the area under study when carrying out studies in environmental geochemistry.

Influence of sampling strategy, lithology, vegetation and rainfall on metal background concentrations in sediment of the tropical Tuy River basin, Venezuela

Abstract The Tuy River basin, north-central Venezuela, was selected to study the influence of the sampling strategy and analytical methods, lithology, rainfall and vegetation on the background concentrations of heavy metals in stream sediments. Stream bed sediment samples (105) were collected during four years of the period 1979–1986 at 15 sites. The sediments were air-dried at room temperature and sieved through a − 120 mesh (125 μm) stainless-steel sieve. The concentrations of Fe, Mn, Co, Cu, Cr, Ni, Ph, Zn and Cd were determined by atomic absorption spectrometry after digestion with a hot (80°C) concentrated mixture of HNO 3 , HClO 4 and HF. The coefficient of variation (CV) due to analytical methods was 60% indicate contamination or mineralized areas. The large difference in average concentration among the tributaries (CV = 29 − 110%) allows distinction between areas with different lithology and vegetation. The northern and southern areas of the Tuy River basin exhibit felsic and mafic lithologies, respectively. The southern area can be further divided in two subunits: the southwestern with savanna vegetation and the southeastern characterized by tropical rainforest. The highest concentrations of metals were found in the southern area (3 times the northern). Especially high values were measured in the southeastern subunit and are likely due to the metavolcanic and mafic bedrock lithologies, and the high weathering intensities associated with this tropical forest area.

Distribution of Total and Organic Mercury in Superficial Soils in the Upper Manzanares River Watershed, Sucre State, Venezuela

Total and organic mercury contents were determined from samples of surface soils (0-5 cm), sieved at ≤63 μm. collected from 10 different locations in the upper Manzanares River watershed, using cold vapor atomic absorption spectroscopy. Methylmercury was determined using a HPLC-UV detector. The mean total mercury concentration was 1.3 μg. g-1, a value permitted by the Canadian environment quality guidelines for farming soils, but high for European standards. Using certified reference materials, we verified that a modification of the method described by Qian et al. (2000) was effective for organic mercury extraction, with a recovery of 92.17% for DORM-2 and 92.11% for TORT-2. This modified method was applied to soil samples, obtaining concentrations of 0.5-1.0 μg.g-1 of organic mercury. The parameters for determining methylmercury using HPLC-UV were optimized; the best results were obtained with a 4.6 mm × 25 cm Zorbax CN– column, with a mobile phase of 70/30 V/V of methanol: ammonium acetate 0.05 mol.l-1, with a flow rate of 0.5 ml.min-1; the methylmercury was detected at 4.99 min retention time. Methylmercury was not found in the soil samples. Using the certified reference material we proved that the method used produced reliable results. The analysis confirmed the existence of mercury in this farming area.

Lead, copper and zinc in atmospheric and fluvial particulates from the Caracas Valley, Venezuela

The atmospheric particulates from the Caracus Valley in Venezuela and the fluvial particulates transported by the Tuy River into the Caribbean sea have been evaluated for Pb, Cu and Zn with the purpose of determining the contamination levels in the study area. The atmospheric particulate samples were collected in the city of Caracas using a low volume sampler whereas the fluvial particulate were collected at the mouth of the Tuy River. The particulate samples were analysed by flame or graphite furnace atomic absorption spectrometry depending upon the concentration levels of the heavy metal under study. The results obtained for the fluvial particulates enabled estimates to be made of the total anthropogenic flux of Cu (383 ton year−1), Pb (528 ton year−1) and Zn (865 ton year−1). These results yield annual per capita inputs for Cu (96 g),Pb (132 g) and Zn (216 g) which greatly exceed those from global anthropogenic emissions. The weighted average concentration of Pb (1.13 %) found in the atmospheric particulates was much higher than those for Cu (140 mg kg−1) and Zn (200 mg kg−1) and reflects the high motor car traffic in the Caracas Valley. The anthropogenic/natural ratios estimated in this study were as follows: 2.6 for Pb; 1.5 for Cu and 1.5 for Zn. This indicates that anthropogenic inputs for Cu, Pb, and Zn in the study area exceed those from natural sources, cars being the major source for Pb and industrial activities the major sources for Cu and Zn.