Carlos Green-Ruiz

Biomonitoring of Cd, Cr, Hg and Pb in the Baluarte River basin associated to a mining area (NW Mexico)

With the purpose of knowing seasonal variations of Cd, Cr, Hg and Pb in a river basin with past and present mining activities, elemental concentrations were measured in six fish species and four crustacean species in Baluarte River, from some of the mining sites to the mouth of the river in the Pacific Ocean between May 2005 and March 2006. In fish, highest levels of Cd (0.06 μg g ⁻¹ dry weight) and Cr (0.01 μg g⁻¹) were detected during the dry season in Gobiesox fluviatilis and Agonostomus monticola, respectively; the highest levels of Hg (0.56 μg g⁻¹) were detected during the dry season in Guavina guavina and Mugil curema. In relation to Pb, the highest level (1.65 μg g⁻¹) was detected in A. monticola during the dry season. In crustaceans, highest levels of Cd (0.05 μg g⁻¹) occurred in Macrobrachium occidentale during both seasons; highest concentration of Cr (0.09 μg g⁻¹) was also detected in M. occidentale during the dry season. With respect to Hg, highest level (0.20 μg g⁻¹) was detected during the rainy season in Macrobrachium americanum; for Pb, the highest concentration (2.4 μg g⁻¹) corresponded to Macrobrachium digueti collected in the dry season. Considering average concentrations of trace metals in surficial sediments from all sites, Cd (p<0.025), Cr (p<0.10) and Hg (p<0.15) were significantly higher during the rainy season. Biota sediment accumulation factors above unity were detected mostly in the case of Hg in fish during both seasons. On the basis of the metal levels in fish and crustacean and the provisional tolerable weekly intake of studied elements, people can eat up to 13.99, 0.79 and 2.34 kg of fish in relation to Cd, Hg and Pb, respectively; regarding crustaceans, maximum amounts were 11.33, 2.49 and 2.68 kg of prawns relative to levels of Cd, Hg and Pb, respectively.

Potential Bioavailability of Heavy Metals in Surface Sediments from the Altata-Ensenada del Pabellón Lagoon, SE Gulf of California

Abstract The total and bioavailable contents of Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in surface sediments from 77 sites in the Altata-Ensenada del Pabellón (AEP) lagoon complex were determined by Atomic Absorption Spectrometry, after inverted aqua regia (HNO3/HCl 3:1) and sodium acetate 1M (adjusting pH = 5 with acetic acid) digestion, respectively. The ratio between the bioavailable fraction and the total concentration (BAP: BioAvailable Proportion), for each metal, was examined according to the chemical parameters of the bottom waters (dissolved oxygen and salinity) and geochemical characteristics of the sediments (organic carbon and total Al, Fe and Mn contents). Highest bioavailable concentrations of metals were associated with agricultural discharges and Culiacán River inputs. According to the Canadian Sediment Quality Guidelines, the Pb bioavailable content can produce adverse effects on organisms. Total concentration of Cu, Mn, Pb and Zn played an important role in the fractioning of these metals. Organic carbon, fine sediment, Fe and Mn hydroxides and aluminosilicates influenced the behaviour of Cu, Fe Ni and Zn BAPs.

Natural attenuation of Cr(VI) contamination in laboratory mesocosms

The processes leading to the natural attenuation of hexavalent chromium (Cr(VI)) in marine systems are not well understood. To determine the rate at which Cr(VI) could be reduced and the effect of Cr(VI) on bacterial communities in marine sediments, we performed mesocosm experiments with 37.85 L aquaria containing San Diego Bay sandy sediments and seawater. Constant levels of 0, 0.25 (low), and 1.5 mM (high) Cr(VI) were maintained in the water column for 2 months. Chemical analyses of sediment cores taken from the mesocosms indicated that Cr accumulated in the upper 5 mm of the sandy sediments. In general, the distribution of total Cr did not correlate with Fe, Mn, or total organic carbon. Enrichment cultures of metal (iron and chromium)- and sulfate-reducing bacteria from the upper horizon (0-5 mm) of sediments were performed to look for the potential contributors in the detoxification/removal process. PCR of 16S rRNA genes and denaturing gradient gel electrophoresis (DGGE) was used to examine the microbial community structure in sediment depth profiles. When Cr(VI) was present, the number of DGGE bands decreased only in the upper 5 mm of sediments indicating an inhibition of certain bacterial populations and/or a selection for Cr-resistant bacteria in this region. Analysis of the DGGE bands was not especially helpful as most sequences were related to unknown, unidentified, or uncharacterized bacterial cloned sequences.

Determination of hydraulic conductivity and fines content in soils near an unlined irrigation canal in Guasave, Sinaloa, Mexico

The determination of hydraulic conductivity is essential for the assessment of fluid migration rates in the subsurface. Geoelectric methods are often used in hydrogeological studies as quick and inexpensive tools. The relation between saturated soil hydraulic conductivity (K), clay content and soil resistivity allows an estimation of clay content and K from electrical measurements made in the field or laboratory. In this work, a methodology for estimating fines (silt + clay) content and K from electrical measurements in silt-loam soils is presented. A textural analysis was performed in 73 soil samples collected from 21 boreholes located in the municipality of Guasave, Sinaloa, Mexico, to determine the sections with a greater infiltration of water from the Valle del Fuerte irrigation canal to the local aquifer. The calculated values of texture and K were used to develop a new empirical equation, K = 0.101176 * FINES -1.62 , which achieved a new relation to properly estimate the K values from the percentage of fines content. Electrical measurements were performed in the laboratory for each soil sample to determine the fines content. The K values, which were determined by a new empirical equation, showed an acceptable correlation with the values obtained by traditional techniques for silt and silt loam soils with a clay content < 35%. Water resistivity measurements were performed for samples collected from wells and flumes, showing that the water salinity of the canal is significantly lower than the groundwater. Due to the location of the Valle del Fuerte canal and soil K values, the water infiltrated from the flume into the subsoil creates a barrier preventing or slowing down the advance of the saltwater intrusion from the Sea of Cortez. Short Electrical Resistivity Tomography (ERT) profiles were carried out to determine the surface stratigraphy. The results achieved by the application of ERT and the groundwater salinity values allowed the recalculation of the geoelectrical sections in the fines content and K sections, resulting in a new, faster and less expensive procedure for the determination of hydraulic and petrophysical parameters.

Preliminary observations of cadmium and copper effects on juveniles of the polychaete Capitella sp. Y (Annelida: Polychaeta) from Estero del Yugo, Mazatlán, México

Se investigaron los efectos de cadmio (Cd) y cobre (Cu) sobre juveniles cultivados de Capitella sp. Y. Organismos juveniles de siete dias de edad fueron expuestos a 13 (control), 60, 160, 240 y 340 mg Cd L-1 y a 17 (control), 50, 120 y 150 mg Cu L-1 durante 30 dias. La mortalidad se incremento significativamente al aumentar las concentraciones de Cu y, en las exposiciones a Cd, solamente fue evidente a 340 mg L-1. El tamano corporal y la produccion de heces fecales disminuyeron antes en los especimenes expuestos a Cu que en los expuestos a Cd, especialmente en las concentraciones mas altas de Cu. Estos resultados indican que los juveniles son mas sensibles al Cu en terminos de mortalidad, alimentacion y crecimiento. La produccion de hemoglobina fue inhibida debido a la escasez de alimento en el sedimento experimental, mas que a exposicion a los metales. La formacion de tubos no fue afectada por la presencia de metales ni por la escasez de alimento. Este estudio sugiere que concentraciones entre 50 y 150 mg L-1 de Cu y de 340 mg L-1 de Cd, podrian afectar la dinamica poblacional de esta especie en ecosistemas naturales