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31.
A mathematical model which represents the transport processes of heavy metals and fine sediments in a fluvial stream was developed.
The model consists of a three-equation system: the first one for total chromium concentration in the water column, C
Tw, the second one for total suspended sediment concentration, S
w, and the third one for chromium concentration in bed sediments, r. The third equation represents the chromium exchange between the water column and bed sediments by two processes: diffusion
of soluble chromium and erosion/deposition of chromium sorbed to sediments. The basic assumption of the model is the instantaneous
equilibrium. The main parameters are the partition coefficients in the water column and bed sediments, the depth of the active
bed sediment layer, and the mass transfer coefficient between the water column and sediment pore water. The numerical model
approximates the equations of advection–dispersion for chromium in water and suspended sediments by using a Eulerian third-order
scheme. Numerical vs. analytical solutions were considered satisfactory for different initial, boundary, and sedimentological
conditions. In order to estimate the impact of a chromium side discharge, the model was implemented for the Salado River in
a reach of 65.6-km long (Santa Fe, Argentina). The results showed the effect of chromium discharge on almost the whole reach,
then the vulnerability of the water quality in the Salado River when the flow was low was evidenced. When comparing the computed
and measured results, the former showed a reasonable representation of the presence of chromium in water and bed sediments. 相似文献
32.
Ordóñez A Alvarez R Charlesworth S De Miguel E Loredo J 《Journal of environmental monitoring : JEM》2011,13(1):128-136
Analytical results of soil samples taken in three different mercury mining sites in Northern Spain are studied to assess the potential adverse health effects of the exposure to trace elements associated with the mining process. Doses contacted through ingestion and inhalation and the dose absorbed through the skin were calculated using USEPA's exposure parameters and the US Department of Energy's toxicity values. The results of the risk assessment indicate that the highest risk is associated with ingestion of soil particles and that the trace element of major concern is arsenic, the exposure to which results in a high cancer risk value for all the sites ranging from 3.3 × 10(-5) to 3.6 × 10(-3), well above the 1 × 10(-5) probability level deemed unacceptable by most regulatory agencies. Regarding non-cancer effects, exposure to polluted soils yields an aggregate hazard index above the threshold value of 1 for all three sites, with As and Hg as the main contributors. Risk assessment has proven to be a very useful tool to identify the contaminants and exposure pathways of most concern in the soils from metal mining sites, as well as to categorize them in terms of action priority to ensure fitness for use. 相似文献
33.
Aram Terchunian Victor Klemas Alberto Segovia Agustin Alvarez Bryon Vasconez Luis Guerrero 《Environmental management》1986,10(3):345-350
A cooperative mangrove mapping project between the Ecuadorian Center for Remote Sensing (CLIRSEN) and the University of Delaware was begun in August 1982. The objectives of the project were to create historical maps of mangrove ecosystem extent and change, while transferring aerial photographic interpretation techniques to Ecuadorian personnel. The result of this cooperation was a series of three 125,000 scale maps of historical mangrove extent and change from 1966 to 1982 in the southern Gulf of Guayaquil. This multitemporal study showed a 16% decrease in mangrove extent and a 27% increase in shrimp pond development. If these rates of change prevail into the future, mangroves in Ecuador will reach parity with shrimp ponds in 1984 and completely disappear by mid-1990. Recognizing the significance of this loss to shellfish and fish production along the coast, Ecuadorian scientists at CLIRSEN have subsequently initiated a nationwide mangrove mapping program to create a historical base for future mangrove management strategies. 相似文献
34.
E. Alonso Alvarez M. Callejón Mochón J.C. Jiménez Sánchez L. Moreno López 《毒物与环境化学》2013,95(1-2):55-63
The application of the electrochemical speciation of heavy metals in tracking groundwater is presented. Three fractions interchangeable, associated to the organic materials and associated to the matter in suspension of the metals Zn, Cd, Pb and Cu by means of the anodic stripping voltammetry were determined. The parameters of the determination were: electrodeposition potential ‐1.2 V, time of deaerating with nitrogen 300 s, time of the electrolysis 90 s (with stirring) and the rest time 40 s. The core of this work was to determine the validity of this scheme of electrochemical speciation in the pursuit of the follow‐up of groundwater pollution caused by heavy metals after the breakdown of the mining raft at the River Guadiamar Basin (Andalusia, Spain). 相似文献
35.
A comparative study of three different methods for the sequential extraction of heavy metals in soil
Three different methods for the sequential extraction of heavy metals from soil (viz those of Tessier et al. (A. Tessier, P.G. Campbell and N. Bisson (1979). Anal. Chem., 51, 844.), Sposito et al. (G. Sposito, L.J. Lund and A.C. Chang (1989). Soil. Sci. Soc. Am. J., 46, 260.) and Mann and Ritchie (S.S. Mann and G.S.P. Ritchie (1993). Aust. J. Soil Res., 31, 255.)) were examined in terms of the distribution of Cu, Zn and Pb in the soil phases and the bioavailability of these elements in soil. To this end, several samples of soils polluted with metals from a copper mine were fractionated by using the three studied methods and analyzed by atomic absorption spectrometry. The results revealed differences in extraction efficiency among the methods due to the extractant used, or its concentration, and to the soil/solution ratio. The three methods were found to provide accurate heavy metal background contents. However, the method of Tessier et al. is to be preferred for quantifying increased levels of heavy metals on account of its high extraction power. 相似文献
36.
Muñoz A García-Duro J Alvarez R Pesqueira XM Reyes O Casal M 《Journal of environmental management》2012,94(1):34-40
In NW Europe, it is known that cutting is a useful tool for managers with regard to decisions about the conservation and management of wet heathlands. Nevertheless it is rarely described quantitatively in the international literature. In Spain, knowledge about this is scarce or lacking. In this study, twenty communities were selected in Galicia (NW Spain) that would represent from one to four stages of vegetation development after cutting. Two 5?×?5?m plots were established for each stage to characterise the vegetation on the basis of its species composition, frequency values, vertical structure and linear cover features. The Diversity Shannon index was calculated and multivariate analyses were performed. As succession advanced, notable changes were produced in the cover of dominant species, Erica ciliaris and Ulex gallii in the first stages and Erica tetralix and Genista berberidea in mature ones. Also, the species richness decreased because of the reduced number of herbs species in the mature stages and, finally, the cover values are indicators of the degree of vegetation development, together with the other parameters of height, overlayering or diversity. Cutting is a useful tool for management of heathlands because the existence of vegetation units belonging to different succession stages increases the internal diversity of communities. On the other hand, the vertical and horizontal structure reflects the formidable resilience of the vegetation community to this practice. This study offers a global vision of the dynamics of wet heathlands after cutting, with very useful ecological information that can be used by the people responsible for their management. 相似文献
37.
38.
Alfredo Montero Alvarez Juan R. Estévez Alvarez Clístenes Williams Araújo do Nascimento Iván Pupo González Oscar Díaz Rizo Lázaro Lima Carzola Roberto Ayllón Torres Jorge Gómez Pascual 《Environmental monitoring and assessment》2017,189(1):28
Epiphytic lichens, collected from 119 sampling sites grown over “Roistonea Royal Palm” trees, were used to assess the spatial distribution pattern of lead (Pb) and identify possible pollution sources in Havana (Cuba). Lead concentrations in lichens and topsoils were determined by flame atomic absorption spectrophotometry and inductively coupled plasma (ICP) atomic emission spectrometry, respectively, while Pb in crude oils and gasoline samples were measured by ICP-time of flight mass spectrometry (ICP-ToF-MS). Lead isotopic ratios measurements for lichens, soils, and crude oils were obtained by ICP-ToF-MS. We found that enrichment factors (EF) reflected a moderate contamination for 71% of the samples (EF > 10). The 206Pb/207Pb ratio values for lichens ranged from 1.17 to 1.20 and were a mixture of natural radiogenic and industrial activities (e.g., crude oils and fire plants). The low concentration of Pb found in gasoline (<7.0 μg L?1) confirms the official statement that leaded gasoline is no longer used in Cuba. 相似文献
39.
40.
The prenatal sonographic findings in a case of Walker-Warburg syndrome are described. The patient was not at risk for this condition. Ultrasound examination at 34 weeks' gestation revealed hydrocephaly, Dandy-Walker anomaly, and striking ocular abnormalities. From a review of the literature it appears that while intracranial abnormalities can lead to the diagnosis in cases at risk for this syndrome, ocular abnormalities are rather characteristic for this syndrome and they should be searched for in every case of hydrocephaly or encephalocele. 相似文献