To examine and compare historical accumulation of metal(loid)s in Mexican lakes and reservoirs, 210Pb and 137Cs dated sediment cores were evaluated: two from the remote Zempoala and Miramar Lagoons and three from Lake Pátzcuaro, and the Intermedia and Silva dams that are affected by human activities. Sediment ecotoxicology was assessed using consensus-based sediment quality guidelines for freshwater ecosystems. The +100 a sediment core from the remote Miramar Lagoon had the highest concentrations of Cr and Ni these being higher than the Probable Effect Levels (PELs). Zinc concentrations were also higher in the Miramar Lagoon compared to the other lakes and reservoirs, with concentrations higher than the Threshold Effect Level (TEL). Mercury concentrations from this lagoon were comparable to those for the Intermedia dam that receives water from urban, industrial and agricultural areas. The higher metal concentrations in the core from the Miramar Lagoon suggest that metal concentrations in the rocks of the watershed are high. Another explanation for the higher metal concentrations is the slow sediment accumulation that causes metals to be accumulated over longer time-periods at the sediment–water interface. A decrease in the concentration of As in the Intermedia dam was observed in sediments corresponding to the last decades. This may be due to an increase in sediment accumulation rate or to the reduction in sources of this metalloid in the watershed. In the Miramar Lagoon, an increase was observed in concentrations of As and Cr in more recent sediments, probably related to increased deforestation in the area or the eruption of El Chichonal volcano in 1982. Concentrations of Pb showed a decreasing tendency over the past decades in the Lake Pátzcuaro, Miramar and Zempoala Lagoons sediment cores while such behavior was not be observed for the Intermedia dam. This reduction in concentrations of Pb was attributed to the decrease in use of leaded gasoline. 相似文献
A zero-dimensional model for the environmental fate of ethylenethiourea (ETU) in soils was formulated. The relevant physicochemical transformation processes were derived from published data, and their dynamics analyzed. Corresponding kinetic submodels for sorption, photodegradation, abiotic oxidation and biodegradation were then developed based on assumptions on the dominant process mechanisms. These submodels, and the overall model of biotic degradation in soil, were applied to literature data with determination coefficients of R2 > 0.9, validating the assumed process dynamics. 相似文献
Micron and submicron-sized dust particles can be lifted from the lunar surface due to continual micrometeoroid bombardment and electrostatic charging. The characteristics of these dust populations are of scientific interest and engineering importance for the design of future equipment to operate on the lunar surface. The mobilized grains are expected to have a low velocity, which makes their detection difficult by traditional methods that are based on momentum transfer or impact energy. We describe a newly developed instrument concept, the Electrostatic Lunar Dust Analyzer (ELDA), which utilizes the charge on the dust for detection and analysis. ELDA consists of an array of wire electrodes combined with an electrostatic deflection field region, and measures the mass, charge, and velocity vector of individual dust grains. The first basic prototype of the ELDA instrument has been constructed, tested and characterized in the laboratory. The instrument is set up to measure over a velocity range 1–100 m/s and is sensitive to particles from an approximate mass range from 2×10−16 to 10−11 kg, depending on the charge state and velocity. 相似文献
High-Ti melanephelinite (3.8–5.9 wt% TiO2), medium-Ti (phono)tephrite (2.7–3.1 wt% TiO2), and low-Ti olivine melanephelinite/basanite (1.9–2.3 wt.% TiO2) are subordinate rock types in the central European Cenozoic Volcanic Province. A contrasting melanephelinite to (phono)tephrite series occurs in the Lou?ná–Oberwiesenthal Volcanic Centre (37–28 Ma) and also as satellite volcanic bodies (26–12 Ma) together with olivine melanephelinite/basanite (17–20 Ma) on the southwestern periphery of the Kru?né hory mountains (Erzgebirge). The volcanic rocks intrude the Variscan basement of the uplifted shoulder of the Oh?e/Eger Rift in the Kru?né hory mountains of the Bohemian Massif. Low Mg# (44–59) and Cr, Ni contents and enrichment of LILE, Zr, Hf, Nb, Ta, U, Th and LREE in the high-Ti melanephelinites contrast with the composition of primitive low-Ti olivine melanephelinites/basanites displaying high Mg# (63–74) and high contents of compatible elements. The high-Ti melanephelinites reveal a wide range in initial 87Sr/86Sr of ca. 0.7034–0.7038 and εNd of 2.4–4.9. The low-Ti melanephelinites show an overlapping range of initial 87Sr/86Sr of ca. 0.7035–0.7036 and εNd of 4.3–5.5. The large variation in initial 87Sr/86Sr ratios at similar εNd values in those rock types is interpreted as evidence for melting of metasomatized lithospheric mantle sources comprising K-bearing phases with radiogenic Sr. Modification of the olivine-free alkali basaltic magmas by differentiation or crustal contamination could give rise to the medium-Ti (phono) tephrites. The initial isotope ratios of all samples are consistent with HIMU-mantle sources and contributions from lithospheric mantle. The olivine-free melanephelinitic rocks often contain alkali pyroxenite–ijolite xenoliths with initial 87Sr/86Sr ratios of ca. 0.7036 and εNd of 3.0. We interpret these xenoliths as samples of an intra-crustal alkali complex derived from similar mantle sources as those for the basaltic volcanic rocks. 相似文献
Mafic and intermediate intrusions occur in the Slavkovsky les as dykes, sills and minor tabular bodies emplaced in metamorphic
rocks or enclosed in late Variscan granites near the SW contact of the Western Krušné hory/Erzgebirge granite pluton. They
are similar in composition and textures to the redwitzites defined in NE Bavaria. Single zircon Pb-evaporation analyses constrain
the age of a quartz monzodiorite at 323.4 ± 4.4 Ma and of a granodiorite at 326.1 ± 5.6 Ma. The P–T range of magma crystallization is estimated at ~1.4–2.2 kbar and ~730–870°C and it accords with a shallow intrusion level
of late Variscan granites but provides lower crystallization temperatures compared to the Bavarian redwitzites. We explain
the heterogeneous composition of dioritic intrusions in the Slavkovsky les by mixing between mafic and felsic magmas with
a minor effect of fractional crystallization. Increased K, Ba, Rb, Sr and REE contents compared to tholeiitic basalts suggest
that the parental mafic magma was probably produced by melting of a metasomatised mantle, the melts being close to lamprophyre
or alkali basalt composition. Diorites and granodiorites originated from mixed magmas derived by addition of about 25–35 and
50 vol.%, respectively, of the acid end-member (granite) to lamprophyre or alkali-basalt magma. Our data stress an important
role of mafic magmas in the origin of late Variscan granitoids in NW Bohemian Massif and emphasize the effect of mantle metasomatism
on the origin of K-rich mafic igneous rocks. 相似文献
During the second Arctic Gas and Aerosol Sampling Program conducted in April 1986, we performed measurements of the optically absorbing carbonaceous component of the ambient aerosol from the NOAA WP-3D aircraft operating between sea level and 10 km altitude. We collected the aerosol of filters that were exposed for several hours; we also operated the aethalometer to measure the concentration of aerosol black carbon in real time. The filter analyses represent averages over the altitude range and time span during which the filter was collecting. The real-time results were sorted by altitude to calculate vertical profiles of black carbon concentration. Values typically ranged from 300 to 500 ng m–3 at lower altitudes, decreasing gradually to 25 to 100 ng m–3 at 8–10 km. Strong stratification at lower altitudes was frequently observed. The magnitude of these concentrations suggests that the sources are distant regions of considerable fuel consumption. The presence of this material in the tropospheric column and its probable deposition to the high-albedo surface may result in perturbations of the solar radiation balance. The concentrations measured at the highest altitudes may mean that particulate carbon and accompanying emissions for which it is a tracer are mixing into the stratosphere. 相似文献
The behaviour of Fe-oxides was investigated during precipitation and co-precipitation, phase transformation and dissolution, while their ability to adsorb and incorporate trace components was examined. Some samples were synthesised and studied under controlled laboratory conditions and other samples were taken from experiments designed to test the effectiveness of waste treatment strategies using iron. Surface-sensitive and high-resolution techniques were used to complement information gathered from classical, macroscopic methods.
Adsorption isotherms for Ni2+ uptake on synthetic ferrihydrite (Fe5HO8·4H2O, often written simply Fe(OH)3), goethite (-FeOOH), hematite (-Fe2O3) and magnetite (Fe3O4) were all similar, increasing as expected at higher pH. Desorption behaviour was also similar, but one third or more of the Ni2+ failed to return to solution. In the past, “irreversible sorption” has been blamed on uptake into micro-fractures or pores, but during examination (using Atomic force microscopy, AFM) of hundreds of Fe-oxide particles, no evidence for such features could be found, leading to the conclusion that Ni2+ must become incorporated onto or into the solids. When solutions of Fe(II) are oxidised in controlled laboratory conditions or during treatment of ash from municipal waste incinerators, two-line ferrihydrite forms rapidly and on never-dried samples, AFM shows abundant individual particles with diameter ranging from 0.5 to several tens of nanometers. Aging in solution at 70°C promotes growth of the particles into hematite and goethite and their identification (by X-ray powder diffraction, XRPD, with Rietveld refinement) becomes possible at the same aging stage as mineral morphology becomes recognisable by AFM. In other experiments that were designed to mimic natural attack by organic acids, colloidal lepidocrocite (γ-FeOOH) was observed in situ by AFM, while reductive dissolution removed material on specific crystal faces. Lath ends are eroded fastest while basal planes are more stable.
In order to help elucidate mechanisms of contaminant immobilisation by Fe-oxides, we examined samples from a reactive barrier made with 90% quartz sand, 5% bentonite and 5% zero-valent iron filings that had reacted with a solution typical of leachate from coal-burning fly ash using time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Fe(0) oxidised to Fe(III), while soluble and toxic Cr(VI) was reduced to insoluble Cr(III). Chemical maps show Fe-oxide coatings on bentonite; Cr is associated with Fe-oxides to some extent but its association with Ca in a previously undescribed phase is much stronger. Other samples taken from municipal waste incinerator ash that had been treated by aeration in Fe(II) solutions were examined with transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS). Pb and some Zn are seen to be dispersed throughout two-line ferrihydrite aggregates, whereas Sn and some Zn are incorporated simply as a result of entrainment of individual ZnSn-oxide crystallites.
Geochemical speciation models that fail to account for contaminant uptake in solid solutions within major phases or as thin coatings or entrained crystals of uncommon phases such as those described here risk to underestimate contaminant retardation or immobilisation. 相似文献