Molecular modeling of Al and benzene interactions with Suwannee fulvic acid

The effects that Al³⁺ and benzene interactions exhibit on a model fulvic acid were investigated. Energy minimizations of the structures mimicking the interactions of Al³⁺-Suwannee fulvic acid (SFA), benzene-SFA and Al³⁺-benzene-SFA were run with a solvation sphere of 60 H₂O molecules with the semi-empirical methods PM3 and PM5. The semi-empirical method PM3 was run with Gaussian 98 and CAChe Workstation Pro 6.1.1 to compare the results of the energy minimization algorithms in the two programs. PM5 calculations were run with CAChe Workstation Pro 6.1.1. Molecular dynamics (MD) simulations were run in Cerius² (Accelrys Inc., San Diego, CA) using the Universal Force Field (UFF) 1.02 [Rappé A. K., Casewit C., Colwell K., Goddard W., and Skiff W. (1992) UFF, a full periodic-table force-field for molecular mechanics and molecular dynamics simulations. J. Am. Chem. Soc.114(25), 10024-10035] and COMPASS force field [Sun H. (1998) COMPASS: an ab initio force-field optimized for condensed-phase applications—overview with details on alkane and benzene compounds. J. Phys. Chem. B102, 7338-7364]. Single point calculations were run on the minimized structures at the B3LYP/6-31G(d) level to obtain more accurate estimates of the energy on the minimized structures derived from the PM3, PM5, and UFF methods and to normalize energies to the same reference state. This methodology was used as the standard of comparison for all the models to assess whether or not a given configuration was reasonably stable.The PM3/G03 energy minimizations predicted the lowest B3LYP/6-31G(d) potential energies of the methodologies examined in this study. Thus, this method is considered the most reliable of those tested. The PM3/G03 method predicted that there would be aromatic-aromatic interactions between benzene and SFA. The presence of Al³⁺ was predicted not to interfere with aromatic-aromatic interactions between benzene and SFA, but benzene may influence the location of metal complexation to SFA.     

A molecular dynamics study of natural organic matter: 1. Lignin, kerogen and soot

Molecular dynamics (MD) simulations were performed on molecular models of a spectrum of natural organic matter (NOM) samples represented by two lignin samples (a softwood lignin and a hardwood lignin), a kerogen (Green River Shale kerogen) and a soot sample (n-hexane soot). Simulated thermodynamic properties of each model, including glass transition temperature (T_g), thermal expansion coefficient (α), density (ρ) and solubility parameter (δ) were compared against experimental data for corresponding samples. Results revealed relatively good agreement for glass transition temperature and solubility parameter for softwood lignin, Green River Shale kerogen and n-hexane soot models. An unexpectedly low solubility parameter for a hardwood lignin model suggests, however, certain model deficiencies in terms of intermolecular interactions. In addition, a lower density for a n-hexane soot model relative to the sample was attributed to the small cluster size and poor parallel stacking of aromatic clusters in the model. Discussion of the results is provided in the context of utilizing thermodynamic properties as constraints for improved structural modeling of NOM.     

Ambient distribution of particulate- and gas-phase <Emphasis Type="Italic">n</Emphasis>-alkanes and polycyclic aromatic hydrocarbons in the Tibetan Plateau

Attention has been paid for the levels, sources and health risks of atmospheric aliphatic and polycyclic aromatic hydrocarbons (n-alkanes and PAHs) in remote areas, however, few studies have focused on those in the Tibetan Plateau. In this study, 18 pairs of atmospheric samples were obtained during the period from August 2006 to July 2007 in Lhasa, the capital city of Tibet. Both gas-phase and particulate-phase n-alkanes and PAHs were measured. Concentrations of n-alkanes (gas + particulate phase, 99.1–480.9 ng/m³) and PAHs (gas + particulate phase, 11.4–72.5 ng/m³) in Lhasa are lower than those in many cities. The sources of n-alkanes related to biological and petroleum sources were 67 and 33%, respectively. According to the results of diagnostic ratios and principal component analysis, emission of traffic vehicles was one of the important PAH sources, and sources of benzo(a)pyrene was likely attributed to incense burning. Good simulations were obtained by traffic soot-based model for fluoranthene, pyrene and benzo(a)anthracene, while, wood soot-based model fitted the experimental results of benzo(a)pyrene better. This meant atmospheric fate of PAHs was mainly influenced by the adsorptive partitioning that occurred during traffic and incense burning procedures. In addition, the benzo[a]pyrene-equivalent carcinogenic power (BaPE) in the present study (0.1–1.6 ng/m³) is lower than those in other cities and also the air quality standard of China, suggesting that atmospheric PAHs caused low health risks.     

Carbon isotopic evidence for the catalytic origin of light hydrocarbons

The molecular proportionality between C₆ and C₇ isomers reported recently (F. D. Mango, Geochim. Cosmochim. Acta, 2000, 64, 1265; ref. 1) is probably the strongest evidence for catalysis yet published. It implicates two cyclopropane-like precursors, [S₆] and [S₇] (where S denotes any substrate), of similar structures, each yielding three isomers along similar kinetic pathways:     

Polycyclic aromatic hydrocarbons in dated sediments from Green Bay and Lake Michigan

Sediment cores from two locations in Green Bay and two in lake Michigan were analyzed for 12 polycyclic aromatic hydrocarbons (PAHs), loss-on-ignition (LOI),²¹⁰Pb,¹³⁷Cs, and⁷Be to study differences in deposition patterns between the freshwater estuary Green Bay, with several local sources, and the open Lake Michigan, dominated by atmospheric inputs. We found that the remote sites receive relatively less high-molecular weight PAHs such as ideno(1,2,3-cd)pyrene and dibenz(ah)anthracene and are more depleted in anthracene and pyrene. This may be related to a low Henry’s law constant for the high molecular compounds and to selective photo-oxidation of anthracene and pyrene during transport. While sedimentation rates are higher in Green Bay than in the open lake, the PAH levels are generally comparable (0.3–8.5 μg g^?1) in the two areas. However, the highest PAH levels are found in a core from Green Bay (GB88G). The two Green Bay cores have total PAH concentration maxima in 1985, which appear to be related to the combustion of petroleum. Also, one Green Bay core (GB88G) and the two from Lake Michigan exhibit PAH maxima in the early 1950s in agreement with observations from other study areas. There is a significant correlation between total PAH and LOI, and thus total organic carbon, for the Green Bay cores, but little or no such correlation for the Lake Michigan cores. This may indicate that PAHs in Green Bay are effectively scavenged by settling detritus.     

Promoted dissipation of phenanthrene and pyrene in soils by amaranth (<Emphasis Type="Italic">Amaranthus tricolor</Emphasis> L.)

A study was conducted to investigate the performance of amaranth, a known hyperaccumulator of cesium, on the promotion of the dissipation of soil phenanthrene and pyrene, which are PAHs (polycyclic aromatic hydrocarbons). Amaranthus tricolor L. een choi was the cultivar used. The presence of Amaranthus tricolor L. evidently enhanced the dissipation of these PAHs in soils with initial phenanthrene concentrations of 7.450–456.5 mg/kg dw (dw, dry weight) and pyrene of 8.010–488.7 mg/kg dw. At the end of the experiment (45 days), the residual concentrations of phenanthrene and pyrene in spiked soils with plants were generally higher than those with no plants. The loss of phenanthrene and pyrene in vegetated soils was 87.85–94.03% and 46.89–76.57% of the soil with these chemicals, which was 2.55–13.66% and 11.12–56.55% larger than the loss in non-vegetated soils, respectively. The accumulation of phenanthrene and pyrene by the plant was evident. Root and shoot concentrations of these chemicals monotonically increased with increasing soil PAH concentrations. Bioconcentration factors (BCFs), defined as the ratio of chemical concentrations in plants and in the soils (on a dry weight basis), of phenanthrene and pyrene by roots were 0.136–0.776 and 0.603–1.425, while by shoots were 0.116–0.951 and 0.082–0.517, respectively. BCFs of phenanthrene and pyrene tended to decrease with the increasing concentrations of soil phenanthrene and pyrene. Plant accumulation only accounted for less than 0.32% (for phenanthrene) and 0.33% (for pyrene) of the total amount enhancement of the dissipated PAHs in vegetated vs. non-vegetated soils. In contrast, plant-promoted microbial biodegradation was the predominant contribution to the plant-enhanced dissipation of soil phenanthrene and pyrene. These results suggested the feasibility of the radionuclide hyperaccumulator in phytoremediating the soil PAH contaminants.     

Quantifying bioirrigation using ecological parameters: a stochastic approach†

Irrigation by benthic macrofauna has a major influence on the biogeochemistry and microbial community structure of sediments. Existing quantitative models of bioirrigation rely primarily on chemical, rather than ecological, information and the depth-dependence of bioirrigation intensity is either imposed or constrained through a data fitting procedure. In this study, stochastic simulations of 3D burrow networks are used to calculate mean densities, volumes and wall surface areas of burrows, as well as their variabilities, as a function of sediment depth. Burrow networks of the following model organisms are considered: the polychaete worms Nereis diversicolor and Schizocardium sp., the shrimp Callianassa subterranea, the echiuran worm Maxmuelleria lankesteri, the fiddler crabs Uca minax, U. pugnax and U. pugilator, and the mud crabs Sesarma reticulatum and Eurytium limosum. Consortia of these model organisms are then used to predict burrow networks in a shallow water carbonate sediment at Dry Tortugas, FL, and in two intertidal saltmarsh sites at Sapelo Island, GA. Solute-specific nonlocal bioirrigation coefficients are calculated from the depth-dependent burrow surface areas and the radial diffusive length scale around the burrows. Bioirrigation coefficients for sulfate obtained from network simulations, with the diffusive length scales constrained by sulfate reduction rate profiles, agree with independent estimates of bioirrigation coefficients based on pore water chemistry. Bioirrigation coefficients for O₂ derived from the stochastic model, with the diffusion length scales constrained by O₂ microprofiles measured at the sediment/water interface, are larger than irrigation coefficients based on vertical pore water chemical profiles. This reflects, in part, the rapid attenuation with depth of the O₂ concentration within the burrows, which reduces the driving force for chemical transfer across the burrow walls. Correction for the depletion of O₂ in the burrows results in closer agreement between stochastically-derived and chemically-derived irrigation coefficient profiles.     

Distribution of REE between clinopyroxene and basaltic melt along a mantle adiabat: effects of major element composition, water, and temperature

The distribution of rare earth elements (REE) between clinopyroxene (cpx) and basaltic melt is important in deciphering the processes of mantle melting. REE and Y partition coefficients from a given cpx-melt partitioning experiment can be quantitatively described by the lattice strain model. We analyzed published REE and Y partitioning data between cpx and basaltic melts using the nonlinear regression method and parameterized key partitioning parameters in the lattice strain model (D ₀, r ₀ and E) as functions of pressure, temperature, and compositions of cpx and melt. D ₀ is found to positively correlate with Al in tetrahedral site (Al ^T ) and Mg in the M2 site (Mg^M2) of cpx and negatively correlate with temperature and water content in the melt. r ₀ is negatively correlated with Al in M1 site (Al^M1) and Mg^M2 in cpx. And E is positively correlated with r ₀. During adiabatic melting of spinel lherzolite, temperature, Al ^T , and Mg^M2 in cpx all decrease systematically as a function of pressure or degree of melting. The competing effects between temperature and cpx composition result in very small variations in REE partition coefficients along a mantle adiabat. A higher potential temperature (1,400°C) gives rise to REE partition coefficients slightly lower than those at a lower potential temperature (1,300°C) because the temperature effect overwhelms the compositional effect. A set of constant REE partition coefficients therefore may be used to accurately model REE fractionation during partial melting of spinel lherzolite along a mantle adiabat. As cpx has low Al and Mg abundances at high temperature during melting in the garnet stability field, REE are more incompatible in cpx. Heavy REE depletion in the melt may imply deep melting of a hydrous garnet lherzolite. Water-dependent cpx partition coefficients need to be considered for modeling low-degree hydrous melting.     

Source apportionment of elevated PAH concentrations in sediments near deep marine outfalls in Esquimalt and Victoria,BC, Canada: Is coal from an 1891 shipwreck the source?

Previous studies have suggested that coal from the 1891 shipwreck of a collier off Victoria, BC, Canada is responsible for elevated parent (unsubstituted) PAH concentrations in sediments near deep marine outfalls from Esquimalt and Victoria in the Strait of Juan de Fuca. To resolve this question, we analysed a comprehensive suite of resolved and unresolved complex mixture (UCM) alkanes, tricyclic terpane, hopane and sterane biomarkers, and parent and alkyl polycyclic aromatic hydrocarbons (PAHs) in samples of coal, wastewater and sediments. Composition patterns, principal components analysis (PCA) models and PAH and biomarker ratios all indicate that coal from the collier does not make a dominant contribution to any sediment sample. Mass balance calculations based on the n-C₂₄ content and 24/4 tetracyclic terpane to 26/3R tricyclic terpane ratio in coal provide a particularly good match between predicted and observed alkyl PAH concentrations for sediments with high alkyl naphthalenes and phenanthrene/anthracenes and low UCM, but the predicted coal contribution substantially underestimates the measured parent PAHs for all sediment samples. Methylbenz[a]anthracene/chrysene profiles for sediments with a dominance of parent PAHs are very close to coal tar, with a marked predominance of methylbenz[a]anthracenes and the possible 10-methylbenz[a]anthracene as a major constituent, while the methylchrysenes predominate in coal. Hence, coal from the collier could account for most alkyl PAHs in the sediments, but dredged sediment containing pyrolised coal waste from a former coal gas plant in Victoria Harbour is a more likely source for the samples with elevated parent PAHs. PAH ratios indicate that these sources are superimposed on combustion PAHs introduced by a combination of atmospheric deposition and delivery via stormwater and the outfalls. Parent PAH distributions also suggest that PAHs in wastewater that originate from oils and soot in liquid fossil fuel combustion are dispersed and degraded, while the larger wood char particles (containing PAHs more protected from degradation) settle closer to the outfalls. Overall, results suggest that PAHs have predominant sources in wood combustion, coal and possibly coke, with a likelihood of much lower bioavailability than would be expected from wastewater dominated by oils and soot from vehicle combustion.     

Levels and distributions of polycyclic aromatic hydrocarbons (PAHs) in middle reach of Huaihe River,China: anthropogenic influences and ecological risks

Polycyclic aromatic hydrocarbons (PAHs) are a group of aromatic hydrocarbons with high toxicity to human health. PAH emissions from industrial activities have become the primary sources of PAH contamination in Chinese watersheds. Here, we analyzed 10 individual priority PAHs in 120 water samples taken from middle reach of Huaihe River, China. The results show that the PAH levels in studied watershed are significantly lower as compared to other Chinese watersheds, approaching or slightly exceeding the PAH levels in watersheds from selected European and North American countries. We observe rather large variation in spatial and vertical PAH distributions, pointing to PAH inputs from local industrial emissions, and PAH cycle among atmosphere, water and sediment. Individual PAH ratios (i.e., phenanthrene/anthracene and fluorene/pyrene) and principal components analysis suggest a primarily pyrolytic PAH sources (combustion of coal and coke) in water column. Other accompanying PAH sources include emissions from steel industry and gasoline. Total toxic benzo[a]pyrene equivalent of PAHs in studied water column indicates that PAHs in watershed of middle reach of Huaihe River pose limited toxicity to the environment.     

Monte Carlo simulation of normal grain growth in 2- and 3-dimensions: the lattice-model-independent grain size distribution

The phenomenon of normal grain growth in pure single phase systems is modeled with the Monte Carlo technique and a series of simulations are performed in 2- and 3-dimensions. The results are compared with natural and experimental monomineralic rock samples. In these simulations various lattice models with different anisotropic features in grain boundary energy are examined in order to check the universality of the simulation results. The obtained microstructure varies with the artificial parameter T ^′ in each lattice model, where T ^′ means scaled temperature and controls thermal fluctuation on grain boundary motion. As T ^′ (thermal fluctuation) increases, the boundary energy anisotropy characterizing each lattice model becomes less important for the evolution of the microstructure. As a result the difference in the grain size distribution among the lattice models, which is significantly large for low T ^′, is reduced with increasing T ^′. The distribution independent of both the lattice model and the dimension is obtained at sufficiently high T ^′ and is very close to the normal distribution when carrying out the weighting procedure with a weight of the square of each grain radius. A comparison of the planar grain size distribution of the natural and experimental rock samples with the 3-D simulation results reveals that the simulations reproduce very well the distributions observed in the real rock samples. Although various factors such as the presence of secondary minerals and a fluid phase, which are not included in the simulation modeling, are generally considered to influence the real grain growth behavior, the good agreement of the distribution indicates that the overall grain growth behavior in real rocks may still be described by the simplified model used in the present simulations. Thus the grain size distribution obtained from the present simulations is possessed of the universal form characterizing real normal grain growth of which the driving force is essentially grain boundary energy reduction through grain boundary migration. Received: 7 January 1997 / Accepted: 25 August 1997     

Interatomic potentials for CaCO3 polymorphs (calcite and aragonite), fitted to elastic and vibrational data

Calcite and aragonite have been modeled using rigid-ion, two-body Born-type potentials, supplemented by O-C-O angular terms inside the CO₃ groups. A shell model has also been developed for calcite. Atomic charges, repulsive parameters and force constants have been optimized to reproduce the equilibrium crystal structures, the elastic constants and the Raman and infrared vibrational frequencies. The rigid-ion potential RIM (atomic charges:z _O= -0.995e,z _C = 0.985e,z _Ca = 2.0e) fitted to calcite properties is able to account for those of aragonite as well. Experimental unit-cell edges, elastic constants, internal and lattice frequencies are reproduced with average relative errors of 2.1, 5.5, 2.4, 15.1% for calcite and of 0.2, 19.4, 2.5, 11.8% for aragonite, respectively. The RIM potential is suitable for thermodynamic and phase diagram simulations in the CaCO₃ system, and is discussed and compared to other potentials.     

Effects of geosorbent and solution properties on sorption and desorption of PAHs

Characteristics of phenanthrene and pyrene’s sorption and desorption on two local soils in solutions of simulated groundwater, simulated lung fluid, and simulated saliva were studied with batch equilibrium experiments to understand the fate of PAHs in the karst region of southwestern China and to assess the environmental exposure and the health risk of PAHs. The results showed that the sorption and desorption isotherms of phenanthrene and pyrene on two target soils in the three solution systems could be adequately described by the Freundlich model, while the fitted isotherm parameters for the simulated groundwater solution distinguished notably from those for the simulated body fluid solutions. For the sorption experiments, in the simulated groundwater, the n values were 0.722 and 0.672 for phenanthrene and were 0.724 and 0.663 for pyrene, respectively, on the yellow soil and the limestone soil; The log K_F values were 3.118 and 3.323 for phenanthrene and were 3.648 and 3.846 for pyrene, respectively, on the yellow soil and the limestone soil. In the simulated body fluids, the n values for phenanthrene and pyrene ranged from 0.622 to 0.836 and from 0.590 to 0.865, respectively, and the log K_F values of phenanthrene and pyrene ranged from 2.845 to 3.327 and from 3.344 to 3.779, respectively. For the desorption experiments, in the simulated groundwater, the n values were 0.662 and 0.744 for phenanthrene and were 0.702 and 0.647 for pyrene, respectively, on the yellow soil and the limestone soil. The log K_F values were 3.666 and 3.686 for phenanthrene and were 4.128 and 4.225 for pyrene, respectively, on the yellow soil and the limestone soil. In the simulated body fluids, the n values for phenanthrene and pyrene ranged from 0.612 to 0.668 and from 0.631 to 0.819, respectively, and the log K_F values of phenanthrene and pyrene ranged from 3.134 to 3.407 and from 3.533 to 3.839, respectively. The limestone soil had relatively higher log K_F values but lower K_OC values compared to those of the yellow soil, indicated that the nature of sorbent soils played the dominant role in sorption and desorption behaviors of PAHs. The experimental results showed a remarkable differences in sorption and desorption behaviors of PAHs in simulated body fluids and groundwater. The nonlinearities of measured isotherms and the measured sorption capacities of soils in simulated body fluids were significantly lower than corresponding those in the simulated groundwater, and HI values for simulated body fluids systems were significantly smaller than corresponding those for the simulated groundwater systems. The results underscore cautions in assessing environmental exposure and health risks of PAHs based on their sorption–desorption data in simulated groundwater as this is traditionally done.

     

Polycyclic aromatic hydrocarbons in an anoxic sediment core from the Pettaquamscutt River (Rhode Island,U.S.A.)

Fifteen sections from an anoxic sediment core were analyzed for polycyclic aromatic hydrocarbons (PAH). Two types of PAH were observed: (a) those from combustion sources such as pyrene and chrysene and (b) those from natural sources such as retene and perylene. The combustion PAH levels in core sections dated between 1900 and 1970 were much higher than in earlier sections; this indicated an anthropogenic origin of these PAH at this location. The perylene and retene core profiles show significant anomalies during the period 1850–1880. Organic carbon does not fluctuate markedly but δC-13 of organic carbon shows several unexplained excursions; one of which correlates with the perylene and retene anomalies.     

Indications for pedogenic formation of perylene in a terrestrial soil profile: Depth distribution and first results from stable carbon isotope ratios

Concentrations and isotope compositions of polycyclic aromatic hydrocarbons (PAHs) were determined in natural soils of Southern Germany. In selected profiles perylene concentrations increased with soil depth when compared to the other PAH compounds present. However, its low solubility made vertical transport by seepage water unlikely. Therefore two mechanisms are discussed that could have caused the unusual distribution of perylene in these soils:

(a) Atmospheric deposition of combustion-derived (i.e. pyrogenic) perylene in the top-soil and

(b) in situ generation in the sub-soil of these specific terrestrial environments. This could have been caused by microbial activities or other catalytic processes yet unknown.

In order to distinguish between pyrogenic and natural generation compound-specific ¹³C/¹²C ratios (δ¹³C) were compared between perylene and other PAHs in samples from the top-soil and sub-soil. Despite successful clean-up of the extracts, low perylene concentrations and peak overlaps with benzo(e)pyrene and benzo(a)pyrene prevented determination of a unique δ¹³C value for perylene in the upper horizon. However, the δ¹³C value of perylene in the sub-soil was 5.7 permille more negative than other equal-mass PAHs (with m/z of 252) in the top-soil, which rather supports in situ generation of perylene in the sub-soil.     

Experimental determination of F and Cl partitioning between lherzolite and basaltic melt

We experimentally determined F and Cl partition coefficients together with that of 19 trace elements (including REE, U-Th, HFSE and LILE) between basaltic melt and lherzolite minerals: olivine, orthopyroxene, clinopyroxene, plagioclase and garnet. Under conditions from 8 to 25 kbars and from 1,265 to 1,430°C, compatibilities of F and Cl are globally ordered as D ^Cpx/melt > D ^Opx/melt > D ^Grt/melt > D ^Ol/melt > D ^Plag/melt, and D _F ^mineral/melt is larger than D _Cl^mineral/melt. Four other major results were brought to light. (1) Chlorine partition coefficients positively correlate with the jadeite component in orthopyroxene, and increase of the CaTs component promotes Cl incorporation in clinopyroxene. (2) Variations of fluorine partition coefficients correlate strongly with melt viscosity. (3) F and Cl partition coefficients correlate with the Young’s modulus (E ₀) of pyroxene octahedral sites (M sites) and with Raman vibrational modes of pyroxenes. This demonstrates a fundamental interaction between the M site of pyroxenes and the incorporation of F and Cl. (4) We also determined the parameters of the lattice-strain model applied to 3+ cation trace elements for the two M sites in orthopyroxene and clinopyroxene: D ₀^M1, D ₀^M2, r ₀^M1, r ₀^M2, E ₀^M1 and E ₀^M2.     

On the velocity covariance for steady flows in heterogeneous porous formations and its application to contaminants transport

We consider groundwater steady flow in a heterogeneous porous formation of random and stationary log-conductivity Y = ln K, characterized by the mean 〈Y〉, and the two point correlation function C _Y which in turn has finite, and different horizontal and vertical integral scales I and I _v , respectively. The fluid velocity V, driven by a given head drop applied at the boundary, has constant mean value U ≡ (U, 0, 0). Approximate explicit analytical expressions for transverse velocity covariances are derived. The adopted methodology follows the approach developed by Dagan and Cvetkovic (Spatial moments of kinetically sorbing plume in a heterogeneous aquifers, Water Resour. Res. 29 (1993) 4053) to obtain a similar result for the longitudinal velocity covariance. Indeed, the approximate covariances of transverse velocities are determined by requiring that they have the exact first order variances as well as zero integral scale (G. Dagan, Flow and Transport in Porous Formations (Springer, 1989)) , and provide the exact asymptotic limits of the displacement covariance of the fluid particles obtained by Russo (On the velocity covariance and transport modeling in heterogeneous anisotropic porous formations 1. Saturated flow, Water Resour. Res., 31 (1995) 129). Comparisons with numerical results show that the proposed expressions compare quite well in the early time regime, and for Ut/I >100. Since most of the applications, like assessing the effective mobility of contaminants or quantifying the potential hazards of nuclear repositories, require predictions over higher times the proposed approximate expressions provide acceptable results. The main advantage related to such expressions is that they allow obtaining closed analytical forms of spatial moments pertaining to kinetically sorbing contaminant plumes avoiding the very heavy computational effort which is generally demanded. For illustration purposes, we consider the movement of one contaminant species, and show how our approximate spatial moments compare with the numerical simulations.     

滇东北会泽超大型铅锌矿Re-Os同位素特征及喜山期成矿作用动力学背景探讨

会泽超大型铅锌矿是滇东北铅锌多金属成矿域中典型的密西西比河谷型(MVT)或会泽型(HZT)矿床,因其独特的成矿系统以及矿床中富锗而被地质学者熟知,由于该类型矿床成矿温度较低且缺少合适的定年矿物,其成矿时代一直存在较大的争议。本文在会泽铅锌矿麒麟厂矿区1584中段0-11号穿脉坑道块状铅锌硫化物矿石中挑选了9件硫化物样品(黄铁矿、方铅矿和闪锌矿),采用负离子热表面电离质谱法进行Re-Os同位素分析,获得Re-Os等时线年龄为40.7±2.6 Ma(n=9),与模式年龄加权平均值40.0±2.6Ma(n=8)在误差内完全一致,闪锌矿和方铅矿模式年龄分别为38.24±0.41 Ma和36.57±0.40 Ma。上述同位素年龄揭示了会泽超大型铅锌矿的成矿时代可能为始新世。结合滇东北铅锌矿集区NE向逆冲断层和冲断褶皱控矿构造区域构造解析以及断裂、矿体构造-岩相蚀变特征,提出会泽超大型铅锌矿经历了燕山期、喜山期两阶段构造-流体贯入的成矿作用模型。     

Vertical transport of polycyclic aromatic hydrocarbons in different particle-size fractions of sandy soils

Vertical transport of selected polycyclic aromatic hydrocarbons (PAHs) in different particle-size fractions of sandy soils was investigated by simulation experiments in soil columns. Tested soil samples were fractionized into three particle-sizes including sand, coarse silt and fine silt (2,000–50, 50–20 and <20 μm). Rainfall simulations were conducted in artificially PAHs contaminated soil columns with 30 cm length and 5 cm diameter in 40 days. PAHs were extracted from soil samples and determined by high performance liquid chromatography (HPLC). Results showed that the residue level of PAHs in fine silt fraction reached 35.85 mg/kg, which was significantly higher than those in sand and coarse silt fraction (16.28 and 11.80 mg/kg, respectively), probably because PAHs in macroporous fractions were prone to volatilize or degrade compared with that in microporous fractions. Linear relationship between the residue levels of individual PAH (R _PAHs) and the value of partition coefficient (log K _oc) was regressed as R _PAHs = 1.55 × log K _oc − 5.86, R ² = 0.91, n = 9. These results indicated that vertical transport of the mixed PAHs in soils were controlled both by the nature of PAHs (i.e. log K _oc, molecular weight), soil particle size and soil organic contents, which could influence the transport of PAHs.     

再生水入渗区典型抗生素分布特征与地下水微生物群落影响因素研究

再生水入渗携带的抗生素污染是地下水污染的来源之一,已经成为城市地下水资源的安全中不可忽视的问题。抗生素对复杂和脆弱地下水环境中的微生物群落及其功能的影响值得关注。本研究基于利用16S rRNA基因高通量测序方法,对3月和9月两个月份再生水渗入区城市地下水中微生物群落结构进行分析。结合现场调查测试和室内分析,测得样品中离子(K~+、Na~+、Ca²⁺、Mg²⁺、NH~+₄、F~-、Cl~-、SO■、NO~-₃、NO~-₂、HCO~-₃、CO■)浓度,并采用超高效液相色谱-串联质谱技术测得主要的抗生素浓度(环丙沙星、诺氟沙星、氧氟沙星、莫西沙星、磺胺吡啶和磺胺醋酰),对研究区地下水环境中微生物群落结构及与环境因子的响应规律进行探讨。结果表明：(1)研究区内3月份地下水中抗生素浓度要高于9月份整体抗生素浓度,以磺胺醋酰和环丙沙星为主,此外除了季节因素外,人类活动可能是影响抗生素分布的又一因素;(2)微生物群落主要由变形菌门(Proteobacteria,81.0...