贡嘎山海螺沟降雪中多环芳烃的短周期分布特征及来源分析

2013年1月在贡嘎山海螺沟3个不同采样点共收集了多个雪样,利用GC-MS分析了雪样中16种优控多环芳烃的含量,探讨了多环芳烃的短周期分布特征与来源,估算了采样点与排放源的直线距离。结果显示,海螺沟各采样点雪样中多环芳烃的总含量在163.7 ng/L~281.4 ng/L之间,其中菲的含量最高。雪样中2~4环多环芳烃占多环芳烃总量的百分比为92.0%~93.7%,表明污染来自较远距离传输,但主要排放源离海螺沟的直线距离不超过357 km。将雪层与气象资料的降雪期对应,结果表明从2012年11月到2013年1月这个短周期内,海螺沟雪样受多环芳烃污染的程度没有太大变化。对海螺沟雪样中的多环芳烃进行了来源分析,结果表明海螺沟雪样中的多环芳烃主要来自煤燃烧,不排除少部分木材燃烧,这一源解析结果与海螺沟及其周边地区主要以煤炭作为燃料的能源特征相吻合。     

Composition and source identification of polycyclic aromatic hydrocarbons in mangrove sediments of Peninsular Malaysia: indication of anthropogenic input

This is a comprehensive study of the composition, origin and sources of specific polycyclic aromatic hydrocarbons (PAHs) in sediments of mangrove estuary in the western part of Peninsular Malaysia. Mangrove sediments were analyzed for 17 PAHs by gas chromatography–mass spectrometry. Total PAH concentrations in the sediments ranged from 20 to 112 ng/g on a dry-weight basis. High molecular weight PAHs were abundant in the sediments. Parent PAH ratios revealed that pyrogenic input has important contribution to the sedimentary PAHs. Ratios of alkylated PAHs indicate that the sedimentary PAHs were influenced by petrogenic PAHs, which implies that petrogenic input has contribution to the sedimentary PAHs but that it is not a major factor in distribution of PAHs within the estuary. Combustion-derived PAHs show a positive and very strong correlation with total PAHs (R ² = 0.926, p < 0.05). Total methylphenanthrenes show very weak correlation with total PAHs (R ² = 0.0928, p < 0.05). The PAH concentrations were found to increase with distance from the upstream of the estuary to the coastal area of the Straits of Malacca. For the assessment of sediment contamination using biological thresholds, none of the individual studied PAH compounds exceeded the values of the effect range low–effect range median guideline and the threshold effects level–probable effects level guideline. This study demonstrates that the sediments of the mangrove ecosystem facing the Straits of Malacca and Sumatra are influenced by anthropogenic PAH inputs as a result of human activities such as biomass burning, vehicle emissions and boating activities.     

Sources and transports of polycyclic aromatic hydrocarbons in the Nanshan Underground River,China

Karst areas have much higher ecological vulnerability and are easy to be contaminated by polycyclic aromatic hydrocarbons (PAHs), which are introduced as health risk pollutants. PAHs ratios were used to understand the sources and transport behavior of PAHs conducted in the karst Nanshan Underground River, China. Water, sediments from the underground river and water, sediments, soil from the surface were collected monthly in 2011 and 2012. Abundant PAHs were found both in the underground river and in the surface system. The detected ΣPAHs concentrations varied from 353 to 13,203 ng L^?1 in the groundwaters and content from 169 to 12,038 ng g^?1 in the sediments of the underground river. The ratios of anthracene to anthracene, plus phenanthrene and fluoranthene to fluoranthene, plus pyrene indicated that PAHs were delivered in the groundwaters from combusted grass, wood, and coal, while in the sediments were a mixture of non-combusted petroleum, grass, wood, coal and combusted grass, wood, coal. The similarities in sources between an underground river and surface system indicated that farmlands play a major role for the transport of PAHs and contamination in the underground river. Karst features are liable for the transport behavior.     

Distribution of polycyclic aromatic hydrocarbons in recent sediments of Sundarban mangrove wetland of India and Bangladesh: a comparative approach

The present work is the first attempt to compare the data of a comprehensive study of the origin and distribution of 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in surface sediments (<63 μm) from 18 sampling stations, 9 from Sundarban of Bangladesh and 9 from Indian counterpart. Σ19PAHs concentration in sediments showed wide variations from 208.3 to 12,993.1 ng g^?1 dry weight in Indian Sundarban, whereas 208.4 to 4,687.9 ng g^?1 in the case of Bangladesh. Fluoranthene, pyrene, benzo(b)fluoranthene, benzo(a)pyrene and dibenzo(a,h)anthracene were predominant species for both the countries. The PAH diagnostic ratios indicated that the PAHs in sediments from both the countries were of mixed source of hydrocarbons of both petrogenic and pyrolytic origin. According to the numerical effect-based sediment quality guidelines, the levels of PAHs in the Sundarban wetland of Bangladesh and India should not exert adverse biological effects. The TEQ values calculated for samples from the Bangladesh and Indian Sundarban varied from 13.68 to 1,014.75 and 1.31 to 2,451 ng g^?1 d.w. with an average of 221.02 and 358.63 ng g^?1, respectively. The overall contamination status of PAH was higher in India than Bangladesh.     

Levels and sources of polycyclic aromatic hydrocarbons (PAHs) in selected irrigated urban agricultural soils in Accra, Ghana

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments including urban soils. Elevated concentrations of PAHs in urban soils are caused by incomplete combustion of petroleum and coal. This study assesses 16 individual PAH compounds in a total of 112 surficial soil samples. The objective was to assess and compare the levels of contamination as well as examine the main sources of PAHs in four urban agricultural soils using molecular ratios of some specific hydrocarbons. The study showed that PAH levels in soil ranged from 1.23 ng/kg in soil collected from Dzorwulu to 2.95 ng/kg in soil collected from Ghana Broadcasting Cooperation (GBC) vegetable irrigation site. Of the total PAHs, the more water soluble PAHs (2–4 rings), which tend to be concentrated in the vapour phase were found to dominate the soils. The percentage dominance were Dzorwulu (52.8 %), Marine Drive (62.5 %), CSIR (53.2 %) and GBC (49.2 %). However, there were significant levels of the more carcinogenic PAHs (5–6 rings) present with percentages as 47.1, 37.5 46.8 and 50.8 % for Dzorwulu, Marine Drive, CSIR and GBC vegetable irrigation sites, respectively, and therefore, may impact negatively on public health. Based on the classification by the Institute of Soil Science and Plant Cultivation in Pulawy, Poland, urban soils in Accra could be classified as contaminated to different levels. Molecular ratios of Flu/pyr and PA/Ant were calculated to determine the main sources of PAHs. Results showed that PAHs could originate mainly from incomplete combustion of petroleum products, especially from atmospheric fallout from automobile exhausts. The study further showed that B(a)P concentration of 0.05 ng/kg in soil from GBC urban vegetable irrigation site requires immediate clean-up exercise and monitoring to mitigate human health impact.     

Polycyclic aromatic hydrocarbons (PAHs) in particle-size fractions of urban topsoils

Polycyclic aromatic hydrocarbons’ (PAHs) concentrations in bulk samples are commonly used to assess contamination but PAHs are unevenly distributed among particle-size fractions. Seventeen urban surface soil samples from the city of Xuzhou, China, were collected and then fractionated into five size fractions (2,000–300, 300–150, 150–75, 75–28, and <28 μm). The concentrations of 12 US EPA PAHs were measured using gas chromatograph/mass spectrometry in various fractions, and the bulk soil samples and distribution patterns of PAHs in different particle-size fractions were investigated. The mean concentration of total PAHs in bulk soil samples was 1,879 ng/g. The median concentrations for all individual PAH were higher for the 75–2,000 μm fraction than for the <75 μm fraction. The distribution factors for various PAHs in <28 μm soil fraction were closely correlated (r = ?0.661, p < 0.019) to bulk soil fugacity capacity. The values of PAH isomer indicated that traffic emissions might be the major origin of PAHs in Xuzhou surface soils. Spearman correlation analysis was performed and the result suggested that soil organic carbon might be a factor controlling the concentrations of PAHs in soils.     

Polycyclic aromatic hydrocarbons (PAHs) in Xuzhou urban street dust: concentration and sources

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments and are considered as the priority pollutants. The main objectives of this study were (1) to assess the contamination extent of 16 PAHs compounds in urban street dust and (2) to identify the anthropogenic sources of contamination. Forty-nine samples were analysed for 16 PAHs by gas chromatography/mass spectrometry. Results showed that total PAHs concentrations varied from 2174 to 24,499 ng/g with an average value of 6616 ng/g. Total PAHs concentrations showed a significant correlation with the total organic carbon (TOC) content (r = 0.599, p < 0.0001), suggesting likely that TOC can influence the distribution of PAHs in Xuzhou street dust. Source identification indices suggested that the primary source of PAHs was automobile exhausts. A factor analysis was performed, and three factors were extracted from the available dataset, explaining a total variance of approximately 84.7%. Results from the factor analysis could be indicative of PAHs with different origins.     

Polycyclic aromatic hydrocarbons in the sediments of Xiangjiang River in south-central China: occurrence and sources

The Xiangjiang River (XR), located in Hunan province in south-central China, is the second largest tributary of the Yangtze River. The occurrence, and sources of the polycyclic aromatic hydrocarbons (PAHs) in the 20 surface sediment samples from XR were analyzed, and the biological risks of the PAHs on the benthic organisms were assessed using sediment quality guidelines. The results showed that the occurrence level of the 16 USEPA priority PAHs in the surface sediments ranged from 190 to 983 ng/g (dry weight) with a mean concentration of 452 ± 215 ng/g. The concentration of phenanthrene was the highest with a mean concentration of 104 ± 44 ng/g. The compositions and principal components analysis indicated that the PAHs in the sediments in XR were mainly from pyrogenic sources which could be attributed to the open burning of rice straws and coal combustion of the local industries in the XR basin. The PAH contamination in the sediments was considered to be moderate, and has posed a small adverse biological effect on the benthic organisms.     

Vibrational spectra of four polycyclic aromatic hydrocarbons under high pressure: implications for stabilities of PAHs during accretion

Infrared and Raman spectra of the polycyclic aromatic hydrocarbons (PAHs) naphthalene, anthracene, phenanthrene, and pyrene have been examined up to 10–55 GPa at 300 K, to probe structural changes in these materials under high-pressures, and to relate these to shock measurements on these materials. The goal is to develop an understanding of how such hydrocarbons might be processed during planetary accretion. A range of phase transitions in PAHs are observed and, in accord with previous investigations, these typically initiate at relatively low pressures (0.3–4.0 GPa): the lower-pressure transitions are likely associated with inter-molecular changes such as changes in symmetry and/or molecular orientation, charge transfer processes, or changes in π electron density, and are often sluggish. Higher-pressure (7–10 GPa) phase transitions in PAHs are likely associated with profound structural changes like dimerization, which are not always reversible. Laser-induced luminescence is encountered at pressures well below those at which PAHs amorphize, and a strong pressure-induced Fermi resonance is identified between the highest-lying inter-molecular modes and lowest-lying intra-molecular modes in each PAH examined. It is the increased strength of inter-molecular interactions under pressure that likely generates increasing overlap of π orbitals and leads to cross-linking (dimerization) of the molecules and the destruction of their planar symmetry. The first step in the amorphization of these compounds is likely dimerization, and amorphization occurs when long-range order is lost and a greater diversity of local structural environments is introduced into these materials, such as carbons being shared between rings, embayed structures, sp, sp², and sp³ hybridized carbon atoms, a broad range of C–H bonding environments, and fewer residual resonance-stabilized C–C units. Our results are consistent with pressure producing amorphous, hydrogenated carbon material from PAH precursors: hence, impact phenomena, coupled with post-shock hydrogen loss, could provide an alternate pathway to produce amorphous carbon assemblages of the type observed within a range of meteorites. Additionally, smaller PAHs tend to be most stable under compression; as these are the most volatile of the PAHs, the combination of shock during accretion, coupled with trends in volatility, may limit the presence of PAHs within objects formed in the early solar system.     

Survey of polycyclic aromatic hydrocarbons and nitrated polycyclic aromatic hydrocarbons in Jiaxing city, China

Polycyclic aromatic hydrocarbon (PAH) and nitrated PAH (NPAH) products are toxic. Thus, determination of their concentrations is of great interest to researchers of soil and water pollution control. In this work, soil samples, surface water samples, and groundwater samples were collected, and the concentrations of 16 priority PAHs and 15 NPAHs were determined using an HPLC-ultraviolet detector. Results showed that the total PAH concentrations ranged within 489.69–1,670.11 ng/g (average = 905.89 ng/g) in soil samples, 4.00–23.4 μg/l (average = 9.84 μg/l) in surface water samples, and 2.14–22.3 μg/l (average = 8.37 μg/l) in groundwater samples. The NPAH concentrations were one to two orders of magnitude lower than the PAH concentrations and ranged within 22.72–128.70 ng/g (average = 63.88 ng/g) in soil samples. 2-Nitropyrene and 6-nitrochrysene were the most abundant compounds, accounting for about 14.3 and 26.5 %, respectively. Source analysis revealed that most PAHs originated from coal combustion around the study area, whereas NPAH studies suggested that the primary emission of gasoline engines and daytime OH reactions were the dominant sources of these compounds.     

PAHs contamination in groundwater from a part of metropolitan city,India: a study based on sampling over a 10-year period

Presence of polycyclic aromatic hydrocarbons (PAHs) in the soil and water is of serious environmental concern as they are carcinogenic in nature. The present study was carried out with an aim to identify the presence of PAHs in groundwater of Chennai, Tamil Nadu, India. This is an industrialised area where petrochemical storage tanks are located. Groundwater sampling was carried out in the years 2001, 2011 and 2012 to understand the variation in PAHs content in this area. Concentration of major ions, pH and EC were measured during the year 2001. Of the 24 groundwater samples collected in the year 2001, most of them were alkaline and 62.5 % were not permissible for drinking based on pH and EC, respectively. Influence of seawater was the major reason for the Na–Cl dominant nature of groundwater. TPH and PAHs analysis of groundwater carried out in 2001 and 2011, and physical examination of groundwater in 2012 indicate the increased level of contamination in the eastern part of the study area. The contamination in the eastern part persists because of the fact that groundwater is flowing towards the east and also due to the presence of petrochemical storage tanks near the coast. Thus this area is affected by PAHs pollution which has endured over the past 50 years. An underground storage tank that was functioning in this area was closed about 50 years ago and leakage of PAHs from this tank was reported in the year 1993. However, the present study indicates the decrease in the area of zone of pollution, possibly due to natural flushing of groundwater zone.     

Spatial and temporal analysis of drought risk during the crop-growing season over northeast China

Northeast China as an important agricultural zone for commercial and economic crop in China suffered from increased drought risk that seriously threatened agricultural production and food security in recent decades. Based on precipitation datasets from 71 stations from 1960 to 2009 and on the reliable statistical methods of the Mann–Kendall test, Sen’s slope and the Standardized Precipitation Index, we analyzed the temporal and spatial variation of drought occurrence during the crop-growing season (from May to September) and summer (from June to August). The results showed that regional mean precipitation during the crop-growing season and summer over the last 40 years has decreased at the rate of ?1.72 and ?1.12 mm/year, respectively. According to timescale analysis of abrupt changes, there were two distinct time series (1965–1983 and 1996–2009) with decreasing precipitation trends at a 95 % confidence level. A comparison between the two time series of these two periods demonstrated that more frequent and more severe drought occurred during 1996–2009. Furthermore, drought risk in recent decades has become even more serious both in severity and in extent. Especially in the crop-growing season of 2001 and summer of 2007, over 25 % (2.0 × 10⁵ km²) of study area experienced severe drought (serious and extreme droughts). Our results highlight the urgent need for the development of effective drought adaptations for cropland over northeast China.     

Impact assessment of anthropogenic activities on air quality, using lichen Remototrachyna awasthii as biomonitor

The study was carried out with an aim to assess the heavy metal (HM) and polycyclic aromatic hydrocarbons (PAHs) in the air of a biodiversity as well as tourist-rich area of Western Ghats by applying a most frequent growing lichen Remototrachyna awasthii (Hale and Patw.) Divakar and A. Crespo, as biomonitor. Thalli of R. awasthii were collected from eight sites of Mahabaleshwar area located in Western Ghats. Samples were prepared for HM and PAHs quantification by ICP-MS and HPLC, respectively. Total metal concentration (HM) ranged from 644 to 2,277.5 μg g^?1 while PAHs concentration between 0.193 and 54.78 μg g^?1. HM and PAHs concentrations were the highest at Bus Stand while control site (Lingmala Fall) exhibited the lowest concentration of HM as well as PAHs followed by samples from Wilson point (both these sites are having trekking route). It was also evident from this study that vehicular emission played a significant role in the release of HM and PAHs as pollutants in the environment. The effectiveness of R. awasthii as biomonitor could be further investigated by comparing this species with other biomonitors.     

Determination of some carcinogenic PAHs with toxic equivalency factor along roadside soil within a fast developing northern city of India

The objective of the present study was to ascertain contamination levels, distribution behaviour and PAHs exposure during summer, winter and autumn during 2011–2012 in one of the developing cities of northern India. Average PAHs concentration was found to be 18.17, 4.04 and 16.38 μg g ^?1, whereas, concentration of 16 individual PAHs was found to vary between 0.02 and 200.23, 0.008 and 28.4 μg g ^?1, and 0.01 and 252.55 μg g ^?1 during summer, winter and autumn seasons, respectively. The average concentration of low and high carcinogenic PAHs during summer, winter and autumn was found to be 5.1 and 31.29, 2.1 and 6.4, 4.74 and 35.08 μg g ^?1 at most intercepts. The average ratio of low to high carcinogenic PAHs was found to be 1:6, 1:3, 1:7.6 during summer, winter and autumn, respectively. Five ringed PAHs were found in higher concentration in all seasons. Dib(ah)A and B(a)P were the two individual PAHs found in highest concentration during summer, winter and autumn seasons. Two tailed T-test was applied for authenticity of the results. Toxic equivalency factor of B(a)P and Dib(ah)A was maximum as compared to other PAHs. The study could be of great significance for the planners while considering environmental remedial measures.     

Distribution and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in sediments of different tropical water ecosystems in Niger Delta,Nigeria

Sediments are considered as suitable matrices to study the contamination levels of aquatic environment since they represent a sink for multiple contaminant sources. In this study, the influence of sediment characteristics on the distribution of polycyclic aromatic hydrocarbons (PAHs) and its potential risk in euryhaline, freshwater and humic aquatic bodies of Douglas/Stubbs creek, Ikpa River and Eniong River, respectively, were investigated. The level of PAHs in sediment was quantified using GC–MS, while sediment properties including total organic carbon (TOC) content and grain size were determined by the wet oxidation and hydrometer methods, respectively. The results revealed that the total levels of PAHs in sediment varied significantly between the euryhaline, freshwater and humic freshwater ecosystems. In Ikpa River freshwater ecosystem, a total PAHs load of 1055.2 ng/g was recorded with the suites concentration ranging from 13.0 ng/g (for acenaphthylene) to 161 ng/g (for pyrene). The humic ecosystem of Eniong River had a total PAH load of 11.06 ng/g, while the suites level recorded ranged from 0.04 ng/g for acenaphthene to 2.65 ng/g for chrysene. The total level of PAHs detected in the euryhaline Douglas/Stubbs creek was 14.47 ng/g, and suite concentrations varied between 4.27 ng/g for naphthalene and 5.13 ng/g for acenaphthylene. This shows variation in quantity and quality of PAH contaminants with the nature of ecosystems. It implies complex and diverse contamination sources as well as different capabilities to recover from PAH contamination. Correlation analysis has shown that sediment particle and TOC content influenced PAHs burden in bottom sediments, but the effects varied with the molecular weight of PAHs and the nature of the ecosystems. The TOC was the most significant determinant of PAHs load and distribution in sediment of the freshwater Ikpa River and euryhaline Douglas/Stubbs but had little or no influence in the humic sediment of Eniong River, while the influence of particle size was generally indefinite but slightly associated with PAHs accumulation in the euryhaline sediment. Generally, the total PAH levels (11.0–1055.2 ng/g) recorded were low and below the allowable limit for aquatic sediments. The ecological risk assessment revealed that these levels were lower than the effects range low and effects range medium values. This indicates no acute adverse biological effect although the accumulation of PAHs in freshwater ecosystem of Ikpa River may pose ecological risks as most of the carcinogenic PAH suites had relatively high pollution indices compared to other ecosystem types studied.     

Initiation of slip along the Xianshuihe fault zone,eastern Tibet,constrained by K/Ar and fission-track ages

The Xianshuihe fault zone (XFZ) forms a boundary that accommodates crustal movement eastwards from central Tibet. The lack of well-defined time constraints has hampered the reconstruction of the geometric and kinematic evolution of the fault zone, and inhibited the development of a consistent regional tectonic model. New geochronological investigations of mica K/Ar and apatite fission-track ages on the Ganzi–Yushu segment of the XFZ indicate that fault activity started ca. 13 Ma before present, which considerably precedes the 5 Ma initiation of offset on the Xiaojiang fault (XjF) segment. Different initiation times for different fault segments clearly demonstrate that the geometric and kinematic evolution of the XFZ can be divided into two periods. The XFZ cut through the Dangjiang, Ganzi, and Gongga Shan areas, and reached the Qinghe–Yanyuan area during an early stage, from ca. 13 to 5 Ma, as a boundary fault with lateral mass transfer from the interior to southeast Tibet. At the southern edge of the XFZ, the movement took advantage of the southern segment of the Longmen Shan thrust fault – the Jinhe–Qinghe thrust fault. During the late stage, from 5 Ma to present, the fault zone passed through the Yushu, Ganzi, and Gongga Shan areas, then offset the Longmen Shan thrust fault belt and reached the Kunming area. The Jinhe–Qinghe fault was abandoned in the later period as the southern part of the XFZ, and the XjF became active because of continuous clockwise rotation of the crust around the eastern syntaxis.     

First geophysical and shallow ice core investigation of the Kazbek plateau glacier,Caucasus Mountains

First-ever ice core drilling at Mt. Kazbek (Caucasus Mountains) took place in the summer of 2014. A shallow ice core (18 m) was extracted from a plateau at ~4500 m a.s.l. in the vicinity of the Mt. Kazbek summit (5033 m a.s.l.). A detailed radar survey showed that the maximum ice thickness at this location is ~250 m. Borehole temperature of ?7 °C was measured at 10 m depth. The ice core was analyzed for oxygen and deuterium isotopes and dust concentration. From the observed seasonal cycle, it was determined that the ice core covers the time interval of 2009–2014, with a mean annual snow accumulation rate of 1800 mm w. eq. Multiple melt layers have been detected. δ¹⁸O values vary from ?25 to ?5‰. The dust content was determined using a particle sizing and counting analyzer. The dust layers were investigated using scanning electron microscopy and X-ray diffraction analysis. Dust can be separated into two categories by its origin: local and distant. Samples reflecting predominantly local origin consisted mainly of magmatic rocks, while clay minerals were a characteristic of dust carried over large distances, from the deserts of the Middle East and Sahara. The calculated average dust flux over three years at Kazbek was of 1.3 mg/cm² a^?1. Neither δ¹⁸O nor dust records appear to have been affected by summer melting. Overall, the conditions on Kazbek plateau and the available data suggest that the area offers good prospects of future deep drilling in order to obtain a unique environmental record.     

Polycyclic aromatic hydrocarbon fingerprints in the Pichavaram mangrove–estuarine sediments,southeastern India

The sources and historical deposition of 16 polycyclic aromatic hydrocarbons (PAHs) were investigated in dated sediment cores from the Pichavaram mangrove–estuarine complex. The ΣPAH flux in mangrove and estuarine sediments was 0.064 ± 0.031 μg/cm²/yr and 0.043 ± 0.020 μg/cm²/yr, respectively. The PAH flux in sediments increased up-core, coinciding with rapid urbanization since the 1970s. The flux showed a decrease in recent years (since 1990), coinciding with less riverine discharge, and perhaps more effective implementation of environmental regulations. The sediments were dominated by low molecular weight PAHs, suggesting anthropogenic input. Ratios of specific PAH isomer pairs suggested a greater input of petrogenic vs. pyrogenic derived PAHs. Notably, the deposition of high molecular weight PAHs increase in mangrove surface sediments was due to lignite and firewood combustion. Because of their overall low concentration in sediments it is unlikely these PAHs pose an immediate ecological hazard.     

First principles simulations of the stability and structure of grain boundaries in Mg2SiO4 forsterite

Our understanding of how grain boundaries (GBs) can dramatically influence key mineral properties such as creep and diffusion depends on knowledge of their detailed atomic and electronic structures. For this purpose, we simulate different types of tilt GBs, (0l1)/[100], (1l0)/[001] and (012)/[100] modeled with stepped and non-stepped surfaces in Mg₂SiO₄ forsterite using a first-principles approach based on density functional theory. Our results suggest that several configurations arising from Mg-terminated planes with tilt angles ranging from 16° to 67° are energetically competitive over the entire pressure regime (0–17 GPa) studied. At the ambient pressure, the predicted important features of the boundaries include distorted bonds (Si–O and Mg–O distances changed by 1 and 4 %, respectively), coordination defects (four and fivefold Mg–O coordination), and void spaces (0.2–0.9 × 10^?10 m³/m²). Also, the interface induces splitting of electronic states from the conduction band and kinks at the top of the valence band. These structural and electronic features continue to exist at higher pressures. The formation enthalpy and excess volume for each boundary configuration studied were shown to systematically increase and decrease, respectively, with pressure. The predicted energy range (0.8–1.7 J/m² at zero pressure) widens by a factor of two at 17 GPa (1.1–2.8 J/m²). The presence of low-density and structurally distorted regions imply that these GBs can serve as primary impurity segregation sites, fast diffusion pathways, and electron-trapped regions, which all are relevant for mantle rheology.     

Simultaneous electrokinetic removal of polycyclic aromatic hydrocarbons and metals from a sediment using mixed enhancing agents

The maintenance of harbor waterways generates large amounts of dredged sediments which are often rich in coexisting organic and inorganic contaminants. Electrokinetic remediation treatments have recently been developed for the simultaneous removal of heavy metals and polycyclic aromatic hydrocarbons (PAHs), using various enhancing agents generally tested sequentially. In this study, different processing fluids were tested, alone or mixed, to improve the decontamination of aged model sediment contaminated with cadmium, lead, chromium, copper, zinc, and five PAHs. Nitric acid (NA) and citric acid (CA) were tested to avoid the formation of an alkaline front into the sediment and favor the metals removal, while an anionic surfactant [sodium dodecyl sulfate (SDS)] and a nonionic surfactant (Tween 20) were tested to solubilize and mobilize PAHs. Processing fluids were circulated under a constant voltage gradient of 1 V cm^?1 for 10–14 days. NA showed an excellent potential to remove metals (76.8–99.9 % removal) and PAHs (70.3–89.7 % removal) in a single run. Besides, the mixture of Tween 20 and CA, more environmental friendly, could be considered as a relatively good processing fluid for the simultaneous removal of metals (10.3–90.8 % removal) and PAHs (53.6–61.6 % removal) from the fine-grained sediment, while SDS mixed to CA was not a good candidate for this purpose (0.1–65 % removal for metals and 34.1–41.0 % removal for PAHs).