Baseline concentrations and spatial distribution of trace metals in surface soils of Guangdong province, China

A total of 260 surface soil samples were collected to investigate the spatial distribution of trace metals in Guangdong province, one of the fast developing regions in China. The results show that the upper baseline concentrations of Cu, Pb, Zn, Cd, Ni, Cr, and Hg were 28.7, 57.6, 77.8, 0.13, 23.5, 87.0, and 0.15 mg kg(-1), respectively. Regional parent materials and pedogenesis are the primary factors influencing the concentrations of trace metals, and various anthropogenic activities are the second most important factors. The spatial distribution of trace metals is correlated to the geological characters with high concentrations of trace metals always located in regional fault areas, basins, and the Pearl River Delta alluvial plain and to the low concentrations associated with the other areas in Guangdong province.     

Identifying Linkages Between Land Use,Geomorphology, and Aquatic Habitat in a Mixed-Use Watershed

The potential impacts of land use on large woody debris (LWD) were examined in Sourdough Creek Watershed, a rapidly growing area encompassing Bozeman, Montana, USA. We identified six land classes within a 250 m buffer extending on either side of Sourdough Creek and assessed aquatic habitat and geomorphologic variables within each class. All LWD pieces were counted, and we examined 14 other variables, including undercut bank, sinuosity, and substrate composition. LWD numbers were generally low and ranged from 0 to 8.2 pieces per 50 m of stream. Linear regression showed that LWD increased with distance from headwaters, riparian forest width, and sinuosity in four of the six land classes. Statistically significant differences between land classes for many aquatic habitat and geomorphologic variables indicated the impacts of different land uses on stream structure. We also found that practices such as active wood removal played a key role in LWD abundance. This finding suggests that managers should prioritize public education and outreach concerning the importance of in-stream wood, especially in mixed-use watersheds where wood is removed for either aesthetic reasons or to prevent stream flooding.     

Removal of organic compounds during treating printing and dyeing wastewater of different process units

Wastewater in Shaoxing wastewater treatment plant (SWWTP) is composed of more than 90% dyeing and printing wastewater with high pH and sulfate. Through a combination process of anaerobic acidogenic [hydraulic retention time (HRT) of 15h], aerobic (HRT of 20h) and flocculation-precipitation, the total COD removal efficiency was up to 91%. But COD removal efficiency in anaerobic acidogenic unit was only 4%. As a comparison, the COD removal efficiency was up to 35% in the pilot-scale upflow anaerobic sludge bed (UASB) reactor (HRT of 15h). GC-MS analysis showed that the response abundance of these wastewater samples decreased with their removal of COD. A main component of the raw influent was long-chain n-alkanes. The final effluent of SWWTP had only four types of alkanes. After anaerobic unit at SWWTP, the mass percentage of total alkanes to total organic compounds was slightly decreased while its categories increased. But in the UASB, alkanes categories could be removed by 75%. Caffeine as a chemical marker could be detected only in the effluent of the aerobic process. Quantitative analysis was given. These results demonstrated that GC-MS analysis could provide an insight to the measurement of organic compounds removal.     

N-doped SiO2/TiO2 mesoporous nanoparticles with enhanced photocatalytic activity under visible-light irradiation

Mesoporous nanocrystalline N-doped SiO2/TiO2 visible-light photocatalysts were prepared by treating SiO2/TiO2 xerogels in a flow of nitrogen gas bubbled through concentrated ammonia solution. Structural characterization and performance analysis results revealed that the addition of SiO2 remarkably altered the phase composition, specific surface area, microstructure, as well as the photocatalytic activity of N-doped TiO2. The presence of SiO2 in N-doped TiO2 particles suppressed the formation of rutile phase and the crystal growth of N-doped TiO2 particles during thermal calcinations. When weight ratio of SiO2/TiO2 was in 0.05-0.20, the N-doped SiO2/TiO2 exhibited higher photocatalytic activity than the N-doped TiO2, and optimum ratio was found to be 0.05. The enhanced photocatalytic activity could be attributed to the higher specific area, larger pore volume, and more surface hydroxyl groups in the catalyst.     

Trace element mobility in soils seven years after the Aznalcóllar mine spill

The long-term influence of the Aznalcóllar mine spill on soils was studied seven years after the accident in the area of Vado del Quema. Soils where the pyritic sludge was not removed after the cleaning operations and soils where this process was accomplished successfully were sampled and studied in detail. Sludge and soil horizons were characterised, determining their physico-chemical parameters, mineralogy and the total concentrations of major and trace elements. Moreover, leaching studies were performed using batch tests. The main mineralogical changes detected in the soil beneath the weathered sludge are the neo-formation of jarosite, gypsum and sainfeldite, together with the almost total depletion of calcite. An important acidification of soil has been also produced, especially in the uppermost soil layers. These two factors show to be the main responsible for the vertical distribution and leachability displayed by trace elements. Critical total concentrations were found for most trace elements in the soil still affected by the sludge weathering. Furthermore, the Cd and Zn leachable contents showed to be extremely high. Therefore, in those areas affected by the mine spill where the removal of sludge was not accomplished properly, special care should be paid to trace elements highly mobile in acidic conditions. Additional restoration measures should be undertaken to avoid further pollutant dispersion.     

Review of the complexation of tetravalent actinides by ISA and gluconate under alkaline to hyperalkaline conditions

Isosaccharinic (ISA) and gluconic acids (GLU) are polyhydroxy carboxylic compounds showing a high affinity to metal complexation. Both organic ligands are expected in the cementitious environments usually considered for the disposal of low- and intermediate-level radioactive wastes. The hyperalkaline conditions imposed by cementitious materials contribute to the formation of ISA through cellulose degradation, whereas GLU is commonly used as a concrete additive. Despite the high stability attributed to ISA/GLU complexes of tetravalent actinides, the number and reliability of available experimental studies is still limited. This work aims at providing a general and comprehensive overview of the state of the art regarding Th, U(IV), Np(IV), and Pu(IV) complexes with ISA and GLU.In the presence of ISA/GLU concentrations in the range 10^− 5–10^− 2 M and absence of calcium, An(IV)(OH)_x(L)_y complexes (An(IV) = Th, U(IV), Np(IV), Pu(IV); L = ISA, GLU) are expected to dominate the aqueous speciation of tetravalent actinides in the alkaline pH range. There is a moderate agreement among their stability, although the stoichiometry of certain An(IV)-GLU complexes is still ill-defined. Under hyperalkaline conditions and presence of calcium, the species CaTh(OH)₄(L)₂(aq) has been described for both ISA and GLU, and similar complexes may be expected to form with other tetravalent actinides.In the present work, the available thermodynamic data for An(IV)–ISA/GLU complexes have been reviewed and re-calculated to ensure the internal consistency of the stability constants assessed. Further modelling exercises, estimations based on Linear Free-Energy Relationships (LFER) among tetravalent actinides, as well as direct analogies between ISA and GLU complexes have also been performed. This approach has led to the definition of a speciation scheme for the complexes of Th, U(IV), Np(IV) and Pu(IV) with ISA and GLU forming in alkaline to hyperalkaline pH conditions, both in the absence and presence of calcium.     

Polycyclic aromatic hydrocarbons in leaf cuticles and inner tissues of six species of trees in urban Beijing

Leaf samples of six tree species were collected along urban roadsides and a campus site in Beijing for measurement of polycyclic aromatic hydrocarbons (PAHs). PAHs in leaves were attributed to two fractions, leaf cuticles and inner leaf tissues, using sequential extraction. Total concentrations of 16 PAHs in the cuticles and the inner tissues were 69.3+/-64.6 microg g(-1) (d.w.) and 1.07+/-0.2 microg g(-1) (d.w.) at roadside and 57.5+/-52.6 microg g(-1) and 0.716+/-0.2 microg g(-1) on campus, respectively. The lipid-normalized inner tissue PAHs varied from 5.8 microg g(-1) to 15.0 microg g(-1). Similarities in PAH spectra between leaf cuticles and airborne particles and between the inner tissues and gaseous phase imply that airborne particulates and gaseous PAHs are likely the sources of PAHs for cuticles and the inner tissues, respectively. Difficulty in migration of heavier PAHs into inner tissues could be another reason.