Relationships between organic matter, black carbon and persistent organic pollutants in European background soils: Implications for sources and environmental fate

Black carbon (BC) and total organic carbon (TOC) contents of UK and Norwegian background soils were determined and their relationships with persistent organic pollutants (HCB, PAHs, PCBs, co-planar PCBs, PBDEs and PCDD/Fs) investigated by correlation and regression analyses, to assess their roles in influencing compound partitioning/retention in soils. The 52 soils used were high in TOC (range 54-460 mg/g (mean 256)), while BC only constituted 0.24-1.8% (0.88%) of the TOC. TOC was strongly correlated (p < 0.001) with HCB, PCBs, co-PCBs and PBDEs, but less so with PCDD/Fs (p < 0.05) and PAHs. TOC explained variability in soil content, as follows: HCB, 80%; PCBs, 44%; co-PCBs, 40%; PBDEs, 27%. BC also gave statistically significant correlations with PBDEs (p < 0.001), co-PCBs (p < 0.01) and PCBs, HCB, PCDD/F (p < 0.05); TOC and BC were correlated with each other (p < 0.01). Inferences are made about possible combustion-derived sources, atmospheric transport and air-surface exchange processes for these compounds.     

In field arsenic removal from natural water by zero-valent iron assisted by solar radiation

An in situ arsenic removal method applicable to highly contaminated water is presented. The method is based in the use of steel wool, lemon juice and solar radiation. The method was evaluated using water from the Camarones River, Atacama Desert in northern Chile, in which the arsenic concentration ranges between 1000 and 1300 μg L⁻¹. Response surface method analysis was used to optimize the amount of zero-valent iron (steel wool) and the citrate concentration (lemon juice) to be used. The optimal conditions when using solar radiation to remove arsenic from natural water from the Camarones river are: 1.3 g L⁻¹ of steel wool and one drop (ca. 0.04 mL) of lemon juice. Under these conditions, removal percentages are higher than 99.5% and the final arsenic concentration is below 10 μg L⁻¹. This highly effective arsenic removal method is easy to use and inexpensive to implement.     

Sorption of polar and nonpolar aromatic compounds to four surface soils of eastern China

Improved predictions on the fate of organic pollutants in surface environments require a better understanding of the underlying sorption mechanisms that control their uptake by soils. In this study, we monitored sorption of nine aromatic compounds with varying physicochemical properties (hydrophobicity, electron-donor/acceptor ability and polarity), including two polycyclic aromatic hydrocarbons, two chlorobenzenes, two nitroaromatic compounds, dichlobenil, carbaryl and 2,4-dichlorophenol in aqueous suspension of four surface soils of eastern China. The tested soils were characterized with respect to organic carbon (OC) content, black carbon content, mineralogy, morphology and size fraction to assess the role of the diverse soil characteristics in sorption. The results of this study show that not only the solute hydrophobicity and the OC content of soil are important to the retention of organic pollutants, but also the solute molecular structure and the soil nature.     

Bioenergy to save the world

BACKGROUND AND AIM: Following to the 2006 climate summit, the European Union formally set the goal of limiting global warming to 2 degrees Celsius. But even today, climate change is already affecting people and ecosystems. Examples are melting glaciers and polar ice, reports about thawing permafrost areas, dying coral reefs, rising sea levels, changing ecosystems and fatal heat periods. Within the last 150 years, CO2 levels rose from 280 ppm to currently over 400 ppm. If we continue on our present course, CO2 equivalent levels could approach 600 ppm by 2035. However, if CO2 levels are not stabilized at the 450-550 ppm level, the consequences could be quite severe. Hence, if we do not act now, the opportunity to stabilise at even 550 ppm is likely to slip away. Long-term stabilisation will require that CO2 emissions ultimately be reduced to more than 80% below current levels. This will require major changes in how we operate. RESULTS: Reducing greenhouse gases from burning fossil fuels seems to be the most promising approach to counterbalance the dramatic climate changes we would face in the near future. It is clear since the Kyoto protocol that the availability of fossil carbon resources will not match our future requirements. Furthermore, the distribution of fossil carbon sources around the globe makes them an even less reliable source in the future. We propose to screen crop and non-crop species for high biomass production and good survival on marginal soils as well as to produce mutants from the same species by chemical mutagenesis or related methods. These plants, when grown in adequate crop rotation, will provide local farming communities with biomass for the fermentation in decentralized biogas reactors, and the resulting nitrogen rich manure can be distributed on the fields to improve the soil. DISCUSSION: Such an approach will open new economic perspectives to small farmers, and provide a clever way to self sufficient and sustainable rural development. Together with the present economic reality, where energy and raw material prices have drastically increased over the last decade, they necessitate the development and the establishment of alternative concepts. CONCLUSIONS: Biotechnology is available to apply fast breeding to promising energy plant species. It is important that our valuable arable land is preserved for agriculture. The opportunity to switch from low-income agriculture to biogas production may convince small farmers to adhere to their business and by that preserve the identity of rural communities. PERSPECTIVES: Overall, biogas is a promising alternative for the future, because its resource base is widely available, and single farms or small local cooperatives might start biogas plant operation.     

Design approaches for a cycling adsorbent/photocatalyst system for indoor air purification: formaldehyde example

A kinetic model for a cycling adsorbent/photocatalyst combination for formaldehyde removal in indoor air (Chin et al. J. Catalysis 2006, 237, 29-37) was previously developed in our lab, demonstrating agreement with lab-scale batch operation data of other researchers (Shiraishi et al. Chem. Engineer. Sci. 2003, 58, 929-934). Model parameters evaluated included adsorption equilibrium and rate constants for the adsorbent (activated carbon) honeycomb rotor, and catalytic rate constant for pseudo-first-order formaldehyde destruction in the titanium dioxide photoreactor. This paper explores design consequences for this novel system. In particular, the batch parameter values are used to model both adsorbent and photocatalyst behavior for continuous operation in typical residential home challenges. Design variables, including realistic make-up air fraction, adsorbent honeycomb rotation speed, and formaldehyde source emission rate, are considered to evaluate the ability of the system to achieve World Health Organization pollutant guidelines. In all circumstances, the size of the required rotating adsorbent bed and photoreactor for single-stage operation and the resultant formaldehyde concentration in the home are calculated. The ability of how well such a system might be accommodated within the typical dimensions of commercial ventilation ducts is also considered.     

Heavy metal resistance and genotypic analysis of metal resistance genes in gram-positive and gram-negative bacteria present in Ni-rich serpentine soil and in the rhizosphere of Alyssum murale

Forty-six bacterial cultures, including one culture collection strain, thirty from the rhizosphere of Alyssum murale and fifteen from Ni-rich soil, were tested for their ability to tolerate arsenate, cadmium, chromium, zinc, mercury, lead, cobalt, copper, and nickel in their growth medium. The resistance patterns, expressed as minimum inhibitory concentrations, for all cultures to the nine different metal ions were surveyed by using the agar dilution method. A large number of the cultures were resistant to Ni (100%), Pb (100%), Zn (100%), Cu (98%), and Co (93%). However, 82, 71, 58 and 47% were sensitive to As, Hg, Cd and Cr(VI), respectively. All cultures had multiple metal-resistant, with heptametal resistance as the major pattern (28.8%). Five of the cultures (about of 11.2% of the total), specifically Arthrobacter rhombi AY509239, Clavibacter xyli AY509235, Microbacterium arabinogalactanolyticum AY509226, Rhizobium mongolense AY509209 and Variovorax paradoxus AY512828 were tolerant to nine different metals. The polymerase chain reaction in combination with DNA sequence analysis was used to investigate the genetic mechanism responsible for the metal resistance in some of these gram-positive and gram-negative bacteria that were, highly resistant to Hg, Zn, Cr and Ni. The czc, chr, ncc and mer genes that are responsible for resistance to Zn, Cr, Ni and Hg, respectively, were shown to be present in these bacteria by using PCR. In the case of, M. arabinogalactanolyticum AY509226 these genes were shown to have high homology to the czcD, chrB, nccA, and mer genes of Ralstonia metallidurans CH34. Therefore, Hg, Zn, Cr and Ni resistance genes are widely distributed in both gram-positive and gram-negative isolates obtained from A. murale rhizosphere and Ni-rich soils.     

Sample storage and extraction efficiencies in determination of polycyclic and nitro musks in sewage sludge

Analytical technology is continuously improving, developing better methods for isolating and concentrating trace compounds in environmental samples. Polycyclic and nitro musks (PNMs) are one group of emerging trace compounds detected in municipal wastewater. Differences in sample storage, preparation, and extraction methods for their measurement have led to variability in results. We analyzed 11 PNMs by GC/MS and compared the results of different storage times and extraction methods (supercritical fluid (SFE) or microwave-assisted (MAE)) for 202 samples of primary sludge, waste activated sludge (WAS), raw sludge, and aerobically/anaerobically digested biosolids collected from Canadian municipal wastewater treatment plants. Sixty-three air-dried samples were extracted by SFE, and 139 air-dried, centrifuged, or filtered samples were extracted by MAE. The mean surrogate recoveries were 89% (standard deviation (SD)=11%) for d(10)-anthracene by SFE and 88% (SD=14%) for d(10)-phenanthrene by MAE. Storage study results showed that PNM concentrations changed by a mean of 7% and 9% for primary sludge and WAS respectively after four weeks and decreased up to 25% after 13.5 months of storage in amber glass containers at -18 degrees C. Air-drying of sludge at room temperature caused losses of about 50% of PNM concentrations compared to centrifugation. The proportions of PNMs present in the liquid phase of sludge samples were less than 5% compared to proportions in the sludge solids. The most complete liquid-solid separation was achieved by filtration of frozen/thawed sludge samples, producing a liquid phase that contained less than 1% of the total musk content of the sample.     

Sonochemical substrate selectivity and reaction pathway of systematically substituted azo compounds

The sonochemical degradation of the systematically substituted azo compound 2,7-dihydroxy-1-phenylazonaphthaline-3,6-disulfonic acid was investigated using a frequency of 850 kHz and an acoustic input power of 61 W. All derivatives were degraded completely within 6h by the ultrasonic treatment. Trifluoromethyl substituted azo compounds exhibited 2-3-fold higher degradation rates in comparison to the reference hydrogen substituted azo compound (k=0.54 h(-1)). In contrast to enzymatic processes (azoreductase or laccase), the ultrasonic treatment for these ortho-, meta-, and para-substituted azo compound showed 1.5-50-fold higher degradation rates. Additionally the ultrasound treatment was characterized by shorter reaction times. As a result of the detection and identification of specific intermediates using LC-MS a reaction pathway of the sonochemical degradation of the analysed azo compound is proposed indicating the formation of cyclohexadienone and naphthalene quinone derivatives.     

Effect of soil moisture dynamics on dense nonaqueous phase liquid (DNAPL) spill zone architecture in heterogeneous porous media

The amount, location, and form of NAPL in contaminated vadose zones are controlled by the spatial distribution of water saturation and soil permeability, the NAPL spill scenario, water infiltration events, and vapor transport. To evaluate the effects of these processes, we used the three-phase flow simulator STOMP, which includes a new permeability-liquid saturation-capillary pressure (k-S-P) constitutive model. This new constitutive model considers three NAPL forms: free, residual, and trapped. A 2-D vertical cross-section with five stratigraphic layers was assumed, and simulations were performed for seven cases. The conceptual model of the soil heterogeneity was based upon the stratigraphy at the Hanford carbon tetrachloride (CT) spill site. Some cases considered co-disposal of NAPL with large volumes of wastewater, as also occurred at the Hanford CT site. In these cases, the form and location of NAPL were most strongly influenced by high water discharge rates and NAPL evaporation to the atmosphere. In order to investigate the impact of heterogeneity, the hydraulic conductivity within the lower permeability layer was modeled as a realization of a random field having three different classes. For six extreme cases of 100 realizations, the CT mass that reached the water table varied by a factor of two, and was primarily controlled by the degree of lateral connectivity of the low conductivity class within the lowest permeability layer. The grid size at the top boundary had a dramatic impact on NAPL diffusive flux just after the spill event when the NAPL was present near the ground surface. NAPL evaporation with a fine grid spacing at the top boundary decreased CT mass that reached the water table by 74%, compared to the case with a coarse grid spacing, while barometric pumping had a marginal effect for the case of a continuous NAPL spill scenario considered in this work. For low water infiltration rate scenarios, the distribution of water content prior to a NAPL spill event decreased CT mass that reached the water table by 98% and had a significant impact on the formation of trapped NAPL. For all cases simulated, use of the new constitutive model that allows the formation of residual NAPL increased the amount of NAPL retained in the vadose zone. Density-driven advective gas flow from the ground surface controlled vapor migration in strongly anisotropic layers, causing NAPL mass flux to the lower layer to be reduced. These simulations indicate that consideration of the formation of residual and trapped NAPLs and dynamic boundary conditions (e.g., areas, rates, and periods of different NAPL and water discharge and fluctuations of atmospheric pressure) in the context of full three-phase flow are needed, especially for NAPL spill events at the ground surface. In addition, NAPL evaporation, density-driven gas advection, and NAPL vertical movement enhanced by water flow must be considered in order to predict NAPL distribution and migration in the vadose zone.     

Mechanism of decolorization and degradation of CI Direct Red 23 by ozonation combined with sonolysis

The decolorization and degradation of CI Direct Red 23, which is suspected to be carcinogenic, were investigated using ozonation combined with sonolysis. The results showed that the combination of ozonation and sonolysis was a highly effective way to remove color from waste water. The operational parameters, namely concentration of the dye, pH, ozone dose and ultrasonic density, were investigated during the process. The decolorization of the dye followed pseudo-first-order kinetics. Increasing the initial concentration of Direct Red 23 led to a decreasing rate constant. The optimum pH for the reaction was 8.0, and both lower and higher pH decreased the removal rate. The effect of the ozone dose on the dye decolorization was much greater than that of the sonolysis density. Intermediates such as naphthalene-2-sulfonic acid, 1-naphthol, urea and acetamide were detected by gas chromatography coupled with mass spectrometry in the absence of pH buffer, while nitrate and sulfate ions and formic, acetic and oxalic acids were detected by ion chromatography. A tentative degradation pathway was proposed without any further quantitative analyses. During the degradation, all nitrogen atoms and phenyl groups of Direct Red 23 were degraded into urea, nitrate ion, nitrogen and formic, acetic and oxalic acids, etc.