Zinc-copper interaction affecting plant growth on a metal-contaminated soil

In order to assess the effects of metal interactions on plant growth, a greenhouse experiment was conducted, in which spring barley was grown for 48 days in a soil to which cadmium, copper, lead and zinc were added singly and in combination. Plant growth was measured as shoot and root dry matter production. At the end of the experiment the plant material was analysed for metal uptake and the soil was extracted with CaCl(2) solution, to measure the plant-available metal content. The most consistent effect on plant growth was an interaction between copper and zinc, which was also important in determining uptake of these metals and the amounts extractable with CaCl(2) solution. An analysis of the underlying mechanism led to the conclusion that the growth of barley was controlled principally by the amount of plant-available zinc, which depended on the amounts of both added zinc and added copper. The effect of the added copper was to increase the toxicity of the added zinc.     

Predicting organic contaminant concentrations in sediment porewater using solid-phase microextraction

Because of its cost and time saving features, solid-phase microextraction (SPME) is a leading candidate as a biomimic technique in assessing the bioavailable fraction of hydrophobic organic contaminants (HOCs) in sediment porewater. However, no predictive modeling framework in which to systematically address the effect of key parameters on SPME performance for this application exists. In this study, we derived two governing equations to predict (1) the minimum sediment volume (V(s)min) required to achieve non-depletive conditions, and (2) dissolved phase HOC porewater concentrations (C(pw)) as functions of HOC- and sediment specific characteristics in a conceptual three compartment system. The resulting model predicted that V(s)min was independent of HOC concentrations both in sediment and porewater, but did vary with hydrophobicity (characterized by logK(ow)), the fraction of sediment porewater (f(pw)), and the volume (V(f)) of the SPME sorbent phase. Moreover, the effects of these parameters were minimized (i.e., V(s)min reached plateaus) as logK(ow) approached 4-5. Model predictions of C(pw), a surrogate for SPME-based detection limits in porewater, decreased with increasing sediment volume (V(s)) at low V(s) values, but rapidly leveled off as V(s) increased. A third result suggested that the sediment HOC concentration required for SPME is completely independent of K(ow). These results suggest that relatively small sediment volumes participate in exchange equilibria among sediment, porewater and the SPME fiber, and that large sediment HOC reservoirs are not needed to improve the detection sensitivity of SPME-based porewater samplers. The ultimate utility of this modeling framework will be to assist future experimental designs and help predict in situ bioavailability of sediment-associated HOCs.     

Enhancement of photocatalytic oxidation of humic acid in TiO2 suspensions by increasing cation strength

This study aimed at improving the photocatalytic (PC) oxidation of humic acids (HA) in TiO2 suspensions by adding cationic ion such as calcium or magnesium. A set of tests was first conducted in the dark to study the adsorption of HA onto TiO2 in suspensions at different pH and calcium concentrations. The experiment demonstrated that the adsorption of HA onto the TiO2 particles was either pH-dependent or calcium strength-dependent due to electrostatic interaction and calcium ion bridging. The photodegradation of HA in the presence of UV irradiation was investigated as a function of pH and the concentration of calcium and magnesium ions. The results showed that the adsorption behavior between HA and TiO2 played a very important role during the PC oxidation process. The PC oxidation could be enhanced at neutral pH by increasing the cation strength. The kinetics of HA PC degradation in TiO2 suspensions with different initial concentrations was also studied using the Langmuir-Hinshelwood model.     

Degradation of carbofuran in water by solar photocatalysis in presence of photosensitizers

The effect of the presence of photosensitizers, methylene blue (MB) and rose Bengal (RB), on the degradation of carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) in water in a solar photocatalytic system was investigated. It was found that as compared to MB, RB generally showed a stronger effect on the decomposition of carbofuran under comparable conditions. Among the conditions studied, adding 2 x 10(-6) M of RB, that corresponding to 2% of the initial concentration of carbofuran solution in the system, rendered the most effective degradation of carbofuran. As a result, a carbofuran removal percentage of 69.9%, a mineralization efficiency of 28.0%, and a microtoxicity reduction of 65.0% could be achieved. The degradation and mineralization of carbofuran was found to follow the pseudo-first order reaction kinetics. The decomposition mechanism of carbofuran was further investigated through identification of the intermediates to elaborate the influence of dye photosensitizer on the solar photocatalysis of carbofuran in water. On the basis of the intermediates identified, including carbofuran phenol, 3-hydroxy carbofuran phenol, and substituted alcohols (3-phenoxy 1-propanol, 2-ethyl 1-hexanol, 2-butoxyl ethanol), it appears that hydrolysis and hydroxylation were the two key mechanisms for decomposing carbofuran during the process of solar photocatalysis with the aid of dye photosensitizer.     

Trends in concentration of ground-level ozone and meteorological conditions during high ozone episodes in the Kao-Ping Airshed, Taiwan

This work analyzes the variations in daily maximum 1-hr ozone (O3) concentrations and the long-term trends in annual means of hourly ambient concentrations of O3, nitrogen oxides (nitrous oxide + nitrogen dioxide), and nonmethane hydrocarbons in the three administrative regions of Kao-Ping airshed in southern Taiwan over a recent 8-yr period. The annual or monthly means of all maxima, most 95th percentiles, and some 90th percentiles of the daily maximum 1-hr O3 concentrations exceed the daily limit of 120 parts per billion by volume in all three regions, namely, Kao-hsiung City, Kso-hsiung County, and P'ing-tung County. The monthly means of daily maximum 1-hr O3 concentrations exhibit distinct seasonal variations, with a bimodal form with the maxima in autumn and late winter to the middle of spring and a minimum in summer. The long-term variations in the annual means of hourly O3 concentrations in the three regions exhibit increasing trends. These increases in O3 are associated with the decline in ambient concentrations of nitrogen oxides and nonmethane hydrocarbons. High O3 episodes occur most often in autumn and most rarely in summer. The seasonal mean mixing heights in descending order follow the order of spring, summer, autumn, and winter. Meteorological parameters in autumn and winter indicate that the ground-level O3 tends to accumulate and trigger a high O3 episode on a warm day with sufficient sunlight and low wind in a high-pressure system, consistent with the low mixing heights in these two seasons.     

Relationship between chlorine consumption and chlorination by-products formation for model compounds

The objective of this research is to investigate the relationship between chlorine decay and the formations of disinfection by-products (DBP), including trichloromethane (TCM) and chloroacetic acid (CAA) in the presence of four model compounds, i.e., resorcinol, phloroglucinol, p-hydroxybenzoic acid, and m-hydroxybenzoic acid. The chlorine degradation in model compounds with OH and/or COOH functional groups were rapid after chlorination. The TCM yields of carboxylic group substituted compounds (3-hydroxybenzoic acid [3-HBA], 4-hydroxybenzoic acid [4-HBA]) were found to be lower than that of the m-dihydroxy substituted compounds. Phloroglucinol, with one more OH substitution group than resorcinol, tends to form significant amounts of CAA after chlorination. However, it was observed that with the COOH substitution of 3-HBA and 4-HBA tend to exhibit more CAA formation potential than resorcinol. The developed parallel second and first-order reaction model for chlorine demand has been successfully utilized for TCM, CAA and DBP formation modeling. A high correlation between CAA and TCM was observed for the model compounds.     

Performance characteristics of PM10 samplers under calm air conditions

The size range of airborne particles that is closely related to specific deposition regions in the human respiratory tract and excess lung burden of these deposited particles is associated with disease. Size-selective sampling, therefore, needs to be performed to assess the related health risks. Performance criteria applied to these samplers must be well characterized in order to provide accurate and reliable results. The PM10 samplers that have been used in place of the total suspended particulate samplers for the collection of ambient air particles are more relevant to potential inhalation hazards. In order to be certified, a PM10 sampler must meet reliable performance specifications, primarily the aerosol penetration test with liquid and solid particles in a wind tunnel (wind speeds of 2, 8, and 24 km/hr). This testing is intended to assure reasonable accuracy in aerosol measurements. However, the sampler performance under calm air conditions has not been well studied. In the present study, the sampling heads of three devices--the Harvard impactor, the Personal Environmental Monitor (PEM), and the Sierra Andersen model 241 dichotomous sampler PM10 inlet head--were tested for aerosol separation efficiency. With the consideration of bias and imprecision of the measurements, five specimens of each type of sampler were chosen for performance testing, repeating the tests 5 times for each specimen. An ultrasonic atomizing nozzle was used to nebulize potassium sodium tartrate tetrahydrate and dioctyl phthalate particles as the solid and liquid challenge aerosols, respectively. The aerosol number concentrations and size distributions upstream and downstream of the samplers were measured by using an aerosizer calibrated against a settling velocity chamber. The results showed that among the samplers tested, the dichotomous sampler PM10 inlet head had the best fit to the PM10 convention, while the other two samplers not only appeared to have a steeper separation-curve slope but also had significant particle bounce when challenged with solid particles. Analysis of variance also confirmed the superiority of the dichotomous samplers. Surface-coating with oil or grease greatly reduced the problem of particle bounce.     

A method for removal of CO from exhaust gas using pulsed corona discharge

An experimental study of the oxidation of CO in exhaust gas from a motorcycle has been carried out using plasma chemical reactions in a pulsed corona discharge. In the process, some main parameters, such as the initial CO concentration, amplitude and frequency of pulses, residence time, reactor volume, and relative humidity (RH), as well as their effects on CO removal characteristics, were investigated. O3, which is beneficial to reducing CO, was produced during CO removal. When the exhaust gas was at ambient temperature, more than 80% CO removal efficiency was realized at an initial concentration of 288 ppm in a suitable range of the parameters.     

Rapid reductive destruction of hazardous organic compounds by nanoscale Fe0

Fe0-mediated reductive destruction of hazardous organic compounds such as chlorinated organic compounds (COCs) and nitroaromatic compounds (NACs) in the aqueous phase is one of the latest innovative technologies. In this paper, rapid reductive degradation of COCs and NACs by synthesized nanoscale Fe0 in anaerobic batch systems was presented. The nanoscale Fe0, characterized by high specific surface area and high reactivity, rapidly transformed trichloroethylene (TCE), chloroform (CF), nitrobenzene (NB), nitrotoluene (NT), dinitrobenzene (DNB) and dinitrotoluene (DNT) under ambient conditions, which results in complete disappearance of the parent compounds from the aqueous phase within a few minutes. GC analysis reported that the main products of the dechlorination of TCE and CF were ethane and methane as well as that most of the nitro groups in NACs were reductively transformed to amine groups. These results suggest that the rapid reductive destruction by nanoscale Fe0 is potentially a viable in situ or aboveground treatment of groundwater contaminated with hazardous organic compounds including COCs and NACs.     

Methodology for management of endosulfan contaminated eluent.

Management of Endosulfan contaminated eluent (24 mg/l) resulting from a treatment process to remove Endosulfan from water with wood charcoal, was attempted using various methods viz. volatilisation, hydrolysis and sorption by viable cell bacteria with and without acclimatisation. Volatilisation failed in giving better result, as Endosulfan was not considerably volatile. It could achieve a removal efficiency of 1.4-2%. Hydrolysis resulted in 28.4% and 17.9% removal of Endosulfan in acidic and alkaline media, respectively. Viable cell bacteria (aerobic) without prior acclimatization showed efficiency of 89.7% and after prior acclimatisation showed 96% removal efficiency. Sorption by the acclimatized biomass was found a suitable method for the removal of Endosulfan at a concentration of 24 mg/l.