Fractionation of fulvic acids: characteristics and complexation with copper

Two fulvic acid samples isolated from Suwannee river (International Humic Substance Society) and Feeitsuey reservoir were subjected to gel filtration chromatography (GFC) for molecular size fractionation. The GFC-eluted samples were separated into three groups corresponding to the molecular weight ranges: < 220, 220-1000, and 1000-4000. Fluorescence quenching techniques were employed for determining the conditional stability coefficient and kinetic parameters of copper complexation with the three fractions of fulvic acids. Experimental conditions were pH 6, 5 x 10(-5)m total copper and 5 mg C litre(-1) of fulvic acids. The conditional stability coefficients of the fulvic acid fractions were in the order of 0.9-3.3 x 10(5)m(-1), and the forward and reverse rate constants were in the order of 6.9-12.4 x 10(3)m(-1) s(-1) and 3.5-8.0 x 10(-2) s(-1). Information could be useful in modelling copper transport in the hydrosphere.     

Effects of ozone and soil water deficit on roots and shoots of field-grown soybeans

Water-stressed and well-watered soybean (Glycine max cvs. Williams and Corsoy) plants were exposed to increasing seasonal doses of ozone (O(3)) using open-top field chambers and ambient air plots. Chamber O(3) treatments included charcoal filtered (CF) air, non-filtered (NF) air, NF + 0.03, NF + 0.06 and NF + 0.09 microl litre(-1) O(3). Soil water potentials measured at 25 and 45 cm averaged -0.40 MPa and -0.05 MPa, respectively, for the plots in the water-stressed and well-watered series. Total root length/core, root length densities, and biomasses (dry weights) were determined. With Williams, a very popular cultivar in recent years, total root length for all O(3) treatments averaged 58% more under water-stress conditions than in well-watered plots, but the range was from 136% to 11% more for NF air and NF + 0.09 microl litre(-1) O(3), respectively. Increasing the O(3) exposure dose did not affect root lengths or weights in the well-watered series. With Corsoy, water stress did not significantly increase root development. In both soil moisture regimes, with both cultivars, there was a linear decrease in seed yield and top dry weight as the O(3) exposure dose increased.     

DMS photochemistry during the Asian dust-storm period in the Spring of 2001: model simulations vs. field observations

This study examines the local/regional DMS oxidation chemistry on Jeju Island (33.17 degrees N, 126.10 degrees E) during the Asian dust-storm (ADS) period of April 2001. Three ADS events were observed during the periods of April 10-12, 13-14, and 25-26, respectively. For comparative purposes, a non-Asian-dust-storm (NADS) period was also considered in this study, which represents the entire measurement periods in April except the ADS events. The atmospheric concentrations of DMS and SO2 were measured at a ground station on Jeju Island, Korea, as part of the ACE-Asia intensive operation. DMS (means of 34-52 pptv) and SO2 (means of 0.96-1.14 ppbv) levels measured during the ADS period were higher than those (mean of 0.45 ppbv) during the NADS period. The enhanced DMS levels during the ADS period were likely due to the increase in DMS flux under reduced oxidant levels (OH and NO3). SO2 levels between the two contrasting periods were affected sensitively by some factors such as air mass origins. The diurnal variation patterns of DMS observed during the two periods were largely different from those seen in the background environment (e.g., the marine boundary layer (MBL)). In contrast to the MBL, the maximum DMS value during the ADS period was seen in the late afternoon at about sunset; this reversed pattern appears to be regulated by certain factors (e.g., enhanced NO3 oxidation). The sea-to-air fluxes of DMS between the ADS and NADS periods were calculated based on the mass-balance photochemical-modeling approach; their results were clearly distinguished with the values of 4.4 and 2.4 micromole m(-2) day(-1), respectively. This study confirmed that the contribution of DMS oxidation to observed SO2 levels on Jeju Island was not significant during our study period regardless of ADS or NADS periods.     

Outdoor/Indoor/Personal ozone exposures of children in Nashville, Tennessee

An ozone (O3) exposure study was conducted in Nashville, TN, using passive O3 samplers to measure six weekly outdoor, indoor, and personal O3 exposure estimates for a group of 10- to 12-yr-old elementary school children. Thirty-six children from two Nashville area communities (Inglewood and Hendersonville) participated in the O3 sampling program, and 99 children provided additional time-activity information by telephone interview. By design, this study coincided with the 1994 Nashville/Middle Tennessee Ozone Study conducted by the Southern Oxidants Study, which provided enhanced continuous ambient O3 monitoring across the Nashville area. Passive sampling estimated weekly average outdoor O3 concentrations from 0.011 to 0.O30 ppm in the urban Inglewood community and from 0.015 to 0.042 ppm in suburban Hendersonville. The maximum 1- and 8-hr ambient concentrations encountered at the Hendersonville continuous monitor exceeded the levels of the 1- and 8-hr metrics for the O3 National Ambient Air Quality Standard. Weekly average personal O3 exposures ranged from 0.0013 to 0.0064 ppm (7-31% of outdoor levels). Personal O3 exposures reflected the proportional amount of time spent in indoor and outdoor environments. Air-conditioned homes displayed very low indoor O3 concentrations, and homes using open windows and fans for ventilation displayed much higher concentrations.     

Catalytic decomposition of hydrogen peroxide and 4-chlorophenol in the presence of modified activated carbons

The objective of this research was to examine the heterogeneous catalytic decomposition of H(2)O(2) and 4-chlorophenol (4-CP) in the presence of activated carbons modified with chemical pretreatments. The decomposition of H(2)O(2) was suppressed significantly by the change of surface properties including the decreased pH(pzc) modified with oxidizing agent and the reduced active sites occupied by the adsorption of 4-CP. The apparent reaction rate of H(2)O(2) decomposition was dominated by the intrinsic reaction rates on the surface of activated carbon rather than the mass transfer rate of H(2)O(2) to the solid surface. By the detection of chloride ion in suspension, the reduction of 4-CP was not only attributed to the advanced adsorption but also the degradation of 4-CP. The catalytic activity toward 4-CP for the activated carbon followed the inverse sequence of the activity toward H(2)O(2), suggesting that acidic surface functional group could retard the H(2)O(2) loss and reduce the effect of surface scavenging resulting in the increase of the 4-CP degradation efficiency. Few effective radicals were expected to react with 4-CP for the strong effect of surface scavenging, which could explain why the degradation rate of 4-CP observed in this study was so slow and the dechlorination efficiency was independent of the 4-CP concentration in aqueous phase. Results show that the combination of H(2)O(2) and granular activated carbon (GAC) did increase the total removal of 4-CP than that by single GAC adsorption.     

Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing phyllosilicates

Abiotic reductive dechlorination of chlorinated ethylenes (tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (c-DCE), and vinylchloride (VC)) by iron-bearing phyllosilicates (biotite, vermiculite, and montmorillonite) was characterized to obtain better understanding of the behavior of these contaminants in systems undergoing remediation by natural attenuation and redox manipulation. Batch experiments were conducted to evaluate dechlorination kinetics and some experiments were conducted with addition of Fe(II) to simulate impact of microbial iron reduction. A modified Langmuir-Hinshelwood kinetic model adequately described reductive dechlorination kinetics of target organics by the iron-bearing phyllosilicates. The rate constants stayed between 0.08 (+/-10.4%) and 0.401 (+/-8.1%) day(-1) and the specific initial reductive capacity of iron-bearing phyllosilicates for chlorinated ethylenes stayed between 0.177 (+/-6.1%) and 1.06 (+/-7.1%) microM g(-1). The rate constants for the reductive dechlorination of TCE at reactive biotite surface increased as pH (5.5-8.5) and concentration of sorbed Fe(II) (0-0.15 mM g(-1)) increased. The appropriateness of the model is supported by the fact that the rate constants were independent of solid concentration (0.0085-0.17 g g(-1)) and initial TCE concentration (0.15-0.60 mM). Biotite had the greatest rate constant among the phyllosilicates both with and without Fe(II) addition. The rate constants were increased by a factor of 1.4-2.5 by Fe(II) addition. Between 1.8% and 36% of chlorinated ethylenes removed were partitioned to the phyllosilicates. Chloride was produced as a product of degradation and no chlorinated intermediates were observed throughout the experiment.     

Effect of formaldehyde on biofilm activity and morphology in an ultracompact biofilm reactor for carbonaceous wastewater treatment.

The effects of formaldehyde on biofilm morphology and biomass activity were investigated in an ultracompact biofilm reactor (UCBR) for carbonaceous wastewater treatment. The wastewater contained a fixed amount of glucose (with a chemical oxygen demand concentration of 600 mg/L) and an increasing concentration of formaldehyde (ranging from 21.4 to 271.1 mg/L). An influent formaldehyde concentration higher than 75 mg/L could facilitate filamentous growth (on biofilm) control and lead to a higher biofilm density, which is desirable as it enhanced the UCBR performance stability. However, at an influent formaldehyde concentration higher than 214.4 mg/L, biomass production was inhibited and deteriorations of biofilm morphology and biomass activity were observed. This study showed that it was desirable to maintain an influent formaldehyde concentration lower than 202.2 mg/L, as this concentration could achieve a good biofilm morphology while not inhibiting its microbial activity.     

Effect of experimental factors on nitrobenzaldehyde photoisomerization

The objective of this study was to compare the effect of various experimental factors on the photoisomerization of nitrobenzaldehyde. The experimental factors included light source, light energy, exposure time, light path distance and the concentration of nitrobenzaldehyde. The results showed that the photoisomerization of nitrobenzaldehyde increased with increasing light exposure. Different light sources and light path distances demonstrated significant impact on the reaction rate constants and half-lives of nitrobenzaldehyde. Although the light energy of UV photoreactor was 47% lower than that of xenon photoreactor, quantum yield and UV/VIS absorption pattern confirmed the finding that the effect of ultraviolet photoreactor on nitrobenzaldehyde was similar to that of xenon photoreactor with the light path of 17 cm. It was caused by the shorter wavelength of UV photoreactor mainly on 254 nn. The product of nitrobenzaldehyde photoisomerization, nitrosobenzoic acid, was detected from samples after 5 or 10 min exposure of three light sources. The concentrations of nitrosobenzoic acid increased with the increasing of exposure time up to 20 or 60 min.     

Uncertainties in current estimates of emissions of ammonia in the United Kingdom

Estimates of the emissions of ammonia have previously concentrated on animal husbandry sources from agricultural systems. Animal husbandry sources still constitute the major fraction of emissions of ammonia, but we have also considered the potential magnitude of other 'minor' sources, which may include coal combustion, waste incineration, road vehicles, sewage treatment plants, fertiliser manufacture and application, vegetation senescence and crop emissions, domestic pets, and human sources. Where possible, a provisional estimate of UK emissions from each of these sources is given. It is concluded that the potential magnitude of emissions from these 'minor' sources may make a significant contribution to the total emissions of ammonia to the atmosphere. On the basis of the available data, and the application of a range of emission factors to the UK situation, an additional annual emission potential lying in the range of approximately 80-140 ktonne year(-1) over and above that from animal husbandry has been calculated. The uncertainties in the emission estimates and instances in which a better resolution of sources is required are discussed. The emission factors used for animals in various inventories are reviewed and applied to the main UK agricultural animal populations. By using this approach, estimates of emissions from these sources range between 113 and 647 ktonne year(-1), which illustrates the uncertainties involved. It is suggested that our knowledge of the sources of ammonia, and their distribution, is far from complete.     

Transformation and adsorption of Fenamiphos, f. sulfoxide and f. sulfone in molokai soil and simulated movement with irrigation

The ban of commonly used soil fumigants, DBCP and EDB, for control of nematodes in pineapple fields has prompted investigations into a non-fumigant nematicide, fenamiphos (Nemacur^®). The transformation and adsorption in soil of fenamiphos and its transformation products, f. sulfoxide and f. sulfone were studied in the laboratory. Fenamiphos adsorption on soil exceeded that of f. sulfoxide and f. sulfone. F. sulfoxide, however, was the most persistent. A one-dimensional simulation model was used to assess the impact of transformation and adsorption on the mobility and distribution of fenamiphos and f. sulfoxide in soil. Simulated results showed that fenamiphos stayed in the topsoil and transformed rapidly to f. sulfoxide. Because of the persistence and mobility of f. sulfoxide, this metabolite leached rapidly and significant amounts remained in the soil. This suggests that for times exceeding three weeks, f. sulfoxide may be the dominant compound providing nematode control in drip-irrigated pineapple.