Characterizing kinetics of transport and transformation of selenium in water-sediment microcosm free from selenium contamination using a simple mathematical model

This study developed a seven-compartment model for predicting the fate of selenium (Se) in an aquatic environment containing a water-sediment boundary. Speciation of Se in water-sediment microcosms under microaerobic conditions was measured to evaluate first-order kinetics of Se transportation and transformation. The microcosm consisted of a 10-ml solution containing 1mM soluble Se as selenate (Se6+) or selenite (Se4+) and 8 g wet sediment that was free from Se contamination, sampled from the Senri, Yamato, or Yodo Rivers in Osaka, Japan. Stepwise reaction coefficients describing transportation and transformation were determined using an inverse method on this model which includes: selenate (Se(W)6+) and selenite (Se(W)4+) in ponded water; selenate (Se(S)6+) and selenite (Se(S)4+), elemental Se (Se0), organic Se (Se2-) in sediment; and gaseous Se (DMSe). During this 1-month experiment, soluble Se was transported from ponded water to the sediment and Se was transformed sequentially to other Se species through biochemical reactions. Experimental and kinetic analyses indicated quantitatively that the Yamato River microcosm, with its high organic matter content, had a high adsorption rate of soluble Se. The Yodo River microcosm had a low adsorption rate for Se6+ and a low Se reduction rate. The Senri River microcosm had an apparent high volatilization rate of DMSe. The model developed in this study is extremely useful for predicting fate of Se in aquatic environment in the field.     

Influence of H<Subscript>2</Subscript> on the decomposition of halides by nonthermal plasma incorporated with in situ alkaline absorption

To control the emission of halides into the environment, an experiment on the nonthermal plasma decomposition of the halides CF₄, CHF₃, C₂HCl₃, and CHClF₂ was conducted in a wire-in-tube corona reactor. It was found that the decomposition of C₂HCl₃ and CHClF₂ was easy compared with the decomposition of CF₄ and CHF₃. With the addition of H₂ in N₂ gas, the decomposition ratio of CF₄, C₂HCl₃, and CHClF₂ increased. In contrast, the decomposition ratio of CHF₃ in a hydrogen-rich atmosphere was lower than that in an N₂ atmosphere. It was demonstrated that the yields of HF and/or HCl formed during halide decomposition clearly increased in the presence of H₂ in N₂ gas. Furthermore, in order to prevent the production of unwanted products from halide decomposition, a combination of plasma decomposition and in situ alkaline absorption was devised by coating a layer of Ca(OH)₂ onto the surface of the grounding electrode. It was demonstrated that the Ca(OH)₂ sorbent played an effective role as a scavenger, participating in halide decomposition by capturing reaction products such as HCl and HF, therefore resulting in increased halide decomposition.     

Diurnal and weekday variations in the source contributions of ozone precursors in California's South Coast Air Basin

For at least 30 years, ozone (O3) levels on weekends in parts of California's South Coast (Los Angeles) Air Basin (SoCAB) have been as high as or higher than on weekdays, even though ambient levels of O3 precursors are lower on weekends than on weekdays. A field study was conducted in the Los Angeles area during fall 2000 to test whether proposed relationships between emission sources and ambient nonmethane hydrocarbon (NMHC) and oxides of nitrogen (NOx) levels can account for observed diurnal and day-of-week variations in the concentration and proportions of precursor pollutants that may affect the efficiency and rate of O3 formation. The contributions to ambient NMHC by motor vehicle exhaust and evaporative emissions, estimated using chemical mass balance (CMB) receptor modeling, ranged from 65 to 85% with minimal day-of-week variation. Ratios of ambient NOx associated with black carbon (BC) to NOx associated with carbon monoxide (CO) were approximately 1.25 +/- 0.22 during weekdays and 0.76 +/- 0.07 and 0.52 +/- 0.07 on Saturday and Sunday, respectively. These results demonstrate that lower NOx emissions from diesel exhaust can be a major factor causing lower NOx mixing ratios and higher NMHC/NOx ratios on weekends. Nonmobile sources showed no significant day-of-week variations in their contributions to NMHC. Greater amounts of gasoline emissions are carried over on Friday and Saturday evenings but are, at most, a minor factor contributing to higher NMHC/NOx ratios on weekend mornings.     

Vertical distribution of <Emphasis Type="Italic">Todarodes pacificus</Emphasis> (Cephalopoda: Ommastrephidae) paralarvae near the Oki Islands,southwestern Sea of Japan

The diel vertical distribution patterns of Japanese common squid, Todarodes pacificus, paralarvae were examined using a Multiple Opening Closing Net and Environmental Sensing System (MOCNESS) in the southwest Sea of Japan near the Oki Islands (Japan) during five late-autumn surveys in 1998–2002. A total of 1,511 paralarvae ranging in mantle length (ML) from 0.7 to 7.3 mm were collected at 63 of the 68 stations surveyed. Most (84%) were collected above 75 m depth and in the mixed layer. The vertical distribution patterns varied little between day and night. Hatchling-sized (<1.0 mm ML) paralarvae were abundant at 0–25 m depth, and paralarval ML increased with increasing sampling depth. Our results suggest that T. pacificus paralarvae do not exhibit large diel vertical migration patterns, but as they increase in size, paralarvae gradually descend in the water column and the variability in depth increases with ontogeny.     

Study on phosphate uptake of the marine cyanophyte Synechococcus sp. NIBB 1071 in relation to oligotrophic environments in the open ocean

Inorganic phosphate (Pi) uptake by the marine cyanophyte Synechococcus sp. NIBB 1071 was studied using cells grown in an artificial seawater medium. The phosphate uptake was markedly enhanced in cells grown in the medium of low phosphate concentrations (phosphate-limited cells) than in cells grown in the phosphate-rich medium (phosphate-replete cells). The diagnosis of kinetics of instantaneous phosphate-uptake showed that V _max of the former was more than two orders of magnitude greater than that of the latter, and the k _m of the former was about 1/20 of that of the latter. The enhancement of the phosphate uptake was completed after a 40-h incubation of phosphate-replete cells in the phosphate-free medium. The activation was suppressed by chloramphenicol, an inhibitor of protein synthesis. The uptake developed in phosphate-limited cells was energy dependent and susceptive to osmotic shock, which suggests the involvement of a periplasmic phosphate-binding protein, analogous to that found in heterotrophic gram-negative eubacterial cells. The relationship between phosphate quota and growth rate, together with the kinetical data for phosphate uptake, predicted that ambient phosphate as low as 0.5 nM could support cell growth at a rate of one division per day. Results indicate that cells can grow rapidly even at phosphate concentrations as low as nanomolar levels. A possible regulatory mechanism of phosphate uptake in marine Synechococcus spp. is discussed in relation to a wide distribution of this picophytoplankton in the ocean environment. Received: 19 March 1997 / Accepted: 2 April 1997     

Changes in the acitivy of fucoxanthin-excited photosynthesis in the marine diatom Phaeodactylum tricornutum grown under different culture conditions

Variations in the photosynthetic activity under monochromatic light was studied in Phaeodactulum tricornutum grown under various culture conditions, with special reference to the composition of photosynthetic pigments. Photosynthetic activity, under light-limiting conditions, was reduced when the cells were grown under strong light. The reduction was more extensive in activity resulting from fucoxanthin-excitation than in that from chlorophyll a-excitation. The diminution in activity for fucoxanthin-excited photosynthesis did not correlate with variations in the pigment content. A similar diminution was observed with chlorophyll a fluorescence upon excitation of fucoxanthin. The change was accelerated by lowering the culture temperature, or limiting the supply of nitrogen source. The results were interpreted in terms of a nitrogen-deficient state for algal cells induced by strong light, low temperature or a limited supply of nitrogen. This leads to a modification of the physicochemical state of in vivo fucoxanthin, so that the excitation energy of fucoxanthin is less efficiently transferred to chlorophyll a. The significance of the phenomenon in the oceanic primary production is discussed.     

Accumulation and excretion of organophosphorous pesticides by willow shiner

Bioconcentration and excretion of 8 organophosphorous pesticides were studied for willow shiner ( ). The average bioconcentration factors (BCF) in the whole body of the fish after 24 – 168 hr exposure were 0.8 for dichlorvos, 76 for salithion, 18 for methidathion, 29 for pyridaphenthion, 481 for fenthion and 36 for phosmet, Further, the BCF values of the other pesticides after 168 hr exposure were 713 for phenthoate and 1682 for EPN. The correlation between n-octanol-water partition coefficients (P_OW) and BCF in willow shiner was investigated for 19 pesticides studied here and already reported. The correlation factor (r) was not so high (0.6819, n=19) but higher (0.9085, n=18) in case excluding captan. The excretion rate constants (k) from the whole body of willow shiner were 0.20 hr⁻¹ for salthion, 0.05 hr⁻¹ for phenthoate, 0.27 hr⁻¹ for methidathion, 0.20 hr⁻¹ for pyridaphenthion, 0.07 hr⁻¹ for fenthion, 0.04 hr⁻¹ for EPN and 0.28 hr⁻¹ for phosmet.     

Determination method of singlet oxygen in the atmosphere by use of α -terpinene

A chemical determination method of singlet oxygen in the atmosphere was established. The method employs a specific reaction of α -terpinene with singlet oxygen to produce the single product, ascaridole. Amberlite XAD-2 coated with α -terpinene was packed into a glass tube shielded from light and sample air was passed through the tube. Ascaridole formed was extracted with hexane from Amberlite XAD-2 and was determined by gas chromatography. The amount of singlet oxygen was calculated from that of ascaridole. Ascaridole was not formed by oxidation of α -terpinene with ozone, hydrogen peroxide and hydroxyl radical, and ascaridole formed by singlet oxygen was stable against these oxidants. The method was applied to actual polluted air and diurnal variations in the singlet oxygen were observed.     

Examining farmland applications of composted biosolid wastes depending on nutrient balance in soils

This study emphasizes nutrient balance of soils in the farmland application of composted biosolid wastes. The loading rates of plant nutrients following the compost application to farmland in Japan were estimated and compared with the nutrient uptake of agricultural plants. Results show that the current compost application in Japan can meet the requirements of agricultural plants for plant nutrient Ca, except for K, Mg, P, Fe, Mn, Cu, and Zn. The compost application could realize the safe disposal of biosolid wastes and the effective recycling of plant nutrients in composts to soils without causing heavy metal accumulation. The application manner of composts affects the heavy metal accumulation in farmlands. Field examination indicates that the excessive compost application has led to the heavy metal accumulation in compost-amended farmlands. Measuring the nutrient balance in compost-amended farmlands is well suitable for explaining the accumulation of heavy metals, such as Cu and Zn.     

高硫酸盐难降解废水高温厌氧处理中限量曝气的应用及影响

由于硫酸盐还原的影响,普通高温UASB反应器处理亚硫酸盐纸浆厂排出的高硫酸盐难降解废水过程中甲烷菌活性受到了严重抑制.考虑到空气对硫化氢的吹脱和对硫化物的氧化作用可能减轻硫化物对甲烷菌的抑制,本研究在厌氧反应器中引入限量曝气措施.试验结果表明,反应器的运行稳定性和处理能力均得到大幅提高.在有机负荷提高到原来2倍的情况下,曝气后COD去除率仍有提高,从40%～50%提高到60%～70%.试验证明部分甲烷菌可以耐氧,而某些种类的水解酸化细菌则对不完全厌氧环境比较敏感.