中国蔬菜硝酸盐和亚硝酸盐污染因素及控制研究

本文综述了近十几年来我国城市蔬菜中硝酸盐和亚硝酸盐污染的研究结果,表明随着氮肥使用量的增大,蔬菜中硝酸盐污染较为严重而亚硝酸盐污染也不容忽视。探讨了蔬菜受硝酸盐和亚硝酸盐污染的影响因素及控制对策     

Simultaneous determination of dissolved organic nitrogen, nitrite, nitrate and ammonia using size exclusion chromatography coupled with nitrogen detector

Accurate quantification of dissolved organic nitrogen (DON) has been a challenge due to the cumulative analytical errors in the conventional method via subtracting dissolved inorganic nitrogen species (DIN) from total dissolved nitrogen (TDN). Size exclusion chromatography coupled with an organic nitrogen detector (SEC-OND) has been developed as a direct method for quantification and characterization of DON. However, the applications of SEC-OND method still subject to poor separations between DON and DIN species and unsatisfied N recoveries of macromolecules. In this study, we packed a series of SEC columns with different lengths and resin materials for separation of different N species and designed an independent vacuum ultraviolet (VUV) oxidation device for complete oxidation converting N species to nitrate. To guarantee sufficient N recoveries, the operation conditions were optimized as oxidation time ≥ 30 min, injection mass (sample concentration × injection volume) < 1000 µL × mg-N/L for macromolecular proteins, and neutral pH mobile eluent. The dissolved O₂ concentration in SEC mobile phase determined the upper limit of VUV oxidation at a specific oxidation time. Compared to conventional HW50S column (20 × 250 mm), HW40S column (20 × 350 mm) with mobile phase comprising of 1.5 g/L Na₂HPO₄·2H₂O + 2.5 g/L KH₂PO₄ (pH = 6.85) could achieve a better separation of DON, nitrite, nitrate, and ammonia. When applied to river water, lake water, wastewater effluent, groundwater, and landfill leachate, the SEC-OND method could quantify DON as well as DIN species accurately and conveniently even the DIN/TDN ratio reached 0.98.     

土壤中重金属测定方法探讨

采用硝酸+氢氟酸+高氯酸全分解方法消解土壤样品,并结合原子吸收分光光度法和标准加入法测定土壤中、锌、铅、镉、镍、总铬的含量.结果表明,该方法具有操作简便、快速,节省试剂,准确可靠等特点:实际土壤样品的检测结果完全能满足环境土壤样品测定的要求.     

厌氧－缺氧－好氧处理城市废水系统缺氧相中的脱氮硫杆菌

利用厌氧－缺氧－好氧处理城市废水的中试规模系统,对其缺氧相中的脱氮硫杆菌进行了研究。结果表明,脱氮硫杆菌的最高脱氮作用率、氧化Na₂S的最高浓度、S^2-的最高污泥负荷率和污泥中脱氮硫杆菌的最高含量（MPN）分别为3.6mg－NO^－₃/gVSS·h、1750mg/L、25mg－S^2-/gVSS·d和1.1×10⁸/gVSS。脱氮硫杆菌在氧化二价硫成硫酸并还原硝酸为氮气的过程中起着相当有意义的作用。     

电极流动分析仪的研制和应用

采用固定电极测试状态的方法，将流动技术引入到离子电极直接电位分析法中，设计并试制了电极流动分析仪。配用市售硝酸根电极、钠电极、氟电极、氯电极和氨电极进行了环境样品的测定。结果表明，电极流动分析仪法的分析速度比直接电位法提高２－３倍，变异系数，２．９％－５．０％之间，回收率在９０％－１０５％之间；直接电位法变异系数在２．３％－６．７％之间，加收率在９０％－１０９％之间。     

Nitrate removal and extracellular polymeric substances of autohydrogenotrophic bacteria under various pH and hydrogen flow rates

In recent years there has been an increasing interest in the use of autohydrogenotrophic bacteria to treat nitrate from wastewater. However, our knowledge about the characteristics of extracellular polymeric substances (EPS) releasing by these activities is not yet very advanced. This study aimed to investigate the change in EPS compositions under various pH values and hydrogen flow rates, taking into consideration nitrogen removal. Results showed that pH 7.5 and a hydrogen flow rate of 90 mL/min were the optimal operating conditions, resulting in 100% nitrogen removal after 6 hr of operation. Soluble and bound polysaccharides decreased, while bound proteins increased with increasing pH. Polysaccharides increased with increasing hydrogen flow rate. No significant change of bound proteins was observed at various hydrogen flow rates.     

Differential N uptake by maize cultivars and soil nitrate dynamics under N fertilization in West Africa

Nitrate is prone to leaching in the sandy soils of the West African moist savannas. Better management of nitrogen (N) resources and maize cultivars with enhanced genetic capacity to capture and utilize soil and fertilizer N are strategies that could improve N-use efficiency. In two field experiments conducted at Zaria, northern Nigeria, five maize (Zea mays L.) cultivars planted early in the season were assessed under various N levels for differences in N uptake, soil N dynamics, and related N losses. Cultivar TZB-SR accumulated more N in the aboveground plant parts in both years than the other cultivars. All, except the semi-prolific late (SPL) variety, met about 50–60% of their N demand by the time of silking (64–69 DAP). In both years, SPL had the greatest capacity to take up N during the grain filling period, and it had the highest grain-N concentration and the least apparent N loss through leaching in the second year. There were no significant differences in soil N dynamics among cultivars in both years. At harvest, the residual N in the upper 90 cm of the profile under all the cultivars ranged from 56 to 72 kg ha⁻¹ in the first year and from 73 to 83 kg ha⁻¹ in the second year. Apparent N loss from 0 to 90 cm soil profile through leaching ranged from 35 to 122 kg ha⁻¹ in both years. N application significantly increased N uptake by more than 30% at all sampling dates in the second year of the experiment, but had no effect on apparent N loss. Results indicate that the use of maize cultivars with high N uptake capacity during the grain filling period when maximum leaching losses occur could enhance N recovery and may be effective in reducing leaching losses of mineral N in the moist savanna soils.     

Improving the knowledge of pesticide and nitrate transfer processes using age-dating tools (CFC, SF6, H) in a volcanic island (Martinique, French West Indies)

Numerous successful examples of CFC and SF₆ groundwater dating applications were recently published. However the proposed CFC/SF₆ method needs various hydrodynamic parameters that are not always available. In order to predict groundwater-quality trends in areas where the hydrogeological context is poorly known, a dating method using tritium, CFC and SF₆ was successfully implemented in Martinique. Hydrogeological understanding is limited in this volcanic island where groundwater contamination by pesticides and nitrate has been recently proven in various areas. A negative correlation was observed between nitrate concentrations and groundwater ages while pesticide contamination showed a more complex schema. Consequently the presence of old groundwater clearly explained the absence or low pesticide and nitrate concentrations in some areas. However a possible degradation of the water quality is to be feared in the future. In view of the relatively long transfer times and the complexity of the remobilization processes of solutes, the expected effects of any modifications in the use of fertilizers, or of changes in pesticide-use legislation, would take a long time to become apparent.     

Long-term variation of PM2.5 levels and composition at rural, urban, and roadside sites in Hong Kong: Increasing impact of regional air pollution

Long-term study of air pollution plays a decisive role in formulating and refining pollution control strategies. In this study, two 12-month measurements of PM_2.5 mass and speciation were conducted in 00/01 and 04/05 to determine long-term trend and spatial variations of PM_2.5 mass and chemical composition in Hong Kong. This study covered three sites with different land-use characteristics, namely roadside, urban, and rural environments. The highest annual average PM_2.5 concentration was observed at the roadside site (58.0±2.0 μg m⁻³ (average±2σ) in 00/01 and 53.0±2.7 μg m⁻³ in 04/05), followed by the urban site (33.9±2.5 μg m⁻³ in 00/01 and 39.0±2.0 μg m⁻³ in 04/05), and the rural site (23.7±1.9 μg m⁻³ in 00/01 and 28.4±2.4 μg m⁻³ in 04/05). The lowest PM_2.5 level measured at the rural site was still higher than the United States’ annual average National Ambient Air Quality Standard of 15 μg m⁻³. As expected, seasonal variations of PM_2.5 mass concentration at the three sites were similar: higher in autumn/winter and lower in summer. Comparing PM_2.5 data in 04/05 with those collected in 00/01, a reduction in PM_2.5 mass concentration at the roadside (8.7%) but an increase at the urban (15%) and rural (20%) sites were observed. The reduction of PM_2.5 at the roadside was attributed to the decrease of carbonaceous aerosols (organic carbon and elemental carbon) (>30%), indicating the effective control of motor vehicle emissions over the period. On the other hand, the sulfate concentration at the three sites was consistent regardless of different land-use characteristics in both studies. The lack of spatial variation of sulfate concentrations in PM_2.5 implied its origin of regional contribution. Moreover, over 36% growth in sulfate concentration was found from 00/01 to 04/05, suggesting a significant increase in regional sulfate pollution over the years. More quantitative techniques such as receptor models and chemical transport models are required to assess the temporal variations of source contributions to ambient PM_2.5 mass and chemical speciation in Hong Kong.