Toxicity models of metal mixtures established on the basis of “additivity” and “interactions”

Observed effects of metal mixtures on animals and plants often differ from the estimates, which are commonly calculated by adding up the biological responses of individual metals. This difference from additivity is commonly referred to as being a consequence of specific interactions between metals. The science of how to quantify metal interactions and whether to include them in risk assessment models is in its infancy. This review summarizes the existing predictive tools for evaluating the combined toxicity of metals present in mixtures and indicates the advantages and disadvantages of each method. We intend to provide eco-toxicologists with background information on how to make good use of the tools and how to advance the methods for assessing toxicity of metal mixtures. It is concluded that statistically significant deviations from additivity are not necessarily biologically relevant. Incorporation of interactions between metals in a model does not on forehand mean that the model is more accurate than a model developed based on additivity only. It is recommended to first use a relatively simple method for effect prediction of uninvestigated metal mixtures. To improve the reliability of toxicity modeling for metal mixtures, further efforts should focus on balancing the relationship between the significance of statistics and the biological meaning, and unraveling the toxicity mechanisms of metals and their mixtures.

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Role of illumination intensity in microcystin development using Microcystis aeruginosa as the model algae

Environmental Science and Pollution Research - Microcystis aeruginosa (M. aeruginosa) is one of the most common genera of cyanobacteria in algal blooms. In the present work, the impact of the...     

Atrazine contamination in agricultural soils from the Yangtze River Delta of China and associated health risks

Atrazine is one of the most widely applied and persistent herbicides in the world. In view of limited information on the regional contamination of atrazine in soils in China, this study investigated the spatial distribution and environmental impacts of atrazine in agricultural soils collected from the Yangtze River Delta (YRD) as an illustrative analysis of rapidly developing regions in the country. The results showed that the concentrations of atrazine in the YRD agricultural soils ranged from <1.0 to 113 ng/g dry weight, with a mean of 5.7 ng/g, and a detection rate of 57.7 % in soils. Pesticide factory might be a major source for the elevated levels of atrazine in Zhejiang Province. The contamination of atrazine was closely associated with land use types. The concentrations and detection rates of atrazine were higher in corn fields and mulberry fields than in rice paddy fields. There was no significant difference in compositions of soil microbial phospholipids fatty acids among the areas with different atrazine levels. Positive relationship (R = 0.417, p < 0.05, n = 30) was observed between atrazine and total microbial biomass. However, other factors, such as soil type and land management practice, might have stronger influences on soil microbial communities. Human health risks via exposure to atrazine in soils were estimated according to the methods recommended by the US EPA. Atrazine by itself in all the soil samples imposed very low carcinogenic risks (<10^?6) and minimal non-cancer risks (hazard index <1) to adults and children.     

A Two-Stage Particle Swarm Optimization Algorithm for MPPT of Partially Shaded PV Arrays

The power-voltage (P-V) characteristic curves of a PV array are nonlinear and have multiple peaks under partially shaded conditions (PSCs). This paper proposes a novel maximum power point tracking (MPPT) method for a PV system with reduced steady-state oscillation based on a two-stage particle swarm optimization (PSO) algorithm. The grouping method of the shuffled frog leaping algorithm (SFLA) is incorporated in the basic PSO algorithm (PSO-SFLA), ensuring fast and accurate searching of the global extremum. An adaptive speed factor is also introduced into the improved PSO to further enhance its convergence speed. Test results show that the proposed method converges in less than half the time taken by the conventional PSO method, and the power is improved by 33% under the worst PSCs, which confirms the superiority of the proposed method over the standard PSO algorithm in terms of tracking speed and steady-state oscillations under different PSCs.     

As（V）在金红石TiO2颗粒表面吸附特性及机理

通过静态动力学和热力学吸附实验,研究了温度、共存离子以及溶质的初始浓度对As（V）在金红石TiO2颗粒表面吸附的影响,探讨了As（V）在金红石TiO2颗粒表面吸附特性及机理。结果表明,在As（V）初始浓度为10mg／L,pH为7的条件下,25℃时的吸附量0．41mg／g高于30℃时的吸附量0．31mg／g,As（V）在金红石TiO,上的吸附为放热过程。CaCl2和MgCl2的添加对As（V）在金红石TiO2表面吸附起到明显的促进作用。T=25℃,Ca2＋或Mg2＋浓度为10mmol／L时,As（V）吸附量分别为0．64和0．56mg／g,Ca2＋比Mg2＋对As（V）吸附促进作用强。As（V）在金红石TiO2的吸附等温线符合Frendlich方程,Lagergren二级动力学方程能较好地描述As（V）在金红石TiO2颗粒表面吸附的动力学过程。     

Direct N2O decomposition over La2NiO4-based perovskite-type oxides

Direct decomposition of N₂O by perovskite-structure catalysts including La₂NiO₄, LaSrNiO₄, and La_0.7Ce_0.3SrNiO₄ was investigated. The catalysts were prepared by the Pechini method and characterized by x-ray diffraction (XRD), BET, scanning electron microscopy (SEM), and O₂-TPD. Experimental results indicate that the properties of La₂NiO₄ are significantly improved by partially substituting La with Sr and Ce. N₂O decomposition efficiencies achieved with LaSrNiO₄ and La_0.7Ce_0.3SrNiO₄ are 44 and 36%, respectively, at 400ºC. As the temperature was increased to 600ºC, N₂O decomposition efficiency achieved with LaSrNiO₄ and La_0.7Ce_0.3SrNiO₄ reached 100% at an inlet N₂O concentration of 1,000 ppm, while the space velocity was fixed at 8,000 hr^?1. In addition, effects of various parameters including oxygen, water vapor, and space velocity were also explored. The results indicate that N₂O decomposition efficiencies achieved with LaSrNiO₄ and La_0.7Ce_0.3SrNiO₄ are not significantly affected as space velocity is increased from 8,000 to 20,000 hr^?1, while La_0.7Ce_0.3SrNiO₄ shows better tolerance for O₂ and H₂O_(g). On the other hand, N₂ yield with LaSrNiO₄ as catalyst can be significantly improved by doping Ce. At a gas hour space velocity of 8,000 hr^?1, and a temperature of 600ºC, high N₂O decomposition efficiency and N₂ yield were maintained throughout the durability test of 60 hr, indicating the long-term stability of La_0.7Ce_0.3SrNiO₄ for N₂O decomposition.

Implications:Nitrous oxide (N₂O) not only has a high global warming potential (GWP₁₀₀ = 310), but also potentially destroys ozone in the stratosphere. Pervoskite-type catalysts including La₂NiO₄, LaSrNiO₄, and La_0.7Ce_0.3SrNiO₄ are applied for direct N₂O decomposition. The results show that N₂O decomposition can be enhanced as Sr and Ce are doped into La₂NiO₄. At 600ºC, N₂O decomposition efficiencies achieved with LaSrNiO₄ and La_0.7Ce_0.3SrNiO₄ reach 100%, demonstrating high activity and good potential for direct N₂O decomposition. Effects of O₂ and H₂O_(g) contents on catalytic activities are also evaluated and discussed.     

气升回流一体化工艺处理生活污水简

针对分散型生活污水处理开发了气升回流一体化工艺,以校园生活污水为对象,研究其对生活污水中污染物的去除效果。该系统由好氧区、厌氧区、沉淀区和气升室组成,以曝气的剩余气体的气升作用实现混合液的回流,节省动力消耗。结果表明,本工艺对COD、氨氮及悬浮物（SS）有较好的去除效果,去除率分别达到80%、90%和75%左右,出水COD、NH₄⁺-N及SS平均浓度在40 mg/L、6.5 mg/L和10 mg/L左右。当进水COD在100~1 000 mg/L之间波动时,出水水质稳定。该工艺有较强的抗冲击负荷能力,且可实现剩余污泥的自消解。本工艺具有结构紧凑、占地少,运行费用低,维护简单的特点。     

热处理时间对餐厨垃圾高温干式厌氧发酵的影响

餐厨垃圾中有机物大部分以大分子的形式存在,对其进行热处理,破坏大分子有机物的存在形式,将会影响其干式厌氧发酵的过程。实验对餐厨垃圾进行了热处理(100℃),处理后将其在含固率(TS)20%、接种率25%的条件下进行高温55℃厌氧发酵。实验结果表明,热处理后,餐厨垃圾的理化性质发生显著变化,累计产气量、TS和VS的去除率均增大。当热处理时间为15 min时,餐厨垃圾的SCOD值最高,为59.49 g/L,比未处理时提高了3.3倍。同样该条件下,累计产气量也最高,为2 782.8 m L,与未处理相比累积产气量提高58.30%,第二产气高峰比未处理提前3天。各发酵瓶发酵前后TS、VS去除率的变化趋势与累计产气量的变化基本一致,累计产气量越大,TS、VS的去除率越大。