Quantitative structure-pharmacokinetic relationship modelling.

This article presents the current methods in quantitative structure-pharmacokinetic relationship (QSPkR) modelling along with examples using chemicals of toxicological significance. The common method involves: (i) collecting pharmacokinetic data or determining pharmacokinetic parameters (e.g. elimination half-life, volume of distribution) by fitting to experimental data; and (ii) associating them with the structural features of chemicals using a Free-Wilson model. Such QSPkRs have been developed for a few series of chemicals but their usefulness is limited to the exposure scenario and conditions under which the experimental data were originally collected. The alternative approach involves the development of quantitative structure-property relationship (QSPR) models for parameters, blood:air partition coefficient, tissue:blood partition coefficient, maximal velocity for metabolism and Michaelis affinity constant, of physiologically-based pharmacokinetic (PBPK) models which are useful for conducting species, route, dose and scenario extrapolations of the tissue dose of chemicals. Mechanistic QSPRs are available for predicting tissue:blood and blood:air partition coefficients from molecular structure information of chemicals, whereas such approaches are not currently available for hepatic metabolism parameters. However, at the present time, the pharmacokinetics of inhaled volatile organic chemicals can be simulated adequately by considering the physiological limits of the hepatic extraction ratio (0-1) and molecular structure-based estimates of partition coefficients in the PBPK model. This current state-of-the-art of structure-based modelling of pharmacokinetics will advance with the development of QSPRs for other chemical-specific parameters of PBPK models. Integrated QSPR-PBPK modelling should facilitate the identification of chemicals of a family that possess desired properties of bioaccumulation and blood concentration profile in both test animals and humans.     

Critical loads of acidity for surface waters in China

Various types of partition coefficients have been used to facilitate the prediction of the concentration of pollutants in different phases in the environment. Many thousands of chemicals may exist in our environment which makes prediction work difficult or impossible due to a deficiency of knowledge of those unfamiliar compounds. In this study, the correlation between an octanol-water partition coefficient (Kow), water solubility (S) and a normalized soil/sediment partition coefficient (Koc) was investigated though the examination of 148 model chemicals. These model chemicals were classified into five major categories for easier adoption in future use. They are aliphatic compounds, aromatic compounds, pesticides, herbicides and polyaromatic hydrocarbons (PAH). Linear models are developed to correlate these partition coefficients in each category. The prediction of unfamiliar chemicals in the same category becomes possible if the fundamental properties of these chemicals (such as solubility) are previously known.     

An experimental study of relative humidity effect on VOCs’ effective diffusion coefficient and partition coefficient in a porous medium

Most building materials are porous media. As a critical environmental factor, the influence of relative humidity on VOCs diffusion is still not well understood. In this study, VOC transport and sorption in a porous medium in the building materials (calcium silicate) were measured under three levels of relative humidity (25%, 50% and 80%) by using a dynamic dual chamber method. Tests were conducted for water-soluble compound (formaldehyde) and non-soluble compound (toluene). In addition, the transport of acetaldehyde, hexanal, benzaldehyde, butanol and decane through the calcium silicate were also tested at 50%RH to study the relationship between the effective diffusion coefficient (D_e), partition coefficient (K_ma) and the VOCs’ physical properties (molecular weight, vapor pressure and Henry’s law constant). Experimental results showed that: relative humidity in the 80%RH led to a higher partition coefficient for formaldehyde compared to 50%RH. However, between 25% and 50%RH, there was no significant difference in partition coefficient. Partition coefficient of toluene decreased with the increase of humidity due to competition of water molecules for pore surface area and the non-solubility nature of toluene. Relative humidity had no significant influence on the effective diffusion coefficient on both formaldehyde and toluene for the range of moisture conditions tested. The solubility of VOCs was found to correlate with the partition coefficient of VOCs. The partition coefficient of VOCs was not simply inversely proportional to the vapor pressure of the compound, but also increased with the increase of Henry’s law constant.     

Methamphetamine absorption by skin lipids: accumulated mass,partition coefficients,and the influence of fatty acids

Occupants of former methamphetamine laboratories, often residences, may experience increased exposure through the accumulation of the methamphetamine in the organic films that coat skin and indoor surfaces. The objectives of this study were to determine equilibrium partition coefficients of vapor‐phase methamphetamine with artificial sebum (AS‐1), artificial sebum without fatty acids (AS‐2), and real skin surface films, herein called skin oils. Sebum and skin oil‐coated filters were exposed to vapor‐phase methamphetamine at concentrations ranging from 8 to 159 ppb, and samples were analyzed for exposure time periods from 2 h to 60 days. For a low vapor‐phase methamphetamine concentration range of ~8–22 ppb, the equilibrium partition coefficient for AS‐1 was 1500 ± 195 μg/g/ppb. For a high concentration range of 98–112 ppb, the partition coefficient was lower, 459 ± 80 μg/g/ppb, suggesting saturation of the available absorption capacity. The low partition coefficient for AS‐2 (33 ± 6 μg/g/ppb) suggests that the fatty acids in AS‐1 and skin oil are responsible for much high partition coefficients. We predict that the methamphetamine concentration in skin lipids coating indoor surfaces can exceed recommended surface remediation standards even for air concentrations well below 1 ppb.     

Flocculation of brackish water from a tidal river

The control of the flocculation of water from tidal rivers is difficult because the water characteristics oscillate rapidly. Especially ionic strength and suspended solids concentration may have 10-fold changes in less than 6 h. Hence a relationship between an optimal dose of coagulant and raw water characteristics was sought with the aid of jar-tests.A pH of 6 was shown to be an acceptable value for flocculation with iron chloride and alum. The influence of change of ionic strength was found to be negligible. Suspended solids concentration proved to be a decisive control parameter. The von Smoluchowski model is appropriate to describe the kinetics of this sweep coagulation.     

Determining diffusion and partition coefficients of VOCs in cement using one FLEC

The diffusion and partition coefficients of eight volatile organic compounds (VOCs) in cement slabs were experimentally determined using a field and laboratory emission cell (FLEC) system based on the method developed in a previous study on the water vapor diffusion. A cement slab planted with a mixture of eight VOCs was placed in an one-FLEC system to undergo the mass diffusion in the slab and the emission to air flowing through the FLEC. The concentration of each VOC in the air flowing out of the FLEC was measured according to the EPA Method TO-17 using sorbent tube-automatic thermal desorption (ATD) and the gas chromatography-mass spectrum detector (GC-MSD) system. The diffusion and partition coefficients were then obtained by solving the inverse problem of the one-dimensional unsteady mass diffusion equations in the cement slab. And, the partition coefficient was also obtained from the total mass transfer estimated from the VOC concentration measurements and air flowrate, which was equivalent to the headspace concentration-weighting method.     

The efficacy and use of small centrifuge for evaluating geotextile tube dewatering performance

Geotextile tube dewatering technology has been widely used over the past two decades for dewatering high water content slurries. The dewatering process in geotextile tubes aims to decrease the volume of the dewatered slurry, which helps in the transportation, disposal, and reuse of the dewatered material. Several researchers have emphasized the effect of the retained sediment (filter cake) properties, in particular final solids content and volume (height) change, on the feasibility of geotextile tube dewatering projects. Retained sediment properties are often evaluated using small scale tests such as rapid dewatering test, falling head test, pressure filtration test (PFT), and field scale tests such as hanging bag test (HBT) and geotextile tube demonstrations test (GDT). In this study, centrifuge test is introduced as an alternative for the widely used pressure filtration and falling head tests to evaluate retained sediments properties. Centrifuge test provides a mechanism for understanding the response of slurries to externally applied pressure in geotextile tube environment. Centrifuge test was used to evaluate maximal solids content of the retained sediments and change in slurry volume of four soils that represent typical dredged soils. Tully sand, Tully fines, Elliott silt loam, and kaolin slurries were used at varying solids concentrations. Slurries were subjected to external stresses between 0.1 and 40 kPa by applying centrifugal speeds between 300 rotation per minute (rpm) and 1800 rpm. Both centrifuge test and PFT were conducted with unconditioned and cationic polyacrylamide conditioned slurries. Centrifuge tests results were compared with PFT results with respect to retained sediments final solids content and volume change. Tests results indicated that the maximal solids concentration of the retained sediments in saturated conditions is unique for each soil and is independent of the initial slurry solids concentration. Tests results also indicated that there is linear relationship between the initial concentration of the slurry and the final volume change at any externally applied stress. Finally, a relationship between the total pumped slurry volume and the final height of the dewatered sediments in a geotextile tube is presented.     

Testing for the toxicity of chemicals with Tetrahymena pyriformis

A test was developed using Tetrahymena pyriformis in order to determine the toxicity of various chemicals. Pre-cultured T. pyriformis was exposed for 24 h at 30 degrees C to various concentrations of chemicals, and the number of T. pyriformis surviving were then counted. The concentration of the chemical, at which the proliferation of T. pyriformis was restricted to one-half of the blank test (EC50), was determined. The method, applied to 57 chemicals, demonstrated that it could be used to detect the chemicals at low concentrations rapidly and with ease. The EC50 values showed a good relationship with 48 h LC50 values for Himedaka (Orizias latipes), and could be explained on the basis of the partition coefficient between water and n-octanol.     

Modeling of ammonia speciation in anaerobic digesters

Anaerobic digestion of high-nitrogen wastes such as animal manure can be inhibited by high concentrations of un-ionized ammonia, NH₃ (aq). Understanding the toxicity of NH₃ (aq) to anaerobic digestion requires a method for determining its concentration. Previous work on ammonia toxicity in anaerobic digesters has utilized a simple equilibrium calculation for estimating NH₃ (aq) concentration from total ammonia, temperature, and pH. This approach is not appropriate for concentrated solutions. In this work, a speciation model for major solutes in anaerobic digesters, based on Pitzer's ion-interaction approach, is presented. Model simulations show that the simple equilibrium calculation (without corrections for non-ideal behavior) substantially overestimates NH₃ (aq) concentration for all but dilute digesters. This error in concentration determination increases with total solids content and is estimated to be greater than 40% for a digester fed dairy manure with 5% total solids or swine manure with 3% total solids. However, including an estimate of the activity coefficient for NH₄⁺ in the simple equilibrium calculation results in much more accurate estimates of NH₃ (aq) concentration. In this case, the estimated error is less than 10% in the absence of struvite precipitation at the highest total solids contents considered.     

Aerial organic chemical release from activated sludge

The objective of this study was to investigate some of the potentially controlling factors influencing the atmospheric release of volatile organic compounds from the activated-sludge sewage treatment process. A bench-scale aeration vessel was used to investigate the influence of aeration rate, suspended solids concentration and detergent concentration on the rate of stripping of hexa-chlorobicycloheptadiene (Hex-BCH) and chloroform from simulated wastewater. These compounds had previously been found to be released from an 80 mgd activated sludge wastewater treatment plant.First order kinetic decay was found for the stripping of Hex-BCH and chloroform. The influences of aeration rate, suspended solids concentration and detergent concentration on the release of Hex-BCH were each statistically significant. The increase in aeration rate appreciably enhanced the release of Hex-BCH, while increasing the concentration of suspended solids inhibited stripping. A linear relationship was found between detergent concentration and stripping rate. Aeration rate was the only significant variable influencing the release of chloroform. The results suggest that Hex-BCH is stripped from an adsorbed state and chloroform from a dissolved state.     

兰州大厚度黄土湿陷性初判方法探索

探索兰州地区大厚度黄土湿陷性与物理指标的关系.通过收集兰州地区100组黄土湿陷性的土工试验资料,分析土粒比重、天然重度γ和孔隙比e0对湿陷性的影响,得到了依据天然重度和孔隙比指标进行黄土湿陷性等级初判的方法.并建议了湿陷系数估算公式.     

Optics of turbid estuarine waters: Approximations and applications

An analysis of the radiative transfer equation is presented which is applicable for the case of angle-independent, exponentially decreasing irradiance. The results indicate that for reflectance ratios less than 10%, the extinction coefficient of downwelling irradiance is due to particle absorption and the fraction of particle scattering that is not directly forward scattered. The equations for extinction coefficient and reflectance ratio are compared to numerical solutions and other approximations. Solar angle dependence is derived from the quasi-single scattering approximation.

Application of these equations to a large data set from the San Francisco Bay Estuary yields estimates of the optical properties of the particles as functions of the concentration of non-volatile suspended solids, algal chlorophyll and suspended detritus. The predictive value of the regression equations are tested using an independent data set. The methods developed appear to be well suited for the development of relationships between optical properties and particle characteristics and concentrations.     

Detailed spatio-temporal solids concentration profiling during batch settling of activated sludge using a radiotracer

In building and tuning good settling models for secondary clarifiers of wastewater treatment plants, there is a need for measured continuous solids concentration profiles during batch settling. Conventional measuring techniques have difficulties in recording this kind of data, either because they are invasive, or because of the low solids concentration and/or solids density of activated sludge. This paper investigates a novel non-invasive measurement technique borrowed from nuclear medicine, using a solids radiotracer and gamma cameras, to obtain solids concentration profiles during the batch settling of activated sludge, in a pilot-scale column with a height of 1m. The technique does not disturb the settling process, does not alter the settling characteristics, gives profiles every minute and every few millimeters, and is capable of measuring in a range of 0-25 g/l with high accuracy. Dynamic solids concentration profile measurements were performed for sludges of different wastewater treatment plants, and at different initial concentrations. The results show a quantitative representation of the settling process, and reveal hindered and compression settling.     

压缩天然气储气容积分区原理与方法

研究了压缩天然气加压站或加气站储气库储气容积分区的原理,指出分区的意义.建立了储气库储气容积分区方程组,得到分区压力、储气库容积、可供汽车气瓶容积等参数之间的关系.经过数值运算发现上述各参数在相当广的储气库储气容积分区比例范围内相当稳定,接近常数.提出了压缩天然气储气库储气容积分区的实用设计步骤.     

考虑表面氯离子质量分数的沿海混凝土桥梁氯离子扩散修正模型

为了研究沿海距海岸距离为5~40 km钢筋混凝土桥梁的氯离子扩散规律,建立与之相适应的氯离子扩散模型,对沈山（沈阳—山关海）高速公路沿线25座钢筋混凝土桥梁进行钻芯取样,研究了表面氯离子质量分数和水胶比的关系。引入表面氯离子质量分数实测值与拟合值的比例系数,建立表面氯离子质量分数和距海岸距离的数学关系,结合氯离子表观扩散系数的时间效应对Fick第二定律的解析解进行修正。通过对比实测值和修正模型的拟合值验证模型的适用性。结果表明:构件表面氯离子质量分数与水胶比成正比,比例系数服从正态分布的统计规律;构件表面氯离子质量分数随着距海岸距离的增加而逐渐减小,二者呈指数关系;由修正后的氯离子扩散模型计算得出的拟合值能够包络大多数实测值,拟合结果偏安全。     

关于夯实水泥土桩承载力的两个问题

夯实水泥土桩承载力的确定是夯实水泥土桩复合地基设计中的最关键问题,通过理论推演和简化分析,结合工程实践找到了夯实水泥土桩侧摩阻力和桩侧土层天然地基承载力标准值之间的理论关系。夯实水泥土桩单桩极限承载力标准值除以分项系数为单桩（容许）承载力标准值,通过上部结构荷载分项系数分析,得出结论,单桩承载力分析系数应采用1.65而不宜再采用2.0。     

Simultaneous estimation of VOCs diffusion and partition coefficients in building materials via inverse analysis

An analytic model describing the one-dimensional transient VOC diffusion in the building material slab was selected. An inverse analysis was applied to estimate the volatile organic compounds (VOCs) constant diffusion coefficient (D) and partition coefficient (K) in the building material. The present parameter estimation problem was solved with Levenberg–Marquardt's method of minimization of the ordinary least-squares norm. The effects of the number and the time step of measurements, errors involved in the initial concentration data in the building material, random errors involved in the measured VOCs concentration data in the chamber air and errors involved in the calculation of the mean convective mass transfer coefficient on the accuracy of estimates were studied. The first two factors were found to have significant effects on the accuracy of the estimates, while the effect of the third factor was insignificant. The results also indicate that D is insensitive to the errors involved in the mean convective mass transfer coefficient. The present study would be useful for obtaining material properties and helpful for designing and improving experiments.     

Variation of sludge volume index with activated sludge characteristics

Activated sludge samples from 2 laboratory units and 12 sewage treatment plants were examined to determine the effect of filamentous microorganisms, floc size and suspended solids concentration on SVI. An attempt was also made to correlate SVI to zone settling velocity. At a suspended solids concentration range of 700–4800 mg 1⁻¹ there was no effect of filamentous microorganisms at filament length concentrations below 10⁷μm (mg SS)⁻¹. However, when it was over 10⁷ μm (mg SS)⁻¹ SVI increased sharply with increasing concentrations of filamentous microorganisms.At all suspended solids concentrations examined SVI varied with floc size at filament length concentrations below 10 μm (mg SS)⁻¹. But, at filament length concentrations higher than this level, no effect of floc size on SVI was observed.The effect of suspended solids concentration on SVI was examined at different levels of filament lengths. It was found that the shape of SVI-suspended solids concentration curve varied with the level of filament lengths. A well defined relationship was found between SVI and zone settling velocity at all suspended solids concentrations examined.     

Aerobic digestion of thickened activated sludge: Reaction rate constant determination and process performance

The aims of this work were to select which parameter—total suspended solids (TSS), volatile suspended solids (VSS) or degradable volatile suspended solids (DVSS)—best expressed the kinetics of aerobic digestion of waste secondary activated sludge: to define the relationship between the reaction rate constant and the initial concentration of sludges; to evaluate the effect of aerobic digestion on the filterability of the treated sludge as measured by the capillary suction time (C.S.T.).Batch experiments of aerobic digestion were performed in our laboratory on samples of sludges at a constant temperature of 20 C. The initial concentration of sludges ranged from 2600 to 22,000 mg l⁻¹.TSS was found to be the parameter which most closely fits the kinetic model of aerobic digestion. The reaction rate constant was a linear, inverse function of the initial sludge concentration with TSS and with VSS as a parameter.Sludge filterability is affected by the process of aerobic digestion; a prolonged aeration time results in poorer dewatering; and the more concentrated the sample, the poorer the dewatering.