Distribution and mode of occurrences of radionuclides in phosphogypsum from the Aqaba and Eshidiya fertilizer plants, Jordan

Phosphogypsum is a waste by-product of the phosphate fertilizer industry that has relatively high concentrations of some U decay-series radionuclides such as ^226Ra and ^210Pb. The distribution and environmental mobility of radionuclides in phosphogypsum are an important concern because this gypsum by-product is used for wallboard, in agriculture and as a soil amendment. This study determined the distribution of ^226Ra, ^210Pb, within phosphogypsum stacks of varying age and among three size fractions （coarse： 〈0.212 mm; medium： 0.212-0.053 mm; fine： 〈0.053 mm）, in phosphogypsum derived from Aqaba and Eshidiya fertilizer plants. The results indicated that ^226Ra and ^210Pb were generally uniformly distributed in phosphogypsum stacks and showed no significant difference in the concentration of these elements with the age of stack. In the Aqaba phosphogypsum ^226Ra was slightly 10% enriched in the coarse fraction, while ^210Pb was 10% enriched in the free size fraction. In the Eshidiya phosphogypsum ^226Ra and ^210Pb contents were both relatively enriched （10%） in the fine size fraction.     

The log-normal distribution for hydraulic conductivity of compacted clays: Two or three parameters?

Risk and uncertainty assessments for waste containment systems employing clay barriers often include spatial variability in the hydraulic conductivity as part of the analysis. The two-parameter log-normal distribution is often used to describe the spatial variability, but for compacted clays the three-parameter form can be more appropriate. A statistical hypothesis test was developed that can be used to determine if the two- or three-parameter form of the log-normal distribution is more appropriate. The test is based on a likelihood ratio, comparing likelihood functions for the two- and three-parameter forms at their maximums. Likelihood functions are used assuming that a data set can be segregated into a set of distinct groups of hydraulic conductivities. A step-by-step calculation procedure is described and the test is applied to data collected from 45 sites.     

山西霍山植物群落主要层LAI垂直分布规律

在山西霍山七里峪林场，采用间接的光学测量方法对沿着海拔分布的植物群落主要层叶面积指数（LAI）进行了测量，从不同的角度对LAI的垂直分布规律进行分析。结果表明：1．海拔不同，LAI表现出很大的差异，海拔1750m左右的LAI值大于较高与较低海拔的；对LAI和海拔之间的关系进行回归，得到LAI分布的拟合方程：y=b0＋b1x＋b2x^2＋b3x^3（R=0．712，P〈0．01）。2．同一海拔样带，阴坡LAI均大于阳坡，但对同种种群来说，阴坡树种平均胸径并不一定均大于阳坡。3．植被类型LAI比较表现为：低山针叶林〈低山灌丛〈落叶阔叶林〈落叶针叶林〈常绿针叶林；而主要群系LAI比较表现为：油松林（0．38）〈落叶松林（0．78）〈山杨林及其混交林（1．09）〈白桦林（2．00）〈辽东栎林及其混交林（3．73）。4．典型群落LAI值变化分析和人工林与天然林以，比较表明，LAI值在一定海拔达到最大值，这对于山西霍山人工林栽培和丰产林培育等具有重要意义。     

Vertical distribution and water solubility of phosphorus and heavy metals in sediments of the St. Lucie Estuary, South Florida, USA

Accumulation and distribution of heavy metals and phosphorus in sediments impact water quality. There has been an increasing concern regarding fish health in the St. Lucie Estuary, which is related to increased inputs of nutrients and metals in recent decades. To investigate vertical changes of contaminants (P, Cd, Cr, Co, Cu, Ni, Pb, Zn, and Mn) in sediments of the St. Lucie Estuary in South Florida, 117 layer samples from six of the 210 to 420 cm depth cores were analyzed for their total and water-soluble P and heavy metals, clay, total Fe, Al, K, Ca, Mg, Na, and pH. Principal component analysis (PCA) was used in two sets of analytical data (total and water-soluble contaminant concentrations) to document changes of contaminants in each core of sediments. The PCA of total contaminants and minerals resulted in two factors (principal components). The first and second factors accounted for 61.7 and 17.2 % of the total variation in all variables, and contrast indicators associated with contaminants of P, Cd, Co, Cr, Ni, Pb, Zn, and Mn and accumulation of Fe and Al oxides, respectively. The first factor could be used for overall assessment of P and heavy metal contamination, and was higher in the upper 45–90 cm than the lower depths of each core. The concentrations of P and heavy metals in the surface layers of sediments significantly increased, as compared with those in the sediments deeper than 45–90 cm. The PCA of water-soluble contaminants developed two factors. The second factor (Cu–P) was higher in the upper than the lower depths of the sediment, whereas the highest score of the first factor (Cd–Co–Cr–Ni–Pb–Zn–Mn) occurred below 100 cm. The water-soluble Cu and P concentrations were mainly dependent on their total concentrations in the sediments, whereas the water-soluble Cd, Co, Cr, Ni, Pb, Zn, and Mn concentrations were mainly controlled by pH.     

Elemental particle size distributions. Measured and estimated dry deposition in Sfax region (Tunisia)

Mass size distribution of the crustal elements (Al, Ca, Fe, Mg, Si, Ti), anthropogenic elements (Zn, Mn, Cr, Cu, K, P, Pb) and sea elements (Na, Cl) were obtained from measurements carried out with an inertial cascade impactor in Sfax. A fitting procedure by data inversion was applied to those data. This procedure yields accurate size distributions of aerosols in the diameter range 0.1–25 μm in two different sites. In a coastal industrial site, the mass distribution of the aerosol showed a bimodal structure; and in urban area, the lower particle mode cannot be observed. The elemental dry deposition flux was calculated as a function of particle size. The element flux size distribution increased rapidly with particle size. The modelling results indicate that the majority of the crustal and anthropogenic elements flux (>90%) was due to particles larger than 3 μm in diameter.     

Cation distribution and structure modelling of spinel solid solutions

 This paper presents an improved generalisation of cation distribution determination based on an accurate fit of all crystal-chemical parameters. Cations are assigned to the tetrahedral and octahedral sites of the structure according to their scattering power and a set of bond distances optimised for spinel structure. A database of 295 spinels was prepared from the literature and unpublished data. Selected compositions include the following cations: Mg²⁺, Al³⁺, Si⁴⁺, Ti⁴⁺, V³⁺, Cr³⁺, Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Zn²⁺ and vacancies. Bond distance optimisation reveals a definite lengthening in tetrahedral distance when large amounts of Fe³⁺ or Ni²⁺ are present in the octahedral site. This means that these cations modify the octahedral angle and hence the shared octahedral edge, causing an increase in the tetrahedral distance with respect to the size of the cations entering it. Some applications to published data are discussed, showing the capacity and limitations of the method for calculating cation distribution, and for identifying inconsistencies and inaccuracies in experimental data. Received: 19 February 2001 / Accepted: 1 June 2001