Natural and anthropogenic lead in sediments of the Rotorua lakes, New Zealand

Global atmospheric sources of lead have increased more than 100-fold over the past century as a result of deforestation, coal combustion, ore smelting and leaded petroleum. Lead compounds generally accumulate in depositional areas across the globe where, due to low solubility and relative freedom from microbial degradation, the history of their inputs is preserved. In lakes there is rapid deposition and often little bioturbation of lead, resulting in an excellent depositional history of changes in both natural and anthropogenic sources. The objective of this study was to use sediments from a regionally bounded set of lakes to provide an indication of the rates of environmental inputs of lead whilst taking into account differences of trophic state and lead exposure between lakes. Intact sediment gravity cores were collected from 13 Rotorua lakes in North Island of New Zealand between March 2006 and January 2007. Cores penetrated sediments to a depth of 16–30 cm and contained volcanic tephra from the 1886 AD Tarawera eruption. The upper depth of the Tarawera tephra enabled prescription of a date for the associated depth in the core (120 years). Each core showed a sub-surface peak in lead concentration above the Tarawera tephra which was contemporaneous with the peak use of lead alkyl as a petroleum additive in New Zealand. An 8 m piston core was taken in the largest of the lakes, Lake Rotorua, in March 2007. The lake is antipodal to the pre-industrial sources of atmospheric lead but still shows increasing lead concentrations from <2 up to 3.5 μg g−1 between the Whakatane eruption (5530 ± 60 cal. yr BP) and the Tarawera eruption. Peaks in lead concentration in Lake Rotorua are associated with volcanic tephras, but are small compared with those arising from recent anthropogenic-derived lead deposition. Our results show that diagenetic processes associated with iron, manganese and sulfate oxidation-reduction, and sulfide precipitation, act to smooth distributions of lead from anthropogenic sources in the lake sediments. The extent of this smoothing can be related to changes in sulfate availability and reduction in sulfide driven by differences in trophic status amongst the lakes. Greatest lead mobilisation occurs in mesotrophic lakes during seasonal anoxia as iron and manganese are released to the porewater, allowing upward migration of lead towards the sediment–water interface. This lead mobilisation can only occur if sulfides are not present. The sub-surface peak in lead concentrations in lake sediments ascribed to lead alkyl in petroleum persists despite the diagenetic processes acting to disperse lead within the sediments and into the overlying water

The synthesis and characterisation of hexagonal ferrite fibres

In two volumesAvailable from British Library Document Supply Centre-DSC:DXN043205 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Effective removal of anionic and cationic dyes by kaolinite and TiO2/kaolinite composites

The present study investigated the removal of methylene blue (MB) and orange II (OII) dyes from synthetic wastewater by means of adsorption and photocatalysis using natural kaolins. For MB adsorption, the raw kaolinite-rich samples showed the greatest adsorption capacity, with rapid uptake (90% after 20 min). The experimental results were fitted better using the Langmuir isotherm model parameters compared to the Freundlich model, suggesting that the adsorption corresponds to monolayer coverage of MB molecules over the kaolinite surface. For OII, neither the Langmuir nor the Freundlich model gave reliable results, because the adsorption of anionic dye molecules by the clayey particles is not favoured. Mixtures of kaolinite/Degussa TiO2 were also prepared, and their photocatalytic properties under UV-light exposure were investigated. Decolourization of MB solutions was observed, even in a mixture with low TiO2 content. This is related to the combined effect of adsorption and photocatalysis and, unlike the pure clay samples, the efficiency of such mixtures against OII was only slightly weaker (80-94%). For TiO2-impregnated clays, with the kaolinite layers separated by sol-gel TiO2 particles, the MB removal was slow and effective only after > 24 h due to the complexity of the bonding of MB molecules. On the other hand, the removal performance against OII solutions was very efficient (nearly 100%) within only 2 h. This excellent performance was attributed to morphological changes in clay particles

Evaluating the Properties of Dielectric Materials for Microwave Integrated Circuits

It is important to be able to accurately evaluate the electrical properties of dielectric materials to enable the accurate design of passive microwave integrated circuit components. This paper reports on research that has been undertaken in this area at London South Bank University. Three measurement techniques are reported. The first is a novel technique for measuring dielectric materials with a large tan δ using a composite resonator. The second is the measurement of the permittivity of ferroelectric thin films using a planar capacitor. The third is the use of an evanescent microwave probe to find the electrical properties at the surface of a sample

A Computational Study of the Properties and Surface Interactions of Hydroxyapatite

Hydroxyapatite (HAP, Ca10(PO4)6(OH)2) was studied from first principles approaches using the local density approximation (LDA) method in combination with various quantum-chemical (QM) and molecular mechanical (MM) methods from HypemChem 7.5/8.0. The data then were used for studies of HAP structures, and the interactions of HAP clusters with ionic species such as citrates. Computed data show that HAP can co-exist in different phases at room temperature, as both hexagonal and monoclinic. Special interest is connected with the ordered monoclinic structure, which could reveal piezoelectric properties. Obtained data on HAP interactions with citrates show the formation of differing HAP nanostructure forms, depending upon the concentration of citrate present