Engineered nanomaterials (ENMs) are materials with at least one dimension between 1–100 nm. The small size of ENMs results in a large surface area to volume ratio, giving ENMs novel characteristics that are not traditionally exhibited by larger bulk materials. Coupled with large surface area is an enormous capacity for surface functionalization of ENMs, e.g., with different ligands or surface changes, leading to an almost infinite array of variability of ENMs. Here we explore the effects of various shaped (spheres, rods) and charged (negative, positive) gold ENMs on Daphnia magna (D. magna) in terms of survival, ENM uptake and production of reactive oxygen species (ROS), a key factor in oxidative stress responses. We also investigate the effects of gold ENMs binding to the carapace of D. magna and how this may induce moulting inhibition in addition to toxicity and stress. The findings suggest that ENM shape and surface charge play an important role in determining ENM uptake and toxicity.
Summary
Previously, it has been suggested that the existence of a variable clay mineralogy was responsible for the anomalous engineering behaviour of Keuper Marl. Using x-ray diffraction techniques and chemical analyses, it is shown here that 80 per cent of the samples examined fall in the mineral suite illite-corrensite-carbonates-quartz-hematite, and that there is good evidence that this mineral assemblage has attained phase equilibrium.
Calculation of the true clay mineral content of the samples analysed shows that much of the clay content is aggregated into silt size units, which accounts for the large range of measured Activities.
Calculation of the true clay-mineral content of samples of Keuper Marl analysed has shown that much of the clay content has been aggregated into silt-size units. This aggregated structure accounts for the large range of measured Activities of the Marl.A system of structural classification used in pedology will conveniently describe the structural features of the more heavily aggregated, overconsolidated clay soils such as Keuper Marl; some preliminary work with the electron micro-probe analyser supports this method of describing soil structure.It is suggested that variations in the structure of these sediments indicate varying conditions of deposition and diagenesis, and are related to differences in the magnesium content of the samples analysed.
From
A. G. DAVIS, N. BIRCH & R. J. CHANDLER:
The author has produced some useful data on the influence of aggregation on the index properties of red clays and Keuper Marl, in particular confirming that the apparently silty nature of Keuper Marl results from the aggregation of clay-mineral particles. We would however like to take up some points made by the author with reference to Keuper Marl.
One point on which we wish to comment is the assumption made by the author that in determining the liquid limit, further mechanical working beyond the 10 minutes specified in B.S. 1377 did not increase the liquid limit. This occurred in spite of an apparent increase in the measured clay-size fraction. The author further assumed that prolonged pre-treatment mixing was sufficient to break down all aggregations, leaving some of the clay-mineral fraction having particle diameters larger than 0–002 mm.
In Fig. 1 we show the variation of liquid limit with mixing time for two similar marl samples. Mixing was carried out in a Hobart paddle mixer which could take a sample of about 1/8 cu ft. It is seen that the liquid limit increased appreciably above that obtained using the B.S. 1377 method. Clearly for this particular marl the liquid limit increases with further working, though we hesitate, in view of the variable nature of Keuper Marl, to state that this will be the case for all marls. We do however question the use of the greaseworker as a substitute for mechanical working
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