Behaviour water lead levels

First examination of experimental results has shown that some parameters are good indieators of the behaviour of the materials in eontaet with water for the purpose of the research pH, aluminium, calcium and potassium. The evolution of these elements is strongly influenced by the material and by test eonditions (preconditioning and test water). Lead and chromium have never been deteeted at significant levels in any of the experiments carried out for the three materials. 

For the general population, the presence of lead in blood results from exposure to a range of environmental influences (water, air, soil) or is derived directly from other specific sources (food cans, paint, etc). Lead in blood levels have been falling in most countries for a number of years now, as the most obvious sources of exposure have been more tightly controlled. Lead levels are now down to lOpg/lOOml or less in most of the industrialised countries. However various clinical studies continue to suggest that child behaviour and intelligence may be adversely affected by even very low concentrations of lead in blood, and this area has become the focus of attention in recent years. 

The apparent influence of lead on children s ability identified in this study is open to interpretations other than the direct influence of lead. Blood lead levels reflect recent exposure to lead, and in this study were measured on one occasion only. Alternative explanations for the observed associations must therefore be considered. As mentioned above, the association could be the result of some confounding variable for which we have not controlled in our analysis. This seems unlikely because of the relatively weak associations in our data between lead levels and the important correlates of the ability tests. A more serious problem for studies of lead exposure is reverse causation. We may be observing an association because children who get low scores on ability tests are more likely to have behaviour which would result in increased lead intake. Examples would be outdoor play in dirty places, lack of hand-washing, and thumbsucking. We cannot rule this out as a contribution to the association we have found. However we might expect that it would be of lesser importance for water, which is an important source in Edinburgh (Raab et al, 1987), than for some other sources of lead. 

In studies of the concentrations of arsenic, bromine, chromium, copper, mercury, lead and zinc in south-eastern Lake Michigan, it was shown that these elements concentrated near the sediment water interface of the fine-grained sediments. The concentration of these elements was related to the amount of organic carbon present in the sediments (161). However, it was not possible to correlate the concentration of boron, berylium, copper, lanthanum, nickel, scandium and vanadium with organic carbon levels. The difficulty in predicting the behaviour of cations in freshwater is exemplified in this study for there is no apparent reason immediately obvious why chromium and copper on the one hand and cobalt and nickel on the other exhibit such variations. However, it must be presumed that lanthanium might typify the behaviour of the trivalent actinides and tetravalent plutonium. 

Increased Si content at the surface of steel leads to a beneficial effect improving the anti-oxidation behaviour. The surface protection is achieved by several mechanisms that take place at the same time, including the formation of silicon oxide films, increased Cr diffusion from the bulk to the surface, formation of phases such as y-Fe, Cr203, Si02, Si FCy, passivation of the surface by oxidation and surface diffusion. As mentioned in references [1-4], silicon seems to retard breakaway in the presence of water vapour in the environment and may facilitate Cr rediffusion from the bulk which would help repassivation observed after breakaway. As a consequence the level of the Cr reservoir possibly may be kept lower than for Si-free steels. At least, a continuous silica layer is not the reason for the improved oxidation behaviour. The positive effect of silicon seems to stabilise at values above 0.5% Si. A possible reason for the influence of silicon seems to be that silicon enhances the diffusion of Cr in the metal matrix. 

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