To examine the metal enrichment in sediment compared to background values, indices entailing geochemical normalization using Aluminium, or comparison to Average Shale content or World Surface has been documented. What are the pros and cons of each method?
Thanks Sebastian. I'd appreciate if you could attach a copy of the publication if you could. Thanks again.
Hi Azubuike,
You should use the Al content in the same sample of yours to normalize a certain chemical element such as Ca, Na, K, or Mg, and so on.The advantage of normalization is that real trend of chemical changes can be identified by ratio vs. ratio plots, such as enrichment and depletion of some elements because Al is an immobile element on the Earth surface in most scenarios. "immobile" means Al content in a system has kept constant during a process you consider. Similar elements there are in the system like Ti, Zr and Hf.
The other advantage of the method is that it can cancel the effect of addition for chemical composition treatment because all chemical composition analysis add together must be one, which can cause spurious correlation between chemical compositions.
Good luck
Hailin
Thanks Hailin for throwing some light on the subject. It was really helpful.
Cheers
The real difference is the fact that, using Al from your samples, you partly take into account the natural geochemical background of your area. Average Shale or any other world trend could give some interesting indications but depending on your questions. Obviously, they do not give you the same trend if you worked on calcareous or granitic watershed. Unless you work at a very larg scale, it's better to use your Al data. If you don't have Al, you can use other conservative elements like Cs, Sc or Li, which are now routinely analyzed by ICP-MS.
Thanks Olivier for your justifying the use of Al and commenting on other conservative elements. but i'd like to ask, why some scientists use elements like Fe for normalization? what could be the justification for this since Fe in the environment could easily be augmented by anthropogenic activities?
I'd also like some expounding or additional insight on the circumstances that would allow the use of Average shale to be a preferable option over the use of Al. Thanks
From what I see of the work of some colleagues, sometimes they use Fe instead of Al just because they analysed it, and not Al. You are right when you said that Fe is not so conservative as Al, but depending on your environment, it could be quite OK. For example if you work along a river path where dissolved concentrations do not change so much, neither pH and O2, you can consider that Fe will be conservative. Fe could be added by anthropogenic activity that's right, but the natural concentration are generally high, and you must have a very large anthropogneic input to see an influence on them.
Concerning your last question, I will say that this choose will change your answer. Comparing your data with average shale may be will show you that you have higher concentration of some metals, but higher than what: the average value ? This is not a clear and definitive example of contamination of your environment. If you work an naturally enriched soils for example, you will find values higher than average shale, but they are completely natural. You can confirm that if you get your own data on Al. Finally, I will said that one of important point for you is maybe to find the good samples representative of the natural background in your area of interest. If you get it, you don't need any kind of world average.
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