Use the Average Shale Content or Average Crustal values as the background values. Thanks

Thanks Adeniyi Adewumi sir.

but where I can find average crust value?

Dear Saiful

Visit http://periodictable.com/Properties/A/CrustAbundance.an.html

It is a very useful link. Type or print them and save them in your library

Thank u so much Adeniyi Sir.

Dear Saiful, You can use  Upper continental crust values for calculation of  Igeo, EF & CF of heavy metals in  sediment.  See the link below:

Rudnick RL, Gao S (2013) Composition of the Continental Crust. In: Treatise on Geochemistry: Second Edition. pp 1–51

Rudnick RL, Gao S (2003) 3.01 - Composition of the Continental Crust. Treatise on Geochemistry 3:1–64. doi: http://dx.doi.org/10.1016/B0-08-043751-6/03016-4

Thank u so much, dear Kaladharan Edavilakathil P Scientist 

this is not an easy question. As a basic approach the comparison with the Earth Crust Abundance values is quite correct.  I also would recommend comparing with average shale values; the values are, by good reasons, generally in the range of the upper crust. You may find tabulated values in the internet,  e.g. at Yuan-Hui Li (author); A Compendium of Geochemistry: From Solar Nebula to the Human Brain; Table VI-5a.

The main problem is the question of sample grain size you are using and the digestion method. A common recommendation to find background values is the use of fine grain sediments, meaning < 2 mm grain size. However, this range of grain size may contain a lot of sand fraction, which in river sediments generally consists of quartz. Due to transport mechanisms there is a general shift to quartz enrichment in river sediments. The more quartz grains in the sample the less will be the metal concentration, and you cannot compare with average values from literature. So, for sampling you should prefer backwater situations in Feni River or sections with slow moving water where you will find fine grained sediment (< 63 µm); or you have to sieve the material. You also should keep in mind that literature values rely on total digestion. So, with only few exceptions, you also have to do total digestion prior to analysis (e.g. digestion by HF, which is a really awkward job).  Some metals will be easily extracted nearly to total by aqua regia digestion, like Pb, Zn, Cd. These element concentrations can be compared to literature. An additional question is whether a comparison to literature values is really helpful when looking for enrichment of metals. A better proposal is comparison to local background values. For this you have to find out stream sediments from uncontaminated sections in your region, possibly rivers with a high catchment area. With some effort uncontaminated sediments can also be found in the lower part of sediment cores from bayous.

Possibly a look to our sediment surveys on Chilika Lake (India) or Elbe bayou sediments (Germany), both in Research Gate, will give you additional ideas, e.g. on the question of availability of heavy metals.

Good luck and kind regards

D. Zachmann

Dear, prof. D. Zachmann

A lot of thanks for clarification & precious time.

Kind regards