Hi Bassant,

If the concentration was very low in water and below the detection limit in sediment, your observation might just be down to the different limits of detection in your methods and so is an artefact of the analysis. It is also possible that the source of the cadmium is some input to the water column upstream of your site and not from the sediment in situ. Cd is soluble over a wide pH range which contributes to mobilisation.

What method do you use?

Do you measure the total Cd in the sediment?

Best!

It depends on the sensitivity of your analysis method!

Dear, Butler and  sell. Thank you for your answers.

Dear, Michal Filipiak

Thank you for your reply. I used acid digestion method (Wade et al., 1993) for total Cd in sediment and samples were analyzed using atomic absorption spectrophotometer. 

Could you please elaborate the details of acids used?

Samples were digested using HNO3 - HF - H3BO4 acids.

I agree with the view of Dr. Butler. The level of Cd in sediments below the detection limit indicates that Cd in water is mainly of anthropological influence contaminating in stream at some point and fails to establish an equilibrium with sediments. In general, the mobility of Cd is higher than other transition metals.  

Thank You  Dr. Srivastava for your answer.

It's probably a recent point source cadmium contamination in the water body

Generally , the leachability of Cd dependent on various factors like pH, type of leachant, time of leaching, L/S ratio etc. Leaching method also play a very inporthant role on release of Cd. In water sample release and  dilution is a main factor. Also it may possible the Cd get precipitated and thus not detected or found BDL.

Thank you for your answers

Dear Basant,

Cd in soil is occurs due to use of ammonia and phosphate base fertilizers. When water come to the contact with soil and create leach and Cadmium reacts slowly with oxygen in moist air at room temperatures, forming cadmium oxide: its limit in water is 0.003 ppm but when you analysis in AAS it gives the not detected then you  can say BDL ( Below Detection Limits ).

Regards

Arvind

Thank you all for your reply