I would prefer to have the data for the different places to have as much information available a possible. Producing average data may mask important differences being present.

You can always calculate average data later on. It will take extra time and money and you can only tell afterwards whether this was a good investment or not. That are the choices that a scientist has to make every now and then.

The average data may be of no use. The absorption of each metal may be from a different mechanism.

Thank You Kan Sir and Bertello Sir.

 Sir I have analysed metal concentration(Cr, Cu, Ni and Pb) in each plant at  different location of my study site(depending upon the availability) and metal concentration in their respective soil samples. Now the question is should i calculate different EF for each plant for a particular metal at different locations or single EF for each plant by making the composites sample of plant for complete study area for eg if a plant species available at 5 locations st my study area then calculate different EF for that plant species at each location with respect to metal concentration at that location only or to calculate an average metal concentration (for each metal) in that plant species and in total study area and then to calculate a single EF  for each methal in that plant species for total study area.

For each site and for each metal EF must be calculated as the ratio of soil and vegetative parts. However TF gives a better understanding of the situation.

Thank You Mitra Sir. I will also calculate TF, but presently the question is mean EF for each plant for  each metal at whole study site or different EF for each plant for each metal at each location of study site.

If all residue data are available, it should not be too complicated to calculate - by way of EXCEL or some similar program - all ratios and to visualise them to facilitate any patterns to be detected.

Kan Sir, I have calculated EF by both ways (for locations and for whole study site), but results are showing large difference.

I assume that you have also plotted the results in different ways and could not detect a pattern. But are the differences present for all metals involved or only for some? Be aware that those metals might be present in different binding forms that might well influence their accumulation patterns.

Either way I see two options: either there is no relationship that explains your results or there is an unknown factor or factors that governs the relationship(s).

You might explore chemical, biological or agricultural factors that might have caused the results to be as they are.

I think  EF should be calculated species specific for each location and can get clear idea for each metal.

You need to know the concentrations of trace metals from each area and then the concentrations in the plant. You may calculate BCF or TF from those values

Kaur, to start with, I suggest you calculate for specific metal per pls t species per site. Determine this for each species in each site and consider the trend. This will give an idea  of the pattern of enrichment in the species. Then you can also consider the same species for all the sites and check if the species have the same pattern of accumulation. That may inform you of accumulation pattern of each species despite the level of contamination in all the site. 

Let me ask at this juncture that how did you determine your enrichment? Because TF and BCF may not give good idea about enrichment like the contamination factor.

for calculating the enrichment factor, sedementary metal concentration as well as metal concentrattion of the plant samples are necessary. 

EF= metals in plants/metals in sediments

I would compare them with plants of the same species in control soil and with the natural quantity, of heavy metal that plant has.

Transfer factor or bio-concentration factor will give a better understanding than EF in plant.