Trying to calculate the Comprehensive Potential Ecological Risk Index for heavy metals in sediments for my dissertation and I have found only the Reference values for Cr, Pb, Zn, Cd, and Cu.
Fe seems to be taken as a crustal element and its been used to calculate other risk indices. I cant say the same for Mn. However, they seem to be higher in most studies (soil/sediment) and therefore can be termed a crustal element. Strictly my opinion