The results of the sequential extraction made by Carlström 2012 show how strongly, and in what way, each metal is bond to the sediment in the specific sample sites. By revealing how large part of the total amount is released from the samples in each step important conclusions can be drawn for the pollution of the sediment. Shown in the diagrams below is the results for all metals detected in the study in the fractions 1,2,3 and residual.
Cd: A metal with high mobility in the sediment
To the right, we see the results for Cadmuim. In three of the four samples fraction 3 is dominating, meaning that a large part of the Cd in these three samples will be released from the sediment in redusing conditions. Also the weak-bond exchangable fraction 1 is significant in these three samples. Combined this would lead us to say that the Cd in this sediments are very mobile, and depending on the total amount the polluted sediment could be hazardous to sorrounding environments.
Ba: A metal with low mobility in the sediment
To the left is the results for Barium in the four sediment samples. The total amount in all samples is very dominated by fraction 4, the residual. This would mean that the Ba in this sediment is bound strongly in the mineral structure of the sediment grains and is not going to be made available to vegetation, groundwater or other by any oxidizing or reducing conditions. For an assesment of the pollution level, this is crucial since it means that the Ba in this sediment do not risk leaking out into the sorrounding environment. For Barium in particular though, this is not surprising since it is a very insoluble element.
Since the different fractions in the sequential extraction represent diffirent bondings to the sediment, there should be some connections between the composition and geochemistry of the sediment and how large a fraction is in that sample.
For example: Fraction 2 metals is largely bound to Fe and Mn oxides making it likely that a higher content of these in the sample will lead to a larger portion of metals in fraction 2. The higher claymineral content could have a similar connection to fraction 1 since these metals are weakly bond to the sediment but tend to absorb onto clay particles. Fraction 3 is made up of metals bond to organic particles and therefor the humic content measured by the LOI could correlate with this fraction. To look for these correlations and whether they exist in the testresults the amounts in each fraction can be plotted against respective parameter (claymineral content, LOI, Fe and Mn). In the Carlström study this was done (see below) but the correlations found were poor and only for a few of the metals. This can be due to the low clay content (2 -3 %), the fact that the study only tested for Fe-oxides and not Mn and that the low LOI values might not be representative for the whole sample.
Connection between results and composition
