Miljögeoadventure
The pictures 2 and 3 are showing the element distribution in the samples. Although there are different particle sizes the amount of contaminants do not differ strongly in both fractions. In the case of our samples the amount of contaminants does not have preferred grain sizes.
Robertson and Taylor (2007) published a data set about metal contents in soil samples, with the separation of the grain fraction <63 µm and 63-300 µm. They also added the group of size of >300 µm. The result showed a clear difference in the amount of pollutants in the different grain size groups. The most pollutions occur in the finest fraction of silt and clay such as lead, manganese, zinc and copper. But for iron, the grain size >300 µm is the most dominant group.
Unfortunately, this result cannot be reflected in our samples and measurements. The differences in the abundance of the polluting elements are not such definite than the results of Robertson and Taylor (2007). That is a good reason to continue with and analyse just the fine fraction-data.
Comparing the element abundance in the soil (Table 2) with data of the literature (Table 1), it can be seen that the elements of our sample are located within the range given from the literature by Lindsay (1979), the only exeption is cadmium. While copper, lead, and zinc are within the common ranges for soil, the cadmium concentration exceeds this range by 100 ppm as well as in the fine fraction as in the whole sample. At a first look the copper concentration within the fine fraction also seems to exceed the literature values but compared with the values by Robertson and Taylor (2007) it can be seen that the concentrations within the fine fraction is normally higher than in the total sample and thereby again within the natural range of abundance.
Interpretation and discussion of our data
Table 1
Lindsay, 1979
Table 2:
Element composition within the bulk and fine fraction, highlighted concentra-
tions are the ones mentioned in the table above as well as the ones mentioned later 0n (dark yellow)
As already seen within the results (Picture 5/6) the concentrations for copper, zinc, cadmium and lead show a decreasing trend with increasing distance from the source. Here it can also be seen that the concentration for cadmium is of a range twice as high. So there can actually be made assumptions that there is some input of those elements from the nearby street that was depicted as a pollution source within the experiment. Especially when it comes to cadmium there has to be a source for that nearby as the concentrations are a lot higher than expected. In this case the street does not have to be the source as the values stay relatively high throughout the whole range of samples and it is not easy to define if the concentrations are decreasing or maybe even increasing.
Another significant value shows the concentration of arsenic as it can only be found within two samples and only in the coarse fraction. However the concentrations are really low, which indicates that there might be some concentrations within the other samples as well, those are just beyond the limit of detection.
Arsenic is the only compound that shows more attraction to the coarse grain fraction whereas the other compounds are analysed for a similuar value within both fractions. So in that term there can not really be made any specific conclusions. The only differences can really be seen with increasing distance from the source as most compounds do decrease in concentration. There does seem to be degradation as well as a slow transportantion rate away from the source.
What does the data tell us? Are there any trends?
What can be said about the data in comparison to literature?
Lindsay, W.L., 1979, Chemical equilibria in soils, John Wiley and Sons, New York.
Robertson, D.J., and Taylor, K.G., 2007, Temporal variability of metal contamination in urban road-deposit sediment in Manchester, UK: implications for urban pollution monitoring, Water Air Soil Pollut, 186, p. 209-220.