Likewise, the presence of zinc is well-known, since the deterioration of the zinc plating covering the crash barriers leads to a high concentration of this contaminant in the soil immediately below.
Toxicity is not the whole story
The preliminary studies were followed up by a Raman spectroscopy analysis, which is used to identify the molecular forms in which the compounds are found. Knowing these forms helps to determine the danger posed by each metal for the environment. And the fact is, as Carrero explains, the actual toxicity of each metal is not the only factor to bear in mind: "It matters whether the metal is in the form of a carbonate, or a nitrate... They are different salts with different solubility. The metals can be retained in the soil, so the toxicity would not be as significant as if they had been in the form of a more soluble substrate, in which case, this substrate could be dissolved by the rainwater and move to other compartments. Then, the toxicity could move to underground water tables or be taken up by plants."
In connection with this, Carrero has simulated the actual conditions that are produced in the environment to observe how the metals react in their presence and whether they become more soluble and, therefore, more hazardous. It turns out that barium and zinc are the metals that need to be closely monitored: "They are emitted as a result of tyre or brake wear, and they are accumulating in the form of oxide in the upper layers, and this has less mobility. However, we have seen that they react with atmospheric CO2 and form carbonates, which are more soluble and permeate. In fact, we have come across a great concentration of carbonate in deeper layers. In the upper layers barium and zinc are present in the form of oxide, and in the lower ones
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