Leaching of polycyclic aromatic hydrocarbons (PAHs) from coal dumps reclaimed with apple trees: a mechanistic insight

Polycyclic aromatic hydrocarbons (PAHs) have been identified as compounds that can be incorporated to run-off waters or to aquifers becoming a real threat not only to aquatic organisms but also to humans due to its carcinogenic and mutagenic activity. This work studies the presence of PAHs in a coal dump pile located in the north of Spain (Asturias), downhill a spoil pile of a cinabrium mine. This unique site gives the opportunity to assess whether acid waters have more potential to leach PAHs than normal rainwater (acidified when it gets in contact with coal spoil). The distribution of PAHs and methyl PAHs has shown that their abundance is higher in the path of acid waters which could be caused by the ability of acid water to break bonds of coal macromolecules. This chemical reaction liberates PAHs of less molecular weight that can be detected by GC-MS. Moreover, less soluble PAHs are concentrated on the acid water circulation area and more soluble PAHs more leached by acid water that rainwater, which indicates that PAHs dissolve more in acid waters than in normal rainwater. In addition, this coal spoil pile has been reclaimed with apple trees to make cider for human consumption. Up to 152 different compounds were identified in the tree samples, but neither PAHs nor methyl PAHs were found, pointing to a possible retention of the PAHs in the roots zone. Apple trees in the acid waters path show more concentration in waxes and flavour compounds, indicating a more mature apple.