Polycyclic aromatic hydrocarbons (PAHs) have several characteristics
that make them more long-term pollutants than water
soluble ionic species and/or acid-leached heavy metals: (i) they
contain benzene rings, whose structure is especially stable and difficult
to break down, so they persist over the long-term (Beck et al.,
1995; Wild et al., 1991; Wild and Jones, 1995);