Desorption of metals K, Al, Ca, Mg, Fe, Ba, Zn, Mn, Cu and Sr from Cetraria
islandica (L.) with solutions whose composition was similar to that of acid
rain, was investigated. Desorption of metals from the lichen was performed by
five successive desorption processes. Solution mixtures containing H2SO4,
HNO3 and H2SO4-HNO3 were used for desorption. Each solution had three
different pH values: 4.61, 5.15 and 5.75, so that the desorptions were
performed with nine different solutions successively five times, always using
the same solution volume. The investigated metals can be divided into two
groups. One group was comprised of K, Ca and Mg, which were desorbed in each
of the five desorption processes at all pH values used. The second group
included Al, Fe, Zn, Ba, Mn and Sr; these were not desorbed in each
individual desorption and not at all pH values, whereas Cu was not desorbed
at all under any circumstances. Using the logarithmic dependence of the metal
content as a function of the desorption number, it was found that potassium
builds two types of links and is connected with weaker links in lichen.
Potassium is completely desorbed, 80% in the first desorption, and then
gradually in the following desorptions. Other metals are linked with one
weaker link (desorption 1-38%) and with one very strong link (desorption
below the metal detection limit).