Methodological aspects of moss sample preparation. Effects of freezing and duration of washing on the cellular distribution of elements in Fontinalis squamosa Hedw.

Aquatic bryophytes are widely used in biomonitoring studies, mainly because of their capacity to act as bioaccumulators. As different methods can be used to preserve and process moss samples, the results of elemental analyses may also vary, particularly if the contents of different cellular compartments are analyzed separately. In the present study, we compared the total concentrations of some elements and the concentrations of these in different cellular locations in frozen-thawed and fresh samples of the aquatic moss Fontinalis squamosa that were also washed for different lengths of time before analysis. We used the sequential elution technique (SET) to extract the different fractions, and we determined the concentrations of K, Mg, Ca, Cd, Co, Cu, Al and Zn in the extracts. The results varied depending on the element, cellular location and moss sampling site. In the moss samples processed after freezing, the greatest differences were in the intracellular concentrations of K, Mg and Cd, which were lower than in the fresh samples. Minor differences were found in the concentrations of elements in other cellular locations and in the total concentrations of elements. The increase in the duration of the initial washing step, carried out to remove soluble and particulate intercellular elements, may also cause the release of elements (e.g. K and Mg) bound to extracellular exchange sites. The concentrations in the other cellular fractions and the total concentrations were less affected by the washing duration. Neither freezing nor the use of long washing times are recommended for processing moss samples prior to extraction of elements by the SET. Further studies are needed to confirm and clarify the observations.