Are terrestrial mosses good biomonitors of atmospheric deposition of Mn?

A series of field and laboratory experiments was carried out to determine whether the terrestrial moss Pseudoscleropodium purum is a good biomonitor of the atmospheric deposition of Mn. Samples of the species were collected from sampling sites located in industrial areas and in unpolluted areas in Galicia (NW Spain). The results showed that: i) uptake of Mn by the moss may be reduced under certain conditions (related with the environment, moss ecophysiology and source and type of emission), even though atmospheric inputs and inputs from vegetation remain the same. The concentration of Mn in moss samples from the surroundings of an aluminium smelter was 6 times lower than in samples from an unpolluted site, in which levels were similar to the regional background level. The low concentrations were maintained over time; ii) the decrease in the uptake of Mn was due to differences in the environmental conditions to which the organisms are exposed. Genetic causes for the differences were ruled out as the study of moss samples transplanted within and between unpolluted and contaminated areas showed that the final concentrations in the transplanted moss in each of the scenarios were very similar; iii) the direct relationship between exposure and concentration was altered in the surroundings of the contaminated sampling site, although the causes of the inhibition of uptake could not be established by incubation of moss samples under laboratory conditions, and v) unlike other metals, there are few sources of emission of Mn to the atmosphere. However, when the emissions were in a particulate form, the concentrations of Mn in the moss varied in accordance with the atmospheric deposition. For all of these reasons, we consider that P. purum is not a good biomonitor of the atmospheric deposition of Mn, except under certain circumstances, and we recommend exclusion of the element from regional surveys.

► Moss P. purum is examined as biomonitor of the atmospheric deposition of Mn.
► Relationship between Mn exposure and moss Mn levels is altered by some factors.
► With few exceptions, P. purum is not a suitable biomonitor of Mn deposition.
► We recommend the exclusion of this element from regional surveys.