Active biomonitoring of element uptake with terrestrial mosses: a comparison of bulk and dry deposition

Moss (Scleropodium purum) transplants were used to study bioconcentration originating from dry and bulk deposition, by measuring the tissue contents of Al, As, Ca, Cu, Fe, Hg, Mn, Ni, Pb, Se and Zn. Furthermore, a laboratory experiment was carried out to determine the sequence of maximum concentration and affinity of Al, Cu, Fe, Hg, Ni, Pb and Zn, in S. purum. We found that in many of the transplants, for the same period of exposure, higher levels of metals were accumulated via dry deposition than via bulk deposition. This result may be explained by the simple washing action of the rain on the surface of the moss, and by the existence of processes that provoke the loss of some of the accumulated elements: intercationic displacement and leaching caused by acid precipitation. Modelling of the final bioconcentration observed, as a balance of inputs and outputs of elements, revealed that this terrestrial moss does not integrate, but rather concentrates atmospheric deposition, and there exists a state of unstable equilibrium between inputs and outputs of elements, a state that is determined by the characteristics of the surrounding environment. On the basis of the results obtained in this study, we can conclude that at present, it is not possible to extrapolate the calibrations between the concentrations of elements accumulated in a certain species of moss to values of atmospheric deposition (bulk deposition) from one place to another with different environmental conditions.