A critical evaluation of the use of the moss technique to monitor air pollution

Resumo

Passive biomonitoring with terrestrial mosses, i.e. the ¿moss biomonitoring technique¿, constitutes a useful tool for the study of the atmospheric deposition of heavy metals. However, it has limitations, some of which have been deeply assessed in this doctoral thesis. Thus, the temporal variability of the concentrations of several nutrients and pollutants in Pseudoscleropodium purum and the effect of growth on the concentrations of elements in segments of different ages of P. purum have been assessed (Chapters I and II respectively). Besides, the possible development of differences in the accumulation capacities of mosses that have grown in environments under different levels of pollution (Chapter III), and the relationship between the concentrations of several heavy metals in mosses and in bulk deposition (Chapters IV, V and VI), have also been discussed. Finally, despite the limitations found in the first part of this thesis (Chapters I to VI), it has been demonstrated that the technique enables researchers to distinguish between contaminated and uncontaminated sites, to identify small scale pollution sources, and to map spatial and temporal patterns of the heavy metals in the atmosphere. However, its application in environmental policy making is still limited due to the lack of a reliable, scientifically rigorous and homogenized protocol for the technique. Therefore a critical review of the available literature on passive biomonitoring with terrestrial mosses has been made (Chapter VII) in order to propose a protocol, as harmonised as possible, based on the results of the methodological studies published to date. Therefore, it can be concluded in the basis of all the results presented in this thesis, together with previously reported findings, that passive biomonitoring studies with terrestrial mosses provide qualitative and/or semi-quantitative rather than quantitative information. Interpretation of the results of this type of study must therefore be reconsidered; however, this does not mean that the information obtained is not useful. Such reconsideration, together with true harmonization of the technique (by publication of a protocol exclusively based on scientific criteria), should bridge the gap between the scientific application of the technique and its application in environmental policy making.