Active biomonitoring of the air quality with terrestrial mossesstandardization and optimization of the technique

Abstract

Terrestrial mosses are excellent biomonitors of air pollution due its physiological and morphological characteristics, and because their use involve a simple and economic technique. The most common type of moss biomonitoring is the use of naturally grown moss in a given area (i.e. native moss). However, sometimes due to the characteristics of the area (eg populated areas and/or industrial areas ), it is very difficult to find native moss, but the use of transplanted moss can solve this problem. In this way, it will be possible to use moss transplants regardless of the level of anthropization the area studied, then calling active versus passive biomonitoring by the uses of native organisms. The ¿moss bag technique¿ is the most common type of active biomonitoring with terrestrial mosses that is reported in the literature. The technique consists of the exposure of moss samples held within mesh bags, in order to monitor the occurrence in the air of contaminants. However, although the moss bag technique has been used for 40 years, standardized protocols have unfortunately still not been developed. Such standardized protocols includes: (i) preparation of the moss; (ii) preparation of the transplants; (iii) exposure of the transplants and (iv) post exposure treatment. So the overall objective of this doctoral Thesis is to proposed an harmonised methodology for preparing and exposing moss transplants that meets the following requisites: (i) that the transplants are easy to prepare and handle; (ii) that they enable replicable results to be obtained; (iii) that they are capable of capturing high concentrations of as many contaminants as possible, and (iv) that they are efficient at capturing contaminants, highlighting their occurrence in the air in a reasonable timespan. Having into account all the mentioned before, the specific objectives are: 1. To carry out a quantitative evaluation of the effect of moss vitality, and thus of growth, on the uptake of heavy metals during the exposure period (Chapter I). For this purpose, self-watering, shaded moss transplants were used, as this enables the physiological properties of the moss to be held constant. 2. To optimize key methodological aspects in the application of the moss bag technique (Chapter II) having into account the provisional protocol proposed in the ¿State of the art¿ section by the selection of the optimal option for: i) selection of species, ii) the relationship between moss weight and bag surface area, iii) duration of exposure and iv) height of exposure on the basis of the replicability and final concentration data (Cd, Cu, Hg, Pb and Zn). For this purpose, the present study was carried out at different sites affected by different degrees of contamination, and different exposure periods were used. 3. To investigate whether the levels of contaminants measured in moss are correlated with the concentrations in bulk deposition (Chapter III). To achieve this objective, the study was carried out with standardized moss bags located in different sites affected by different degrees of contamination, for different exposure periods. 4. To validate the technique by studying the spatial patterns of dispersion of contaminants (heavy metals and PAHs) in an industrial area, an urban area and an area affected by heavy road traffic (Chapter IV). Keywords: air pollution, moss bags, heavy metals, bioindication