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Due to the capacity of some vegetation species to accumulate metals from the growing media, they have been used as bioindicators in areas polluted with such contaminants. In this sense, XRF has been applied, for example, in some studies as an analytical technique for determining multi‐elemental composition of different vegetation species in areas affected by mining activities [3, 18, 39] or to study heavy metals in wild edible mushrooms under different pollution conditions [40]. In Figure 2.4, as an example, EDXRF spectra obtained in the analysis of leaves of Betula Pendula species sampled in a mining landfill and in a non‐polluted area are compared. As it can be seen, XRF spectra enable the discrimination between a sample growing on the mining waste landfill studied and the other one collected in a non‐polluted area (control sample) in a fast an easy way. Another interesting approach of multi‐elemental information derived from XRF analysis is the possibility to monitor other essential elements present in the vegetation sample that may change as a result of metal accumulation (i.e. K).

Figure 2.4 EDXRF spectra obtained in the analysis of leaves of Betula Pendula species collected in a mining landfill and in a non‐polluted area (control sample).

In the last years, the employment of plants to remediate areas polluted by metals (phytoremediation) has acquired popularity as an alternative or complementary technology to other more sophisticated remediation methods. Moreover, some vegetation species have also shown their potential use to avoid erosion, to stabilize wastes and to reduce effects of metal pollution (phytostabilization). To increase the efficiency of such technologies, it is important to learn more about the specific plant physiological processes involved.

Usually these kinds of studies are performed in the laboratory by exposing the plant to the target metal for a predefined period of time. After the exposure, in addition to the determination of the metal content in roots and shoots, the localization and distribution of metals within the plant tissues as well as their chemical forms (metal ligand environment) is of paramount importance to understand metal uptake, translocation and tolerance mechanisms. Usually μ‐XRF and X‐ray absorption techniques in combination with synchrotron radiation are used for such purposes [41].

The incorporation of metals into plants is principally attained by uptake from the substrate through the roots, but it may be achieved also from deposition of meals on the leaves from aerosol or atmospheric particulate. For this reason, vegetation species are also extensively used in air pollution studies. In particular, mushrooms, mosses, and lichens are well‐suited for this purpose because of their lack of tissue development that causes a non‐barrier effect and, therefore, accumulation ability. A wide range of articles dealing with the use of mosses as bioindicators near roads with high density traffic and in industrial areas have been published using XRF as analytical technique [42]. Due to the low amount of moss available in some of these studies, TXRF is preferred since a multi‐elemental analysis using less than 10 mg of sample can be performed [23]. The advantages of this analytical approach have also been highlighted for multi‐elemental analysis of pollen as atmospheric pollution indicator [43].

Finally, biofilms and algae have also been used to monitor the quality of the aquatic environment. In the case of biofilm analysis, TXRF plays an important role since the amount of sample required for the analysis is lower than with other XRF configurations and even the analysis can be performed directly on the support (quartz reflector) where the biofilm is grown [22]. Algae are also influenced by ambient environmental conditions and, in this respect, the distribution and occurrence of certain species may often reflect local water quality. As such, multi‐elemental analysis of this type of samples has been also the topic of research of several scientific contributions. In this sense, it is interesting to highlight the study of Turner and co‐workers, which used a portable XRF system to identify hot‐spots of contamination by analyzing fresh sample sections of coastal macro algaes [44].