Concentrations of the heavy metals Ni, Cu, Zn, Cd, Pb and Hg, accumulated by
Pleurozium schreberi mosses samples differ from each other within and between study periods of a given year. The concentration of individual elements is influenced by the moss species used and their accumulation capacity, exposure time and other environmental factors (interactions among elements, temperature, humidity)
[37][38][39]. The changes in concentrations between the two study periods are also due to the global lockdown situation caused by the coronavirus pandemic restrictions. In the literature, one can find results indicating that air pollution has decreased significantly in this period in comparison to the values previously reported
[40][41]. The impact of the pandemic on air pollution in terms of biological monitoring has so far been described by only one known publication, where is indicated that concentrations of selected metals accumulated by the moss
Pleurozium schreberi, as part of passive biomonitoring studies, decreased by lockdown
[42]. Our study confirms the above statements that heavy metal concentrations during the “NYE” period and in 2020/2021 were lower compared to the same period a year earlier (see
Figure 1). This was influenced by national restrictions related to the limited possibility of overcrowding and participation in mass events celebrating the New Year, which had an impact on the reduced emissions from fireworks fired. According to the literature, air concentrations of heavy metals such as Cu, Zn and Pb are related to their emission during the fireworks burning
[17][18][20][43][44][45] as was also confirmed by this research. During moss exposure for only 2 days (NYE period) [31 December and 1 January], concentrations of these elements were characterised by values comparable or higher to periods of longer exposure to moss contamination with these analytes (see also
Figure 1). In our opinion, the results presented here represent the first environmental experiment using the moss-bag technique to determine the concentrations of heavy metals accumulated by mosses during New Year’s Eve (due to fireworks burning), together with the impact of the pandemic on air pollution at this time using active moss biomonitoring.
Figure 1. Concentrations of heavy metals in mosses samples (mg kg−1/day): (a) Ni, (b) Cu, (c) Zn, (d) Cd, (e) Hg and (f) Pb depending on the exposure time (y1, y2—period 2019/2020 and 2020/2021 respectively).
RAF values higher than 1.00 indicate significant elemental enrichment
[46]. Such values were recorded for copper and lead in 2019/2020 and the impact of increases in these elements was related to the fireworks being fired. In contrast, high increments for nickel and mercury may be related to other air pollutants sources such as local, low level emissions
[47].
The actual quantum efficiency of PSII photochemistry in the light measures the fraction of the absorbed light energy that is actually being used to drive photochemistry at PSII
[48]. Its value is influenced by a number of factors, such as a change in metal concentration
[49][50] and a positive effect on the increase in fluorescence yield over the course of the experiment may have been due to variable hydration
[51]. The dependence of chlorophyll fluorescence yield variability on water content has been reported previously for
Pleurozium moss
[52] and our actual quantum yield values of PSII photochemistry were comparable with the results obtained by other authors for this species
[53][54]. Due to the association of chlorophyll fluorescence with other vital parameters (chlorophyll content, osmotic indices, antioxidant enzyme activities)
[55], we know that biomonitoring studies have been conducted on a living air quality bioindicator
[56].