Performance of bees and beehive products as indicators of elemental tracers of atmospheric pollution in sites of the Rome province (Italy)

In this survey, we studied the levels of relevant atmospheric elements well known as tracers of vehicular traffic (i.e., Cu, Sb, Sn, Fe, Mn); biomass burning (i.e., K, Rb, Cs, Li, Tl); and soil resuspension (Si, Al, Ca, Ti) in bees and beehive products (honey, wax, pollen, propolis) in five selected sites in the Rome province (Italy). To attentively support the sustainable management of the involved ecosystems, we have enhanced the information variety endowment (fourteen elements, up to 454 samples, five sites, about thirteen thousand analytical determinations) by six sampling campaigns conducted in a one-year survey (2018–2019). The control charts of the considered elements were built for the first time, employing Johnson’s probabilistic method in the Rome province area. Thus, we have measured the metal concentration overlap ranges in the selected biomonitor/indicators (as well as medians and distribution) and the overlap bioaccumulation index (OBI) with respect to the lowest (OBI-Lower) and the highest (OBI-Upper) extreme values of the overlap elements’ concentration ranges. The advantage of the OBI is that we can build the control charts by considering the extremes of the bioaccumulation curves of the elements in the matrices simultaneously, thus creating a ranking among the biomonitor/indicators. This study strongly confirms the selected biomonitor/indicators’ ability (excluding honey) to reflect the atmospheric deposition of environmental tracers of traffic, biomass burning, and soil in the area of Rome province. Bees and wax resulted in being very strong accumulators of environmental tracers (i.e., Cu, Sn, Mn for traffic; K, Rb, Cs, and Li for biomass burning; and Al, a soil tracer), showing high OBI-U values. For instance, bees have high bioaccumulation surplus with OBI-U values of 68.6 and 92.7 for Cu and Mn, respectively. This confirms their ability as excellent biomonitors when assessing different environmental contamination cases becomes necessary. To a lesser extent, pollen and propolis showed high levels for several tracers for OBI-U and OBI-L values. Honey often showed a univocal bioaccumulation pattern with high OBI-L values (i.e., 53.7; 154.4; and 112.0 for Cu, Fe, and Mn, respectively), indicating the low transfer capability of contaminants from the environment to the final food product, and confirming its good quality. This further confirms that honey is not appropriate as an environmental indicator. Eventually, the OBI-L index can be applied as an early warning signal when the contamination process is in its initial stages. The OBI index boosts the observer’s information variety about the performance of bees, wax, pollen, and propolis as element biomonitors in atmospheric ecosystems.