Honey Bees and Associated Matrices as Biomonitors of Soil Trace Elements: Assessment of Their Sensitivity in a Regional Rural Environment.

Honey bees (Apis mellifera L.) represent a random bio-sampler integrating pollutants over space and time. An effective biomonitor for trace element (TE) pollution should provide a linear response to TE levels in the environment. However, uncertainties in detecting TEs originating in soil limit their use. To address this, nine experimental sites with multiple apiaries were established in the Upper Palatine Forest, Czech Republic. The soils surrounding the hives were characterised by estimations of the pseudo-total and (bio)available pools of TEs. Our study aimed to: (i) quantify the linear relationships between soil TE indices and TE contents in bees, bee bread, honey, and wax; and (ii) verify the bio-barrier function protecting honey from TE contamination. Lead (0.046-0.140 µg g -1 ) and nickel (0.12-4.30 µg g -1 ) contents in bees showed strong linear correlations with (bio)available Pb (0.012-0.254 µg g -1 ) and pseudo-total Ni (17.1-36.4 µg g -1 ) in soil (Pearson's r = 0.95 and 0.88, p < 0.005), providing high spatial resolution. A weaker, insignificant correlation was observed for Cr (r = 0.65) and V (0.44), while no correlation was found for Cd. However, the lack of associations for Cr, V, and Cd may result from the low soil TE levels in the region, negligible differences among the majority of sites, and temporal concerns related to different time scales of the biomonitors, impacting the linear model's sensitivity. Biochemical traits in bees, such as the bio-barrier function, and different bioavailability of TEs from ingested matter may affect the matrix-to-matrix transfer of TEs in an element-dependent manner. Consequently, the linear response of bee-related biomonitors to TE levels in the environment may significantly deteriorate.