Honey bees as integrative bioindicators of environmental pollution: Trace elements and pesticide residues across...

Honey bees (Apis mellifera) are sophisticated bioindicators due to their capacity to integrate contamination signals from multiple environmental matrices. This study investigated pesticide residues and multi-element accumulation, including rare earth elements (REEs), in worker honey bees across four distinct ecological contexts in Calabria (Southern Italy): two protected montane forests (S1 and S2, Sila National Park), one suburban, and one urban site. A total of 778 agrochemicals and 46 trace elements were targeted using gas and liquid chromatography-tandem mass spectrometry (GC-MS/MS and LC-ESI-MS/MS), and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. Chemometric analyses were applied to assess spatial variability and evaluate the discriminant power of the elemental fingerprint. Pesticide residues were predominantly below quantification limits, with the exception of the fungicide ametoctradin at site S2, likely reflecting localized agricultural proximity. Elemental analyses revealed pronounced, site-specific accumulation patterns driven by landscape context. Urban honey bees (S4) exhibited significant enrichments in Pb, Ni, Cr, and Se, consistent with traffic-related emissions, while suburban bees (S3) showed higher levels of Ba, Mn, As, and Zn. Surprisingly, bees from the protected Natura 2000 site (S2) displayed the highest diversity and concentrations of REEs, suggesting an interplay between lithogenic sources and agricultural inputs. Furthermore, we identified striking inter-individual variability in accumulation-a critical, yet often overlooked, dimension likely driven by age, foraging range, and micro-scale environmental heterogeneity. These findings challenge current biomonitoring paradigms and underscore the role of honey bees as high-resolution tools for assessing both emerging contaminants (REEs) and anthropogenic pressures in terrestrial ecosystems.