Biases and blind spots in the global research agenda on metallic pollution and bees

Abstract

Metallic pollution is an emerging and underappreciated stressor contributing to global bee declines, yet the evidence base remains fragmented across metals, taxa, endpoints, and geographic regions. Here, we provide the first hypothesis-driven scientometric synthesis of the global literature on metallic pollutants and bees. Using Web of Science records, we compiled 154 experimental and field-based studies and quantitatively tested five predictions regarding taxonomic, methodological, and thematic biases. Publication output increased sharply after 2013, with China, the United States, and Brazil leading research activity. Research effort was disproportionately concentrated on managed honey bees ( Apis mellifera and Apis cerana ), adult workers, and dietary exposure pathways, while larvae, wild bee taxa, and environmentally mediated exposures were less examined. Physiological, behavioural and mortality endpoints dominated the literature, whereas reproductive and microbiome impacts remained major blind spots. Adverse outcomes predominate across metals, although essential elements (Zn, Cu, Se) tended to produce less severe effects than non-essential toxic metals (Cd, Pb, Hg), this difference disappeared when exposure concentration and duration were considered. Experimental concentrations varied significantly among metals in food-based exposure studies, indicating substantial heterogeneity in dosing regimes across the literature. Multi-metal studies were not statistically underrepresented, although only a narrow subset of metal combinations has been repeatedly tested. Overall, this synthesis highlights strong structural biases in current knowledge production and identifies priorities for future research, including broader taxonomic coverage, inclusion of early life stages, standardised field-realistic exposures, and integration of chronic, sublethal, and multi-stressor scenarios. Expanding evidence toward more ecologically representative designs will be essential for robust risk assessment of metallic contamination in pollinator communities.

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