Heavy metal bioaccumulation in Neotropical dung beetles across land-use and mining gradients

Mining operations contribute to metal contamination in tropical ecosystems, yet the extent to which terrestrial invertebrates accumulate elements across different land-use types remains poorly understood. Dung beetles have been proposed as potential bioindicators owing to their close interactions with soil and vertebrate dung. In this study, we investigated the accumulation of nine elements (Mn, Cu, Mg, Fe, Cd, Zn, Pb, Hg, and As) in five common dung beetle species across old-growth forests, forest understory habitats, pastures, croplands, and mining-impacted habitats in southern Ecuador. Elemental concentrations were measured by atomic absorption spectrophotometry following acid digestion of dried tissues. Differences among land-use types and species were assessed using linear and linear mixed-effects models, while multielement patterns were examined using PERMANOVA and principal component analysis (PCA). Concentrations varied descriptively across habitats, with mining-impacted sites showing higher mean concentrations of some metals, particularly Fe, Pb, and Zn. However, no statistical significant differences were detected among land-use types or species. Multivariate analyses also revealed substantial overlap in elemental composition among habitats, without a statistically significant land-use effect. Hg and As were below analytical detection limits in most tissue samples and were therefore excluded from statistical comparisons. The detection of multiple elements in dung beetle tissues provides baseline information on elemental accumulation across the study landscape, although the sources of exposure could not be determined. These findings support further investigation of dung beetles as potential biomonitoring organisms but do not establish their ability to reliably distinguish mining-impacted from reference habitats. Future studies incorporating concurrent environmental matrix measurements, standarized temporal sampling, and greater spatial replication are needed to evaluate their reliability as indicators of mining-related contamination.