Mercury accumulation in tropical insects is structured by trophic gradients and contaminant risk landscapes

Abstract

Abstract Mercury (Hg) contamination from artisanal and small-scale gold mining (ASGM) is widespread in the Amazon, yet its dynamics in terrestrial food webs remain poorly understood. Here, we quantified total mercury (THg) concentrations in 492 insects spanning nine taxa across three sites in the Peruvian Amazon representing contrasting mining influence. Taxa were selected to capture a gradient of resource use from plant-based to animal-derived organic matter. Using linear mixed-effects models, we evaluated the relative roles of trophic structure, spatial variation, environmental exposure, and biological traits in shaping THg accumulation. Trophic structure emerged as the dominant driver, with models incorporating feeding guilds explaining the majority of variation (R²ₘ ≈ 0.82) and outperforming all alternatives (ΔAIC > 60). THg concentrations increased monotonically along the trophic gradient, with an approximately 39-fold difference between herbivorous and necrophagous taxa. Spatial variation across sites reflected underlying contamination, with THg increasing ~ 7-fold from the least to most impacted site, but explained substantially less variation than trophic structure. Species-specific responses further modulated accumulation, partly associated with body weight. Environmental variables showed consistent but comparatively weak effects. To our knowledge, this study provides the first evidence from the Amazon Basin integrating Hg contamination in terrestrial insects within a trophic gradient framework.