Ground Beetle Responses to Heavy Metal in Soils: Carabus coriaceus as an Ecological Indicator

Heavy metal contamination in soil poses significant ecological risks, particularly within agricultural and forest ecosystems. This study evaluates the bioaccumulation of heavy metals (Cr, Co, Ni, Cu, Zn, As, Mo, Pb) by the ground beetle Carabus coriaceus Linnaeus, 1758, across contrasting Croatian ecosystems, with a focus on the role of soil pH in shaping metal dynamics. Concentrations in soils (0–30 and 30–60 cm) and beetle tissues were measured using portable X-ray fluorescence (pXRF), which provides total concentrations; inferences on bioavailability were based on soil properties such as pH and organic matter. Orchard soils showed higher Cu (49.9 mg/kg), Mo (10.3 mg/kg), and Ni (32.5 mg/kg), whereas forest soils contained elevated Zn (105.6 mg/kg), Pb (84.5 mg/kg), As (29.7 mg/kg), and Co (16.3 mg/kg). Beetles accumulated up to 481.0 mg/kg Zn at the orchard and 90.0 mg/kg Cu at the forest site. Bioaccumulation factors exceeded 1.0 for Co, Cu, and Zn, with particularly high values for Zn (2.20–5.75) suggesting both site-specific availability and possible physiological regulation. Soil and beetle analyses were complementary rather than equivalent: soils indicated total load, while beetles reflected biologically relevant fractions. C. coriaceus, therefore, represents a sensitive bioindicator, suitable for biodiversity-based soil contamination monitoring.