Mosses and Snails as Bioindicators Reflecting the Biologically Relevant Fraction of Toxic Elements

: Air pollution is a major environmental and public health issue, largely driven by human activities. The present study evaluates the combined use of two bioindicators from different taxonomic groups, the moss Rhytidiadelphus squarrosus and the terrestrial snail Cornu aspersum, to assess early biological effects induced by atmospheric exposure to toxic elements. Both species, chosen for their sensitivity, simple physiology, and suitability for field transplantation, were exposed for 30 days at two sites in southern Italy with contrasting environmental conditions. Toxic element accumulation in moss biomass and snail tissues was measured using ICP-OES, while snail shell composition was analyzed using FTIR spectroscopy. Biological responses were assessed through oxidative stress biomarkers (ROS levels and catalase activity), HSP70 expression determined by Western blotting, and structural damage, including ultrastructural changes in mosses and histopathological alterations in snails. Results showed site-dependent patterns of toxic elements accumulation in both organisms, consistent with increased oxidative stress and induction of HSP70 expression. Enlargement of the albumen gland and histological alterations in digestive tubules and reproductive systems were found in snails. Mosses showed severe ultrastructural alterations. FTIR analysis revealed changes in snail shell composition consistent with metal exposure. Principal component analysis highlighted clear patterns linking contamination, oxidative stress, and structural damage, supporting the complementarity of the two bioindicators and their ability to capture distinct exposure pathways and biological effects.