Assessing the surface reactivity of volcanic ashes in view of their potential respiratory hazard: the Pomici di Avellino eruption (3.9 ka BP)

Volcanic ashes from the Pomici di Avellino (PdA) eruption, an Early Bronze Age (ca. 3.9 ka BP) Plinian event from Somma-Vesuvius, had a wide dispersal area including most of the Central-South regions of Italy. The finest fraction of volcanic ashes can impact the human respiratory apparatus and induce severe respiratory difficulties and pathologies. Particle size, shape and composition, as well as surface reactivity are the key properties that define health hazard of volcanic ashes. Recent studies evidenced that volcanic ashes could generate significant amounts of free radicals. The particle-derived free radicals can contribute, together with the reactive species (ROS) produced by the cells, to the onset of oxidative stress. To evaluate the potential health impact of volcanic ashes both in proximal and distal areas we examined some physical and chemical characteristics of PdA ashes that may play a role in the onset of adverse health effects. Specifically, the particle size distribution (PSD) and surface properties (the specific surface area (SSA), the mobilization of bio-accessible iron ions and the ability to generate hydroxyl radicals) of PdA ashes have been measured.    

PSD was obtained by automated image analysis coupled with electron microscopy. Bio-available iron was quantified using specific iron chelator and colorimetric reactions. The physisorption of N₂ at 77 K (N₂ BET method) was used to measure the specific surface area. Electron Paramagnetic Resonance (EPR) coupled with spin trapping technique was used to quantify the ·OH radical generation.  

The results show a high surface area value, the presence of an amount of removable iron, and a reactivity in the formation of hydroxyl radicals. Furthermore, the ·OH radical generation is continuous in time. In particular, PdA volcanic ashes reactivity is probably related to the presence of surface bio-accessible iron, which is able to generate free radicals. Thus, free radical generation could make Mt. Vesuvius ashes potentially toxic and threaten people’s health causing respiratory problems. Overall, the physico-chemical characteristics of ash particles from Somma-Vesuvius might pose a significant health hazard even in distal areas, where the transport and the inhalation of fine-grained ashes from explosive eruptions might cause respiratory diseases. In light of these new data, further investigation (e.g. crystalline silica amount) to assess Somma-Vesuvius ashes toxicity is required.