Selenium in Volcanic Environments (SELVES)

Selenium (Se) is a naturally-occurring metalloid that is nutritionally-required in small amounts but can become toxic at concentrations only twice recommended doses. UK soils are typically Se-deficient and require supplementation, but in volcanic regions and in soils overlying phosphate or organic-rich shales Se may be present in excess, representing a significant health challenge. Selenium is of critical importance in photovoltaics, glass production, fertilisers and batteries; Se demand is projected to rise 5-10 times by 2050. Volcanoes dominate the natural sources of Se (and its chemical 'twin', sulfur) to the environment. Due to its extreme volatility Se is enriched in volcanic gases and aerosol and in hydrothermal fluids, from which Se is deposited in porphyries and mined as a by-product with copper. Up to now, due to the technical challenges involved with sampling Se in volcanic gases and analysing it precisely in volcanic rocks, our quantitative understanding of volcanic Se is extremely limited.

We propose the launch of a set of new studies of Se geochemistry (and that of other environmentally-important trace volatile metals) which take advantage of the recent development of using unoccupied aerial vehicles to sample high temperature gases; and new, precise analytical protocols for Se measurements. We have a range of suitable samples in hand already, from a diverse suite of samples of lavas, and gas/aerosol, collected by the investigators during recent explosive basaltic eruptions in a range of settings (hotspot: Cumbre Vieja, La Palma, 2021; Kilauea, USA, 2018, Fagradalsfjall, Iceland, 2021; subduction zone: Ambrym Volcano, Vanuatu, 2018; and Villarrica, Chile, 2018). We will quantify the flux of outgassing Se from each eruption, along with sulfur, and the controls on it; and establish in what chemical, bioavailable form Se is delivered to the surface environment via eruptions.

The successful achievement of these objectives provides the basis for larger, integrative, high impact studies focussed on heavy metals (e.g. mercury, thallium and lead, as well as Se) delivered to the surface environment by volcanic activity, their environmental fate, biological uptake, including the competing effects of Se and S uptake by plants and incorporation into groundwater, both in the modern-day and in the history of our planet. This study lays the groundwork for improved hydrothermal models of Se partitioning into porphyry deposits and sustainable and efficient Se ore resource utilisation. This project explores the frontiers of a wide-ranging topic with impacts across the NERC remit through the nexus of health, environment and economy.