PTEs in river ecosystems: exploring their natural and anthropogenic sources in the Ombrone Grossetano River Basin (OGRB, Italy)

Although living organisms need varying quantities of specific Potentially Toxic Elements (PTEs) (such as Fe and Zn) for their development, their accumulation in river ecosystems can disrupt biota equilibrium. As PTEs originate from both natural processes (e.g. rock weathering) and human activities (e.g. industrial), geochemical tools able to discern their sources are crucial to gain insights into the ecological and geological interplay. This study focuses on the main sources of PTEs and their potential effects on the aquatic ecosystems in the Ombrone Grossetano River Basin (OGRB, Italy), which was selected as a pilot area due to specific features, including: i) lithological heterogeneity; ii) predominant agricultural land use; iii) presence of abandoned mining sites and protected natural areas; iv) thermo-mineral water inputs and seawater intrusion. Surface waters and suspended solids (sampled under diverse discharge conditions), together with sediments, have been or are about to be analysed in terms of major, minor, nutrients, trace elements and PTEs. Stream waters display a wide chemical variability: from Ca(Mg)-HCO3 to Ca(Mg)-SO4(Cl) and Na-Cl, along with local enrichments in Mn, Co, Ni, Cu and Zn, due to both diversified waterrock interaction processes and natural (e.g. seawater intrusion) and anthropogenic (e.g. agricultural runoff) stressors. PTEs content in sediments can be primarily associated with the lithological features within the sub-basins, the presence of ore deposits and past mining activities As a key point of this survey is to understand the provenance of PTEs, ongoing analysis of stable and radiogenic isotopes (C and Sr in all three matrices; N, S, Nd and Pb in suspended solids and sediments) will be used to better constrain the sources of these elements. Biodiversity evaluation will also be pivotal to link abiotic and biotic components of the ecosystem and achieved via innovative monitoring techniques such as eDNA and eRNA sequential analysis.