A study aimed at unravelling arsenic (As) speciation by means of XAS spectroscopy in the carbonate sediments and the total suspended particulate (TSP) occurring at the Piscine Carletti spring system (CSS), part of the larger Bullicame (Viterbo, Central Italy) thermal area, has been undertaken. At CSS, hot water emerges in an artificial pool and flows along a constructed channel (ca. 100 m long) covered by travertine deposits partially coated by differently coloured microbial mats indirectly favouring mineral deposition (Venturi et al., 2023). In this spring system, As occurs as a geogenic anomaly, and its mobility is affected by inorganic and microbiological processes which can differentiate its speciation and mobility. The determination of As speciation in both the rock and TSP is essential to validate the models on the fate of As in this “natural laboratory”. 8 rock and 8 TSP samples were collected in the CSS, in step of 14 m along the channel starting from the water spring and following the change in temperature and physico-chemical features of the system. Some water samples for the determination of the chemical and physical parameters of the environment were also collected. Solid samples were analysed, without manipulation, by means of X-ray Absorption Spectroscopy, at the As K edge (11864 eV) in fluorescence mode, and at low temperature (range 77-20 K). Experiments on rock and TSP samples were carried out at BM08 and BM26, respectively. The main results point to an almost constant As(III) over As(tot) ratio over the whole spring system in the rock samples, As(III) being about 30% of the As(tot). Considering samples discriminated by the colour (with reference to different abundances and speciation of microbiologic populations), no apparent spectral changes were observed. TSP samples, analysed with a specific procedure due to their ultra-diluted nature, appear also constant, and, compared to the corresponding rocky samples, slightly enriched in As(III). These data have to be compared to a water environment, which evolves towards more oxidising and higher pH conditions while increasing the distance from the spring, as testified from the change of the As(III)/As(tot) ratio from an initial 70% down to a final 40% (unpublished data). This complex set of experimental results will be discussed on the light of two possible interpretations schemes, i.e., a kinetically constrained precipitation mechanism, and a microbiologically constrained change of As speciation.
Arsenic in the Piscine Carletti Thermal Spring System (Viterbo, Italy): a XAS speciation study / Montegrossi G., Venturi S., Baroni T., Casentini B., Fazi S., Rimondi V., Costagliola P., Di Benedetto F.. - ELETTRONICO. - (2023), pp. 0-0. (Intervento presentato al convegno Congresso congiunto SIMP, SGI, SOGEI, AIV "The Geoscience paradigm: Resources, Risks and future perspectives").
Arsenic in the Piscine Carletti Thermal Spring System (Viterbo, Italy): a XAS speciation study
Venturi S.;Rimondi V.;Costagliola P.;
2023
Abstract
A study aimed at unravelling arsenic (As) speciation by means of XAS spectroscopy in the carbonate sediments and the total suspended particulate (TSP) occurring at the Piscine Carletti spring system (CSS), part of the larger Bullicame (Viterbo, Central Italy) thermal area, has been undertaken. At CSS, hot water emerges in an artificial pool and flows along a constructed channel (ca. 100 m long) covered by travertine deposits partially coated by differently coloured microbial mats indirectly favouring mineral deposition (Venturi et al., 2023). In this spring system, As occurs as a geogenic anomaly, and its mobility is affected by inorganic and microbiological processes which can differentiate its speciation and mobility. The determination of As speciation in both the rock and TSP is essential to validate the models on the fate of As in this “natural laboratory”. 8 rock and 8 TSP samples were collected in the CSS, in step of 14 m along the channel starting from the water spring and following the change in temperature and physico-chemical features of the system. Some water samples for the determination of the chemical and physical parameters of the environment were also collected. Solid samples were analysed, without manipulation, by means of X-ray Absorption Spectroscopy, at the As K edge (11864 eV) in fluorescence mode, and at low temperature (range 77-20 K). Experiments on rock and TSP samples were carried out at BM08 and BM26, respectively. The main results point to an almost constant As(III) over As(tot) ratio over the whole spring system in the rock samples, As(III) being about 30% of the As(tot). Considering samples discriminated by the colour (with reference to different abundances and speciation of microbiologic populations), no apparent spectral changes were observed. TSP samples, analysed with a specific procedure due to their ultra-diluted nature, appear also constant, and, compared to the corresponding rocky samples, slightly enriched in As(III). These data have to be compared to a water environment, which evolves towards more oxidising and higher pH conditions while increasing the distance from the spring, as testified from the change of the As(III)/As(tot) ratio from an initial 70% down to a final 40% (unpublished data). This complex set of experimental results will be discussed on the light of two possible interpretations schemes, i.e., a kinetically constrained precipitation mechanism, and a microbiologically constrained change of As speciation.
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