Arsenic speciation and transport associated with the release of spent geothermal fluids in Mutnovsky field (Kamchatka, Russia)

► Reduced high temperature geothermal fluid has high As content. ► Mixed surface waters and waste fluid are at thermodynamic disequilibrium. ► Arsenic is transported downstream in dissolved and adsorbed forms. ► As(III)/(V) form bi-nuclear bi-dentate complexes with Al- and Fe-rich substrates.