Coastal waters contamination by mining tailings: What triggers the stability of iron in the dissolved and soluble fractions?

Abstract

The solubility of iron (Fe) in seawater is greatly enhanced by complexation with organic ligands, predominantly occurring as humic substances (HS) in coastal areas. Mining exploitation is believed to change the natural biogeochemical cycle of Fe in coastal waters, even though its impacts on the physical and chemical speciation of the Fe fractions are not known. Here we show that dissolved and soluble Fe concentrations in coastal waters affected by a mining catastrophe (Fundão dam, Southeast Brazil) remain very high, even almost 3 years later, with concentrations of dissolved Fe up to 2.8 μM (0.45 μm filtration) or 700 nM (0.22 μm filtration), and soluble Fe (0.02 μm) up to 40 nM. Levels of humic substances can only explain the binding of 2% and 10% (median values) of dissolved Fe (0.22 μm) and soluble Fe concentrations, respectively, which shows that processes other than complexation with humic substances are at play to maintain such high dissolved Fe concentrations. We hypothesize that the colloidal phase that dominates the dissolved Fe fraction occurs as Fe(III) oxyhydroxides while the soluble fraction is comprised of Fe(III) complexes with amine compounds (widely used in the ore extraction process). Mass balance of dissolved Fe in the water column suggests that sediment resuspension on the continental shelf is by far the dominant process delivering dissolved Fe to coastal and shelf waters. Estimates of dissolved Fe yearly fluxes highlight the sheer magnitude of this catastrophe that might provide a non-negligible amount of dissolved Fe to the open ocean.

Ecological trap for seabirds due to the contamination caused by the Fundão dam collapse, Brazil

“…The maintenance of prey availability for seabirds may be associated with the non-lethal effect of tailings, due to their composition and dynamics (Sá et al, 2021). Fe was the most abundant element in the tailings, which is considered a limiting factor for primary productivity in the oceans (Martin, 1992;Longhini et al, 2019Longhini et al, , 2021. Input in Fe concentrations can stimulate the growth of phytoplankton especially in areas far from the coast where it is a limiting factor for phytoplankton grow (de Baar et al, 1990) and may have contributed to the consistent use of the area by seabirds, as suggested by the biologging data.…”

Sources, sinks, and cycling of dissolved organic copper binding ligands in the ocean

“…B Concentrations of electroactive humic substances expressed in terms of their potential Cu-binding equivalent concentration, based on values calculated for SRHA in Whitby et al 43 . Amazon, Mersey, and Sapelo data use the CuHS technique 43 ; San Francisco Bay, Fundao Dam, and Irish Sea use the FeHS technique [243][244][245] , while Loire Estuary uses the MoHS technique 92 ; different methods have been shown to give comparable eHS concentrations 35,246 . Sediments.…”

Contaminação aquática por rejeito de mineração: o caso do desastre ambiental de Mariana (MG)

“…Apesar da resolução CONAMA (420/2009) não contemplar concentrações aceitáveis de Fe, Mn e Al, nota-se a ordem de grandeza em que estes metais foram encontrados.Segundo os autores, o rejeito estocado na barragem era composto principalmente de ferro, sílica, alumínio e metais traço como As, Cr, Cd, Hg e Pb(PIRES et al 2003; MORGENSTERN et al, 2016;GOMES et al 2017). E, assim como observado nesteestudo, al., 2017;LONGHINI et al, 2020;SÁ et al, 2021). Neste trabalho, os metais Pb, Zn, Al e Cd foram também quantificados na água, na maioria dos casos, em quantidades maiores que as permitidas em resolução CONAMA(357/2005).…”