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.

中文翻译：

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采矿尾矿对沿海水域的污染：是什么触发了铁在溶解和可溶部分中的稳定性？

通过与有机配体络合，铁（Fe）在海水中的溶解度大大提高，这些有机配体主要在沿海地区以腐殖质（HS）的形式出现。采矿开采被认为会改变沿海水域中铁的自然生物地球化学循环，即使它对铁馏分的物理和化学形态的影响尚不清楚。在这里，我们表明，溶解在受采矿灾难（芳戴尔坝，东南巴西）沿海水域的可溶性铁浓度仍然很高，甚至近3年后，随着Fe溶出浓度高达2.8 μ M（0.45  μ米过滤）或700纳米（0.22  μ米过滤），和可溶性的Fe（0.02  μm）高达40 nM。腐殖质水平只能解释的溶解的Fe的2％和10％（中位值）的结合（0.22  μm）和可溶性Fe的浓度，这表明与腐殖质络合以外的过程仍在起作用，以保持如此高的溶解性Fe浓度。我们假设主导溶解的Fe部分的胶体相以羟基氢氧化Fe（III）的形式出现，而可溶性部分则由Fe（III）与胺化合物的配合物组成（广泛用于矿石提取过程中）。水柱中溶解的铁的质量平衡表明，到目前为止，陆架上的沉积物再悬浮是将溶解的铁输送到沿海和陆架水域的主要过程。每年对溶解铁的通量的估算突显了这场灾难的严重程度，这可能为开阔海洋提供了不可忽略的溶解铁量。