Pattammattel Ajith, Leppert Valerie J, Aronstein Paul, Robinson Matthew, Mousavi Amirhosein, Sioutas Constantinos, Forman Henry Jay, O'Day Peggy A
Sierra Nevada Research Institute and School of Natural Sciences, University of California, Merced, 95343, USA.
School of Engineering, University of California, Merced, 95343, USA.
Atmos Environ (1994). 2021 Jan 15;245. doi: 10.1016/j.atmosenv.2020.117988. Epub 2020 Oct 14.
The speciation, oxidation states, and relative abundance of iron (Fe) phases in PM samples from two locations in urban Los Angeles were investigated using a combination of bulk and spatially resolved, element-specific spectroscopy and microscopy methods. Synchrotron X-ray absorption spectroscopy (XAS) of bulk samples (i.e., without extraction or digestion) was used to quantify the relative fractions of major Fe phases, which were corroborated by spatially resolved spectro-microscopy measurements. Ferrihydrite (amorphous Fe(III)-hydroxide) comprised the largest Fe fraction (34-52%), with hematite (α-FeO; 13-23%) and magnetite (FeO; 10-24%) identified as major crystalline oxide components. An Fe-bearing phyllosilicate fraction (16-23%) was fit best with a reference spectrum of a natural illite/smectite mineral, and metallic Fe(0) was a relatively small (2-6%) but easily identified component. Sizes, morphologies, oxidation state, and trace element compositions of Fe-bearing PM from electron microscopy, electron energy loss spectroscopy (EELS), and scanning transmission X-ray microscopy (STXM) revealed variable and heterogeneous mixtures of Fe species and phases, often associated with carbonaceous material with evidence of surface oxidation. Ferrihydrite (or related Fe(III) hydroxide phases) was ubiquitous in PM samples. It forms as an oxidation or surface alteration product of crystalline Fe phases, and also occurs as coatings or nanoparticles dispersed with other phases as a result of environmental dissolution and re-precipitation reactions. The prevalence of ferrihydrite (and adsorbed Fe(III) has likely been underestimated in studies of ambient PM because it is non-crystalline, non-magnetic, more soluble than crystalline phases, and found in complex mixtures. Review of potential sources of different particle types suggests that the majority of Fe-bearing PM from these urban sites originates from anthropogenic activities, primarily abrasion products from vehicle braking systems and engine emissions from combustion and/or wear. These variable mixtures have a high probability for electron transfer reactions between Fe, redox-active metals such as copper, and reactive carbon species such as quinones. Our findings suggest the need to assess biological responses of specific Fe-bearing phases both individually and in combination to unravel mechanisms of adverse health effects of particulate Fe.
采用整体和空间分辨的元素特异性光谱及显微镜方法相结合，研究了洛杉矶市区两个地点的颗粒物（PM）样本中铁（Fe）相的形态、氧化态和相对丰度。对整体样本（即未进行提取或消解）进行同步加速器X射线吸收光谱（XAS）分析，以量化主要铁相的相对含量，空间分辨光谱显微镜测量结果证实了这些含量。水铁矿（无定形Fe(III) - 氢氧化物）占铁的比例最大（34 - 52%），赤铁矿（α - FeO；13 - 23%）和磁铁矿（FeO；10 - 24%）被确定为主要的结晶氧化物成分。含铁层状硅酸盐部分（16 - 23%）与天然伊利石/蒙脱石矿物的参考光谱拟合最佳，金属铁（Fe(0)）是相对较少（2 - 6%）但易于识别的成分。电子显微镜、电子能量损失光谱（EELS）和扫描透射X射线显微镜（STXM）对含铁PM的尺寸、形态、氧化态和微量元素组成的分析揭示了铁物种和相的可变且不均匀的混合物，这些混合物通常与含碳物质相关，并存在表面氧化的证据。水铁矿（或相关的Fe(III)氢氧化物相）在PM样本中普遍存在。它作为结晶铁相的氧化或表面蚀变产物形成，也作为环境溶解和再沉淀反应导致的与其他相分散的涂层或纳米颗粒出现。在环境PM研究中，水铁矿（和吸附的Fe(III)）的普遍存在可能被低估了，因为它是非晶态、无磁性、比结晶相更易溶解且存在于复杂混合物中。对不同颗粒类型潜在来源的综述表明，这些城市地点的大部分含铁PM源自人为活动，主要是车辆制动系统的磨损产物以及燃烧和/或磨损产生的发动机排放物。这些可变混合物极有可能发生铁、铜等氧化还原活性金属以及醌等活性碳物种之间的电子转移反应。我们的研究结果表明，需要分别评估特定含铁相的生物学反应以及它们的组合反应，以揭示颗粒态铁对健康产生不良影响的机制。
