Origin, Reactivity, and Bioavailability of Mercury in Wildfire Ash
Origin, Reactivity, and Bioavailability of Mercury in Wildfire Ash
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DOI：
10.1021/acs.est.8b03729
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发表时间：
2018-12-18
影响因子：
11.4
通讯作者：
Chow, Alex T.
中科院分区：
文献类型：
--
作者：
Ku, Peijia;Tsui, Martin Tsz-Ki;Chow, Alex T.
由于气候变化，预计全球范围内的野火将变得更加频繁和密集。许多研究都集中在燃烧的森林中汞的损失；然而，人们对火灾后景观中残余灰材料中汞的来源、浓度、反应性和生物利用度知之甚少。我们检查了最近两次北加州野火产生的黑灰（BA，低燃烧强度）和白灰（WA，高燃烧强度）中的汞含量和反应性，并记录了所有灰烬样品中都含有可测量的，但变化很大的汞含量，范围从4到125 ng/g干重（n = 28）。在选定的灰烬样品中测量的稳定汞同位素组成表明，野火灰烬中的大多数汞来自植被。灰分样品中顽固性汞的含量变化很大（0-75%），这种顽固性汞池似乎与灰分中的黑碳组分有关。在控制条件下，BA和WA对水中无机汞有较强的固相作用，而对气态元素汞没有较强的固相作用。在与自然地表水的缺氧培养过程中，我们发现大多数灰样品中的汞释放量很小，甲基化电位很低。因此，野火灰烬的形成可以将汞隔离成相对非生物可利用的形式，减弱汞侵蚀和随野火灰烬被侵蚀而向水生环境运输的潜在不利影响。
Wildfires are expected to become more frequent and intensive at the global scale due to climate change. Many studies have focused on the loss of mercury (Hg) from burned forests; however, little is known about the origins, concentration, reactivity, and bioavailability of Hg in residual ash materials in postfire landscapes. We examine Hg levels and reactivity in black ash (BA, low burn intensity) and white ash (WA, high burn intensity) generated from two recent northern California wildfires and document that all ash samples contained measurable, but highly variable, Hg levels ranging from 4 to 125 ng/g dry wt. (n = 28). Stable Hg isotopic compositions measured in select ash samples suggest that most Hg in wildfire ash is derived from vegetation. Ash samples had a highly variable fraction of Hg in recalcitrant forms (0-75%), and this recalcitrant Hg pool appears to be associated with the black carbon fraction in ash. Both BA and WA were found to strongly sequester aqueous inorganic Hg but not gaseous elemental Hg under controlled conditions. During anoxic ash incubation with natural surface water, we find that Hg in most ash samples had a minimal release and low methylation potential. Thus, the formation of wildfire ash can sequester Hg into relatively nonbioavailable forms, attenuating the potentially adverse effects of Hg erosion and transport to aquatic environments along with eroded wildfire ash.