Critical evaluation of the ability of sequential extraction procedures to quantify discrete forms of selenium in sediments and soils.
Critical evaluation of the ability of sequential extraction procedures to quantify discrete forms of selenium in sediments and soils.
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DOI：
10.1021/es0342650
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发表时间：
2003-08
影响因子：
11.4
通讯作者：
Michael T. Wright;D. Parker;C. Amrhein
中科院分区：
文献类型：
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作者：
Michael T. Wright;D. Parker;C. Amrhein
连续提取法（SEPs）已被广泛用于表征土壤和沉积物中微量元素的移动性、生物有效性和潜在毒性。虽然经常受到批评，这些方法可能与氧化还原不稳定的元素（砷，汞，硒），更离散的地球化学相可能会出现从氧化值的变化最好的表现。我们严格评估了两个已发表的SEPs硒的特异性和精度，通过将它们应用于四个离散的组件在惰性二氧化硅基质：可溶性硒（VI）（硒酸盐），硒（IV）（亚硒酸盐）吸附到针铁矿，元素硒，和金属硒化物（FeSe; achavalite）。这些都是单独提取和混合模型沉积物。对两种方法中更具选择性的方法进行了修改，以进一步提高其选择性（SEP 2 M）。SEP 1和SEP 2 M都定量回收了可溶性硒酸盐，但吸附的亚硒酸盐的回收率不完全（分别为64%和81%）。SEP 1利用0.1 M K2 S2 O 8来靶向“有机缔合”Se，但该提取剂也溶解了模型沉积物的大部分元素（64%）和硒化铁（91%）组分。在SEP 2 M中，在步骤III中使用的Na 2SO 3在提取元素Se方面是有效的，但也从硒化铁中提取了17%的Se，使得如果两种形式共存，则元素分数将被高估。应用SEP 2 M到8个湿地沉积物中进一步表明，在步骤III中的Na 2SO 3提取一些有机缔合的Se，因此预先插入NaOH提取以产生进一步的改性，SEP 2 OH。使用这五步程序的结果表明，四步SEP 2 M可以高估元素硒高达43%，由于有机硒的溶解。虽然在其选择性仍然不完善，SEP 20 H可能是最合适的程序常规，准确的土壤和沉积物中的硒分馏。然而，在最后一步中使用的强氧化剂（NaOCl）不能区分硒的难熔有机形式和硫还原条件下可能形成的黄铁矿硒。
Sequential extraction procedures (SEPs) have been widely used to characterize the mobility, bioavailibility, and potential toxicity of trace elements in soils and sediments. Although oft-criticized, these methods may perform best with redox-labile elements (As, Hg, Se) for which more discrete biogeochemical phases may arise from variations in oxidation number. We critically evaluated two published SEPs for Se for their specificity and precision by applying them to four discrete components in an inert silica matrix: soluble Se(VI) (selenate), Se(IV) (selenite) adsorbed onto goethite, elemental Se, and a metal selenide (FeSe; achavalite). These were extracted both individually and in a mixed model sediment. The more selective of the two procedures was modified to further improve its selectivity (SEP 2M). Both SEP 1 and SEP 2M quantitatively recovered soluble selenate but yielded incomplete recoveries of adsorbed selenite (64% and 81%, respectively). SEP 1 utilizes 0.1 M K2S2O8 to target "organically associated" Se, but this extractant also solubilized most of the elemental (64%) and iron selenide (91%) components of the model sediment. In SEP 2M, the Na2SO3 used in step III is effective in extracting elemental Se but also extracted 17% of the Se from the iron selenide, such that the elemental fraction would be overestimated should both forms coexist. Application of SEP 2M to eight wetland sediments further suggested that the Na2SO3 in step III extracts some organically associated Se, so a NaOH extraction was inserted beforehand to yield a further modification, SEP 2OH. Results using this five-step procedure suggested that the four-step SEP 2M could overestimate elemental Se by as much as 43% due to solubilization of organic Se. Although still imperfect in its selectivity, SEP 20H may be the most suitable procedure for routine, accurate fractionation of Se in soils and sediments. However, the strong oxidant (NaOCl) used in the final step cannot distinguish between refractory organic forms of Se and pyritic Se that might form under sulfur-reducing conditions.