Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
Water Environ Res. 2012 Nov;84(11):2037-44. doi: 10.2175/106143012x13373575830872.
The role of ferrous iron in the phosphorus cycle of an aquatic ecosystem is poorly understood because of a lack of suitable methods to quantitatively evaluate ferrous iron phosphorus (FIP) phases. Using sediments sampled from Fubao Bay of Dianchi Lake in China, a novel extraction method for FIP using 2,2'-bipyridine was explored. Total phosphorus and iron in the sediments ranged from 1.0 to 5.0 mg/g (dry weight) and 28.5 to 90.6 mg/g, respectively. Organic content (as indicated by loss on ignition or LOI) and iron(II) ranged from 3.1 to 27.0% and 26.5 to 64.9 mg/g, respectively. The dissolution dynamics of FIP extraction with a low solid/liquid ratio (1:25) indicated that a single application of 0.2% 2,2'-bipyridine extracted both iron(II) (Fe(II)) and phosphorus (as PO4(3-)) in sediments with different organic contents with low efficiency. The extraction efficiency of Fe(II) was improved by alteration of the solid/liquid ratio, but the effect was limited. However, addition of a 1:1000 solid/liquid ratio of 0.5 M potassium chloride to a 0.2% 2,2'-bipyridine solution significantly accelerated extraction of FIP with the release of Fe(II) and phosphorus toward equilibrium at approximately 150 hours. Further investigation demonstrated that 2,2'-bipyridine exhibited a higher selectivity in distinguishing FIP from phosphorus bound to ferric (Fe(III)) oxides or precipitated by calcium (Ca2+). Air-drying sediments significantly decreased the amount of extracted FIP, which indicates that fresh, wet sediment should be used in this type of FIP extraction. Based on experimental results using the proposed extraction protocol, (1) FIP in sediments of Fubao Bay had a predominant status in the lake sediment and accounted for 23.4 to 39.8% of total phosphorus, and (2) Fe(II)(FIP) released in the extraction is directly proportional to phosphorus(FIP) (Fe(II)(FIP) = 2.84 x P(FIP) + 0.0007; R2 = 0.97) with an average molar ratio of Fe(II)(FIP)/P(FIP) of 2.7. This study shows that FIP extraction with 2,2'-bipyridine is a robust method for releasing ferrous iron associated with phosphorus. Further, the high percentage of FIP in total phosphorus (40%) measured in the study site using this extraction method suggests that FIP might have been often underestimated in previous studies.
铁在水生生态系统磷循环中的作用还不甚清楚，这是因为缺乏定量评估亚铁磷（FIP）相的合适方法。本研究采用 2,2'-联吡啶从中国滇池抚仙湖富宝湾采集的沉积物中探索了一种新的 FIP 提取方法。沉积物中总磷和铁的含量范围分别为 1.0 至 5.0 mg/g（干重）和 28.5 至 90.6 mg/g，有机含量（以灼烧损失或 LOI 表示）和铁（II）的含量范围分别为 3.1 至 27.0%和 26.5 至 64.9 mg/g。低固液比（1:25）下 FIP 提取的溶解动力学表明，单次应用 0.2%的 2,2'-联吡啶对不同有机含量的沉积物中铁（II）（Fe（II））和磷（以 PO4（3-）形式存在）的提取效率较低。通过改变固液比可以提高 Fe（II）的提取效率，但效果有限。然而，向 0.2%的 2,2'-联吡啶溶液中添加 1:1000 的固液比 0.5 M 氯化钾可显著加速 FIP 的提取，Fe（II）和磷的释放在大约 150 小时后达到平衡。进一步的研究表明，2,2'-联吡啶在区分与铁（III）氧化物结合的 FIP 或由钙（Ca2+）沉淀的磷方面具有更高的选择性。风干沉积物显著降低了提取的 FIP 量，这表明应在这种类型的 FIP 提取中使用新鲜、湿的沉积物。基于使用所提出的提取方案进行的实验结果，（1）抚仙湖富宝湾沉积物中的 FIP 在湖泊沉积物中占据主导地位，占总磷的 23.4%至 39.8%，（2）提取过程中释放的 Fe（II）（FIP）与磷（FIP）直接成正比（Fe（II）（FIP）= 2.84 x P（FIP）+ 0.0007；R2 = 0.97），平均摩尔比 Fe（II）（FIP）/P（FIP）为 2.7。本研究表明，2,2'-联吡啶的 FIP 提取是一种释放与磷结合的亚铁的有效方法。此外，使用该提取方法在研究地点测量的总磷中 FIP 的高比例（40%）表明，在先前的研究中，FIP 可能经常被低估。
