Lusa M, Bomberg M, Aromaa H, Knuutinen J, Lehto J
Laboratory of Radiochemistry, Department of Chemistry, P.O. Box 55, 00014 University of Helsinki, Finland.
VTT Technical Research Centre of Finland, P.O. Box 1000, 02044, VTT, Finland.
J Environ Radioact. 2015 May;143:110-122. doi: 10.1016/j.jenvrad.2015.02.022. Epub 2015 Mar 9.
Batch sorption experiments were conducted to evaluate the sorption behaviour of iodide and the microbial impact on iodide sorption in the surface moss, subsurface peat, gyttja, and clay layers of a nutrient-poor boreal bog. The batch distribution coefficient (Kd) values of iodide decreased as a function of sampling depth. The highest Kd values, 4800 L/Kg dry weight (DW) (geometric mean), were observed in the fresh surface moss and the lowest in the bottom clay (geometric mean 90 mL/g DW). In the surface moss, peat and gyttja layers, which have a high organic matter content (on average 97%), maximum sorption was observed at a pH between ∼ 4 and 5 and in the clay layer at pH 2. The Kd values were significantly lower in sterilized samples, being 20-fold lower than the values found for the unsterilized samples. In addition, the recolonization of sterilized samples with a microbial population from the fresh samples restored the sorption capacity of surface moss, peat and gyttja samples, indicating that the decrease in the sorption was due to the destruction of microbes and supporting the hypothesis that microbes are necessary for the incorporation of iodide into the organic matter. Anoxic conditions reduced the sorption of iodide in fresh, untreated samples, similarly to the effect of sterilization, which supports the hypothesis that iodide is oxidized into I2/HIO before incorporation into the organic matter. Furthermore, the Kd values positively correlated with peroxidase activity in surface moss, subsurface peat and gyttja layers at +20 °C, and with the bacterial cell counts obtained from plate count agar at +4 °C. Our results demonstrate the importance of viable microbes for the sorption of iodide in the bog environment, having a high organic matter content and a low pH.
进行了批量吸附实验，以评估碘化物的吸附行为以及微生物对贫营养北方沼泽地表面苔藓、地下泥炭、泥炭土和粘土层中碘化物吸附的影响。碘化物的批量分配系数（Kd）值随采样深度而降低。在新鲜的表面苔藓中观察到最高的Kd值，为4800 L/Kg干重（几何平均值），而在底部粘土中最低（几何平均值为90 mL/g干重）。在有机质含量高（平均97%）的表面苔藓、泥炭和泥炭土层中，在pH值约为4至5时观察到最大吸附，而在粘土层中在pH值为2时观察到最大吸附。灭菌样品中的Kd值显著较低，比未灭菌样品中的值低20倍。此外，用新鲜样品中的微生物群体对灭菌样品进行再定殖，恢复了表面苔藓、泥炭和泥炭土样品的吸附能力，这表明吸附减少是由于微生物的破坏，并支持了微生物对于碘化物纳入有机质是必要的这一假设。缺氧条件降低了新鲜未处理样品中碘化物的吸附，类似于灭菌的效果，这支持了碘化物在纳入有机质之前被氧化为I2/HIO的假设。此外，在+20°C时，Kd值与表面苔藓、地下泥炭和泥炭土层中的过氧化物酶活性呈正相关，在+4°C时与平板计数琼脂获得的细菌细胞计数呈正相关。我们的结果表明，在有机质含量高且pH值低的沼泽环境中，有活力的微生物对于碘化物的吸附非常重要。
