Department for Environmental Biotechnology, Helmholtz Centre for Environmental Research-UFZ, Permoserstr. 15, 04318, Leipzig, Germany,
Environ Sci Pollut Res Int. 2014;21(15):9002-15. doi: 10.1007/s11356-013-1685-y. Epub 2013 Apr 16.
At many contaminated field sites in Europe, monitored natural attenuation is a feasible site remediation option. Natural attenuation includes several processes but only the microbial degradation leads to real contaminant removal and very few methods are accepted by the authorities providing real evidence of microbial contaminant degradation activity. One of those methods is the recently developed in situ microcosm approach (BACTRAP®). These in situ microcosms consist of perforated stainless steel cages or PTFE tubes filled with an activated carbon matrix that is amended with 13C-labelled contaminants; the microcosms are then exposed within groundwater monitoring wells. Based on this approach, natural attenuation was accepted by authorities as a site remediation option for the BTEX-polluted site Zeitz in Germany. Currently, the in situ microcosms are restricted to the use inside groundwater monitoring wells at the level of the aquifer. The (classical) system therefore is only applicable on field sites with a network of monitoring wells, and only microbial activity inside the monitoring wells at the level of the aquifer can be assessed. In order to overcome these limitations, a new Direct-Push BACTRAP probe was developed on the basis of the Geoprobe® equipment. With respect to the mechanical boundary conditions of the DP technique, these new probes were constructed in a rugged and segmented manner and are adaptable to various sampling concepts. With this new probe, the approach can be extended to field sites without existing monitoring wells, and microbial activity was demonstrated to be measureable even under very dry conditions inside the vadose zone above the aquifer. In a field test, classical and Direct-Push BACTRAPs were applied in the BTEX-contaminated aquifer at the ModelPROBE reference site Zeitz (Germany). Both types of BACTRAPs were incubated in the centre and at the fringe of the BTEX plume. Analysis of phospholipid fatty acid (PLFA) patterns showed that the bacterial communities on DP-BACTRAPs were more similar to the soil than those found on classical BACTRAPs. During microbial degradation of the (13)C-labelled substrate on the carrier material of the microcosms, the label was only slightly incorporated into bacterial biomass, as determined by PLFA analysis. This provides clear indication for decreased in situ natural attenuation potential in comparison to earlier sampling campaigns, which is presumably caused by a large-scale source remediation measure in the meantime. In conclusion, Direct-Push-based BACTRAPs offer a promising way to monitor natural attenuation or remediation success at field sites which are currently inaccessible by the technique due to the lack of monitoring wells or due to a main contamination present within the vadose zone.
在欧洲的许多污染场地，监测的自然衰减是一种可行的场地修复选择。自然衰减包括多种过程，但只有微生物降解才能真正去除污染物，并且只有少数方法得到当局的认可，为微生物污染物降解活动提供了真正的证据。其中一种方法是最近开发的原位微宇宙方法（BACTRAP®）。这些原位微宇宙由穿孔不锈钢笼或 PTFE 管组成，内部填充了用 13C 标记的污染物的活性炭基质；然后将微宇宙暴露在地下水监测井中。基于这种方法，自然衰减被当局接受为德国 Zeitz 的 BTEX 污染场地的一种场地修复选择。目前，原位微宇宙仅限于在含水层监测井水平的地下水监测井中使用。因此，该系统仅适用于具有监测井网络的场地，并且只能评估含水层监测井水平的微生物活动。为了克服这些限制，在 Geoprobe®设备的基础上开发了一种新的直接推入式 BACTRAP 探头。考虑到 DP 技术的机械边界条件，这些新探头以坚固和分段的方式构建，并可适应各种采样概念。使用这种新探头，可以将该方法扩展到没有现有监测井的场地，并且即使在含水层上方的包气带中非常干燥的条件下，也可以测量微生物活性。在现场测试中，经典和直接推入式 BACTRAP 应用于德国 Zeitz（德国）的 ModelPROBE 参考场地的 BTEX 污染含水层。这两种类型的 BACTRAP 都在 BTEX 羽流的中心和边缘进行了孵育。磷脂脂肪酸（PLFA）模式分析表明，DP-BACTRAP 上的细菌群落与土壤比经典 BACTRAP 上的细菌群落更相似。在微宇宙载体材料上的（13C）标记底物的微生物降解过程中，通过 PLFA 分析仅发现标记物略有掺入细菌生物量。这表明与早期采样活动相比，原位自然衰减潜力降低，这可能是由于同时进行了大规模的源修复措施。总之，基于直接推入式的 BACTRAP 为监测目前由于缺乏监测井或由于包气带中存在主要污染物而无法通过该技术到达的场地的自然衰减或修复成功提供了一种很有前景的方法。
