KLETOR Ministry of Education, Yangtze University, Wuhan, China.
University of Leicester, University Road, Leicester, LE1 7RH, UK.
Environ Sci Pollut Res Int. 2021 Feb;28(7):8476-8485. doi: 10.1007/s11356-020-11216-x. Epub 2020 Oct 15.
There are two widely used methods to estimate the time taken for phytoremediation for the removal of the target pollutants, i.e., using the data of metal uptake by the harvested parts of the selected plant or using the decrement in average element content between the beginning and end of the remediation. The latter not only depends on sampling points but is also determined by sampling time because even if the soil is initially perfectly homogenized, plant growth itself heterogenizes the soil as time goes by. In this study, phytoremediation was tested on one homogenized soil obtained from various soil samples taken within an e-waste dismantling and recycling site, and the remediation time for different points of bulk and rhizosphere soil was estimated using the two methods. Phytoremediation efficiency, as assessed by the change in soil metal concentrations over 100 days, widely varied depending on which of the six soil compartments of the pot was sampled, and the standard deviations of Cd, Zn, Pb, and Cu increased as the experiment proceeded, indicating the inaccuracy of this method. When applied to rhizosphere soil, this method led to a large overestimation of phytoremediation efficiency for Cd and Zn, which was 81- and 77-fold that was obtained by measuring the actual amount of metals taken up by Noccaea caerulescens. The significant difference between the two methods indicated that the blended soil became heterogeneous during the phytoremediation process because the species extracted metals from different soil parts, manifested by the variation in the metal content. The gap between these two estimation methods decreased when the soil was mixed thoroughly at the end of the experiment. This work shows that calculating the metal decontamination efficiency based on the measurement of the actual amount of metal taken by the plant is more robust than estimating it based on the evolution of soil metal concentration over time. In addition, our study reveals that using N. caerulescens may not be appropriate in Pb- or Cu-polluted soil, since this species mobilized these metals but did not extract them.
有两种广泛使用的方法来估计植物修复去除目标污染物所需的时间，即使用所选植物收获部分的金属吸收数据或使用修复开始和结束时平均元素含量的减少。后者不仅取决于采样点，而且还取决于采样时间，因为即使土壤最初完全均匀化，随着时间的推移，植物生长本身也会使土壤变得不均匀。在这项研究中，在一个从电子废物拆解和回收现场采集的各种土壤样本中获得的均匀土壤上进行了植物修复测试，并使用这两种方法估计了不同体积和根际土壤的修复时间。通过在 100 天内土壤金属浓度的变化评估的植物修复效率，根据从盆中的六个土壤隔室中的哪一个采样而广泛变化，并且 Cd、Zn、Pb 和 Cu 的标准偏差随着实验的进行而增加，表明该方法的不准确性。当应用于根际土壤时，该方法导致 Cd 和 Zn 的植物修复效率被大大高估，这两种金属的效率分别是通过测量 Noccaea caerulescens 实际吸收的金属量所获得的 81 倍和 77 倍。这两种方法之间的显著差异表明，在植物修复过程中，混合土壤变得不均匀，因为该物种从不同的土壤部分提取金属，这表现为金属含量的变化。当实验结束时彻底混合土壤时，这两种估计方法之间的差距会缩小。这项工作表明，基于植物实际吸收的金属量来计算金属净化效率比基于土壤金属浓度随时间的变化来估计要更稳健。此外，我们的研究表明，在 Pb 或 Cu 污染的土壤中使用 N. caerulescens 可能不合适，因为该物种会使这些金属移动，但不会提取它们。
