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. 2017 Jan 9;12(1):e0169688.
doi: 10.1371/journal.pone.0169688. eCollection 2017.

Effects of Pulp and Na-Bentonite Amendments on the Mobility of Trace Elements, Soil Enzymes Activity and Microbial Parameters Under Ex Situ Aided Phytostabilization

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Effects of Pulp and Na-Bentonite Amendments on the Mobility of Trace Elements, Soil Enzymes Activity and Microbial Parameters Under Ex Situ Aided Phytostabilization

Daniel Wasilkowski et al. PLoS One. .
Free PMC article


The objective of this study was to explore the potential use of pulp (by-product) from coffee processing and Na-bentonite (commercial product) for minimizing the environmental risk of Zn, Pb and Cd in soil collected from a former mine and zinc-lead smelter. The effects of soil amendments on the physicochemical properties of soil, the structural and functional diversity of the soil microbiome as well as soil enzymes were investigated. Moreover, biomass of Festuca arundinacea Schreb. (cultivar Asterix) and the uptake of trace elements in plant tissues were studied. The outdoor pot set contained the following soils: control soil (initial), untreated soil (without additives) with grass cultivation and soils treated (with additives) with and without plant development. All of the selected parameters were measured at the beginning of the experiment (t0), after 2 months of chemical stabilization (t2) and at the end of the aided phytostabilization process (t14). The obtained results indicated that both amendments efficiently immobilized the bioavailable fractions of Zn (87-91%) and Cd (70-83%) at t14; however, they were characterized by a lower ability to bind Pb (33-50%). Pulp and Na-bentonite drastically increased the activity of dehydrogenase (70- and 12-fold, respectively) at t14, while the activities of urease, acid and alkaline phosphatases differed significantly depending on the type of material that was added into the soil. Generally, the activities of these enzymes increased; however, the increase was greater for pulp (3.5-6-fold) than for the Na-bentonite treatment (1.3-2.2-fold) as compared to the control. Soil additives significantly influenced the composition and dynamics of the soil microbial biomass over the experiment. At the end, the contribution of microbial groups could be ordered as follows: gram negative bacteria, fungi, gram positive bacteria, actinomycetes regardless of the type of soil enrichment. Conversely, the shift in the functional diversity of the microorganisms in the treated soils mainly resulted from plant cultivation. Meanwhile, the highest biomass of plants at t14 was collected from the soil with Na-bentonite (6.7 g dw-1), while it was much lower in a case of pulp treatment (1.43-1.57 g dw-1). Moreover, the measurements of the heavy metal concentrations in the plant roots and shoots clearly indicated that the plants mainly accumulated metals in the roots but that the accumulation of individual metals depended on the soil additives. The efficiency of the accumulation of Pb, Cd and Zn by the roots was determined to be 124, 100 and 26% higher in the soil that was enriched with Na-bentonite in comparison with the soil that was amended with pulp, respectively. The values of the soil indices (soil fertility, soil quality and soil alteration) confirmed the better improvement of soil functioning after its enrichment with the pulp than in the presence of Na-bentonite.

Conflict of interest statement

The authors have declared that no competing interests exist.


Fig 1
Fig 1. The scheme of experimental design.
Fig 2
Fig 2. The plant biomass collected from the untreated and treated soils at t14.
Means with the same letter(s) are not significant at p <0,05 within parameter between the untreated and treated soils.
Fig 3
Fig 3
Projection of individual phospholipid fatty acids along PC1 and PC2 (A, B, C) and the PLFA profiles of the control, untreated and treated soils (A1, B1, C1) at t0 (A, A1), t2 (B, B1) and t3 (C, C1). The samples with similar PC1 and PC2 values are included into a cluster.
Fig 4
Fig 4. The activity of microorganisms in tested soils at t0—t14 (mean±SD; n = 3).
The response of each compound was presented as a color scale ranging from dark green (0 OUs) to burgundy (1500 OUs).
Fig 5
Fig 5
The activity of dehydrogenase (A), urease (B), acid phosphatase (C) and alkaline phosphatase (D) in the control, untreated and treated soils at t0–t14 (mean±SD; n = 3). Means with the same letter(s) are not significant at p <0,05 within tested parameter between the control, untreated and treated soils.
Fig 6
Fig 6. Cluster display of physicochemical and biological parameters of the control, untreated and treated soils at t0, t2 and t14 (mean±SD; n = 3).
Legend: Zn–bioavailable fraction of Zn; Pb–bioavailable fraction of Pb; Cd–bioavailable fraction of Cd; M–moisture; OM–organic matter; Deh–dehydrogenase activity; Pac–acid phosphatase activity; Pal–alkaline phosphatase activity; U–urease activity; AA–amines/amides; Pol–polymers; A–amino acids; CA–carboxylic acids; CH–carbohydrates; BB–bacterial biomass; BA–actinomycetes biomass; FB–fungal biomass; TB–total biomass.

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Grant support

This project was funded by National Science Centre, Poland No. 2015/17/N/NZ9/01109. The funders had no role in study, design, data collection and analysis, decision to publish, or preparation of the manuscript.