Effects of wood bark and fertilizer amendment on trace element mobility in mine soils, Broken Hill, Australia: implications for mined land reclamation

Use of waste materials to prevent tetracycline antibiotics toxicity on the growth of soil bacterial communities

The increase of concentrations of tetracycline antibiotics in agricultural soils worldwide is of special concern, due to its potential toxic effects on soil bacterial communities. In the present work, the reuse of two waste/by-product materials as soil amendments was tested as a preventive practice for reducing tetracycline antibiotics toxicity in soils. Pine bark (PB), with high percentage of organic carbon, and crushed mussel shell (CMS), a frequent natural liming material, were added to 4 soils in doses 0, 6, 12 and 48 g of by-product per kg^-1 of soil (dry weight) of each one (separately). The soils and soil-waste mixtures were then spiked with tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC). After one day of incubation, the bacterial growth was estimated in soils and soil-mixtures using the leucine incorporation technique. The addition of PB to the soils showed two different behaviors, depending on the antibiotics. The toxicity of TC and OTC decreased with the addition of PB (toxicities going from 6 to 25% and from 5 to 36%, respectively). However, CTC toxicity did not change, or even increased in response to the PB amendment. Regarding soil amendment with CMS, it was not effective to prevent the toxicity of any of the three antibiotics studied.

Phosphate treatment alleviated acute phytotoxicity of heavy metals in sulfidic Pb-Zn mine tailings

Phytostabilization of sulfidic PbZn tailing landscapes may be one of interim options of tailings management, but which is limited by acute phytotoxicity of heavy metals in the tailings. The present study aimed to investigate the effectiveness of soluble phosphate (i.e., K₂HPO₄) in immobilizing soluble Pb, Cd and Zn and lowering their acute phytotoxicity. The addition of soluble phosphate improved the growth of native plants Acacia chisholmii and survival rate of A. ligulata, where the latter exhibited 100% survival rate. This was in contrast to effects of conventional organic amendment in the tailings on metal solubility (e.g., elevated metal levels in porewater) and plant survival (e.g., only 42%). Organic amendment with mulch did not lower the levels of water-soluble Cd, Pb and Zn and their concentrations in plant tissues after 56 days of plant growth in the treatment. In contrast, the tailings amended with K₂HPO₄ significantly decreased metal concentrations in the porewater and plant tissues by about 80-92% and 56-88%, respectively. The metal immobilization by phosphate was due to the formation of insoluble or sparingly soluble metal (Pb, Cd and Zn)-phosphate minerals in the tailings with circumneutral pH conditions, as revealed by using X-ray diffraction and scanning electron microanalyses. The reduced metal concentrations in roots and shoots of Acacia species after direct root contact with the K₂HPO₄ amended tailings suggested that metals (i.e., Pb, Cd and Zn) were effectively immobilized by the phosphate treatment of the tailings. These findings indicate that addition of high dosage of soluble phosphate may provide a low cost option to treat sulfidic PbZn tailings for rapid phytostabilization of the tailings surface, as an interim option to manage environmental risks of sulfidic PbZn tailings.

Effect of fresh and mature organic amendments on the phytoremediation of technosols contaminated with high concentrations of trace elements

Organic compounds resulting from the decomposition of organic amendments are used in the remediation of trace element (TE) contaminated soils. The mobility, phytoavailability and soil exposure intensity of molybdenum (Mo), chromium (Cr), zinc (Zn), copper (Cu), Cobalt (Co) and Arsenic (As) were evaluated in the phytoremediation of contaminated technosols after the addition of two organic matter types, fresh ramial chipped wood (RCW) and composted sewage sludge (CSS). The experiment consisted of nine main treatment blocks: (A) 3X unamended soil (NE), (B) 3X soil amended with RCW and (C) 3X soil amended with mature CSS. Total dissolved TE concentrations were determined in soil pore water (SPW) sampled by Rhizon samplers. The soil exposure intensity was assessed by standard Chelex 100 DGT (diffusive gradient in thin films) probes. TE phytoavailability was characterized by growing dwarf beans on potted soils and analyzing their foliar TE concentrations. The results of the present study indicate that the addition of fresh RCW and CSS has a positive effect on contaminated technosols. RCW decreased the mobility of all the studied TE in the SPW, whereas CSS reduced the mobility of Mo, Cr and Co, while it increased the mobility of Zn, Cu and As compared with the NE soil. The Zn soil exposure intensity assessed by DGT was not significantly changed by the addition of RCW and CSS, while the Cr soil exposure intensity was significantly decreased after RCW addition compared with the soil treated with CSS and the NE soil. In contrast Cu and Co were non labile in the three soils. Both RCW and CSS decreased the foliar concentration and the mineral mass of Mo, Zn, Cr, As and Co in the bean leaves but increased the foliar Cu concentration.

Evaluation of different amendments to stabilize antimony in mining polluted soils

Soil pollution with antimony is of increasing environmental concern worldwide. Measures for its control and to attenuate the risks posed to the ecosystem are required. In this study the application of several iron and aluminium oxides and oxyhydroxides as soil amendments was evaluated in order to assess their feasibility to stabilize Sb in mining polluted soils. Mine soils with different pollution levels were amended with either goethite, ferrihydrite or amorphous Al oxide at various ratios (0-10%). The effectiveness of such treatments was assessed by both batch and column leaching tests. The use of ferrihydrite or amorphous Al oxide proved to be highly effective to stabilize Sb. Immobilization levels of 100% were found when doses of 5% ferrihydrite or 10% amorphous Al oxide were applied, regardless of the soil Sb load. Column leaching studies also showed a high Sb leaching reduction (>75%) when soils were amended with 1% ferrihydrite or 5% amorphous Al oxide. Moreover, such treatments proved to simultaneously immobilize As and Pb in a great extent when soils were also polluted with such toxic elements.

Importance of dynamic soil properties in metal retention: an example from long-term Cu partitioning and redistribution studies using model systems

The effect of initial conditions and reaction pathways in the long term solid-solution partitioning and solid-phase distribution of Cu among ferrihydrite, leaf compost (LC), and montmorillonite (K-SWy2) were established using compartmentalized batch reactors by varying the sequence of mixing of the sorbents. Copper was allowed to react with a single solid phase for 30 days (1st equilibration) before introducing the other two solid phases and equilibration for 8 additional months (2nd equilibration). The systems were labeled Fe-Ox, Organic, or Smectitic reflecting the single initial solid phase present during the first equilibration. Total dissolved Cu and total Cu in individual solid phases were determined as a function of time during the first and second equilibrations. Results showed that different initial conditions elicited different dynamic responses where the generation of dissolved organic carbon (DOC) and diffusion of colloidal ferrihydrite seemed to influence the long-term partitioning and distribution of Cu. Trends in total dissolved Cu for the systems at the end of the first equilibration were Fe-Ox > Organic > Smectitic, while at the end of the second equilibration the organic system was the least effective in the removal of Cu from solution (Organic > Fe-Ox ≈ Smectitic). Furthermore, our results indicated Cu redistribution toward organic matter and montmorillonite, with small amounts of Cu retained by ferrihydrite. These results are attributed to reaction pathways where the formation of soluble Cu-organic complexes and colloidal Cu-ferrihydrite, and their subsequent reaction with the solids present in the systems, were operative. The experiments reported herein show dynamic properties dictate Cu reaction pathways in multiphase-multicomponent systems and might help to explain unexpected higher mobility of metals after soil remediation.