Phytostabilization of amended soils polluted with trace elements using the Mediterranean shrub: Rosmarinus officinalis

Phytoremediation Assessment of Mentha crispa L. in Zinc-Contaminated Oxisols: Tolerance and Accumulation Dynamics

This study assessed the phytoremediation potential of Mentha crispa L. grown in Oxisol contaminated with varying zinc concentrations. Mentha crispa was cultivated in soil with Zn levels from 0 to 1920 mg kg-1. Growth parameters, Zn concentrations in plant parts, bioaccumulation, and translocation factors were measured. The results revealed that Mentha crispa exhibited a high tolerance to elevated Zn levels, accumulating up to 1875 mg kg-1 in its leaves and 2047 mg kg-1 in its roots. The bioaccumulation factor ranged from 1.2 to 4.5, and the translocation factor ranged from 1.2 to 2.7, indicating effective Zn uptake and distribution within the plant. The metal extraction rates varied across treatments, with the estimated time for Zn removal ranging from 12 to 34 years. These findings underscore the suitability of Mentha crispa as a candidate for phytoremediation of Zn-contaminated tropical soils, particularly Oxisols, which are characterized by high metal adsorption capacity. Additionally, its ability to produce essential oils enhances its viability for integrated environmental and economic applications.

Significance of Arbuscular Mycorrhizal Fungi in Mitigating Abiotic Environmental Stress in Medicinal and Aromatic Plants: A Review

Medicinal and aromatic plants (MAPs) have been used worldwide for thousands of years and play a critical role in traditional medicines, cosmetics, and food industries. In recent years, the cultivation of MAPs has become of great interest worldwide due to the increased demand for natural products, in particular essential oils (EOs). Climate change has exacerbated the effects of abiotic stresses on the growth, productivity, and quality of MAPs. Hence, there is a need for eco-friendly agricultural strategies to enhance plant growth and productivity. Among the adaptive strategies used by MAPs to cope with the adverse effects of abiotic stresses including water stress, salinity, pollution, etc., their association with beneficial microorganisms such as arbuscular mycorrhizal fungi (AMF) can improve MAPs' tolerance to these stresses. The current review (1) summarizes the effect of major abiotic stresses on MAPs' growth and yield, and the composition of EOs distilled from MAP species; (2) reports the mechanisms through which AMF root colonization can trigger the response of MAPs to abiotic stresses at morphological, physiological, and molecular levels; (3) discusses the contribution and synergistic effects of AMF and other amendments (e.g., plant growth-promoting bacteria, organic or inorganic amendments) on MAPs' growth and yield, and the composition of distilled EOs in stressed environments. In conclusion, several perspectives are suggested to promote future investigations.

Potentially Toxic Elements’ Contamination of Soils Affected by Mining Activities in the Portuguese Sector of the Iberian Pyrite Belt and Optional Remediation Actions: A Review

Both sectors of the Iberian Pyrite Belt, Portuguese and Spanish, have been exploited since ancient times, but more intensively during and after the second half of the 19th century. Large volumes of polymetallic sulfide ore were extracted in open pits or in underground works, processed without environmental concerns, and the generated waste rocks and tailings were simply deposited in the area. Many of these mining sites were abandoned for years under the action of erosive agents, leading to the spread of trace elements and the contamination of soils, waters and sediments. Some of these mine sites have been submitted to rehabilitation actions, mostly using constructive techniques to dig and contain the contaminated tailings and other waste materials, but the remaining soil still needs to be treated with the best available techniques to recover its ecosystem functions. Besides the degraded physical structure and poor nutritional status of these soils, they have common characteristics, as a consequence of the pyrite oxidation and acid drainage produced, such as a high concentration of trace elements and low pH, which must be considered in the remediation plans. This manuscript aims to review the results from studies which have already covered these topics in the Iberian Pyrite Belt, especially in its Portuguese sector, considering: (i) soils’ physicochemical characteristics; (ii) potentially toxic trace elements’ concentration; and (iii) sustainable remediation technologies to cope with this type of soil contamination. Phytostabilization, after the amelioration of the soil’s properties with organic and inorganic amendments, was investigated at the lab and field scale by several authors, and their results were also considered.

Implication of phytometabolites on metal tolerance of the pseudo-metallophyte -Rosmarinus officinalis- in a Mediterranean brownfield

This study highlights the trace metal and metalloid (TMM) accumulation in Rosmarinus officinalis L. and its chemical responses when exposed to high levels of contamination. R. officinalis individuals growing along a gradient of mixed TMM soil pollution, resulting from past industrial activities, were analysed. Several plant secondary metabolites, known to be involved in plant tolerance to TMM or as a plant health indicator, were investigated. The levels of thiol compounds and phytochelatin precursors (cysteine and glutathione) in the shoots were measured in the laboratory, while a portable non-destructive instrument was used to determine the level of phenolic compounds and chlorophylls directly on site. The level of Pb, As, Sb and Zn contaminations within the soil and plants was also determined. The results highlighted a decrease of TMM translocation with increases of soil contamination. The concentration of TMM in the shoots followed the Mitscherlich equation and reached a plateau at 0.41, 7.9, 0.37, 51.3 mg kg^-1 for As, Pb, Sb and Zn, respectively. In the shoots, the levels of thiols and phenols were correlated to concentrations of TMM. Glutathione seems to be the main thiol compounds involved in the tolerance to As, Pb and Sb. Phenols indices, using non-destructive measurements, may be considered as an easy way to establish a proxy to estimate the TMM contamination level of the R. officinalis shoots. The study highlights metabolic processes that contribute to the high potential of R. officinalis for phytostabilisation of TMM in contaminated areas in the Mediterranean.

Suitability of aromatic plants for phytoremediation of heavy metal contaminated areas: a review

This review briefly elucidates the research undertaken and benefits of using aromatic plants for remediation of heavy metal polluted sites. A sustainable approach to mitigate heavy metal contamination of environment is need of the hour. Phytoremediation has emerged to be one of the most preferable choices for combating the metal pollution problem. Aromatic plants can be used for remediation of contaminated sites as they are non-food crops thus minimizing the risk of food chain contamination. Most promising aromatic plants for phytoremediation of heavy metal contaminated sites have been identified from families - Poaceae, Lamiaceae, Asteraceae, and Geraniaceae. They act as potential phytostabilisers, hyper accumulators, bio-monitors, and facultative metallophytes. Being high value economic crops, monetary benefits can be obtained by growing them in tainted areas instead of food crops. It has been observed that heavy metal stress enhances the essential oil percentage of certain aromatic crops. Research conducted on some major aromatic plants in this context has been highlighted in the present review which suggests that aromatic plants hold a great potential for phytoremediation. It has been reported that essential oil from aromatic crops is not contaminated by heavy metals significantly. Thus, aromatic plants are emerging as an ideal candidate for phytoremediation. Highlights • Aromatic plants hold a great potential for phytoremediation of heavy metal contaminated sites. • Being high value economic crops, monetary benefits can be obtained by growing them in contaminated areas instead of food crops. • Research done on some major aromatic plants in this context has been highlighted in the present review.

Soil-plant relationships and contamination by trace elements: A review of twenty years of experimentation and monitoring after the Aznalcóllar (SW Spain) mine accident

Soil contamination by trace elements (TE) is a major environmental problem and much research is done into its effects on ecosystems and human health, as well as into remediation techniques. The Aznalcóllar mine accident (April 1998) was a large-scale ecological and socio-economic catastrophe in the South of Spain. We present here a literature review that synthesizes the main results found during the research conducted at the affected area over the past 20years since the mine accident, focused on the soil-plant system. We review, in depth, information about the characterization of the mine slurry and contaminated soils, and of the TE monitoring, performed until the present time. The reclamation techniques included the removal of sludge and soil surface layer and use of soil amendments; we review the effects of different types of amendments at different spatial scales and their effectiveness with time. Monitoring of TE in soil and their transfer to plants (crops, herbs, shrubs, and trees) were evaluated to assess potential toxicity effects in the food web. The utility of some plants (accumulators) with regard to the biomonitoring of TE in the environment was also evaluated. On the other hand, retention of TE by plant roots and their associated microorganisms was used as a low-cost technique for TE stabilization and soil remediation. We also evaluate the experience acquired in making the Guadiamar Green Corridor a large-scale soil reclamation and phytoremediation case study.

Potential of Eucalyptus camaldulensis for phytostabilization and biomonitoring of trace-element contaminated soils

Soil pollution by trace elements (TEs) from mining and industrial activity is widespread and presents a risk to humans and ecosystems. The use of trees to immobilize TEs (phytostabilization) is a low-cost and effective method of soil remediation. We aimed to determine the chemical composition of leaves and flower buds of Eucalyptus camaldulensis in seven sites along the Guadiamar River valley (SW Spain), an area contaminated by a mine-spill in 1998. E. camaldulensis trees in the spill-affected area and adjacent non affected areas were growing on a variety of soils with pH from 5.6 to 8.1 with low concentration of plant nutrients. The spill affected soils contained up to 1069 mg kg^-1 of As and 4086 mg kg^-1 of Pb. E. camaldulensis tolerated elevated TE concentrations in soil and, compared to other species growing in the same environment, had low TE concentrations in the aerial portions. Besides tolerance to soil contamination, E. camaldulensis had low bioaccumulation coefficients for soil contaminants. TE concentrations in the aboveground portions were below levels reported to be toxic to plants or ecosystems. Flower buds had even lower TE concentrations than leaves. Despite the relatively low concentration of TEs in leaves they were significantly correlated with the soil extractable (0.01 M CaCl₂) Cd, Mn and Zn (but not Cu and Pb). The general features of this tree species: tolerance to impoverished and contaminated soils, fast growth and deep root system, and low transfer of TEs from soil to aboveground organs makes it suitable for phytostabilization of soils contaminated by TEs. In addition, eucalyptus leaves could be used for biomonitoring the soil extractability of Cd, Mn and Zn but not Cu or Pb.

Soil plant interactions of Populus alba in contrasting environments

The effects of the Populus alba tree on different biochemical soil properties, growing in a contaminated area, were studied for two years under field conditions. Two types of trace element contaminated soils were studied: a neutral contaminated soil (NC) and an acid contaminated soil (AC). One neutral non-contaminated area was studied as control. Soil samples were collected at depths of 0-20 cm and 20-40 cm. Leaves and litter samples were analysed. The addition of organic matter, through root exudates and litter, contributed to an increase in soil pH, especially in acid soil. Microbial Biomass Carbon (MBC) was significantly increased by the presence of the trees in all studied areas, especially in the upper soil layer. Similar results were also observed for protease activity. Both MBC and Protease activity were more sensitive to contamination than β-glucosidase activity. These changes resulted in a decrease of available trace element concentrations in soil and in an improvement of soil quality after a 2-year study. The total concentration of Cd and Zn in soil did not increase over time due to litter deposition. Analysis of P. alba leaves did not show a significant nutritional imbalance and trace element concentrations were normal for plants, except for Cd and Zn. These results indicate that P. alba is suitable for the improvement of soil quality in riparian contaminated areas. However, due to the high Cd and Zn concentrations in leaves, further monitoring of this area is required.

Transfer of metals and metalloids from soil to shoots in wild rosemary (Rosmarinus officinalis L.) growing on a former lead smelter site: human exposure risk

This study aimed at estimating exposition risks to wild rosemary used as herbs in the contaminated area of the former smelting factory of L'Escalette (South of Marseille, France). Metals and metalloids i.e. Pb, As, Sb, Zn, and Cu concentrations were analyzed in soils and in rosemary aerial parts (stems and leaves) on two sites: one heavily contaminated and the other far away from the pollution source, considered as reference. The metal and metalloid transfer into water during the brewing process of herbal tea was also determined. A mixed contamination by the above-cited contaminants was demonstrated in soils of the factory site, with average concentrations of 9253, 1127, 309, 2698 and 32 mg/kg for Pb, As, Sb, Zn and Cu, respectively. However, metals and metalloids' transfer in rosemary aerial parts was limited, as bioaccumulation factors were under 1. Thus, Pb, As and Cu concentrations in leaves were below international regulation limits concerning ingestion of medicinal herbs (no regulation values available for Sb and Zn). This study highlighted that, if contaminated rosemary leaves were ingested, health risks may be limited since acceptable daily intake (ADI) for Pb, As, Sb and Cu (no ADI value available for Zn) will only be reached if very high quantities are consumed. Furthermore, we aimed to establish if this mixed contamination could alter rosemary's essential oil quality, and thereby the compositions of essential oils obtained from individuals on the heavily contaminated soil were compared to those obtained from the reference population. An increased biosynthesis of antioxidant compounds was favored in essential oils from rosemary individuals growing in contaminated site. Although the health risk of a long-term exposition of low level of the mixed contamination by rosemary ingestion is not easy to elucidate, the use of rosemary essential oils from contaminated site appears as safe.