Keep and promote biodiversity at polluted sites under phytomanagement

Co-culture between Miscanthus x giganteus and Trifolium repens L. to enhance microbial activity, biomass and density in a PAH contaminated technosol

Phytoremediation is a biological soil remediation technique using plants and their associated microorganisms to clean-up contaminated soils and improve soils' quality. We tested whether a co-culture between Miscanthus x giganteus (MxG) and Trifolium repens L. would enhance the soil biological quality. The objective was to determine the influence of MxG in mono- and in co-culture with white clover on the soil microbial activity, biomass and density. MxG was tested in mono- and in co-culture with white clover in a mesocosm over 148 days. The microbial respiration (CO2 production), the microbial biomass and the microbial density of the technosol were measured. Results showed that MxG induced an increase in microbial activity in the technosol compared to the non-planted condition with the co-culture having a greater impact. Regarding the bacterial density, MxG in mono- and in co-culture significantly increased the 16S rDNA gene copy number. The co-culture increased the microbial biomass, the fungal density and stimulated the degrading bacterial population, contrary to the monoculture and the non-planted condition. We can conclude the co-culture between MxG and white clover was more interesting than MxG monoculture in regards to the technosol biological quality and its potential for PAH remediation improvement.

Source apportionment of heavy metals and their effects on the species diversity of plant communities in the Caizi Lake wetland, China

This study investigated the effects of heavy metals on the species diversity of the Xinjian Dyke Wetland, an ecosystem where reclaimed farmlands are being transformed back into wetlands through the introduction of indigenous plants. The sources of soil heavy metals were analyzed, and correlation analyses were conducted to assess the relationships between heavy metal content and biodiversity indices. The results indicated that (1) the mean contents of Hg, Cd, Cu, Zn, As, Cr, and Pb were higher than the control values, with the content of Hg, Cd, Cu, and Zn exceeding the national standard; (2) the soil heavy metals mainly came from pesticides, chemical fertilizer, transportation, sewage irrigation, and the soil matrix; and (3) Hg and As were not significantly correlated with the diversity indices, but there was a highly positive correlation for Cu, Cr, and Pb, and a significant negative correlation for Zn and Cd. Collectively, our findings indicated that heavy metals have different effects on the plant species diversity inXinjian Dyke reconstruction area. The ecological restoration of wetlands from reclaimed farmlands should reasonably increase tolerant species and maximize the ecological niche differentiation of the species. Moreover, functionally redundant species should not be planted.

Field evaluation of industrial non-food crops for phytomanaging a metal-contaminated dredged sediment

Phytomanagement is a concept fit for a bio-based circular economy that combines phytotechnologies and biomass production for non-food purposes. Here, ten annual and perennial industrial non-food crops (Sorghum Biomass 133, Sorghum Santa Fe red, Linum usitatissimum L., Eucalyptus sp., Salix Inger, Salix Tordis, Beta vulgaris L., Phacelia tanacetifolia Benth., Malva sylvestris L., and Chenopodium album L.) were studied under field conditions for phytomanaging a metal (Cd, Cu, Pb, and Zn)-contaminated dredged sediment in the North of France. The crops were selected according to their relevance to pedoclimatic and future climatic conditions, and one or more non-food end-products were proposed for each plant part collected, such as biogas, bioethanol, compost, natural dye, ecocatalyst, and fiber. Based on the soil-plant transfer of metals, eight out of the crops cultivated on field plots exhibited an excluder behavior (bioconcentration factor, BCF < 1), a trait suitable for phytostabilization. However, these crops did not change the metal mobilities in the dredged sediment. The BCF < 1 was not sufficient to characterize the excluder behavior of crops as this factor depended on the total dredged-sediment contaminant. Therefore, a BCF group ranking method was proposed accounting for metal phytotoxicity levels or yield decrease as a complemental way to discuss the crop behavior. The feasibility of the biomass-processing chains was discussed based on these results and according to a survey of available legislation in standard and scientific literature.

Plant growth-promoting bacteria in phytoremediation of metal-polluted soils: Current knowledge and future directions

Soil metal contamination is a major concern due to the ever-rising number of areas afflicted worldwide and the detrimental effects of metals to the environment and human health. Due to their non-biodegradability and toxicity, it is paramount to prevent further metal contamination and remediate the thousands of contaminated sites across the planet. Yet, conventional reclamation based on physical and chemical methods is often expensive, impractical, and triggers secondary pollution issues. Hence, microbe-aided phytoremediation has been gaining significant traction due to its environment-friendly character, cost-effectiveness, and the breakthroughs achieved during the past few decades. Microorganisms are an essential part of natural ecosystems and play a crucial role in their restoration. Indeed, plant-microbe associations in metal-polluted soils are pivotal for plants to tolerate metal toxicity and thrive in these harsh environments. Therefore, improving the understanding of this intricate relationship is invaluable for boosting phytoremediation. In this review, we focus on the potential of plant growth promoting bacteria (PGPB) for enhancing phytoremediation of metal-polluted soils. We discuss the mechanisms employed by microbes to promote plant growth and assist the removal or immobilization of metals in soil, thereby enhancing phytoextraction and phytostabilization, respectively. Microbe-mediated metal removal and detoxification through processes entailing adsorption, chelation, transformation, and precipitation, to list but a few, are also critically examined. Moreover, this work covers the direct and indirect mechanisms used by PGPB to facilitate plant acquisition of nutrients like nitrogen and phosphorus, supply and regulate phytohormones, and exert control over antagonistic microorganisms. Lastly, we provide an outlook on the future directions of microbe-aided phytoremediation and phytomining. Clearly, to fully validate and comprehend the potential of PGPB-aided phytoremediation, a considerable shift from bench-scale to field research is necessary. What's more, it is envisaged that recent advancements in genetic engineering may soon help furthering the efficiency of microbe-assisted phytoremediation.

Facilitation of Morus alba L. intercropped with Sedum alfredii H. and Arundo donax L. on soil contaminated with potentially toxic metals

Tree-herb intercropping is a prospective approach for the ecological remediation of soil contaminated with potentially toxic metals (PTMs). In this study, the facilitation and microbial community response of woody plant Morus alba L. intercropped with Cd/Zn hyperaccumulator Sedum alfredii H. and pioneer plant Arundo donax L. were carried out in the PTM-contaminated soil. The results indicated that the intercropping system can improve M. alba L. growth, as well as increase its PTMs uptake. The dried biomass of M. alba L. in the intercropping system was increased observably (p < 0.05) by 55.1%. Meanwhile, the contents of chlorophyll in M. alba L. leaves, PTMs contents in M. alba L. roots, and the relative abundance of Rhizobiaceae, Singulisphaera, Isosphaeraceae, and Arthrobacter in the M. alba L. rhizosphere were also notably (p < 0.05) enhanced. Meanwhile, the interactions of microorganisms in the intercropped plants rhizosphere might contribute to improving the biological quality of the contaminated soil. Soil sucrase and acid phosphatase activities in the intercropping system were significantly (p < 0.05) increased by 97.03% and 34.91% relative to the control. Furthermore, in the intercropping system, 93.61%, 61.30%, and 79.18% of Cd, Pb, and Zn were extracted by S. alfredii H., 72.16% of Cu was extracted by A. donax L., and 46.38% of Mn was extracted by M. alba L., which indicated that the extraction amounts of PTMs among the intercropped plants were relatively compensated. The results suggested that the tree-herb intercropping might increase the coexistence of plants and facilitate the adaptability for ecological remediation of PTM-contaminated soils.

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.

A risk management framework for Gentle Remediation Options (GRO)

Gentle Remediation Options (GRO) are remediation measures involving plants, fungi, bacteria, and soil amendments that can be applied to manage risks at contaminated sites. Several studies and decision-support tools promote the wider range of benefits provided by GRO, but there is still skepticism regarding GRO implementation. Key issues that need to be better communicated are the various risk mitigation mechanisms, the required risk reduction for an envisioned land use, and the time perspective associated with the risk mitigation mechanisms. To increase the viability and acceptance of GRO, the phytomanagement approach implies the combination of GRO with beneficial green land use, gradually reducing risks and restoring ecosystem services. To strengthen the decision basis for GRO implementation in practice, this paper proposes a framework for risk management and communication of GRO applications to support phytomanagement strategies at contaminated sites. The mapping of the risk mitigation mechanisms is done by an extensive literature review and the Swedish national soil guideline value model is used to derive the most relevant human health exposure pathways and ecological risks for generic green land use scenarios. Results indicate that most of the expected risk mitigation mechanisms are supported by literature, but that knowledge gaps still exist. The framework is demonstrated to support the identification of GRO options for the case study site given two envisioned land uses: biofuel park and allotment garden. A more easily understandable risk management framework, as proposed here, is expected to act as a communication tool to educate decision-makers, regulatory bodies and other stakeholders for better understanding of risk mitigation mechanisms and preliminary timeframes of various GRO, particularly in the early stages of a brownfield redevelopment project.

Environmental conservation value of an endangered species: the case of Cypripedium Japonicum

The South Korean government is seeking information on the environmental conservation value (ECV) of Cypripedium japonicum, a plant on the first-level priority endangered species list of the Korea Ministry of Environment, as well as on the Red List of the International Union for Conservation of Nature. This research paper aims to assess the ECV by employing contingent valuation (CV) to elicit people's willingness to pay (WTP) for its conservation. To achieve this aim, in May 2020, a CV survey of 1,000 interviewees in South Korea was carried out employing a closed-ended question. The average household WTP is estimated to be KRW 3,770 (USD 3.07) per annum and secures statistical significance. From a national point of view, using information on the national population, this value comes to KRW 76.72 billion (USD 62.42 million) per year. Although the cost of conserving the species has not yet been accurately estimated, the ECV seems to be larger than the cost of conservation. Thus, it is socially desirable to conserve Cypripedium japonicum, and the conservation should be carried out in a stable and continuous manner.

Recent Trends in Sustainable Remediation of Pb-Contaminated Shooting Range Soils: Rethinking Waste Management within a Circular Economy

Soil metal contamination in recreational shooting ranges represents a widespread environmental problem. Lead (Pb) is the primary component of traditional ammunition, followed by metalloids such as antimony (Sb) and arsenic (As). Lead-based bullets and pellets deposited on the soil surface are subject to steady weathering; hence, metal(loid)s are released and accumulated in the underlying soil, with potential adverse consequences for ecosystem function and human health. Amongst the currently available environmentally-safe technologies for the remediation of metal-contaminated soils, chemical immobilization is recognized as the most practical and cost-effective one. This technology often uses inorganic and organic amendments to reduce metal mobility, bioavailability and toxicity (environmental benefits). Likewise, amendments may also promote and speed up the re-establishment of vegetation on metal-affected soils, thus facilitating the conversion of abandoned shooting ranges into public green spaces (social benefit). In line with this, the circular economy paradigm calls for a more sustainable waste management, for instance, by recycling and reusing by-products and wastes in an attempt to reduce the demand for raw materials (economic benefit). The objective of this manuscript is to present a state-of-the-art review of the different industrial and agro-food by-products and wastes used for the remediation of metal-contaminated shooting range soils.