Does Samarco's spilled mud impair the growth of native trees of the Atlantic Rainforest?

Growth-tolerance tradeoffs shape the survival outcomes and ecophysiological strategies of Atlantic Forest species in the rehabilitation of mining-impacted sites

The initial performance of seedlings of tree species from different functional groups, regarding the growth-defense tradeoff, might determine its long-term success during the rehabilitation of mining areas. We monitored the field performance of six native tree species of the Atlantic Forest in the Fundão dam tailing that has been under rehabilitation for 35 months. Additionally, we explored the morphophysiological traits driving the superior performance of three species. The study examined the survival strategies of pioneer species (Anadenanthera colubrina, Bixa orellana, Peltophorum dubium) and secondary species (Cedrela fissilis, Handroanthus impetiginosus, Handroanthus serratifolius), as well as the photosynthetic, nutritional, and antioxidant metabolism of the successful species. Most species accumulated excessive Fe in their leaves, except for the pioneer species A. colubrina and P. dubium. However, the nutritional status of the plants, concerning leaf nutrient concentration, was adequate for their growth in the waste. The species A. colubrina, C. fissilis, and H. serratifolius exhibited poor physiological performance, primarily due to substrate compaction and excessive foliar metal concentrations. The successful performance of P. dubium was attributed to avoidance mechanisms, allowing a cost-effective growth-defense tradeoff, thus maintaining photosynthetic efficiency at the expense of energy investment in antioxidant protection. The excess Fe allocation in the photosynthetic tissues of B. orellana was linked to a greater investment in antioxidant metabolism, which was related to the protection of the photosynthetic machinery. The Fe hyperaccumulation in H. impetiginosus led to increased oxidative damage, which was mitigated by investments in tolerance mechanisms, including photosynthetic adjustments (stomatal limitation, non-photochemical energy dissipation), as well as the activation of the enzymatic antioxidant system. The persistence and success of the Atlantic Forest tree species were not related to their ecological successional classification. Instead, it was the different mechanisms of tolerance and avoidance that allowed both pioneer and secondary species to thrive in the impacted area.

An overview of soil and plant assessment for predicting site quality and recovery strategies of one the largest tailings dam failures worldwide

Brazil's Fundão dam collapse is one of the world's largest disasters of tailing dam failures. Previous research has evaluated toxic metals and non-metals (Cd, Cr, Ni, Pb, As, Hg) in the same soil samples used in this study, and results have indicated that only Fe and Mn concentrations increased above the original baseline (Melo et al., 2023). Consequently, the present study's focus has shifted towards assessing and integrating changes in soil quality regarding chemical fertility and morphological, physical, and mineralogical attributes in the floodplains post-dam collapse. Soil samples from 0 to 0.2 and 0.2-0.4 m depths, and samples of Urochloa sp. were collected along ten transects, spanning 100 km perpendicular to the Doce River channel. This sampling strategy targeted specific landscape positions including areas affected by deposited iron tailings (DIT), soil tailing mixture (STM), and control soil (CS) devoid of iron tailing interference. Results showed no discernible alterations in Ca, Mg, K, and P concentrations in Urochloa sp., and the most severe negative impacts observed regarded the replacement of kaolinitic pre-disaster matrix for hematitic matrix, reduction in organic carbon, and the prevalence of sand and silt particles. These factors collectively contributed to triggering: (i) decrease in chemical fertility and cation exchange capacity and (ii) significant decline in physical quality, evidenced by increased density and reduced total porosity and macroporosity. Addressing these adverse effects would require the augment of organic matter levels and offset the dominance of the hematitic matrix in the DIT. Furthermore, it is imperative to decompact the DIT by mechanized or plant cultivation means.

Residues from the Fundão Dam Accident in Brazil and their Effects on Photosynthetic Efficiency of Two Restinga Plant Species

In 2015, a breach in the Fundão Dam in Mariana (Minas Gerais State, Brazil) resulted in the release of contaminated tailings into the Doce River basin. This accident increased the concentrations of arsenic (As), lead (Pb), cadmium (Cd), vanadium (V), and manganese (Mn) in the soil, posing a potential hazard to the physiology of native species. The purpose of this study was to assess whether chlorophyll a fluorescence (ChlF) in Allagoptera arenaria and Guapira pernambucensis changed following this accident when tested under different precipitation regimes in relation to soil properties and metal(loid) absorption. Our research was conducted in two sites located in the state of Espírito Santo in southeastern Brazil. Five independent biological replicates of A. arenaria and G. pernambucensis were selected at each site for nutritional and chlorophyll a fluorescence analysis. Five years after the dam rupture, A. arenaria and G. pernambucensis had absorbed As, Pb, and V. The increased amounts of metal(loid)s absorbed did not significantly impair the OJIP curve configuration for either species during the evaluated periods. However, A. arenaria at Biological Reserve of Comboios (RBC) during the rainy season showed increases in the values of maximum quantum yield of PSII photochemistry (φP0) and total performance index on absorption basis (PITOTAL). These changes indicated more efficient tolerance mechanisms for increases in the concentrations of As, Pb, and V than those observed in G. pernambucensis. It was concluded that A. arenaria and G. pernambucensis exhibited an acclimation strategy in response to increased absorption of metal(loid)s.

Integrated environmental assessment of iron ore tailings in floodplain soils and plants after the Fundão Dam disaster in Brazil

Previous studies of the Doce River basin (Brazil) seem to be contradictory regarding the contamination of soils with potentially harmful elements (PHE). This research aimed to perform an integrated assessment of PHE in the soil-plant-tailing system from the area most affected by the iron waste after the Fundão Dam disaster in 2015. Different fractions of PHE (exchangeable, nonexchangeable, reducible, and pseudo-total) were determined on deposited iron waste (DIW), soil waste mixture (SWM), and control soil (CS) samples. Total contents of PHE in Poaceae were also determined, and Allium cepa bioassays were performed to determine DIW and CS cytotoxicity and/or genotoxicity to plants. The Fe and Mn contaminations were the only ones related to the deposition of DIW on floodplains, and other harmful element content (such as As, Hg, Ni, Cd, Cr, and Pb) was not found above baseline values for soils. In addition, a significant part of the Fe and Mn in DIW is readily available or subject to acidification and prolonged flood reduction processes. The high available content of Fe favored its excessive accumulation by Brachiaria. The DIW chemical conditions reduced biological functions of A. cepa under a controlled environment. However, more drastic effects, such as genetic damage, were not seen. The postdisaster action of covering DIW with CS resulted in undesirable enrichment of Pb on the floodplain soils. The integrated results allow the conclusion that the iron waste is not a time bomb for PHE contamination of soils between the Fundão and Risoleta Neves Hydroelectric Dam (~100 km away from Fundão). Integr Environ Assess Manag 2024;20:117-132. © 2023 SETAC.

Removal of heavy metals using Iris species: A potential approach for reclamation of heavy metal-polluted sites and environmental beautification

Globally, the number of heavy metal (HM)-polluted sites has increased rapidly in recent years, posing a serious threat to agricultural productivity, human health, and environmental safety. Hence, it is necessary to remediate HM-polluted sites to increase cultivatable lands for agricultural productivity, prevent hazardous effects to human health, and promote environmental safety. Removal of HMs using plants (phytoremediation) is a promising method as it is eco-friendly. Recently, ornamental plants have been widely used in phytoremediation programs as they can simultaneously eliminate HMs and are aesthetically pleasing. Among the ornamental plants, Iris species are frequently used; however, their role in HM remediation has not been reviewed yet. Here, the importance of Iris species in the ornamental industry and their different commercial aspects are briefly described. Additionally, the mechanisms of how the plant species absorb and transport the HMs to the above-ground tissues and tolerate HM stress are highlighted. The variation in HM remediation efficiency depending on the plant species, HM type and concentration, use of certain supplements, and experimental conditions are also discussed. Iris species are able to remove other hazards as well, such as pesticides, pharmaceutical compounds, and industrial wastes, from polluted soils or waste-water. Owing to the valuable information presented in this review, we expect more applications of the species in reclaiming polluted sites and beautifying the environment.

Revegetation of an area impacted by iron ore tailings: evaluating fertilization alternatives in native pioneer and secondary trees

The iron ore tailings released into the Rio Doce basin after the Fundão dam collapse (Brazil), suppressed a large extent of local vegetation. The use of native species and appropriate fertilization techniques, with less economic and environmental impact, must be considered in the process for the restoration of affected areas by the tailings. For this purpose, six native tree species, pioneer (Anadenanthera colubrina, Bixa orellana, and Peltophorum dubium) and secondary (Cedrela fissilis, Handroanthus impetiginosus, and Handroanthus serratifolius), were selected. We used different conditions of fertilization: (1) inorganic fertilization, (2) inoculation with arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria, (3) combined treatment (fertilizer + inoculum), to evaluate leaf nutrient concentrations, photosynthetic capacity [chlorophyll index, maximum quantum efficiency of photosystem II (Fv/Fm) and gas exchange variables], and oxidative metabolism (H₂O₂, MDA, and antioxidant enzymes). Inoculation resulted in higher concentrations of foliar nitrogen, especially in pioneer species. In all treatments, the secondary species exhibited iron values considered phytotoxic, but showed reduced photosynthetic capacity only when inoculated. The highest concentrations of MDA were observed in inoculated plants of both successional groups. The antioxidant system proved to be effective in preventing oxidative damage for most of the species. These results showed that the use of inoculum can be considered an ecological alternative to inorganic additives in the area affected by iron ore tailings. Despite presenting different photosynthetic and antioxidant strategies, the evaluated species demonstrated potential for use in tailings revegetation projects.

Diazotrophic bacteria improve Hymenaea courbaril seedlings growth and survival in iron mine tailings

One of the largest accidents with mine tailings happened in Brazil in 2015, with the rupture of the Fundão dam, and the physical characteristics of these tailings make it difficult to recover degraded areas. Hymenaea courbaril is a tree species native to Brazil that has low nutritional and water requirements, besides its capacity for survival in contaminated environments. In this study we hypothesized that inoculation with diazotrophs would improve the growth and physiology of H. courbaril in tailings, favoring the reforestation process aiming the recovery of the accident site. Every 20 days for 60 days, we investigated the morphophysiology of H. courbaril grown in iron mine tailings or soil, with the addition of nitrate (N-positive control), non-inoculation (negative control) or inoculation with native diazotrophic bacteria previously isolated from the tailings (UNIFENAS100-569; UNIFENAS100-654 and UNIFENAS100-638). We found that H. courbaril has survival capacity under mine tailings, with no growth alteration in the tailings, although there were signs of reduced ability for photoprotective responses. Inoculation with diazotrophic bacteria improved physiological aspects of H. courbaril and strain UNIFENAS100-638 was the most effective in favoring total growth of plants, net photosynthetic rate and root morphology under mine tailings. The survival capacity and growth of H. courbaril indicates the possibility of its use for reforestation in areas degraded by mine tailings. Further studies are necessary in field conditions and with a larger experimental period to more thoroughly understand H. courbaril tolerance.

Cultivating vegetables in tailings from the Fundão dam collapse: metal accumulation and risks to food safety

A great amount of iron ore tailings from the collapse of the Fundão dam in Southeast Brazil was deposited in an extensive agricultural area. The presence of this material creates insecurity for the resumption of agricultural activities, especially the cultivation of vegetables, which can accumulate metals at potentially toxic levels. In this study, two vegetables consumed in the affected area, arugula and radish, were cultivated in tailings and in soil. Productivity, photosynthetic pigment content, photosynthetic performance, metal accumulation, and the possible risk to food safety were analyzed. The productivity of both vegetables, arugula and radish, did not differ between cultivation in tailings and in soil. There were no differences in pigment content nor substantial differences in the photosynthetic parameters of plants grown in the two substrates. Plants grown in tailings had higher Fe, Mn, and Na contents than those grown in soil, reflecting the higher levels of these elements in the former. There were no visual signs of metal toxicity for plants grown in the tailings. The levels of metals potentially ingested through estimated consumption of arugula and radish grown in the tailings were below the maximum allowable limits for human consumption. In addition, calculated risk indices suggest a low potential for harm to the health of consumers of cultivated vegetables in the tailings. The results presented here suggest that agricultural cultivation in the tailings is viable and contribute to the resumption of vegetable cultivation in the region affected by the tailings released with the collapse of the Fundão dam.

Fertilization assures mineral nutrition but does not overcome the effects of Fe accumulation in plants grown in iron ore tailings

The rupture of Fundão dam was the biggest environmental disaster of the worlds' mining industry, dumping tons of iron ore tailings into the environment. Studies have shown that the Fundão dam's tailings are poor in nutrients and have high Fe and Mn concentration. In this context, our objective was to evaluate the growth performance of two native tree species (Bowdichia virgilioides and Dictyoloma vandellianum) in two treatments: fertilized soil and fertilized tailings. We hypothesize that the high concentrations of iron and manganese in the tailings can impair the growth performance of plants by interfering with the absorption of nutrients made available through fertilization. Soil and tailings samples were collected in the municipality of Barra Longa (MG, Brazil), and then fertilized with mixed mineral fertilizer ("Osmocote Plus 15-9-12" at 7.5 g L^-1). The experiment was conducted for 75 days in a greenhouse using 180 cm³ tubes. We evaluate chlorophyll content, maximal PSII quantum yield, root length, shoot length, root:shoot ratio, leaf area, specific leaf area and leaf area ratio, dry mass, macro- and micronutrients concentration in the tissues, and metal translocation factor. Although assuring the adequate levels of the main nutrients to plant growth (N, P, K, Ca, and Mg), the fertilization did not reverse the negative effect of tailing on these species. The high concentration of Fe in the tissues associated with less biomass production, lower plant height, smaller leaf area, bigger specific leaf area, and reduced chlorophyll content indicates a probable phytotoxic effect of iron present in the tailings for D. vandellianum. Our results base further field evaluations and longer experiments, which will facilitate the understanding of the performance of tree species submitted to tailings with fertilization. So far, this study suggests that B. virgilioides are more tolerant to excess Fe from the tailings of Fundão dam than D. vandellianum.

Phytoremediation by ornamental plants: a beautiful and ecological alternative

Phytoremediation is an eco-friendly and economical technology in which plants are used for the removal of contaminants presents in the urban and rural environment. One of the challenges of the technique is the proper destination of the biomass of plants. In this context, the use of ornamental plants in areas under contamination treatment improves landscape, serving as a tourist option and source of income with high added value. In addition to their high stress tolerance, rapid growth, high biomass production, and good root development, ornamental species are not intended for animal and human food consumption, avoiding the introduction of contaminants into the food web in addition to improving the environments with aesthetic value. Furthermore, ornamental plants provide multiple ecosystem services, and promote human well-being, while contributing to the conservation of biodiversity. In this review, we summarized the main uses of ornamental plants in phytoremediation of contaminated soil, air, and water. We discuss the potential use of ornamental plants in constructed buffer strips aiming to mitigate the contamination of agricultural lands occurring in the vicinity of sources of contaminants. Moreover, we underlie the ecological and health benefits of the use of ornamental plants in urban and rural landscape projects. This study is expected to draw attention to a promising decontamination technology combined with the beautification of urban and rural areas as well as a possible alternative source of income and diversification in horticultural production.

Synergistic effects between arbuscular mycorrhizal fungi and rhizobium isolated from As-contaminated soils on the As-phytoremediation capacity of the tropical woody legume Anadenanthera peregrina

The synergistic relationship between arbuscular mycorrhizal fungi and plant species may play a key role in phytoremediation of arsenic(As)-contaminated soils. By using modified Leonard jars, we investigated both the distinct and integrative roles of arbuscular mycorrhizal fungi (AMF-Acaulospora scrobiculata) and rhizobia (BH-ICB-A8) isolated from As-contaminated soil on the capacity of Anadenanthera peregrina to reclaim arsenate [As(V)] from soil. AMF inoculation greatly increased plant phosphorous nutrition, as reflected in greater growth, and increased As-concentrations in the roots and shoots. While rhizobia inoculation alone increased nitrogen nutrition it did not promote plant growth or As-uptake. Rhizobia and AMF inoculation together had synergistic effects, however, increasing both the growth and the As-phytoremediation capacity of A. peregrina. Joint inoculation with rhizobia and AMF should therefore be considered a potential technique for rehabilitating As-contaminated areas using A. peregrina.