Biostimulant Response of Foliar Application of Rare Earth Elements on Physiology, Growth, and Yield of Rice.

Rare earth elements (REEs) have been intentionally used in Chinese agriculture since the 1980s to improve crop yields. Around the world, REEs are also involuntarily applied to soils through phosphate fertilizers. These elements are known to alleviate damage in plants under abiotic stresses, yet there is no information on how these elements act in the physiology of plants. The REE mode of action falls within the scope of the hormesis effect, with low-dose stimulation and high-dose adverse reactions. This study aimed to verify how REEs affect rice plants' physiology to test the threshold dose at which REEs could act as biostimulants in these plants. In experiment 1, 0.411 kg ha-1 (foliar application) of a mixture of REE (containing 41.38% Ce, 23.95% La, 13.58% Pr, and 4.32% Nd) was applied, as well as two products containing 41.38% Ce and 23.95% La separately. The characteristics of chlorophyll a fluorescence, gas exchanges, SPAD index, and biomass (pot conditions) were evaluated. For experiment 2, increasing rates of the REE mix (0, 0.1, 0.225, 0.5, and 1 kg ha-1) (field conditions) were used to study their effect on rice grain yield and nutrient concentration of rice leaves. Adding REEs to plants increased biomass production (23% with Ce, 31% with La, and 63% with REE Mix application) due to improved photosynthetic rate (8% with Ce, 15% with La, and 27% with REE mix), favored by the higher electronic flow (photosynthetic electron transport chain) (increase of 17%) and by the higher Fv/Fm (increase of 14%) and quantum yield of photosystem II (increase of 20% with Ce and La, and 29% with REE Mix), as well as by increased stomatal conductance (increase of 36%) and SPAD index (increase of 10% with Ce, 12% with La, and 15% with REE mix). Moreover, adding REEs potentiated the photosynthetic process by increasing rice leaves' N, Mg, K, and Mn concentrations (24-46%). The dose for the higher rice grain yield (an increase of 113%) was estimated for the REE mix at 0.72 kg ha-1.

Artisanal mining of monazite and cassiterite in the Amazon: Potential risks of rare earth elements for the environment and human health.

Artisanal mining is intensely carried out in developing countries, including Brazil and especially in the Amazon. This method of mineral exploration generally does not employ mitigation techniques for potential damages and can lead to various environmental problems and risks to human health. The objectives of this study were to quantify the concentrations of rare earth elements (REEs) and estimate the environmental and human health risks in cassiterite and monazite artisanal mining areas in the southeastern Amazon, as well as to understand the dynamics of this risk over time after exploitation. A total of 35 samples of wastes classified as overburden and tailings in active areas, as well as in areas deactivated for one and ten years were collected. Samples were also collected in a forest area considered as a reference site. The concentrations of REEs were quantified using alkaline fusion and ICP-MS. The results were used to calculate pollution indices and environmental and human health risks. REEs showed higher concentrations in anthropized areas. Pollution and environmental risk levels were higher in areas deactivated for one year, with considerable contamination factors for Gd and Sm and significant to extreme enrichment factors for Sc. Human health risks were low (< 1) in all studied areas. The results indicate that artisanal mining of cassiterite and monazite has the potential to promote contamination and enrichment by REEs.

Clean and accurate soil quality monitoring in mining areas under environmental rehabilitation in the Eastern Brazilian Amazon.

Soil quality monitoring in mining rehabilitation areas is a crucial step to validate the effectiveness of the adopted recovery strategy, especially in critical areas for environmental conservation, such as the Brazilian Amazon. The use of portable X-ray fluorescence (pXRF) spectrometry allows a rapid quantification of several soil chemical elements, with low cost and without residue generation, being an alternative for clean and accurate environmental monitoring. Thus, this work aimed to assess soil quality in mining areas with different stages of environmental rehabilitation based on predictions of soil fertility properties through pXRF along with four machine learning algorithms (projection pursuit regression, PPR; support vector machine, SVM; cubist regression, CR; and random forest, RF) in the Eastern Brazilian Amazon. Sandstone and iron mines in different chronological stages of rehabilitation (initial, intermediate, and advanced) were evaluated, in addition to non-rehabilitated and native forest areas. A total of 81 soil samples (26 from sandstone mine and 55 from iron mine) were analyzed by both traditional wet-chemistry methods and pXRF. The available/exchangeable contents of K, Ca, B, Fe, and Al, in addition to H+Al, cation exchange capacity at pH = 7, Al saturation, soil organic matter, pH, sum of bases, base saturation, clay, and sand were accurately predicted (R2 > 0.70) using pXRF data, with emphasis on the prediction of Fe (R2 = 0.93), clay content (R2 = 0.81), H+Al (R2 = 0.81), and K+ (R2 = 0.85). The best predictive models were developed by RF and CR (86%) and when considering pXRF data + mining area + stage of rehabilitation (73%). The results highlight the potential of pXRF to accurately assess soil properties in environmental rehabilitation areas in the Amazon region (yet scarcely evaluated under this approach), promoting a more agile and cheaper preliminary diagnosis compared to traditional methods.

Assessment of the reproduction of six collembolan species in tropical soils naturally rich in potentially toxic elements.

Laboratory ecotoxicological tests are important tools for the management of environmental changes derived from anthropogenic activities. Folsomia candida is usually the model species used in some procedures. However, this species may not be sufficiently representative of the sensitivity of the other collembolan species. This study aimed to evaluate (i) the effects of soils naturally rich in potentially toxic elements (PTE) and soil characteristics on the reproduction and survival of different collembolan species, (ii) whether the habitat function of these soils is compromised, and (iii) to what extent F. candida is representative of the other collembolan species. For this, reproduction tests with six collembolan species were conducted in 14 different samples of soils. In general, collembolan reproduction was not completely inhibited in none of the natural tested soils. Even soils with high pollution load index values did not negatively affect collembolan reproduction for most of the species. In contrast, the lowest collembolan reproduction rates were found in a visually dense soil (lowest volume/weight ratio), highlighting that soil attributes other than total PTE concentration also interfere in the reproduction of collembolans. Our results support the idea that the F. candida species might not be representative of other collembolan species and that laboratory tests to assess soil contaminations should be conducted using diverse collembolan species.

Exogenous Nitric Oxide Alleviates Water Deficit and Increases the Seed Production of an Endemic Amazonian Canga Grass.

Open pit mining can cause loss in different ecosystems, including damage to habitats of rare and endemic species. Understanding the biology of these species is fundamental for their conservation, and to assist in decision-making. Sporobolus multiramosus is an annual grass endemic to the Amazon canga ecosystems, which comprise rocky outcrop vegetation covering one of the world's largest iron ore reserves. Here, we evaluated whether nitric oxide aids S. multiramosus in coping with water shortages and examined the physiological processes behind these adaptations. nitric oxide application improved the water status, photosynthetic efficiency, biomass production, and seed production and germination of S. multiramosus under water deficit conditions. These enhancements were accompanied by adjustments in leaf and root anatomy, including changes in stomata density and size and root endodermis thickness and vascular cylinder diameter. Proteomic analysis revealed that nitric oxide promoted the activation of several proteins involved in the response to environmental stress and flower and fruit development. Overall, the results suggest that exogenous nitric oxide has the potential to enhance the growth and productivity of S. multiramosus. Enhancements in seed productivity have significant implications for conservation initiatives and can be applied to seed production areas, particularly for the restoration of native ecosystems.

Human and environmental exposure to rare earth elements in gold mining areas in the northeastern Amazon.

Rudimentary methods are used to exploit gold (Au) in several artisanal mines in the Amazon, producing hazardous wastes that may pose risks of contamination by rare earth elements (REEs). The objectives of this study were to quantify the concentrations of REEs and assess their environmental and human health risks in artisanal Au mining areas in the northeastern Amazon. Thus, 25 samples of soils and mining wastes were collected in underground, colluvial, and cyanidation exploration sites, as well as in a natural forest that was considered as a reference area. The concentrations of REEs were quantified using alkaline fusion and inductively coupled plasma mass spectrometry, and the results were used to estimate pollution indices and risks associated with the contaminants. All REEs showed higher concentrations in waste deposition areas than in the reference area, especially Ce, Sc, Nd, La, Pr, Sm, and Eu. Pollution and enrichment levels were higher in the underground and cyanidation mining areas, with very high contamination factors (6.2-27) for Ce, Eu, La, Nd, Pr, Sm, and Sc, and significant to very high enrichment factors (5.5-20) for Ce, La, Nd, Pr, and Sc. The ecological risk indices varied from moderate (167.3) to high (365.7) in the most polluted sites, but risks to human health were low in all areas studied. The results of this study indicate that artisanal Au mining has the potential to cause contamination, enrichment, and ecological risks by REEs in the northeastern Amazon. Mitigation measures should be implemented to protect the environment from the negative impacts of these contaminants.

Mercury in multimedia system of Itacaiúnas Basin, Brazilian Amazon: An integrated approach to understand its distribution, origin, and ecological risk.

This study presents the first integrated study on total Hg (THg) level in surface soil (SS), bottom soil (BS), stream sediments (SD), lake sediments (LS), stream water (SW), and lake water (LW) of Itacaiúnas River Watershed (IRW), Brazil to investigate the source and distribution of Hg in different environmental media considering contrasts of geological domains and sub-basins and its potential ecological and human risk. Hg content in most of the soils and sediments were above the upper crustal average values (56 µg/kg), however, when compared to the legal limits set by the Resolution CONAMA (Conselho Nacional de Meio Ambiente: soil 500 µg/kg; sediment 486 µg/kg), only 1 soil sample from Parauapebas sub-basin and 4 sediment samples from Violão Lake exceeded the limit. None of the SW and LW samples (<0.2 µg/L; CONAMA limit for Class II freshwater) are markedly contaminated by Hg. The SS and BS show similar contents and spatial distribution of Hg with higher contents being registered mostly in the Itacaiúnas and Parauapebas sub-basins, which are closely correlated with SD. This suggests that Hg levels are largely of geogenic origin and anthropogenic effect is highly limited. Principal Component Analysis (PCA) results show that Hg is strongly associated with total organic carbon (TOC), loss on ignition (LOI), and SO3, indicating organic matter as the main factor controlling the distribution of Hg and this is the major cause of accentuated Hg enrichment in lake sediments. The ecological risk index revealed a low pollution risk for most of the solid samples, except 11% LS and <1.5% SS and SD samples, which registered moderate risk. Health risk assessment indicated no adverse non-carcinogenic health effect on either adults and children in terms of Hg contamination. This information will be useful for Hg risk assessment in the Carajás region and future environmental research in this direction in the Amazonia.

Rock n' Seeds: A database of seed functional traits and germination experiments from Brazilian rock outcrop vegetation.

Advancing functional ecology depends fundamentally on the availability of data on reproductive traits, including those from tropical plants, which have been historically underrepresented in global trait databases. Although some valuable databases have been created recently, they are mainly restricted to temperate areas and vegetative traits such as leaf and wood traits. Here, we present Rock n' Seeds, a database of seed functional traits and germination experiments from Brazilian rock outcrop vegetation, recognized as outstanding centers of diversity and endemism. Data were compiled through a systematic literature search, resulting in 103 publications from which seed functional traits were extracted. The database includes information on 16 functional traits for 383 taxa from 148 genera, 50 families, and 25 orders. These 16 traits include two dispersal, six production, four morphological, two biophysical, and two germination traits-the major axes of the seed ecological spectrum. The database also provides raw data for 48 germination experiments, for a total of 10,187 records for 281 taxa. Germination experiments in the database assessed the effect of a wide range of abiotic and biotic factors on germination and different dormancy-breaking treatments. Notably, 8255 of these records include daily germination counts. This input will facilitate synthesizing germination data and using this database for a myriad of ecological questions. Given the variety of seed traits and the extensive germination information made available by this database, we expect it to be a valuable resource advancing comparative functional ecology and guiding seed-based restoration and biodiversity conservation in tropical megadiverse ecosystems. There are no copyright restrictions on the data; please cite this paper when using the current data in publications; also the authors would appreciate notification of how the data are used in publications.

O avanço da ecologia funcional depende fundamentalmente da disponibilidade de dados sobre traços reprodutivos, incluindo dados de plantas tropicais, que têm sido historicamente subrepresentados em bancos de dados de traços funcionais globais. Embora alguns bancos de dados valiosos tenham sido criados recentemente, eles são restritos principalmente a áreas temperadas e a traços vegetativos, como traços de folhas e madeira. Neste artigo apresentamos Rock n' Seeds, um banco de dados de traços funcionais de sementes e experimentos de germinação de vegetações associadas a afloramentos rochosos do Brasil, os quais são reconhecidos como centros notáveis de diversidade e endemismo. Os dados foram compilados através de uma revisão sistemática na literatura, resultando em 103 publicações das quais foram extraídos os traços funcionais das sementes. O banco de dados inclui informações de 16 traços funcionais para 383 taxa de 148 gêneros, 50 famílias e 25 ordens. Estes dezesseis traços incluem dois traços de dispersão, seis de produção, quatro morfológicos, dois biofísicos e dois germinativos; os eixos principais do espectro ecológico da semente. O banco de dados também fornece os dados brutos para 48 experimentos de germinação para um total de 10.187 registros para 281 taxa. Os experimentos de germinação no banco de dados avaliaram o efeito de uma ampla gama de fatores abióticos e bióticos sobre a germinação e diferentes tratamentos de quebra de dormência. Particularmente, 8.255 desses registros incluem a contagem diária da germinação. Estas informações facilitarão a síntese de dados de germinação e a utilização deste banco de dados para uma grande variedade de questões ecológicas. Dada a variedade de traços das sementes e as amplas informações sobre germinação disponibilizadas por este banco de dados, esperamos que ele seja um recurso valioso para o avanço da ecologia funcional comparativa e para orientar a restauração baseada em sementes e a conservação da biodiversidade em ecossistemas tropicais megadiversos. Não há restrições de direitos autorais sobre os dados; favor citar este artigo ao utilizar os dados nas publicações e os autores agradeceriam uma notificação de como os dados são utilizados nas publicações.

El avance de la ecología funcional depende fundamentalmente de la disponibilidad de datos sobre rasgos reproductivos-incluyendo los de las plantas tropicales-los cuales han estado poco representados en las bases de datos globales de rasgos. Aunque recientemente se han creado algunas bases de datos valiosas, estas se encuentran restringidas principalmente a las zonas templadas y a los rasgos vegetativos, como los de las hojas y la madera. En este artículo presentamos Rock n' Seeds, una base de datos de rasgos funcionales de semillas y experimentos de germinación de la vegetación asociada a afloramientos rocosos de Brasil, los cuales son destacados centros de diversidad y endemismo. Los datos se recopilaron mediante una búsqueda bibliográfica sistemática, que dio como resultado 103 publicaciones de las que se extrajeron los rasgos funcionales de las semillas. La base de datos incluye información de dieciséis rasgos funcionales para 383 taxones de 148 géneros, 50 familias y 25 órdenes. Estos rasgos incluyen dos rasgos de dispersión, seis de producción, cuatro morfológicos, dos biofísicos y dos de germinación; siendo estos los principales ejes del espectro ecológico de las semillas. La base de datos también proporciona los datos brutos de 48 experimentos de germinación, para un total de 10.187 registros de 281 taxones. Dichos experimentos de germinación evaluaron el efecto de una amplia gama de factores abióticos y bióticos sobre la germinación y de diferentes tratamientos para romper la dormancia. En particular, 8.255 de estos registros cuentan con conteos diarios de germinación. Esto facilitará la síntesis de los datos de germinación y el uso de esta base de datos para una gran diversidad de preguntas ecológicas. Dada la variedad de rasgos de las semillas y la amplia información sobre germinación que ofrece esta base de datos, esperamos que sea un recurso valioso para el avance de la ecología funcional comparativa y para orientar la restauración basada en semillas y la conservación de la biodiversidad en ecosistemas tropicales megadiversos. No hay restricciones de derechos de autor sobre los datos; se solicita citar este documento cuando se utilicen los datos en publicaciones y los autores agradecerán ser notificados sobre cómo se utilizan los datos en las publicaciones.

Molecular Mechanisms Underlying Mimosa acutistipula Success in Amazonian Rehabilitating Minelands.

Mimosa acutistipula is endemic to Brazil and grows in ferruginous outcrops (canga) in Serra dos Carajás, eastern Amazon, where one of the largest iron ore deposits in the world is located. Plants that develop in these ecosystems are subject to severe environmental conditions and must have adaptive mechanisms to grow and thrive in cangas. Mimosa acutistipula is a native species used to restore biodiversity in post-mining areas in canga. Understanding the molecular mechanisms involved in the adaptation of M. acutistipula in canga is essential to deduce the ability of native species to adapt to possible stressors in rehabilitating minelands over time. In this study, the root proteomic profiles of M. acutistipula grown in a native canga ecosystem and rehabilitating minelands were compared to identify essential proteins involved in the adaptation of this species in its native environment and that should enable its establishment in rehabilitating minelands. The results showed differentially abundant proteins, where 436 proteins with significant values (p < 0.05) and fold change ≥ 2 were more abundant in canga and 145 in roots from the rehabilitating minelands. Among them, a representative amount and diversity of proteins were related to responses to water deficit, heat, and responses to metal ions. Other identified proteins are involved in biocontrol activity against phytopathogens and symbiosis. This research provides insights into proteins involved in M. acutistipula responses to environmental stimuli, suggesting critical mechanisms to support the establishment of native canga plants in rehabilitating minelands over time.

Cross-species transcriptomes reveal species-specific and shared molecular adaptations for plants development on iron-rich rocky outcrops soils.

BACKGROUND: Canga is the Brazilian term for the savanna-like vegetation harboring several endemic species on iron-rich rocky outcrops, usually considered for mining activities. Parkia platycephala Benth. and Stryphnodendron pulcherrimum (Willd.) Hochr. naturally occur in the cangas of Serra dos Carajás (eastern Amazonia, Brazil) and the surrounding forest, indicating high phenotypic plasticity. The morphological and physiological mechanisms of the plants' establishment in the canga environment are well studied, but the molecular adaptative responses are still unknown. To understand these adaptative responses, we aimed to identify molecular mechanisms that allow the establishment of these plants in the canga environment. RESULTS: Plants were grown in canga and forest substrates collected in the Carajás Mineral Province. RNA was extracted from pooled leaf tissue, and RNA-seq paired-end reads were assembled into representative transcriptomes for P. platycephala and S. pulcherrimum containing 31,728 and 31,311 primary transcripts, respectively. We identified both species-specific and core molecular responses in plants grown in the canga substrate using differential expression analyses. In the species-specific analysis, we identified 1,112 and 838 differentially expressed genes for P. platycephala and S. pulcherrimum, respectively. Enrichment analyses showed that unique biological processes and metabolic pathways were affected for each species. Comparative differential expression analysis was based on shared single-copy orthologs. The overall pattern of ortholog expression was species-specific. Even so, we identified almost 300 altered genes between plants in canga and forest substrates with conserved responses in the two species. The genes were functionally associated with the response to light stimulus and the circadian rhythm pathway. CONCLUSIONS: Plants possess species-specific adaptative responses to cope with the substrates. Our results also suggest that plants adapted to both canga and forest environments can adjust the circadian rhythm in a substrate-dependent manner. The circadian clock gene modulation might be a central mechanism regulating the plants' development in the canga substrate in the studied legume species. The mechanism may be shared as a common mechanism to abiotic stress compensation in other native species.

Changes in soil properties during iron mining and in rehabilitating minelands in the Eastern Amazon.

Open-cast iron mining causes drastic disturbances in soil properties. Recovery of soil chemical and physical properties is essential for successful revegetation and landscape rehabilitation. To identify changes in soil properties during the mining and revegetation process, soil samples were collected from undisturbed sites represented by forest and ferriferous savannas stocking above iron outcrops, called "cangas," in open-pit benches, and in rehabilitation chronosequences of iron waste piles in the Carajás Mineral Province (CMP), Eastern Amazon, Brazil. The samples were analyzed for chemical and physical properties. Our results showed that iron mining operations resulted in significant alteration of the chemical soil properties when forest and canga vegetation are suppressed to form open-pit benches or waste piles in the CMP. Mining substrates showed lower contents of soil organic matter (SOM) and nutrients than undisturbed areas of forests and cangas. In order to achieve the success of revegetation, nutrients have been added prior to plant establishment. We have demonstrated how soil fertility changes along with mineland rehabilitation, and the variation among chronosequence was attributable mainly due to contents of SOM, K, and B in the soil. The slight improvement of SOM found in rehabilitated waste piles reinforces the notion that recovery of soil quality can be a slow process in iron minelands in the CMP.

Soil-sediment linkage and trace element contamination in forested/deforested areas of the Itacaiúnas River Watershed, Brazil: To what extent land-use change plays a role?

Trace elements (TE) contamination in forested areas of the Itacaiúnas River Watershed (IRW), Brazilian Amazon, arouses growing interest owing to the rapid deforestation and mining activities. In this study, soils (surface, SS; bottom, BS) and stream sediments (SD) from forested/deforested areas of IRW were analyzed with the aim of (1) evaluating the major sources of TE (mainly As, Ba, Cd, Cu, Co, Cr, Hg, Mo, Mn, Ni, Pb, V, and Zn), and (2) examining the soil-sediment TE link related to land-use change and/or geologic factors. Compositional data analysis (CoDA) was used to eliminate data closure issues and the centred log-ratio (clr) transformation yielded better results in Principal Component Analysis (PCA). The TE distribution pattern was significantly different (p < 0.05) between forested and deforested areas, but in both areas the TE distribution pattern is significantly correlated between SS, BS, and SD, indicating a strong lithogenic control. PCA (clr-transformed) identified the major geochemical bedrock signature as Fe-Ti-V-Cu-Cr-Ni, which is nearly similar in soil and sediments. The more accentuated enrichment and the maximum number of anomalies of these elements were found in the Carajás Basin and are highly coincident with mineral deposits/local lithologies without clear indication of anthropogenic contamination from point sources. Besides geogenic factors, deforestation is also affecting TE distribution in the basin. In deforested areas, Mn was significantly enriched in the surface horizon. Furthermore, linear regression analysis shows stronger TE relationships between soils and sediments in deforested areas than in forested ones, reflecting higher erosion in the former. This could be the reason for the relatively higher enrichment of TE (e.g., Fe, Mn, Cu, Cr, Ni) in deforested sediments. The TE contamination using regional background values provides more accurate results than worldwide reference values. Thus, the former should be considered for a more realistic environmental risk assessment in IRW and other forest ecosystems in the Brazilian Amazon.

Levels and environmental risks of rare earth elements in a gold mining area in the Amazon.

Artisanal gold (Au) mining may have increased the concentrations of rare earth elements (REEs) in the Serra Pelada mine (southeastern Amazon, Brazil), which has not been evaluated so far. The objectives of this study were to determine the concentrations of cerium (Ce), lanthanum (La), scandium (Sc), and yttrium (Y) in the surroundings of the Serra Pelada mine, as well as the environmental risks associated with these elements. Therefore, 27 samples were collected in agricultural, forest, mining, and urban areas, and submitted to chemical and particle size characterization. The concentrations of REEs were quantified by inductively coupled plasma mass spectrometry (ICP-MS) and used to estimate pollution indices and environmental risks of the studied elements. All REEs had higher levels in the anthropized areas when compared to the forest area, except Sc in the mining and urban areas. Pollution load indices revealed that all areas are contaminated (>1) by the combined effect of REEs, especially the agricultural areas (index of 2.3). The element of greatest enrichment in the studied areas was Y, with enrichment factors of 18.2, 39.0, and 44.4 in the urban, agriculture, and mining areas, respectively. However, the potential ecological risk indices were low (<150) in all areas, indicating that there are no current environmental risks by the studied REEs.

Proteomic Profiling and Rhizosphere-Associated Microbial Communities Reveal Adaptive Mechanisms of Dioclea apurensis Kunth in Eastern Amazon's Rehabilitating Minelands.

Dioclea apurensis Kunth is native to ferruginous rocky outcrops (known as canga) in the eastern Amazon. Native cangas are considered hotspots of biological diversity and have one of the largest iron ore deposits in the world. There, D. apurensis can grow in post-mining areas where molecular mechanisms and rhizospheric interactions with soil microorganisms are expected to contribute to their establishment in rehabilitating minelands (RM). In this study, we compare the root proteomic profile and rhizosphere-associated bacterial and fungal communities of D. apurensis growing in canga and RM to characterize the main mechanisms that allow the growth and establishment in post-mining areas. The results showed that proteins involved in response to oxidative stress, drought, excess of iron, and phosphorus deficiency showed higher levels in canga and, therefore, helped explain its high establishment rates in RM. Rhizospheric selectivity of microorganisms was more evident in canga. The microbial community structure was mostly different between the two habitats, denoting that despite having its preferences, D. apurensis can associate with beneficial soil microorganisms without specificity. Therefore, its good performance in RM can also be improved or attributed to its ability to cope with beneficial soil-borne microorganisms. Native plants with such adaptations must be used to enhance the rehabilitation process.

Biochar mitigates bioavailability and environmental risks of arsenic in gold mining tailings from the eastern Amazon.

Artisanal gold mining has generated tailings highly contaminated by arsenic (As) in Cachoeira do Piriá, eastern Amazon, leading to severe risks to the environment. Such risks should be mitigated considering the bioavailable concentration of the element, since it implies immediate damage to the ecosystem. The objective of this study was to evaluate the potential of biochars in mitigating the environmental risks of bioavailable As concentrations in gold mining tailings from underground and cyanidation exploration. The biochar addition increased mineral components, cation retention, phosphorus in all fractions, and organic and inorganic carbon. The bioavailability of As was reduced after adding the biochars, following the order palm kernel cake biochar > Brazil nut shell biochar > açaí seed biochar, with reductions of up to 13 mg kg-1 in the underground mining tailings and 17 mg kg-1 in the cyanidation mining tailings. These results contributed to the statistically significant reduction of the environmental risks in both mining tailings (6-17% in the underground mining tailings and 9-20% in the cyanidation mining tailings), which was emphasized by Pearson's correlation and multivariate analyzes. The incorporation of the bioavailable fractions of As (from sequential extraction) in the environmental risk assessment was a promising method for evaluating the efficiency of biochars in mitigating the damage caused by this metalloid in gold mining tailings.

Copper mining in the eastern Amazon: an environmental perspective on potentially toxic elements.

Mining activity is of great economic and social importance; however, volumes of metallic ore tailings rich in potentially toxic elements (PTEs) may be produced. In this context, managing this environmental liability and assessing soil quality in areas close to mining activities are fundamental. This study aimed to compare the concentrations of PTEs-arsenic (As), barium (Ba), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), mercury (Hg), molybdenum (Mo), nickel (Ni), lead (Pb) and zinc (Zn)-as well as the fertility and texture of Cu tailings and soils of native, urban and pasture areas surrounding a Cu mining complex in the eastern Amazon. The levels of PTEs were compared with soil prevention values, soil quality reference values, global average soil concentrations and average upper continental crust concentrations. The contamination factor (CF), degree of contamination (Cdeg), potential ecological risk index (RI), geoaccumulation index (Igeo) and pollution load index (PLI) were calculated. The levels of Co, Cu and Ni in the tailings area exceeded the prevention values, soil quality reference values and average upper continental crust concentrations; however, the tailings area was considered unpolluted according to PLI and RI and presented a low potential ecological risk. The high concentrations of PTEs are associated with the geological properties of the area, and the presence of PTEs-rich minerals supports these results. For the urban and pasture areas, none of the 11 PTEs analyzed exceeded the prevention values established by the Brazilian National Environment Council.

Impact of copper mining wastes in the Amazon: Properties and risks to environment and human health.

Improper disposal of copper mining wastes can threaten the ecosystem and human health due to the high levels of potentially toxic elements released into the environment. The objective of this study was to determine the properties of Cu mining wastes generated in the eastern Amazon and their potential risks to environment and human health. Samples of forest soil and artisanal/industrial Cu mining wastes were collected and subjected to characterization of properties and pseudo-total concentrations of Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, and Zn, in addition to chemical fractionation of Cu. The pH ranged from near neutrality to alkaline. Pseudo-total concentrations of Cu were high in all wastes, mainly in the artisanal rock waste, with 19,034 mg kg-1, of which 61% is concentrated in the most reactive fractions. Pollution indices indicated that the wastes are highly contaminated by Cu and moderately contaminated by Cr and Ni. However, only the artisanal rock waste is associated with environmental risk. Non-carcinogenic and carcinogenic human health risks were detected, especially from exposure to Cr in the artisanal rock waste. Prevention actions and monitoring of the artisanal mining area are necessary to avoid impacts to the local population.

Artisanal gold mining in the eastern Amazon: Environmental and human health risks of mercury from different mining methods.

Artisanal gold (Au) mining is the activity with the highest consumption of mercury (Hg) and the main source of environmental contamination by this element, which is a recurring problem in the Amazon. In this study, contamination and risks caused by Hg to the environment and human health were evaluated in different forms of artisanal Au mining in the Brazilian Amazon. For this purpose, 25 samples of soils and tailings were collected in three types of artisanal mine and one native forest. The mineralogical analysis revealed that there is no occurrence of minerals constituted by Hg. However, the concentrations of Hg in underground mining tailings were very high and exceeded the prevention values established by Brazilian environmental legislation, indicating elevated risk to the ecosystem and human health. The enrichment factor indicated that underground mining tailings are enriched by Hg, submitted to cyanidation or not, suggesting anthropogenic source for the high concentrations of Hg. The geoaccumulation index and the contamination factor showed that the colluvial mining tailings are moderately contaminated, and the tailings from underground mining are highly to extremely contaminated, leading to very high risks to the environment and the health of children from the region. These results represent a great contribution to the Amazon, since they provide subsidies for the definition of policies to mitigate environmental contamination and associated risks.

Native Amazonian Canga Grasses Show Distinct Nitrogen Growth Responses in Iron Mining Substrates.

Native species may have adaptive traits that are advantageous for overcoming the adverse environmental conditions faced during the early stages of mine land rehabilitation. Here, we examined the nitrogen (N) growth responses of two native perennial grasses (Axonopus longispicus and Paspalum cinerascens) from canga in nutrient-poor iron mining substrates. We carried out vegetative propagation and recovered substantial healthy tillers from field-collected tussocks of both species. These tillers were cultivated in mining substrates at increasing N levels. The tillering rates of both species increased with the N application. Nonetheless, only in P. cinerascens did the N application result in significant biomass increase. Such growth gain was a result of changes in leaf pigment, stomatal morphology, gas exchanges, and nutrients absorption that occurred mainly under the low N additions. Reaching optimum growth at 80 mg N dm-3, these plants showed no differences from those in the field. Our study demonstrates that an input of N as fertilizer can differentially improve the growth of native grasses and that P. cinerascens plants are able to deposit high quantities of carbon and protect soil over the seasons, thus, making them promising candidates for restoring nutrient cycling, accelerating the return of other species and ecosystem services.

Bioavailability of copper and nickel in naturally metal-enriched soils of Carajás Mining Province, Eastern Amazon, Brazil.

Naturally elevated contents of copper (Cu) and nickel (Ni) are found in soils worldwide, and their potential toxicity is better understood when geochemical reactive fractions are identified and monitored. Thus, this study aimed to assess the bioavailability of Cu and Ni and estimate environmental risks in naturally metal-enriched soils of Carajás Mining Province, Eastern Amazon, Brazil. For that, 58 surficial soil samples were analyzed for their extractable contents of Cu and Ni by Mehlich 1. Next, 13 soil samples were selected for additional single and sequential extractions, for the determination of metal content in the shoots of grasses naturally growing in these soils and for calculating the risk assessment code. Despite the naturally high total concentrations, the contents of easily available Cu and Ni are a minor fraction of total concentrations (up to 10.15%), and the reducible oxide and residual pools hold the major proportion of total content of metals. This contributed to low bioavailability, low environmental risk, and also to low concentrations of these metals on grasses collected in the field. Soil organic matter, Fe2O3, Al2O3 and clay content have a dominant role in metals retention on studied soils. Our findings on the bioavailability of Cu and Ni in a region of great economic relevance for Brazil are important not only for predicting the elements' behavior in the soil-plant system but also for refining risk assessments and to provide useful data for environmental quality monitoring.