ABSTRACT Brazilian semi-arid tropical is responsible for the production and export of fine table grapes, but the demand for phosphate fertilizers and other agricultural inputs increases the cost of production and threatens local water bodies by leaching of phosphorus (P). The objectives of this study were to quantify the organic and inorganic fractions of P and to determine chemical and microbiological attributes related to its mineralization in soils cultivated with vines in São Francisco Valley. It was hypothesized that P fractions and microbial activity would increase in areas fertilized with phosphate. Soil samples from vines were collected in cultivated areas and in fallow systems. P fractionation, macro-elements analysis, microbial biomass phosphorus (Pmic), and phosphatase enzyme activity were determined and correlated with each other and with the total proportion of synthesized glomalin. In both treatments, the inorganic P fractions exceeded the organic ones, and the total phosphorus available in those soils was associated with the most recalcitrant fractions, reducing risks of leaching of this element and contamination of water bodies. Pmic was higher in the winery areas due to the presence of phosphate fertilizers and organic matter, hence the activity of alkaline phosphatase enzymes and the production of total glomalin increased respectively in three and four evaluated areas, indicating that P-mineralized bacteria and arbuscular mycorrhizal fungi have been positively affected by the current agricultural system.

ABSTRACT Ultramafic soils are originated from ultramafic rocks such as peridotite and serpentinite and are highly enriched in metals (e.g., Ni, Cr, and Co) and depleted in plant nutrients (e.g., P, K, and Ca). Such characteristics make these soils unfavorable for agriculture and have raised environmental concerns on metal release to the environment. From another perspective, ultramafic soils host a diverse flora with higher endemism than surrounding non-ultramafic areas, which has provided scientists with an opportunity to investigate the evolutionary genetics of plant adaptation. Some plant species adapted to these stressful edaphic conditions developing the ability to accumulate uncommonly high metal concentrations in the harvestable biomass. Such species, called metal hyperaccumulators, can extract metals from ultramafic soils, especially Ni, in a circular economy approach in which the metal-rich biomass is incinerated to generate valuable bio-ores. Phytomining promises to turn ultramafic soils and low-grade ore bodies into economically viable alternatives to metal extraction. Here, we review the current knowledge on ultramafic soils and the most promising hyperaccumulators used to exploit them in temperate and tropical climates. In the tropics, including Brazil, the search for new hyperaccumulator candidates for phytomining and the knowledge to crop these species is incipient and holds untapped opportunities. Despite the feasibility of the phytomining chain has been proven, large-scale demonstrations of profitability are needed to establish the technology.

Resumo Estudos florísticos de plantas e floras associadas a ecossistemas aquáticos realizados na região Neotropical têm demonstrado a predominância e coocorrência das mesmas famílias de plantas em diferentes condições climáticas. Uma forma de interpretar essa coocorrência de grupos com padrões não aleatórios em assembléias é entender sua estrutura filogenética. Aqui, apresentamos uma investigação que estudou a regra de montagem filogenética em plantas associadas a reservatórios em uma climosseqüência tropical no nordeste do Brasil. Estudamos oito áreas durante os períodos seco e chuvoso e caracterizamos seus aspectos climáticos, fatores químicos e elementos-traços, bem como a riqueza, diversidade e estrutura filogenética de suas assembleias. Encontramos predominância das famílias Fabaceae, Poaceae e Cyperaceae, principalmente nas áreas de borda. Dentre as espécies levantadas, destacamos aquelas com forma de vida anfíbia, síndrome de dispersão do tipo autocórico e táxons com padrões de ampla distribuição geográfica. Observamos que o efeito sazonal governou padrões de estrutura filogenética com tendência à não co-familiaridade. A qualidade da água e o sedimento foram os fatores abióticos mais eficientes como preditores de riqueza e variações nas métricas filogenéticas. Nesse sentido, a coocorrência familiar identificada nas assembléias foi menos determinística do que a esperada pela não aleatoriedade, pois temporalmente as guildas se estruturaram distintamente em função da sazonalidade.

Abstract Floristic studies of aquatic plants and flora associated with aquatic ecosystems carried out in the Neotropical region have demonstrated the predominance and co-occurrence of the same plant families under different climatic conditions. One way to interpret this co-occurrence of groups with non-random patterns in assemblages is to understand their phylogenetic structure. Herein, we present an investigation that studied the rule of phylogenetic assembly on plants associated with reservoirs in a tropical climosequence in Northeast Brazil. We studied eight areas during the dry and rainy periods and characterized their climatic, chemical, and trace elements, as well as richness, diversity, and phylogenetic structure of their assemblages. We found a predominance of the families Fabaceae, Poaceae and Cyperaceae, especially in border areas. Among the species surveyed, we highlight those with amphibian life-form, autochoric-type dispersion syndrome and the taxa with patterns of wide geographical distribution. We observed that the seasonal effect ruled patterns of phylogenetic structure with tendency for non-co-familiarity. Water quality and sediment were the abiotic factors most efficient as predictors of richness and variations in phylogenetic metrics. In this sense, the family co-occurrence identified in the assemblages was less deterministic than expected through non-randomness, because temporally, guilds were distinctly structured in function of seasonality.

ABSTRACT. Melon bacterial fruit blotch (BFB) is the major bacterial melon disease in Northeastern Brazil. We evaluated the effects of applying a silicon (Si) slag on BFB suppressiveness in two melons cultivars as well as in soil chemical attributes and plant growth and nutrition. Slag was incorporated into the soil at concentrations equivalent to 0.00, 0.12, 0.24, 0.47, 0.71, and 1.41 g kg-1 of silicon. Plants were inoculated with Acidovorax citrulli 20 days after emergence. Results showed that amending the soil with Si slag improved the resistance of two melon cultivars against bacterial fruit blotch. Such an effect is probably related not only to the Si uptake by plants but also to changes in soil characteristics and improvement in plant nutrition. Both hybrid cultivars (AF4945 and Medellín) increased biomass, nutrient and Si accumulation as a function of Si doses applied to soil. According to Si concentration and Si to Ca ratio in plant tissue, both cultivars are regarded as intermediary Si-accumulators. We also observed that an intermediate dose of Si (0.71 g kg-1) posed better results on controlling melon bacterial fruit blotch than the highest dose tested. Long-term, field experiments testing Si slag rates and effects on melon yields are warranted.

RESUMO: Considerando que o cádmio (Cd) apresenta alta persistência no ambiente e toxicidade aos seres humanos, estratégias para diminuir ou evitar a entrada de Cd na cadeia trófica são fundamentais para garantir a segurança alimentar. Neste contexto, avaliamos os efeitos de silício (Si) aplicado como fertilizante a base de terra diatomácea na amenização da toxicidade do Cd em milho cultivado em solo contaminado, com e sem correção de pH. Além de determinar as concentrações de Si e Cd, o acúmulo de nutrientes nas plantas (N, P, K, Ca, Mg, Fe, Mn, Cu e Zn) em função das doses de Si aplicadas ao solo foi avaliado. Os resultados mostraram que tanto a calagem quanto o Si tiveram efeitos positivos na biomassa e na absorção de nutrientes, mas o efeito do Si no desenvolvimento das plantas foi independente da reação do solo. O Si reduziu a fitotoxidade por Cd em ambos os solos, corrigidos e não corrigidos, diminuindo a concentração de Cd na parte aérea. A amenização da toxicidade de Cd foi mais efetiva em solos sem correção, devido à maior disponibilidade de Cd em solos ácidos. Os benefícios da aplicação de Si sobre a produção de biomassa, composição mineral e fitotoxidade do Cd foram observados em plantas cultivadas em solos com e sem correção. Considerando a transferência reduzida de Cd para a parte aérea promovida pelo Si, é provável que ocorra menor acúmulo de Cd nos grãos de milho, com implicações para a segurança alimentar.

ABSTRACT: Given that cadmium (Cd) poses high persistence in the environment and toxicity to humans, strategies to either decrease or avoid Cd entry in the trophic chain are fundamental to secure food safety. Here we assessed the effects of applying rates of Si as a diatomaceous Earth-based fertilizer on the amelioration of Cd toxicity towards maize plants grown on soil with or without pH correction. Besides determining Si and Cd concentrations, we also evaluated plant accumulation of nutrients (N, P, K, Ca, Mg, Fe, Mn, Cu, and Zn) as a function of Si doses applied to the soil. Results showed that both the Si application and the liming had a positive effect on biomass and nutrient uptake, but the Si effect on plants’ performance took place irrespectively to the soil pH. Silicon ameliorated Cd phytotoxicity in both limed and unlimed soils by decreasing Cd concentration in shoots and improving biomass yield and plant nutrition. Silicon alleviation of Cd-inhibitory effects on plants was more effective in the unlimed soil owing to the higher Cd availability in acidic soils. Also, taking into account the reduced transfer of Cd to shoots driven by Si, lower Cd accumulation in maize grains is likely, with implications to food safety. So, further studies on field conditions are warranted.

ABSTRACT: Environmental impacts caused by the addition of rare earth elements (REEs) to agricultural soils are a growing concern. The sedimentary basin of the Gurguéia River is located in one of the last agricultural frontiers in Brazil; nevertheless, data regarding quality reference values (QRVs) for REEs in soils are still scarce. The objective of this study was therefore to determine the natural concentration and establish the QRVs of REEs in soils of Gurguéia watershed, Brazil. Fifty-five composite soil samples were collected at sites under no or minimal anthropic interference. The average REE natural concentrations in soils from the Gurguéia watershed were lower than those found in other regions of Brazil and worldwide, following the order (mg kg−1): Ce (14.01) > Nd (6.19) > La (5.52) > Pr (2.51) > Sm (1.45) > Gd (0.93) > Dy (0.63) > Er (0.42) > Yb (0.39) > Tb (0.28) > Eu (0.26) > Lu (0.20). The parent material was the main factor that controlled the distribution of REEs in soils. The QRVs in soils followed the order (mg kg−1): Ce (18.8) > Nd (7.92) > La (6.32) > Pr (3.3) > Sm (1.97) > Gd (1.35) > Dy (0.85) > Er (0.55) > Yb (0.47) > Tb (0.37) > Lu (0.25). These values serve as a basis to assist the development of legislation, including REE thresholds for Brazilian soils.

ABSTRACT Soil contamination by metals threatens both the environment and human health and hence requires remedial actions. The conventional approach of removing polluted soils and replacing them with clean soils (excavation) is very costly for low-value sites and not feasible on a large scale. In this scenario, phytoremediation emerged as a promising cost-effective and environmentally-friendly technology to render metals less bioavailable (phytostabilization) or clean up metal-polluted soils (phytoextraction). Phytostabilization has demonstrable successes in mining sites and brownfields. On the other hand, phytoextraction still has few examples of successful applications. Either by using hyperaccumulating plants or high biomass plants induced to accumulate metals through chelator addition to the soil, major phytoextraction bottlenecks remain, mainly the extended time frame to remediation and lack of revenue from the land during the process. Due to these drawbacks, phytomanagement has been proposed to provide economic, environmental, and social benefits until the contaminated site returns to productive usage. Here, we review the evolution, promises, and limitations of these phytotechnologies. Despite the lack of commercial phytoextraction operations, there have been significant advances in understanding phytotechnologies' main constraints. Further investigation on new plant species, especially in the tropics, and soil amendments can potentially provide the basis to transform phytoextraction into an operational metal clean-up technology in the future. However, at the current state of the art, phytotechnology is moving the focus from remediation technologies to pollution attenuation and palliative cares.

RESUMO O aporte de metais pesados é inerente à atividade de mineração, contudo a ausência de medidas de controle da poluição nas áreas mineradas concorre para a ampliação do potencial de contaminação do solo, da água e dos organismos. O objetivo deste trabalho foi avaliar o efeito do tempo de exposição de pilhas de estéril e rejeito que não atendem às medidas de proteção ambiental sob o estágio de contaminação do solo por metais pesados em minas de scheelita. Amostras de solo foram coletadas na camada de 0-20 cm em uma mina ativa e em uma mina desativada há quatro décadas. As amostras de solo foram submetidas às análises de granulometria, de pH e de teores dos metais pesados Fe, Mn, Cr, Ni, Cd, Cu, Zn e Pb. Os incrementos nos teores de metais pesados em níveis similares nas minas ativa e desativada indicam que mesmo um menor tempo de exposição das pilhas de estéril e rejeito tem efeito prejudicial quando não são adotadas medidas de proteção e recuperação ambiental. Esses incrementos alertam para o risco de contaminação das áreas adjacentes às minas em decorrência de erosões tanto eólicas quanto hídricas durante os eventos chuvosos intermitentes característicos da região semiárida. Os teores de Cd, Cu e Pb superiores aos valores de investigação agrícola indicam que há risco à saúde humana e que é necessária a remediação das áreas mineradas.

ABSTRACT Heavy metals contribution is inherent to mining activity, however the absence of pollution control measures in mined areas contributes to the expansion of the contamination potential of soil, water, and organisms. The aim of this work was to evaluate the effect of exposure time of tailings and overburden deposition without environmental protection measures over soil heavy metal contamination stage in scheelite mines. Soil samples were obtained from 0-20 cm depth in active scheelite mine and in deactivated scheelite mine since four decades ago. Soil samples were submitted to analyses of particle-size, pH and contents of heavy metals Fe, Mn, Cr, Ni, Cd, Cu, Zn, and Pb. The increases of heavy metals contents at similar levels in active and deactivated mines indicate that even a smaller exposure time of overburden and tailings has a harmful effect when environmental protection and recovery measures were not adopted. These increases alert to the contamination risk of adjacent areas due to wind erosion and hydric erosion during the intermittent rainy events of semi-arid region. Cd, Cu, and Pb contents higher than values of agricultural investigation indicate that there is a risk to human health and that there is need for remediation of mined areas.

ABSTRACT The two main bottlenecks for a successful phytoremediation program are the metal availability in soil and the metal uptake and transfer to shoots of high biomass plants. Several agronomical practices have been tested to boost the bioavailability of metals in soils and accumulation in plants. Here we assessed the feasibility of plant-growth-promoting bacteria (PGPB) isolated from a site contaminated by gold ore processing activities to assist the phytoremediation of As, Cd, and Pb by Sorghum bicolor and mitigate the metal toxicity in plants. The bacteria Kluyvera intermedia, Klebsiella oxytoca, and Citrobacter murliniae were evaluated in single, double, and triple inoculations. They are regarded as metal resistant and were isolated from the rhizosphere of species naturally growing on the metal contaminated site. The treatments comprised two soils (contaminated and non-contaminated) and single (K. intermedia, K. oxytoca, or C. murliniae) or multiple inoculations (K. intermedia + K. oxytoca; K. intermedia + C. murliniae; K. oxytoca + C. murliniae; K. intermedia + K. oxytoca + C. murliniae). Plants were grown for 42 days after inoculation. The results showed that the PGPB K. oxytoca and the combination of K. intermedia + K. oxytoca and K. intermedia + C. murliniae were able to mitigate the metal toxicity in the contaminated soil and hence increase the shoot biomass, with implications to the effectiveness of phytoextraction. The sorghum ability to translocate Cd to shoots in the contaminated soil was enhanced through the single inoculation with K. oxytoca, C. murliniae, and K. oxytoca, as well as by the joint-inoculation with K. oxytoca + C. murliniae, and K. intermedia + K. oxytoca + C. murliniae. Higher accumulation of metals in shoots is a crucial factor in successful phytoextraction. Arsenic and Pb, on the other hand, had their uptake and concentration in roots stimulated by the inoculation. Therefore, regarding these two metals, phytostabilization programs could benefit from the use of the bacteria studied here.

ABSTRACT Micronutrient research for sugarcane in northeastern Brazil is scarce and most works on this issue date back to the 70’s and 80’s. The objectives of this study were to assess the available and reserve pools of Fe, Mn, Cu, and Zn in soils cultivated with sugarcane under three geological contexts in northeastern Brazil as well as to diagnose the micronutrient nutritional status of sugarcane grown on these areas in order to identify pedogeological conditions in which micronutrient deficiencies are likely. Results showed that the soils cultivated with sugarcane in the states of Paraíba and Pernambuco posed available and reserve contents of micronutrients related to the parent materials and soil textural classes. The reserve contents of Fe, Mn, Zn, and Cu in all the soil samples analyzed were below the background values established for the region, which indicates a continuous exportation of micronutrients through cultivation. The mean and median contents of Mn, Zn, and Cu in diagnostic leaves of sugarcane were below their respective nutritional optimum ranges recommended to Brazil while Fe contents achieved the crop nutritional requirement. This is the first time such an approach based on pedogeological contexts is used to study the available and reserve pools of micronutrients in soils of Northeast Brazil.

ABSTRACT. We studied the mineralogical properties and chemical composition of different granites using energy dispersive X-ray spectroscopy coupled with scanning electron microscopy to understand the relationship between granite signatures and soil characteristics, including weathering patterns and soil fertility status. The discriminant analysis (DA) was based on soil physical and chemical properties and was used to differentiate soils developed from I- and S-type granites across contrasting climatic conditions in northeast Brazil. The DA identified the highest values of organic carbon, clay and plant nutrients as key variables to recognize soil profiles derived from I-type granites. In contrast, the greater sand contents and Al saturation distinguished soils developed from S-type granites. These results were related to the mineralogical characteristics of each granite type, such as a high percentage of silica-bearing minerals in the S-type granites. The highest concentrations of K, Ca, Mg, and P in I-type granites were found in feldspars, amphiboles, and apatite. These elements account for the majority of nutrients derived in their soil profiles. However, it seems that the harsh conditions of the humid tropical environment equalized the effect of the rocks on weathering rates-the difference in chemical index of alteration is more extreme in the dry region.

ABSTRACT. Metal concentrations in suspended sediments of one of the most polluted rivers in Brazil were measured. Concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were determined by inductively coupled plasma while Hg and As were analyzed with hydride generation flow injection atomic absorption spectroscopy. Contamination of As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn was assessed using pollution indices, ecological risk assessment, statistical multivariate techniques and comparison with sediment quality guidelines. Suspended sediments of the upstream portion of the Ipojuca River are moderately contaminated, especially with Mn and As. On the other hand, sediments of the downstream section are highly contaminated, mainly with Zn, Pb, and As. Furthermore, the mean Ei (potential ecological risk) values of Pb and As showed considerable ecological risk in the downstream cross section. The comparison of our data with sediment guideline values indicated that the concentrations of Mn and Pb in the upstream section of the Ipojuca River pose a risk to sediment-dwelling organisms, while Pb and Zn are the metals of concern in the downstream section.

ABSTRACT. The relationship between soil and health is important for populations that depend on the local environment to meet their nutritional needs. This study aimed to evaluate the concentrations of major and trace elements in the soils, edible parts of crops and urine of farmers in agroecological communities. We collected samples of soil, edible parts of crops and urine of farmers and family members in 23 crop fields in agroecological communities from northeast Brazil. These samples were analyzed to concentrations of Al, As, Ca, Cr, Cu, Fe, Hg, Mg, Zn, and Pb in urine and discriminant analysis and principal component analysis were used to assess the data. Concentrations of potentially toxic elements in soils and crops of agroecosystems were below regulatory levels. Farmers living in agroecological communities present most of the essential and toxic elements in urine within the reference ranges. In general, results showed that urinary concentration of toxic elements among farmers and their families were below allowable limits, which may be due to the agroecological practices.

RESUMO. A remediação de áreas contaminadas com Pb é uma prática relevante e difícil, pois este é um elemento praticamente imóvel no solo. A fitoestabilização é uma prática considerada ambientalmente atraente para manejo de áreas contaminadas por metais pesados. A mamona é uma espécie produtora de óleo não comestível e apresenta relativa tolerância a metais pesados. O presente trabalho avaliou a toxicidade por Pb utilizando a técnica da fluorescência de clorofila e as alterações provocadas pelo metal na produção de biomassa, produção de pigmentos fotossintéticos, na atividade de enzimas antioxidantes e concentração de proteínas solúveis total. Os resultados demonstraram que a fluorescência de clorofila é um indicador eficiente para detectar precocemente as alterações no fotossistema II causadas pela toxicidade por Pb. As doses de Pb não provocaram alterações nos pigmentos fotossintéticos, na atividade das enzimas antioxidantes e nas proteínas solúveis total nas folhas. A mamona, por sua tolerância e capacidade de acumular Pb nas raízes, pode ser uma alternativa ambiental e economicamente atraente para fitoestabilização e fitoatenuação de áreas contaminadas por Pb. A mamona apresenta adicional vantagem econômica decorrente da utilização do óleo para produção de bioenergia e fins industriais durante o processo de remediação.

ABSTRACT. The remediation of lead-contaminated areas poses a serious challenge to soil chemists because Pb has low solubility in soil. Thus, Pb phytostabilization is considered to be an attractive remediation technique. Castor bean (Ricinus communis) is an oilseed crop known for its tolerance to heavy metals, and our aim was to assess the early detection of Pb toxicity and the effects of Pb on the biomass, photosynthetic pigments, antioxidative enzyme activities, and total soluble proteins of this plant. Specimens were grown in a nutrient solution spiked with Pb concentrations of 25, 50, 100, 150, or 200 µmol L-1. A control without Pb was also grown. The results show that X-ray chlorophyll fluorescence is an efficient technique for the early detection of photosystem II alterations driven by Pb toxicity. Castor bean was tolerant to the Pb doses tested; plants presented no changes in photosynthetic pigments, defense enzyme activities, or total soluble proteins in leaves. Given its ability to tolerate and accumulate Pb in its roots, castor bean is a viable alternative for phytostabilization and phytoattenuation of lead-contaminated areas. It is also economically attractive for industrial and biofuel oil production while being used for remediation.

ABSTRACT Growth in the agricultural and industrial sectors has increased the demand for rare earth elements (REEs) in the production of technological devices and fertilizers. Thus, the accumulation of these elements in the soil has become an environmental concern. Here, we aim to determine the natural contents of REEs in soils derived from different parent materials and under climatic conditions ranging from humid to semi-arid. We then evaluate the influence of major elements and soil properties on the geochemistry of REEs. The contents of REEs were determined using inductively coupled plasma optical emission spectroscopy. Major elements were determined by X-ray fluorescence spectrometry. The mean content of REEs in soils from Rio Grande do Norte (RN), Brazil, were in the followed order (mg kg-1): Ce (40.4) > La (18.9) > Nd (15.8) > Pr (7.3) > Sm (3.0) > Gd (2.6) > Dy (1.0) > Er (0.7) > Yb (0.6) > Eu (0.5) = Tb (0.5) > Ho (0.3) > Lu (0.2). The parent material was the main factor that governed the geochemistry of the REEs in soils of RN. Higher levels of REEs were observed in soils derived from igneous and metamorphic rocks. In contrast, sedimentary rocks - except for the region formed from limestone - generated soils with lower contents of REEs in the state. In addition, soils developed from the same parent material and under different climatic conditions showed the same geochemical signatures for REEs in soils. These results confirm the small effect of climate on REE geochemistry in soils of RN and lead to the conclusion that the geochemical signature of REEs in these soils reflects the composition of the underlying parent material. The lack of significant correlation between (La/Yb)N ratio and the Chemical Alteration Index also confirms the low influence of climate on soil REE geochemistry. Among the major elements, Fe and Si had a greater influence on soil REE geochemistry. Higher REEs were seen in areas with more Fe and less Si. These REE levels were clearly controlled by the type of parent material. The Nd, Sm, Tb, Dy, Ho, Yb, and Er levels showed strong spatial dependence; this dependence was moderate for the Pr, La, Ce, Eu, Gd, and Lu levels. Spatial variability maps of REEs are particularly important to identify areas under environmental impact. Our results represent the most detailed study of the surface geochemistry of REEs in Brazilian soils and contribute to the scarce data available on these elements in Brazil.