The use of a portable X-ray fluorescence spectrometer for measuring nickel in plants: sample preparation and validation.

X-ray fluorescence is a fast, cost-effective, and eco-friendly method for elemental analyses. Portable X-ray fluorescence spectrometers (pXRF) have proven instrumental in detecting metals across diverse matrices, including plants. However, sample preparation and measurement procedures need to be standardized for each instrument. This study examined sample preparation methods and predictive capabilities for nickel (Ni) concentrations in various plants using pXRF, employing empirical calibration based on inductively coupled plasma optical emission spectroscopy (ICP-OES) Ni data. The evaluation involved 300 plant samples of 14 species with variable of Ni accumulation. Various dwell times (30, 60, 90, 120, 300 s) and sample masses (0.5, 1.0, 1.5, 2.0 g) were tested. Calibration models were developed through empirical and correction factor approaches. The results showed that the use of 1.0 g of sample (0.14 g cm-2) and a dwell time of 60 s for the study conditions were appropriate for detection by pXRF. Ni concentrations determined by ICP-OES were highly correlated (R2 = 0.94) with those measured by the pXRF instrument. Therefore, pXRF can provide reliable detection of Ni in plant samples, avoiding the digestion of samples and reducing the decision-making time in environmental management.

Assessing heavy metal contamination in a Brazilian metropolis: a case study with a focus on (bio)indicators.

The continuous expansion of the global vehicle fleet poses a growing threat to environmental quality through heavy metal contamination. In this scenario, monitoring to safeguard public health in urban areas is necessary. Our study involved the collection of 36 street dust and 29 moss samples from roads of a Brazilian metropolis (Recife) with varying traffic intensities as follows: natural reserve (0 vehicles per day), low (< 15,000 vehicles per day), medium (15,000-30,000 vehicles per day), and high (> 30,000 vehicles per day). ICP-AES analysis was performed to determine the concentrations of nine potentially toxic metals (Ba, Cd, Cr, Cu, Mn, Ni, Pb, V, and Zn) to assess the influence of vehicular flow on urban contamination. In the street dust samples, the mean metal concentrations (mg kg-1) exhibited the following order: Ba (503.7) > Mn (303.0) > Zn (144.4) > Cu (95.3) > Cr (56.1) > Pb (34.2) > V (28.7) > Ni (11.3) > Cd (1.5). Conversely, in the moss samples, the metal concentration order was as follows (mg kg-1): Mn (63.8) > Zn (62.5) > Ba (61.0) > Cu (17.7) > Cr (8.0) > V (7.3) > Pb (7.0) > Ni (2.9) > Cd (0.3). Roads with higher traffic volumes exhibited the highest metal enrichments in moss samples for all metals and in dust samples for Cd, Cr, Mn, Ni, and V. However, dust from low-flow roads had higher enrichments for Ba, Cu, and Zn, indicating the influential role of other traffic-related factors in metal deposition. Our findings highlight traffic flow as the predominant source of pollution in urban centers, with both street dust and moss serving as sensitive indicators of metal input attributable to vehicular traffic. These indicators offer valuable insights for urban quality monitoring and pollution control efforts.

Assessing ecological risks and spatial distribution of potentially toxic elements in soils from anthropized environments in a watershed at the caatinga-Atlantic forest ecotone in Brazil.

Understanding the processes of mobility and availability of potentially toxic elements in soil is crucial for informed decision-making in the development of public policies aimed at minimizing environmental impacts. Monitoring, in combination with the determination of natural concentrations, can provide effective tools for controlling pollution sources. In this study, enrichment, pollution, and ecological risk indices were used for some potentially toxic elements in an anthropogenically influenced watershed in southwestern Bahia, Brazil. The study involved 63 composite surface soil samples collected from areas with natural forest, crops, pastures, and urbanization. The samples were analyzed for fertility and particle size. Metal extraction followed the EPA 3051A method, and element determination was carried out via ICP-OES. The soils in the Verruga River watershed exhibit a high variability in fertility and granulometric attributes. The Kruskal-Wallis test at a 5% significance level was employed to assess the impact of land management on the availability of elements (As, Co and Pb), while Spearman's correlation, along with hierarchical clustering analysis, was used to comprehend element dynamics. Geostatistics were applied to identify pollution hotspots. Consequently, it became evident that potentially toxic elements can accumulate in the soil depending on land use and management practices (As, Co, and Pb), as well as the weathering process linked to the type of source material, such as diamictite deposits (Ni and Co). Soils in the Verruga River watershed qualify as having minimal enrichment, low pollution levels, and individual ecological risk concerning Cd. The percentage of samples enriched with Cu, As, Zn, and Cd exceeded 67%, with agricultural activities being the primary source of pollution. Meanwhile, in pasture and urban areas, Co and Pb were notably prominent, respectively.

Watershed-scale assessment of environmental background values of soil potential toxic elements from the Caatinga and Atlantic forest ecotone in Brazil.

The evaluation of the concentration of a potentially toxic element (PTE) in soils under native vegetation is the base study to obtain the quality reference values (QRVs), and the watershed is the strategic planning unit for decision making. The objective of this study was to determine the natural concentrations of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn and to establish QRVs for the Verruga river basin. Soils with no or minimal anthropic intervention from the surface layer (0.0-0.2 m) were collected and processed, and PTEs were extracted according to the USEPA 3051A method and determined by ICP‒OES. The quality of the analyses was checked by blank tests and soil samples certified SRM 2709 - San Joaquin Soil. The data set was subjected to exploratory analysis and multivariate statistics. The mean background concentrations of PTEs in soils showed high variability compared to other locations in Brazil and in the world and were (mg kg-1) Fe (24,300) > Mn (211.10) > Cr (40.98) > Zn (28.28) > Cu (10.68) > Ni (9.44) > Pb (4.95) > Co (4.08) > As (3.48) > Cd (0.09). The QRVs for the PTEs were established based on the 75th percentile, where (mg kg-1) Mn (124.59) > Cr (54.51) > Zn (31.66) > Cu (7.89) > Ni (7.20) > Pb (5.98) > As (4.05) > Co (3.40) > Cd (0.10). The chemical attributes and topography variation along the watershed are very heterogeneous and influence the dynamics of the PTEs. This survey will support future research on the impact of human activities on soil contamination in the watershed. This survey will support future research on environmental monitoring and the impacts caused by increased human activities on soil contamination in the Verruga river watershed, in the state of Bahia, Brazil.

Revealing the environmental pollution of two estuaries through histopathological biomarkers in five fishes from different trophic guilds of northeastern Brazil.

Estuaries in Brazil are mostly anthropically affected due to the discharge of industrial and domestic effluents. In two of them, the Santa Cruz Channel Estuary (ITAP) and Sirinhaém River Estuary (SIR), historically affected by mercury pollution and sugarcane industry in Northeast Brazil, we assessed environmental pollution using liver and gill histopathological biomarkers in fish from different trophic levels. Liver samples exhibited serious damages such as hepatic steatosis, necrosis, and infiltration. The gills showed moderate to severe changes, such as lifting of epithelial cells, lamellar aneurysm, and rupture of lamellar epithelium. Most of the changes in the liver and gills were reported for species Centropomus undecimalis and the Gobionellus stomatus, which were considered as good sentinels of pollution. The combination of biomarker methodologies was efficient in diagnosing the serious damage to the species, reinforcing the need for monitoring the health of the ecosystems evaluated.

Baseline concentrations, source apportionment, and probabilistic risk assessment of heavy metals in urban street dust in Northeast Brazil.

Heavy metal pollution by accelerating urbanization is an emerging socio-environmental issue that poses a potential risk to human health and the environment. In this scenario, street dust is a primary source of contaminants. Here, the metal concentrations in street dust of one of the biggest Brazilian cities were assessed aiming to identify and quantify the sources of contamination. The metal bioaccessibility and estimated probabilistic (non)-carcinogenic risks to humans were also evaluated. Thirty-six dust samples were collected in the metropolitan region of Recife. Results showed that the traffic governed the distribution and accumulation of metals in street dust. Emissions from vehicles were the primary source (> 70 %) of heavy metals, except for Cd, which had a mixed origin (natural, traffic, and industrial). Moderate to heavy dust contamination by Ba, Cu, Mn, Pb, and Zn were found, with a very high potential ecological risk. The main exposure route depended on the metal. Barium, Cu, and Pb had ingestion rather than dermal contact as the main route of exposure, while inhalation and dermal contact posed the main risks to Mn and Cr, respectively. The risk for children was higher than for adults. The probabilities of unacceptable carcinogenic risk scenarios (TCRI >10-6) for children and adults were 27 and 4 %, respectively, with Cr being the most concerning metal for the health of the urban population.

Effect of Salinity and Silicon Doses on Onion Post-Harvest Quality and Shelf Life.

Salt stress during pre-harvest limits the shelf life and post-harvest quality of produce; however, silicon nutrition can mitigate salt stress in plants. Thus, we evaluated the effects of salinity and fertilization with Si, in pre-harvest, on the morpho-physiological characteristics of onion bulbs during shelf life. The experiment was set up in randomized complete blocks, with treatments arranged in split-split plots. The plots had four levels of electrical conductivity of irrigation water (0.65, 1.7, 2.8, and 4.1 dS m-1). The subplots had five fertilization levels with Si (0, 41.6, 83.2, 124.8, and 166.4 kg ha-1). The sub-sub plots had four shelf times (0, 20, 40, and 60 days after harvest). Irrigation water salinity and shelf time reduced firmness and increased the mass loss of onion bulbs during shelf life. Salt stress reduced the contents of sugars and total soluble solids of onion bulbs during storage; however, Si supply improved the contents of these variables. Salinity, Si supply, and shelf time increased the concentrations of pyruvic and ascorbic acids in onion bulbs during shelf life. Si doses between 121.8 and 127.0 kg ha-1 attenuated the impacts caused by moderate salinity, increasing the synthesis of metabolites and prolonging the onion bulbs' shelf life.

Soil degradation and Cu, Cr, Ni, Pb and Zn contamination in dumpsites of humid and semiarid tropical regions in northeastern Brazil.

We investigated soil characteristics and heavy metal content changes in 12 inactive dumpsites in humid and semiarid tropical climates in Northeast Brazil. The metals Cu, Cr, Ni, Pb and Zn in soil samples were determined by atomic absorption spectrophotometry. Other parameters measured include pH, electric conductivity, soil texture, soil organic carbon, total porosity and available P. The soil contents of sand, clay, soil organic carbon, available P and heavy metals, and soil bulk density, total porosity and pH were efficient indicators of soil degradation. We found no influence of current use, soil class or climate on the soil response. The mean concentrations of heavy metals in the dumpsite soils followed the order Zn (49.96 mg kg-1) > Cu (38.48 mg kg-1) > Pb (24.64 mg kg-1) > Cr (21.94 mg kg-1) > Ni (7.77 mg kg-1). They were 6- to 36-fold higher than the background values for the region and were above the Brazilian guideline values for metals. The four dumpsite soils that showed simultaneous contamination with two or more heavy metals were located in the semiarid region. This challenges the assumption that soil impacts in the semiarid region are minimal due to lower leaching and high evaporation. Soil changes increase with time under activity, size and decommission time of the dumpsite. These data are important for local authorities to establish more effective targeting policies for closure of dumps and control of the spread of contaminants in areas impacted by the disposal of municipal waste.

Influence of parent material on soil chemical characteristics in a semi-arid tropical region of Northeast Brazil.

Soil parental material is one of the main factors that influence pedogenesis. Several studies evaluated the relationship between the parent material and soil chemistry, but few studies have assessed such a relationship in semi-arid tropical regions. This investigation was carried out to assess the effect of different parent materials on the chemical composition and available concentrations of macronutrients and micronutrients, including potentially toxic elements (Cd, Cr, Ni, and Pb) in soils in a semi-arid tropical setting. The chemical composition of the soils inherited the geochemical signature of their parent materials. Quartz sandstones, augen gneisses, and peraluminous granites exhibited the lowest reservoirs of plant nutrients and formed sandy, acid, and infertile soils. On the other hand, alkaline soils and soils with high concentrations of nutrients formed on ultramafic rocks (harzburgite), marble, and anorthosite. The pH, clay content, and CEC were the main attributes of the soils governing the availability of macro and micronutrients. The low soil organic carbon contents did not influence the availability of the nutrients. The parent material also influenced the soil texture. Parent materials that are richer in silica formed more sandy soils. The availability of Cd, Cr, and Pb in soils was low; however, the elevated Ni concentrations of soils derived from ultramafic rocks may pose risks to the environment and human health. Cluster and discriminant analyses were used to discriminate the natural fertility of soils. These results are useful for the agro-pedological zoning of the Brazilian semi-arid tropical region and for land use planning.

Geospatial modeling and ecological and human health risk assessments of heavy metals in contaminated mangrove soils.

Heavy metal-contaminated wastes can threaten mangrove forests, one of the most biodiverse ecosystems in the world. The study evaluated the geospatial distribution of heavy metals concentrations in soils, the ecological and human health risks, and metal contents in soil fractions and mangrove organisms in the Botafogo estuary, Brazil, one of the most environmentally impacted estuaries in the country. The metal concentrations exceeded by up to 2.6-fold the geochemical background; 91%, 59%, 64%, 31%, and 82% of the soils were contaminated with Cr, Zn, Pb, Cu, and Ni, respectively. Adverse effects to the biota may occur due to Cr, Cu, Ni and Pb exposures. Contents of clay and organic matter were the main factors governing the distribution of metals in soil, contributing to up to 63% of the total variability. However, the geospatial modeling showed that the predictive ability of these variables varied spatially with the metal and location. The ecological and human health risks assessments indicated that the metal concentrations in soils are safe for the environment and human beings. There was a low transfer of metals from the soil to the biota, with values of sediment-biota accumulation factor (SBAF) and biological accumulation coefficients (BAC) lower than 1.0, except for Zn (SBAF = 13.1). The high Zn bioaccumulation by Crassostrea rhizophorae may be associated with the concentrations of Zn in the bioavailable fractions.

Distribution of rare earth elements in soils of contrasting geological and pedological settings to support human health assessment and environmental policies.

Establishing quality reference values (QRVs) for rare earth elements (REEs) in soils is essential for the screening of these emergent contaminants. Currently, Brazil has the second-largest reserve of REEs, but data regarding background concentrations and distributions in soils remain scarce. The aim of this study was to establish the QRVs and assess the spatial distribution of REEs in soils, including REE fractionations and anomalies in (Piauí) state (251,529.186 km2), northeastern Brazil. This study reports the most detailed data on REE geochemistry in Brazilian soils. A total of 243 composite soil samples was collected at 0-20 cm depth. The mean background concentrations in soils followed the abundance of the earth's upper crust: Ce > La > Nd > Pr > Sm > Dy > Gd > Er > Yb > Eu > Tb > Lu. The ∑REEs (mg kg-1) showed the following order based on the individual mesoregions of Piauí state: Southeast (262.75) > North and Central-North (89.68) > Southwest (40.33). The highest QRVs were observed in the Southeast mesoregion. The establishment of QRVs based on the mesoregion scale improves data representativeness and the monitoring of natural REE values by identifying hot spots. Geostatistical modeling indicated significant local variability, especially in the Southeast mesoregion. The levels of these elements in this spatial zone are naturally higher than the other values across Piauí state and the mesoregion itself and indicate a high potential to exceed the QRVs. Our approach provides much needed data to help strengthen policies for both human health and environmental protection.

Phytoattenuation of Cd, Pb, and Zn in a Slag-contaminated Soil Amended with Rice Straw Biochar and Grown with Energy Maize.

Biochar has attracted interest due to its ability to improve soil fertility, soil carbon, and crop yield. Also, biochar can adsorb metals and render them less bioavailable. We investigated the soil availability, sequential extraction, and maize uptake of Cd, Pb, and Zn in a highly contaminated soil amended with rice straw biochar rates (0.0, 5.0, 10.0, 20.0, and 30.0 Mg ha-1). We hypothesized that biochar application to the soil cultivated with maize attenuates metal toxicity and mobility in slag-polluted soils near an abandoned Pb smelting plant in Brazil. Results showed that applying biochar increased the soil organic carbon, CEC, and P up to 27, 30, and 107, respectively. Plant accumulation of P and N was 104 and 32% higher than control, while aerial and root biomasses were increased by 18 and 23%. The sequential extraction showed that Pb and Zn in the original soil were retained mainly in residual fractions (94 and 87%, respectively), while Cd was mostly allocated in the organic fraction (47%). Biochar rates increased the proportion of Cd in the organic fraction to 85%, while Pb and Zn were redistributed mainly into iron oxides. The Cd, Pb, and Zn bioavailability assessed by DTPA decreased 32% in the biochar-amended soil, reducing plants' metal uptake. The maize biomass increase, metal soil bioavailability decrease, and low metal concentration in shoots driven by biochar indicate that phytoattenuation using rice straw biochar and maize cultivation could reduce risks to humans and the environment in the polluted sites of Santo Amaro.

Risk assessment of heavy metals in soils and edible parts of vegetables grown on sites contaminated by an abandoned steel plant in Havana.

Food production in areas contaminated by industrial wastes poses a serious risk to farmers and consumers. Here, we evaluate Cd, Cr, Ni, and Pb concentrations in the soils and the edible parts of lettuce, chives, tomatoes, pepper, and cassava plants grown by small farmers in areas contaminated by slag from an abandoned steel plant in Havana, Cuba. The total, environmentally available, and bioavailable concentrations of metals in the soils and the metals bioconcentration factor in the plants were determined. The risks to human health from food and soil ingestion were estimated. The total and environmentally available concentrations of Cd, Cr, and Pb were above values considered safe by international standards, with likely adverse effect on human health. Cadmium was the most bioavailable metal, reflected in the highest accumulation in the crops' edible parts. Even with negligible DTPA-available Cr concentrations in soils, the Cr concentrations in edible parts of the crops exceeded regulatory levels, suggesting that rhizosphere mechanisms may increase Cr availability. The consumption of vegetables represented 70% of the daily intake dose for Cr, Cd, and Ni, while accidental ingestion of contaminated soil is the predominant human exposure route for Pb. Our results demonstrated the health risks associated with cultivating and consuming vegetables grown on metal contaminated soils in Havana and can assist public policies capable of guaranteeing the sustainability of urban agriculture and food security.

Imaging Zn and Ni distributions in leaves of different ages of the hyperaccumulator Noccaea caerulescens by synchrotron-based X-ray fluorescence.

Mapping of leaves of hyperaccumulators can provide insights into the mechanisms these species utilize to accumulate high metal concentrations. We used synchrotron-based X-ray fluorescence (SXRF) to perform Zn and Ni imaging in leaves of different ages of Noccaea caerulescens. A mature leaf of the related non-hyperaccumulator Thlaspi arvense was also imaged. The concentrations of Zn, Ni, Co, and Cr in N. caerulescens grown on an ultramafic soil were 9-, 10-, 12-, and 3-fold higher than T. arvense. N. caerulescens showed an exceptional ability to accumulate Zn from the soil, posing a bioconcentration factor of 6.7. T. arvense had Zn and Ni distributed uniformly in the leaf blade with doubling fluorescence counts in the tip and margins, suggesting a strategy to excrete metals and avoid toxicity. On the other hand, N. caerulescens displayed distinctly different Zn and Ni accumulation patterns, regardless of the age or metal concentration in the leaves. Zinc was mainly distributed in the cells surrounding the central and secondary veins. Nickel accumulated in the margins and tips of the leaf blade. Given the time required to image large leaves in synchrotron facilities, small leaves can be used to represent the leaf distribution of Zn and Ni in N. caerulescens.

Assessing the spatial distribution and ecologic and human health risks in mangrove soils polluted by Hg in northeastern Brazil.

The emission of mercury (Hg) by chlor-alkali plants can pollute soils and sediments, posing risks to the environment and human health. Mangrove ecosystems are particularly sensitive to Hg contamination. Here, we studied the Hg spatial distribution and associated human and ecologic risks in mangrove soils impacted by a chlor-alkali plant. Sixty-six samples of superficial soils were collected from the mangrove of the Botafogo River, Brazil. Mercury contents were determined and ecological and human health risks were estimated from the soil. The Hg contents exceeded the local Hg background by up to 180 times, indicating the substantial anthropic contribution that occurred in the area. Mercury concentrations followed a gradient as a function of the distance from the chlor-alkali plant, with an apparent contribution from the estuary's hydrodynamic regime. The ecological risk was considered high in all the soils evaluated, while the daily average exposure for humans, considering multiple exposure routes to soil, is below the tolerable dose recommended by the World Health Organization (WHO). However, the risk to human health was unacceptable in the estuary section closest to the plant, mainly for children. Vapor inhalation was the main route for estimating non-carcinogenic risk. The results of this study indicate a severe scenario of Hg pollution with unacceptable risks to the ecosystem and the health of human beings, especially of the communities that live from fishery and shellfish colletion and are exposed daily to soils polluted by mercury. Studies on the organomercurial species in the food chain and Hg levels in individuals living close to the estuary are warranted. This research is an important reference in the world regarding the contamination of mangrove areas by Hg.

In-depth investigation of Sodium percarbonate as oxidant of PAHs from soil contaminated with diesel oil.

Sodium percarbonate (SPC, 2Na2CO3∙3H2O2), is a compound that can be used under multiple environmental applications. In this work, SPC was employed as oxidant in the treatment of soil contaminated with diesel oil. The soil samples were collected during the earthmoving stage of RNEST Oil Refinery (Petrobras), Brazil. Then, the samples were air-dried, mixed and characterized. Subsequently, raw soil was contaminated with diesel and treated by photo-Fenton reaction (H2O2/Fe2+/UV). SPC played a significant role in the generation of hydroxyl radicals under the catalytic effect of ferrous ions (Fe2+), hydrogen peroxide (H2O2) and radiation. These radicals provoked the photodegradation of polycyclic aromatic hydrocarbons (PAHs), in the soil remediation. A factorial design 33 was carried out to assess the variables which most influenced the decrease in total organic carbon (TOC). The study was performed with the following variables: initial concentration of [H2O2] and [Fe2+], between 190.0 and 950.0 mmol L-1 and 0.0-14.4 mmol L-1, respectively. UV radiation was supplied from sunlight, blacklight lamps, and system without radiation. All experiments were performed with 5.0 g of contaminated soil in 50.0 mL of solution. The initial concentration of Fe2+ showed the statistically most significant effect. The oxidation efficiency evaluated in the best condition showed a decrease from 34,765 mg kg-1 to 15,801 mg kg-1 in TOC and from 85.750 mg kg-1 to 20.770 mg kg-1 in PAHs content. Moreover, the sums of low and high molecular weight polycyclic aromatic hydrocarbons (LMW-PAHs and HMW-PAHs) were 19.537 mg kg-1 and 1.233 mg kg-1, respectively. Both values are within the limits recommended by the United Sates Environmental Protection Agency (USEPA) and evidenced the satisfactory removal of PAHs from contaminated soil, being an alternative to classic oxidation protocols.

Cadmium, silicon and nutrient accumulation by maize plants grown on a contaminated soil amended with a diatomaceous Earth fertilizer / Acúmulo de cádmio, silício e nutrientes por plantas de milho cultivadas em solo contaminado e adubado com fertilizante terra diatomáceas

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.

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.

Near-infrared spectroscopy for the prediction of rare earth elements in soils from the largest uranium-phosphate deposit in Brazil using PLS, iPLS, and iSPA-PLS models.

The largest uranium-phosphate deposit in Brazil also contains considerable levels of rare earth elements (REEs), which allows for the co-mining of these three ores. The most common methods for REE determination are time-consuming and demand complex sample preparation and use of hazardous reagents. Thus, the development of a safer and faster method to predict REEs in soil could aid in the assessment of these elements. We investigated the efficiency of near-infrared (NIR) spectroscopy to predict REEs in the soil of the uranium-phosphate deposit of Itataia, Brazil. We collected 50 composite topsoil samples in a well-distributed sampling grid along the deposit. The NIR measures in the soils ranged from 750 to 2500 nm. Three partial least squares regressions (PLSR) were selected to calibrate the spectra: full-spectrum partial least squares (PLS), interval partial least squares (iPLS), and successive projections algorithms for interval selection in partial least squares (iSPA-PLS). The concentrations of REEs were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). In addition to raw spectral data, we also used spectral pretreatments to investigate the effects on prediction results: multiplicative scatter correction (MSC), Savitzky-Golay derivatives (SG), and standard normal variate transformation (SNV). Positive results were obtained in PLS for La and ΣLREE using MSC pretreatment and in iSPA-PLS for Nd and Ce using raw data. The accuracy of the measurements was related to the REE concentration in soil; i.e., elements with higher concentrations tended to present more accurate results. The results obtained here aim to contribute to the development of NIR spectroscopy techniques as a tool for mapping the concentrations of REEs in topsoil.

Background concentrations and quality reference values for potentially toxic elements in soils of Piauí state, Brazil.

The background concentration of potentially toxic elements (PTE) in soils is influenced by the parent material composition and soil forming processes. The soil natural concentration of PTE is a first step to establish regulatory levels for the monitoring of these elements in soils suspected of contamination. In the present study, we performed a natural background concentration survey of PTE in soils of the Piauí state, Brazil. The study provides the basis for establishing soil quality reference values (QRVs) for a large area (over 251,000 km2) with different pedological features. A total of 262 geo-referenced soil samples (0.0-0.2 m) were collected in areas relatively undisturbed by human activity. The concentrations of Ba, Cd, Co, Cr, Cu, Fe, Mo, Ni, Pb, Sb, V, and Zn were determined by ICP-OES. Univariate statistical methods and multivariate exploratory techniques were used to understand the relationship between soil characteristics, geological features, and PTE concentrations in soils. The mean background concentrations of PTE in the soils were generally lower than those reported in other countries and/or other Brazilian states, and followed the order: Fe > Ba > V > Cr > Cu > Pb > Zn > Ni > Pb > Co > Mo > Sb > Cd. The main factors governing the concentrations of PTE in soils were the parent material and the soil texture. The different geological features in the study area influenced the spatial distribution of PTE and divided the state into three regions presenting low, high, and intermediate values. Given this geological and pedological complexity, we proposed establishing three sets of QRV rather than a single QRV for the whole state to avoid misinterpretation regarding the investigation of areas suspected of contamination. This background concentration survey contains a wealth of information that provides the basis for the soil guideline values in the state and supports future research on the impact of anthropogenic activities in soil contamination.

Solos de minas de scheelita como fontes de contaminação por metais pesados / Scheelite mines soils as sources of heavy metal contamination

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.