Alkaline extract from vermicompost reduced the stress promoted by As on maize plants and increase their phytoextraction capacity.

Arsenic (As) represents an environmental risk and phytoremediation has been identified as a good technique to recover contaminated soils. Plants defense mechanisms needed to be enhanced against As stress-promoting action by biostimulants such as humic materials. This work sought to determine the effectiveness of an alkaline vermicompost extract (AEV) and in mitigating stresses promoted by As in maize plants, increasing their potential use for phytoextraction. The AEV were extracted from vermicompost and two preliminary assays in Leonard pots were carried out: the first one to define the best AEV concentration-response dose and the second to point out the toxic As concentration. The second step was to set up a 28-day long experiment with the following four treatments: control, AEV, As, As + AEV. AEV attenuated As-induced stress in maize plants. Maize dry biomass was reduced in the As treatment and rebalanced to values similar to the control in the As + HS treatment while the plants treated only with HS showed the highest biomass among the treatments. The concentrations of P, Fe, Cu, Mn and Ni, and catalase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD) antioxidant activity increased in the As treatment and decreased in the As + AEV treatment. The rate of photosynthesis decreased, and the internal CO2 concentration increased with stress induced by As, where both effects were attenuated by AEV. Our results show the positive effect of the AEV in alleviating As abiotic stress on maize growth, offering new options of employment of humic substances in phytoremediation process.

Novel K-enriched organomineral fertilizer from sewage sludge-biochar: Chemical, physical and mineralogical characterization.

Sewage sludge biochar (SSB) is a multi-nutrient fertilizer with very low K concentration. This study presents a novel K-enriched SSB fertilizer with the potential to increase K use efficiency by crops. The object of this work was therefore to evaluate the physical-chemical, morphological and mineralogical characteristics of a SSB organomineral fertilizer (OSSB) enriched with K. SSB was enriched with KCl and K2SO4 using three technological methods (granules, pellets and powders). The enrichment of SSB with K ensured a K2O content about 75 times higher than the pure SSB. Organominerals in powder form had higher levels of total nitrogen, calcium, sulfur, phosphorus and higher pH than granules and pellets. The morphology and physical characteristics of enriched OSSBs were more influenced by the form of the fertilizer than by the source of K. In general, the enriched OSSBs are influenced by the quantities of feedstocks and the enrichment technology.

The residual effect of sewage sludge biochar on soil availability and bioaccumulation of heavy metals: Evidence from a three-year field experiment.

Conversion of sewage sludge (SS) into biochar through pyrolysis is an alternative to make this residue useful for agricultural purposes. Despite advances in interpreting the functions of SS biochar (SSB) for improving soil quality, it is still necessary to understand its residual effect on the dynamics of heavy metals (HM), especially under field conditions in tropical soils. Therefore, the objective of this study was to evaluate the residual effect of the application of SSB obtained at different pyrolysis temperatures on the accumulation, availability and bioaccumulation of HMs by corn cultivated in a tropical soil. For this purpose, a field experiment was conducted for three years to assess the total and available levels of HMs in the soil and the leaf concentration after suspending the application of 30 t ha-1 of SSB produced at 300 °C (BC300) and 500 °C (BC500). In general, the HM contents were below the maximum allowed by environmental legislation in several countries. SSB, regardless of temperature, was effective in immobilizing non-essential HMs for plants, such as Cd, Co, Cr and Pb, in the soil. On the other hand, SSB was able to supply micronutrients to corn plants after amendment ceased. Thus, the lack of negative long-term effects confirms the feasibility and safety of using SSB in agricultural areas with regards to contamination by HM, and makes it an alternative for the disposal of domestic SS.

Effects of different humic substances concentrations on root anatomy and Cd accumulation in seedlings of Avicennia germinans (black mangrove).

Mangrove areas are among most threatened tropical ecosystems worldwide. Among polluting agents Cadmium is often found in high concentrations in mangrove sediments. Humic substances, complex biomolecules formed in soil and sediments during animal and plant residuals decomposition, have a known biostimulant activity and can be adopted to counteract various plant stresses. This study explores, in controlled conditions, the effect of humic substances on Avicennia germinans seedlings, with or without cadmium contamination. Humic compounds significantly changed plant root architecture, and, when coupled with cadmium, root anatomy and Cortex to Vascular Cylinder diameter ratio. These modifications led to lower Cd uptake by humic substances-treated plants. Humic substances amendment could be effective, depending on their concentrations, on improving plant health in mangrove areas, for forest recuperation and/or dredged sediments phytoremediation purposes.

Geochemistry and spatial variability of metal(loid) concentrations in soils of the state of Minas Gerais, Brazil.

Since 2009 a policy has been implemented in Brazil to establish the natural concentrations of potentially toxic substances in soil for each state. Historically a 'mining state', Minas Gerais established a Quality Reference Value for metal(loid)s for all of the soils in the state. To successfully establish these values it is important to study the spatial geochemical diversity for the state. In this context, the objectives of this work are: (1) to evaluate the natural concentrations of metal(loid)s in pristine Minas Gerais soils and (2) to interpret the spatial variability in concentration of these elements. The 0-20 cm layer of soils was sampled for 697 georeferenced sites including the main geological materials and soil groups. Soil properties were analyzed according to methodologies suitable for Brazilian soils. The concentration of metal(loid)s was determined by acid extraction according to EPA 3051A. Descriptive statistics, Pearson correlation and spatial variability analyses were performed. The dominance of acidic pH and low CEC values reflects the pervasive deep acid weathering. The variability of metal(loid) concentrations for soils of the state may be attributed to geological diversity and different pedogenesis. Correlation and spatial analysis indicated that the Fe concentration is strongly associated with metal(loid) concentrations in topsoil. According to the spatial geochemical diversity of the state, a k-means cluster analysis was performed which identified four clusters. A significant difference in the mean values of metal(loid) concentrations between the clusters confirmed that the single Quality Reference Value established does not represent the geochemical diversity of soils in Minas Gerais.

Pedogeochemistry in NE-Brazil - compared to Australia and Europe.

A soil geochemical dataset (major and minor elements), based on low-density sampling, is provided for NE-Brazil (ca. 1.7 million km²). It covers an area from about 2°S to 12°S, and from 34°W to 49°W, and refers to top (TOP: 0-20 cm) and bottom (BOT: 30-50 cm) mineral soils. Results are put in perspective using two recent and comparable studies, the National Geochemical Survey of Australia (NGSA) and the European Geochemical Mapping of Agricultural Soils (GEMAS). All median element concentrations in the Brazilian samples are depleted compared to World Soil Averages (WSA), except for Al2O3 and SiO2, which are respectively similar to WSA and enriched in Brazil. While the depletion is moderate for Fe2O3, MnO, P2O5, and TiO2, it reaches an order of magnitude and more for K2O, MgO, CaO, and Na2O. The difference between TOP and BOT concentrations is lower than the variation of either TOP or BOT concentrations between sample sites. Similar spatial distribution and the high correlation between TOP and BOT concentrations suggest that (1) similar processes and parameters are of general relevance for the geochemical composition of TOP and BOT samples, and (2) topsoil and subsoil are not decoupled. Cluster analysis revealed similar results for TOP and BOT samples, yielding three groups of elements/oxides displaying similar behavior: Gr.1 comprising Al2O3, Fe2O3, TiO2, and P2O5; Gr.2 comprising CaO, K2O, MgO, MnO, and Na2O; and Gr.3 being SiO2. Weathering indicators are significantly positively correlated and show similar spatial distributions in TOP and BOT samples. All elements deliver similar mass removal times (time to export all material from a 10 cm soil layer) and clearly discern between the regions: Europe with the fastest "depletion" (12,200 ± 300 years), followed by Australia (33,200 ± 3000 years) and Brazil (86,700 ± 3000 years). Similar results emerge when calculating denudation rates, using independent fluvial denudation data in large basins.