Biochars have been shown as promising materials for cadmium remediation. However, the different precursors and the pyrolysis process operating conditions can yield very different surface functional groups, and as a result, different cadmium sorption mechanisms can be observed in biochars. Herein we present the results of cadmium sorption on biochars produced from the pyrolysis of different agro-residues, namely, coffee husk, quinoa straw, and oil palm kernel shell. The adsorption isotherms were used to determine the influence of the biochar’s physicochemical characteristics to their sorption behavior. The biochars prepared from quinoa residues showed much higher cadmium uptakes than the other biochars. The concentration of base cations was found to be a critical factor for cadmium sorption. Although the quinoa biochars presented large uptakes, it was found that base cations were supported on the biochars and could be removed by leaching. Results from this study suggest that concentration of base cations on biochars could be used as predictors of the biochar capabilities for the removal of cadmium in aqueous solution.

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Soil contamination by Pb can result from different anthropogenic sources such as lead-based paints, gasoline, pesticides, coal burning, mining, among others. This work aimed to evaluate the potential of P-loaded biochar (Biochar-based slow-release P fertilizer) to remediate a Pb-contaminated soil. In addition, we aim to propose a biomonitoring alternative after soil remediation. First, rice husk-derived biochar was obtained at different temperatures (450, 500, 550, and 600 °C) (raw biochars). Then, part of the resulting material was activated. Later, the raw biochars and activated biochars were immersed in a saturated KH2PO4 solution to produce P-loaded biochars. The ability of materials to immobilize Pb and increase the bioavailability of P in the soil was evaluated by an incubation test. The materials were incorporated into doses of 0.5, 1.0, and 2.0%. After 45 days, soil samples were taken to biomonitor the remediation process using two bioindicators: a phytotoxicity test and enzyme soil activity. Activated P-loaded biochar produced at 500 °C has been found to present the best conditions for soil Pb remediation. This material significantly reduced the bioavailability of Pb and increased the bioavailability of P. The phytotoxicity test and the soil enzymatic activity were significantly correlated with the decrease in bioavailable Pb but not with the increase in bioavailable P. Biomonitoring using the phytotoxicity test is a promising alternative for the evaluation of soils after remediation processes.

The contamination of soil and water by metals such as mercury (Hg) and cadmium (Cd) has been increasing in recent years, because of anthropogenic activities such as mining and agriculture, respectively. In this work, the changes in the rhizosphere microbiome of Lolium perenne L. during the phytoremediation of soils contaminated with Hg and Cd were evaluated. For this, two soil types were sampled, one inoculated with mycorrhizae and one without. The soils were contaminated with Hg and Cd, and L. perenne seeds were sown and harvested after 30 days. To assess changes in the microbiome, DNA isolation tests were performed, for which samples were subjected to two-step PCR amplification with specific 16S rDNA V3-V4 primers (337F and 805R). With mycorrhizae, changes had been found in the absorption processes of metals and a new distribution. While with respect to microorganisms, families such as the Enterobacteriaceae have been shown to have biosorption and efflux effects on metals such as Hg and Cd. Mycorrhizae then improve the efficiency of removal and allow the plant to better distribute the absorbed concentrations. Overall, L. perenne is a species with a high potential for phytoremediation of Cd- and Hg-contaminated soils in the tropics. Inoculation with mycorrhizae modifies the phytoremediation mechanisms of the plant and the composition of microorganisms in the rhizosphere. Mycorrhizal inoculation and changes in the microbiome were associated with increased plant tolerance to Cd and Hg. Microorganism-assisted phytoremediation is an appropriate alternative for L. perenne.

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The purpose of this study was to evaluate the capability of Aspergillus tubingensis and Talaromyces islandicus to solubilize inorganic phosphorus sources, their activity under abiotic stress, and the enhancement of P availability in soils and plant growth. The P-solubilizing capability and acidification mechanism of the strains were assessed in vitro using tricalcium phosphate and rock phosphate. Independent assays were conducted with rock phosphate under NaCl and fungicides carbendazim, chlorothalonil, and propamocarb hydrochloride using a factorial design. Thereafter, the effects of fungal inoculations in rock phosphate-amended soil and P nutrition of Zea mays were assessed in a greenhouse experiment. Both fungi solubilized P in vitro via acidification through the exudation of acetic, citric, lactic, malic, quinic, and succinic acids. The P-solubilizing efficiency of A. tubingensis was maintained above 97.5% under 0.5 to 3.0% NaCl, up to 28.7% in the treatment with carbendazim, up to 5.3% with chlorothalonil, and above 96.5% with propamocarb hydrochloride; while T. islandicus efficiency decreased to 45.2% in a NaCl concentration-dependent trend, and maintained it above 80% in the fungicide treatments. The inoculation with A. tubingensis increased the available P in the amended soil by up to 65% after 30 days and resulted in 87% higher foliar P content, 111% greater plant height, and 25% greater dry weight of maize shoots. Similarly, T. islandicus contributed to these parameters in 55, 67, 90, and 17%, respectively. These findings suggest their potential as qualified phosphorus solubilizing microorganisms to develop novel and sustainable approaches for P fertilization in agriculture.