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The release of cadmium into the environment is a significant global concern due to its toxicity, non-biodegradability, and persistence in nature. There is an urgent need for effective, eco-friendly, and cost-effective systems for removing Cd because of the many drawbacks of conventional physicochemical techniques. This study investigated the ability of the extremophile red microalgal strain Galdieria sulphuraria CCMEE 5587.1 to tolerate and remove Cd (II) ions at acidic pH in a controlled laboratory environment. Three distinct concentrations of Cd (1.5 mg L−1, 3 mg L−1, and 6 mg L−1) were introduced to the cyanidium medium, and G. sulphuraria cells were introduced in the medium and grown for ten days. Four distinct aspects were identified regarding Cd removal: time course Cd removal, total Cd removal, extracellular Cd removal, and intracellular Cd removal. The inhibitory effects of Cd on G. sulphuraria growth were observed using a daily growth profile. Initial incubation days showed an inhibition of G. sulphuraria growth. In addition, increasing the Cd concentration in the medium decreased the growth rate of G. sulphuraria. Rapid Cd removal occurred on the first day of the experiment, followed by a steady removal of Cd until the last day. The highest total removal efficiency occurred in a medium containing 3 mg L−1 of Cd ions, which was 30%. In contrast, the highest sorption capacity occurred in a medium containing 6 mg L−1 of Cd ions, which was 1.59 mg g−1 of dry biomass. In all media compositions, a major fraction (>80%) of Cd removal occurred via adsorption on the cell surface (extracellular). These results showed that G. sulphuraria cells can remove Cd ions from aqueous solution, which makes them a potential bioremediation option for heavy metal removal.

Biochar (BC) boasts diverse environmental applications. However, its potential for environmental biomonitoring has, surprisingly, remained largely unexplored. This study presents a preliminary analysis of BC’s potential as a biomonitor for the environmental availability of ionic Cd, utilizing the lichen Evernia prunastri (L.) Ach. as a reference organism. For this purpose, the lichen E. prunastri and two types of wood-derived biochar, biochar 1 (BC1) and biochar 2 (BC2), obtained from two anonymous producers, were investigated for their ability to accumulate, or sequester and subsequently release, Cd when exposed to Cd-depleted conditions. Samples of lichen and biochar (fractions between 2 and 4 mm) were soaked for 1 h in a solution containing deionized water (control), 10 µM, and 100 µM Cd2+ (accumulation phase). Then, 50% of the treated samples were soaked for 24 h in deionized water (depuration phase). The lichen showed a very good ability to adsorb ionic Cd, higher than the two biochar samples (more than 46.5%), and a weak ability to release the metal (ca. 6%). As compared to the lichen, BC2 showed a lower capacity for Cd accumulation (−48%) and release (ca. 3%). BC1, on the other hand, showed a slightly higher Cd accumulation capacity than BC2 (+3.6%), but a release capacity similar to that of the lichen (ca. 5%). The surface area and the cation exchange capacity of the organism and the tested materials seem to play a key role in their ability to accumulate and sequester Cd, respectively. This study suggests the potential use of BC as a (bio)monitor for the presence of PTEs in atmospheric depositions and, perhaps, water bodies.

The release of cadmium into the environment is a significant global concern due to its toxicity, non-biodegradability, and persistence in nature. There is an urgent need for effective, eco-friendly, and cost-effective systems for removing Cd because of the many drawbacks of conventional physicochemical techniques. This study investigated the ability of the extremophile red microalgal strain Galdieria sulphuraria CCMEE 5587.1 to tolerate and remove Cd (II) ions at acidic pH in a controlled laboratory environment. Three distinct concentrations of Cd (1.5 mg L -1 , 3 mg L -1 , and 6 mg L -1 ) were introduced to the cyanidium medium, and G. sulphuraria cells were introduced in the medium and grown for ten days. Four distinct aspects were identified regarding Cd removal: time course Cd removal, total Cd removal, extracellular Cd removal, and intracellular Cd removal. The inhibitory effects of Cd on G. sulphuraria growth were observed using a daily growth profile. Initial incubation days showed an inhibition of G. sulphuraria growth. In addition, increasing the Cd concentration in the medium decreased the growth rate of G. sulphuraria . Rapid Cd removal occurred on the first day of the experiment, followed by a steady removal of Cd until the last day. The highest total removal efficiency occurred in a medium containing 3 mg L -1 of Cd ions, which was 30%. In contrast, the highest sorption capacity occurred in a medium containing 6 mg L -1 of Cd ions, which was 1.59 mg g -1 of dry biomass. In all media compositions, a major fraction (>80%) of Cd removal occurred via adsorption on the cell surface (extracellular). These results showed that G. sulphuraria cells can remove Cd ions from aqueous solution, which makes them a potential bioremediation option for heavy metal removal.

The green synthesis of metal oxide nanoparticles is presented as an excellent sustainable alternative for achieving nanostructures, with potential applications. This research provides important information regarding the influence of the type of solvent used in extracting organic reducing agents from E. globulus on the FeO NPs green synthesis protocol. A broad approach to characterization is presented, where UV-vis spectrophotometry suggests the presence of this type of nanoparticulate material. Likewise, the reduction mechanism was evaluated by FT-IR and the magnetic properties were evaluated by PPSM. In addition, characterizations were linked via elemental analysis (EDX), crystallographic characterization (XRD), electron microscopy (SEM/STEM), and Z potential to evaluate colloidal stability. The results show the influence of the type of solvent used for the extraction of organic reducing agents from E. globulus, and the effect on the synthesis of FeO NPs. In addition, the nanostructure material obtained showed excellent efficiency in the remediation of agricultural soil, eliminating metals such as Cr-VI, Cd, and, to a lesser extent, Pb.

Biochar (BC) boasts diverse environmental applications. However, its potential for environmental biomonitoring has, surprisingly, remained largely unexplored. This study presents a preliminary analysis of BC's potential as a biomonitor for the environmental availability of ionic Cd, utilizing the lichen Evernia prunastri (L.) Ach. as a reference organism. For this purpose, the lichen E. prunastri and two types of wood-derived biochar, biochar 1 (BC1) and biochar 2 (BC2), obtained from two anonymous producers, were investigated for their ability to accumulate, or sequester and subsequently release, Cd when exposed to Cd-depleted conditions. Samples of lichen and biochar (fractions between 2 and 4 mm) were soaked for 1 h in a solution containing deionized water (control), 10 µM, and 100 µM Cd 2+ (accumulation phase). Then, 50% of the treated samples were soaked for 24 h in deionized water (depuration phase). The lichen showed a very good ability to adsorb ionic Cd, higher than the two biochar samples (more than 46.5%), and a weak ability to release the metal (ca. 6%). As compared to the lichen, BC2 showed a lower capacity for Cd accumulation (-48%) and release (ca. 3%). BC1, on the other hand, showed a slightly higher Cd accumulation capacity than BC2 (+3.6%), but a release capacity similar to that of the lichen (ca. 5%). The surface area and the cation exchange capacity of the organism and the tested materials seem to play a key role in their ability to accumulate and sequester Cd, respectively. This study suggests the potential use of BC as a (bio)monitor for the presence of PTEs in atmospheric depositions and, perhaps, water bodies.

A novel core-shell magnetic Prussian blue-coated Fe3O4 composites (Fe3O4@PB) were designed and synthesized by in-situ replication and controlled etching of iron oxide (Fe3O4) to eliminate Cd (II) from micro-polluted water. The core-shell structure was confirmed by TEM, and the composites were characterized by XRD and FTIR. The pore diameter distribution from BET measurement revealed the micropore-dominated structure of Fe3O4@PB. The effects of adsorbents dosage, pH, and co-existing ions were investigated. Batch results revealed that the Cd (II) adsorption was very fast initially and reached equilibrium after 4 h. A pH of 6 was favorable for Cd (II) adsorption on Fe3O4@PB. The adsorption rate reached 98.78% at an initial Cd (II) concentration of 100 μg/L. The adsorption kinetics indicated that the pseudo-first-order and Elovich models could best describe the Cd (II) adsorption onto Fe3O4@PB, indicating that the sorption of Cd (II) ions on the binding sites of Fe3O4@PB was the main rate-limiting step of adsorption. The adsorption isotherm well fitted the Freundlich model with a maximum capacity of 9.25 mg·g−1 of Cd (II). The adsorption of Cd (II) on the Fe3O4@PB was affected by co-existing ions, including Cu (II), Ni (II), and Zn (II), due to the competitive effect of the co-adsorption of Cd (II) with other co-existing ions.

Agricultural wastes have great potential for the removal of heavy metal ions from aqueous solution. The contamination of water by toxic heavy metals is a worldwide environmental problem. Unlike organic pollutants, the majority of which are susceptible to biological degradation, heavy metals do not degrade into harmless end products. Discharges containing cadmium, in particular, are strictly controlled because of the highly toxic nature of this element and its tendency to accumulate in the tissues of living organisms. This work aims to develop inexpensive, highly available, effective metal ion adsorbents from natural wastes as alternatives to existing commercial adsorbents. In particular, Tamrix articulata wastes were modified chemically by esterification with maleic acid to yield a carboxyl-rich adsorbent. The adsorption behavior of treated Tamrix articulata wastes toward cadmium ions in aqueous solutions in a batch system has been studied as a function of equilibration time, adsorbent dose, temperature and pH. Results showed that the maximum adsorption capacity was 195.5 mg/g in a pH 4 solution at 30 °C with a contact time of 120 min, an initial concentration of 400 mg/L and an adsorbent dose of 0.3 g/L. The kinetic data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. It was shown that the adsorption of cadmium could be described by a pseudo-second-order equation. The experimental data were also analyzed using the Langmuir and Freundlich models of adsorption. Thermodynamic parameters such as ΔGo, ΔHo and ΔSo have been evaluated and it has been found that the sorption process was spontaneous and exothermic in nature. From all of our data, we conclude that the treated Tamrix articulata wastes investigated in this study showed good potential for cadmium removal from aqueous solutions.