Microbial-assisted soil chromium immobilization through zinc and iron-enriched rice husk biochar

Soil chromium toxicity usually caused by the tannery effluent compromises the environment and causes serious health hazards. The microbial role in strengthening biochar for its soil chromium immobilization remains largely unknown. Hence, this study evaluated the effectiveness of zinc and iron-enriched rice husk biochar (ZnBC and FeBC) with microbial combinations to facilitate the chromium immobilization in sandy loam soil. We performed morphological and molecular characterization of fungal [Trichoderma harzianum (F1), Trichoderma viride (F2)] and bacterial [Pseudomonas fluorescence (B1), Bacillus subtilis (B2)] species before their application as soil ameliorants. There were twenty-five treatments having ZnBC and FeBC @ 1.5 and 3% inoculated with bacterial and fungal isolates parallel to wastewater in triplicates. The soil analyses were conducted in three intervals each after 20, 30, and 40 days. The combination of FeBC 3%+F2 reduced the soil DTPA-extractable chromium by 96.8% after 40 days of incubation (DAI) relative to wastewater. Similarly, 92.81% reduction in chromium concentration was achieved through ZnBC 3%+B1 after 40 DAI compared to wastewater. Under the respective treatments, soil Cr(VI) retention trend increased with time such as 40 > 30 > 20 DAI. Langmuir adsorption isotherm verified the highest chromium adsorption capacity (41.6 mg g⁻¹) with FeBC 3% at 40 DAI. Likewise, principal component analysis (PCA) and heat map disclosed electrical conductivity-chromium positive, while cation exchange capacity-chromium and pH-organic matter negative correlations. PCA suggested the ZnBC-bacterial while FeBC-fungal combinations as effective Cr(VI) immobilizers with >70% data variance at 40 DAI. Overall, the study showed that microbes + ZnBC/FeBC resulted in low pH, high OM, and CEC, which ultimately played a role in maximum Cr(VI) adsorption from wastewater applied to the soil. The study also revealed the interrelation and alternations in soil dynamics with pollution control treatments. Based on primitive soil characteristics such as soil metal concentration, its acidity, and alkalinity, the selection criteria can be set for treatments application to regulate the soil properties. Additionally, FeBC with Trichoderma viride should be tested on the field scale to remediate the Cr(VI) toxicity.

Microbial application in remediation of heavy metals: an overview

Heavy metal contamination poses a menacing threat to all living forms in the natural world due to its catastrophic consequences, contributing to environmental pollution. The need for human beings increasing each day along with anthropological activity is contributing directly to the destruction of the environment with the release of a large number of heavy metals into the food chain. These metals can be accumulated in the food chains and are very extremely toxic even at low concentrations. Heavy metals aggregation can deteriorate the healthy ecosystem of the water bodies as well. One of the major concerns is the diminution and administration of the heavy metals aggregating in marine water bodies and lakes. Heavy metals are not degradable and thus tend to remain in the environment for a prolonged time period. Heavy metal aggregation can demonstrate immediate repercussions such as DNA damage, inhibition of respiration and photosynthesis, and rapid reactive oxygen species generation. Conventional or standard chemical and physical methods for remediation of heavy metals are uneconomical and lead to the production of a large magnitude of chemical waste. This shifts the focus and interest towards the utilization of microbes in remediation of heavy metals from the environment which is eco-friendly and economical. To contend with heavy metals, microorganisms have a specific mechanism such as biotransformation, biosorption, and homeostasis. The microbial system is responsive to the toxicity that is created by the heavy metals which are easily water-soluble and available in the environment. The current review article describes the sources and effects of metal ions in the environment followed by bioremediation strategies followed in their remediation. Microbial approaches in remediation of metal ions from extraterrestrial materials are depicted in the paper.

Toxic heavy metals: impact on the environment and human health, and treatment with conducting organic polymers, a review

Water pollution by heavy metals has many human origins, such as the burning of fossil fuels, exhaust gases of vehicles, mining, agriculture, and incineration of solid and liquid wastes. Heavy metals also occur naturally, due to volcanoes, thermal springs activity, erosion, infiltration, etc. This water contamination is a threat for living beings because most heavy metals are toxic to humans and to aquatic life. Hence, it is important to find effective techniques for removing these contaminants in order to reduce the level of pollution of the natural waters. In this work, we have reviewed the toxicity of several heavy metals (mercury, lead, cadmium, chromium, nickel), their impact on the environment and human health, and the synthesis and characterization methods of conducting organic polymers (COPs) utilized for the removal of heavy metals from the environment. Therefore, this review was essentially aimed to present recent works and methods (2000-2020) on the environmental impact and toxicity of heavy metals and on the removal of toxic heavy metals, using chemically and/or electrochemically synthesized COPs. We have also stressed the great interest of COPs for the removal of toxic heavy metals from waters.

Molecular basis of arsenite (As⁺³)-induced acute cytotoxicity in human cervical epithelial carcinoma cells

BACKGROUND

Rapid industrialization is discharging toxic heavy metals into the environment, disturbing human health in many ways and causing various neurologic, cardiovascular, and dermatologic abnormalities and certain types of cancer. The presence of arsenic in drinking water from different urban and rural areas of the major cities of Pakistan, for example, Lahore, Faisalabad, and Kasur, was found to be beyond the permissible limit of 10 parts per billion set by the World Health Organization. Therefore the present study was initiated to examine the effects of arsenite (As(+3)) on DNA biosynthesis and cell death.

METHODS

After performing cytotoxic assays on a human epithelial carcinoma cell line, expression analysis was done by quantitative polymerase chain reaction, western blotting, and flow cytometry.

RESULTS

We show that As(+3) ions have a dose- and time-dependent cytotoxic effect through the activation of the caspase-dependent apoptotic pathway. In contrast to previous research, the present study was designed to explore the early cytotoxic effects produced in human cells during exposure to heavy dosage of As(+3) (7.5 µg/ml). Even treatment for 1 h significantly increased the mRNA levels of p21 and p27 and caspases 3, 7, and 9. It was interesting that there was no change in the expression levels of p53, which plays an important role in G2/M phase cell cycle arrest.

CONCLUSION

Our results indicate that sudden exposure of cells to arsenite (As(+3)) resulted in cytotoxicity and mitochondrial-mediated apoptosis resulting from up-regulation of caspases.