Anita Mukherjee

Allium cepa (A. cepa) root tip assay is considered an excellent genetic model for genotoxicity screening and monitoring of environmental mutagens. The assay is highly versatile for genetic endpoints, inexpensive, quick, and easy to use. It can be used with a range of environmental conditions, pH, and temperature, and does not require any ethical regulations as required for animal models and cell lines. In this chapter, we describe the modifications of the assay to analyze different endpoints of genotoxicity. They include the most commonly used chromosome aberrations, the mitotic index to evaluate cytotoxicity, and the analysis of micronuclei to verify the mutagenicity of different chemicals. Moreover, the A. cepa test system also provides a sensitive method for the evaluation of DNA damage and DNA repair capacity at the single-cell level by the Comet assay.

Rapid growth in the use of aluminium oxide nanoparticles (Al₂O₃ NPs) in various fields such as medicine, pharmacy, cosmetic industries, and engineering creates concerns since the literature is replete with data regarding their toxicity in living organisms. The objective of the present study was to demonstrate the potential toxicological manifestations of repeated exposure to Al₂O₃ NP at low doses in vivo. In the present study, Al₂O₃ NP was orally administered at 15, 30 or 60 mg kg⁻¹ body weight for 5 days to Swiss albino male mice. A battery of well-defined assays was undertaken to evaluate aluminium (Al) bioaccumulation, haematological and histological changes, oxidative damage and genotoxicity. Physico-chemical characterisation demonstrated increases in hydrodynamic diameter along the concentration gradient of Al₂O₃ NP dispersed in MilliQ water. Brain, liver, spleen, kidney and testes showed high Al retention levels. Histopathological lesions were prominent in the brain and liver. Al₂O₃ NP treatment increased levels of lipid peroxidation and decreased glutathione content in the test organs at all dose levels. The enzyme activities of catalase and superoxide dismutase were also significantly altered. DNA damage quantified using the comet assay was markedly increased in all the soft organs studied. Anatomical abnormalities, redox imbalance and DNA damage were positively correlated with Al retention in the respective organs. Size, zeta potential and colloidal state might have contributed to the bio-physico-chemical interactions of the NPs in vivo and were responsible for the non-linear dose response. The overall data indicate that Al₂O₃ NP exposure may result in adverse health consequences, inclusive of but not limited to disturbed redox homeostasis, hepatocellular toxicity, neurodegeneration and DNA damage.

This study reports the efficiency of Saccharum spontaneum and Saccharum munja for phytoextraction and phytostabilization of metal-contaminated coal fly ash (FA) dumpsites. Pot experiments with FA and garden soil (GS) as control were conducted for a period of one year. Heavy metals in FA and their relative translocation to root and shoot tissues were analyzed. The accumulation of heavy metals in the roots was higher than the shoots. A considerable amount of heavy metals was sequestered and accumulated by the roots but the amount of contaminants was not translocated to the shoot system. This could be supported by the translocation factor (TF) values. Values of bioaccumulation factor (BAF) greater than unity indicated that Saccharum is a potential heavy metal accumulator. The BAF values for roots in S. spontaneum plants grown on FA were higher (8.01, 1.40, 3.02, 0.92, 1.66 and 1.47 for Zn, Pb, Cu, Ni, Cd and As, respectively) than those of S. munja (Zn – 8.54, Pb – 1.66, Cu – 3.24, Ni – 0.76, Cd – 1.63 and As – 1.41). The BAF of the metals was less than unity in shoots. This is congruent with the results on DNA damage that increased significantly in the root cells and remained unaffected in the shoot. Results suggest that the plants are suitable for extracting Zn, Cu, Cd, Pb and As from FA and stabilize them in the underground plant parts. Therefore, for long-term management and restoration of FA, use of Saccharum plants for phytoremediation will be an effective strategy.

The growing usage of nanoscale zerovalent iron particles (nZVI) in the remediation of soil, ground/surface water has elicited large‐scale environmental release triggering human exposure. The size of nanomaterials is a key regulator of toxicity. However, the effect of a variable size of nZVI on genotoxicity is unexplored in human cells. To the best of our knowledge, in this study, the cytotoxic, genotoxic and hemolytic potential of nZVI‐1 (15 nm) and nZVI‐2 (50 nm) at concentrations of 5, 10 and 20 μg/mL was evaluated for the first time in human lymphocytes and erythrocytes treated for 3 hours. In erythrocytes, spherocytosis and echinocytosis occurred upon exposure to nZVI‐1 and nZVI‐2, respectively, leading to hemolysis. Lymphocytes treated with 20 μg/mL nZVI‐2 and 10 μg/mL nZVI‐1, incurred maximum DNA damage, although nZVI‐2 induced higher cyto‐genotoxicity than nZVI‐1. This can be attributed to higher Fe ion dissolution and time/concentration‐dependent colloidal destabilization (lower zeta potential) of nZVI‐2. Although nZVI‐1 showed higher uptake, its lower genotoxicity can be due to lesser Fe content, Fe ion dissolution and superior colloidal stability (higher zeta potential) compared with nZVI‐2. Substantial accumulation of Ca²⁺, superoxide anions, hydroxyl radicals and H₂O₂ leading to mitochondrial impairment and altered antioxidant enzyme activity was noted at the same concentrations. Pre‐treatment with N‐acetyl‐cysteine modulated these parameters indicating the indirect action of reactive oxygen species in nZVI‐induced DNA damage. The morphology of diffused nuclei implied the possible onset of apoptotic cell death. These results validate the synergistic role of size, ion dissolution, colloidal stability and reactive oxygen species on cyto‐genotoxicity of nZVI and unlock further prospects in its environmental nano‐safety evaluation.