Genotoxicity evaluation of environmental pollutants using analysis of nucleolar alterations

Toxicogenetic, biochemical, and anatomical effects of the herbicide Clethodim on Allium cepa L

Pesticides are compounds with several chemical or biological agents developed to potentiate the biocide action. Their use is associated with increased economic and agricultural productivity worldwide but can harm health and the environment, damaging existing biota. Clethodim is a systemic post-emergent herbicide for grasses, highly selective for cotton, coffee, onions, carrots, soybeans, etc. Therefore, this work aimed to evaluate the harmful effect of the herbicide Clethodim with the model plant Allium cepa. A series of tests were conducted to evaluate the effects of the herbicide under study. Germination tests, root growth, cell, and nucleolar cycle analysis, as well as oxidative stress assessment and histological analysis of the roots, were performed. The results indicated that the herbicide demonstrated phytotoxicity, inhibiting germination at C1 (1.92 g/L) and C3 (0.84 g/L), and root growth at all concentrations, presenting mutagenicity at C1 (1.92 g/L) and C4 (0.24 g/L), evidenced by the increased frequency of micronuclei. In addition, changes were observed in the enzymatic activity of the enzymes catalase at concentrations C1 (1.92 g/L) and C2 (0.96 g/L) and ascorbate peroxidase at concentrations C1 (1.92 g/L), C2 (0. 96 g/L), and C3 (0.48 g/L) and in cell elongation at concentrations C1 (1.92 g/L) and C3 (0.48 g/L), demonstrated in histological analyses of the root apex.

Genotoxicity of surface waters in Brazil

Brazil has abundant surface water resources, huge aquatic biodiversity and is home to 213 million people. Genotoxicity assays are sensitive tools to detect the effects of contaminants in surface waters and wastewaters, as well as to determine potential risks of contaminated waters to aquatic organisms and human health. This work aimed to survey the articles published in 2000-2021 that evaluated the genotoxicity of surface waters within Brazilian territory to unveil the profile and trends of this topic over time. In our searches, we considered articles focused on assessing aquatic biota, articles that conducted experiments with caged organisms or standardized tests in the aquatic sites, as well as articles that transported water or sediment samples from aquatic sites to the laboratory, where exposures were performed with organisms or standardized tests. We retrieved geographical information on the aquatic sites evaluated, the genotoxicity assays used, the percentage of genotoxicity detected, and, when possible, the causative agent of aquatic pollution. A total of 248 articles were identified. There was a trend of increase in the number of publications and annual diversity of hydrographic regions evaluated over time. Most articles focused on rivers from large metropolises. A very low number of articles were conducted on coastal and marine ecosystems. Water genotoxicity was detected in most articles, regardless of methodological approach, even in little-studied hydrographic regions. The micronucleus test and the alkaline comet assay were widely applied with blood samples, mainly derived from fish. Allium and Salmonella tests were the most frequently used standard protocols. Despite most articles did not confirm polluting sources and genotoxic agents, the detection of genotoxicity provides useful information for the management of water pollution. We discuss key points to be assessed to reach a more complete picture of the genotoxicity of surface waters in Brazil.

Efficiency of rice husk ash to adsorb chromium(VI) using the Allium cepa toxicity test

Adsorption is widely used in the treatment of effluents and contaminated water. However, the removal of the pollutant alone does not ensure that the effluent can be safely discharged in the environment. Controlling effluent toxicity may become an important tool to ensure that the quality of the treated effluent is compatible with that of the receiving water body. In this sense, this study evaluated the efficiency of rice husk ash (RHA) to adsorb chromium(VI) using the Allium cepa toxicity test. Adsorption was assessed based on the variables adsorption time, initial concentration, and pH. The data obtained were fitted the pseudo-second-order and the pseudo-first-order models, and the Langmuir and Freundlich isotherms. Kinetic analysis indicated removal rates between 43 and 100%. All data were best fitted by the pseudo-second-order model. Also, pH 1 and pH 2 data were best fitted by the Freundlich and Langmuir isotherms, respectively. In the Allium cepa test, pH 2 solutions were toxic. At pH 7, the Alium cepa test confirmed the efficiency of chromium(VI) adsorption by RHA, ensuring acceptable germination index values.

Nucleolar alterations are reliable parameters to determine the cytogenotoxicity of environmental pollutants

Pollution generated by deposition of industrial activity waste in the environment without due care can lead to serious environmental consequences. Bioassays in higher plants are means of understanding the cytogenotoxic effects of these substances. In the present work, Allium cepa L. was used as a model species to assess nucleolar changes induced by environmental pollutants. The substances used were Methyl Methane Sulfonate (MMS), cadmium (Cd), Spent Potliner (SPL) and the herbicide Atrazine. Water was used as a negative control. The silver-stained nucleolar organizer region (AgNOR) assay was used making it possible to evaluate how nucleolar parameters (number of nucleoli per nucleus and nucleoli area) behave when facing stress caused by such pollutants. The results obtained showed a variation in the observed parameters: an increase in the number of nucleoli in the treated cells and tendency to a reduction in nucleolar area, indicating that the tested pollutants may have impaired nucleolar activity. In addition, it was possible to establish a relationship between the behavior of the nucleolus with other changes as plantlet growth, cell proliferation, and DNA damage.

Genotoxicity of titanium dioxide nanoparticles and triggering of defense mechanisms in Allium cepa

Titanium dioxide nanoparticles (TiO2NPs) are widely used and may impact the environment. Thus, this study used a high concentration of TiO2NP (1000 mg/L) to verify the defense mechanisms triggered by a plant system - an indicator of toxicity. Furthermore, this study aimed at completely characterizing TiO2NP suspensions to elucidate their toxic behavior. TiO2NPs were taken up by meristematic cells of Allium cepa, leading to slight inhibition of seed germination and root growth. However, severe cellular and DNA damages were observed in a concentration-dependent manner (10, 100, and 1000 mg/L). For this reason, we used the highest tested concentration (1000 mg/L) to verify if the plant cells developed defense mechanisms against the TiO2NPs and evaluated other evidences of TiO2NP genotoxicity. Nucleolar alterations and plant defense responses (i.e., increased lytic vacuoles, oil bodies and NP phase change) were observed in meristematic cells exposed to TiO2NP at 1000 mg/L. In summary, TiO2NPs can damage the genetic material of plants; however, plants displayed defense mechanisms against the deleterious effects of these NPs. In addition, A. cepa was found to be a suitable test system to evaluate the cyto- and genotoxicity of NPs.

X-ray fluorescence spectrometry characteristics of oily waste water from steel processing and an evaluation of its impact on the environment

Metal-cutting fluids, one of the most consumed materials in the metallurgy industry, turn into oily wastewater after being used in the metalworking processes. The amount of cutting fluids used can reach up to millions of tons. And these invaluable fluids are difficult to distil and expensive, and impossible to store. Even after it is disposed and recaptured, the end product has no commercial value. In this study, the effect of this mixture was examined on the ecosystem using the Allium cepa test system in which onion root tips were treated with three different concentrations of waste-cutting fluid, based on a 24- and 48-h cell cycle. The oily wastewater exhibited a mechanism which triggered the chromosomal and nuclear abnormalities in the onion root-tip meristem and reduced the mitotic index. Common abnormalities observed in the experimental groups based on the water concentration were chromosome stickiness, c-mitosis, and micronuclei formation. In the experimental group with the lowest water concentration, budding nuclei were observed at a different level than all of the other experimental groups. The x-ray fluorescence analysis showed that the concentrations of elements, such as silicon, calcium, iron, and zinc, were higher in the oily wastewater than those in the unused cutting oil.

Hydropower reservoirs: cytotoxic and genotoxic assessment using the Allium cepa root model

Hydropower offers a reliable source of electricity in several countries, and Brazil supplies its energy needs almost entirely through hydropower plants. Nevertheless, hydropower plants comprise large buildings and water reservoirs and dams, resulting in huge ecological disruptions. Here, we analyzed the impact of four hydropower reservoirs construction in metals and pesticides incidence and the cytotoxic and genotoxic potential of sediment elutriate of rivers from southern Brazil. Our analyses have evidenced the elevated incidence of different metals (lead, iron, cadmium, and chrome) and pesticides (methyl parathion, atrazine, and 2,4-dichlorophenoxyacetic acid). We showed that Allium cepa exposed to sediment elutriates did not change the seed germination rate and mitotic index. However, roots from Allium cepa exposed to reservoirs sediment elutriates showed increased occurrence of chromosomal aberrations and nuclear abnormalities. Therefore, the results obtained in our study indicate that sediment from reservoirs present elevated concentration of metals and pesticides and a significant genotoxic potential. Taken together, our data support that hydropower reservoirs represent an environmental scenario that could impact surrounding wildlife and population.

Assessment of the cytotoxic, genotoxic and mutagenic effects of the commercial black dye in Allium cepa cells before and after bacterial biodegradation treatment

The present study evaluated the cytotoxic, genotoxic and mutagenic actions of different concentrations (50 and 200 μg/L) of BDCP (Black Dye Commercial Product) used by textile industries, before and after bacterial biodegradation, by the conventional staining cytogenetic technique and NOR-banding in Allium cepa cells. Differences in the chromosomal and nuclear aberrations and alterations in the number of nucleoli were observed in cells exposed to BDCP with and without the microbial treatment. The significant frequencies of chromosome and nuclear aberrations noted in the tests with bacterially biodegraded BDCP indicate that the metabolites generated by degradation are more genotoxic than the chemical itself. Losses of genetic material characterize a type of alteration that was mainly associated with the action of the original BDCP, whereas chromosome stickiness, nuclear buds and binucleated cells were the aberrations that were preferentially induced by BDCP metabolites after biodegradation. The significant frequencies of cell death observed in the tests with biodegraded BDCP also show the cytotoxic effects of the BDCP metabolites. The reduction in the total frequency of altered cells after the recovery treatments showed that the test organism A. cepa has the ability to recover from damage induced by BDCP and its metabolites after the exposure conditions are normalized.