Reliability of plant root comet assay in comparison with human leukocyte comet assay for assessment environmental genotoxic agents

Bioactivity of hydroalcoholic extracts from tropaeolum majus L. (tropaeolaceae) on the germination, initial plant development and cell cycle of Lactuca sativa L

Natural products are usually considered harmless; however, these substances need to be consumed with caution. Biological assays with plant models are a suitable alternative for prospective studies to assess natural product-initiated toxicity. The aim of this study was to examine the toxic potential of leaf and flower extracts derived from Tropaeolum majus L. a widely used plant in traditional medicine. Seeds of Lactuca sativa L. were exposed to T. majus extracts and based upon the seedling growth curve values, the 50% Inhibition Concentration (IC50) was calculated and applied for cell cycle analysis exposure. Both extracts contained organic acids, proteins, amino acids, and terpene steroids. Sesquiterpene lactones and depside were detected in leaf extracts. The higher concentration tested exhibited a marked phytotoxic effect. The extracts induced clastogenic, aneugenic cytotoxic, and potential mutagenic effects. The possible relationships between the classes of compounds found in the extracts and effects on cells and DNA were determined.

Evaluation of Toxicity and Genotoxicity of Concrete Cast with Steel Slags Using Higher Terrestrial Plants

The potential impact of concrete mixtures containing steel slag (SS) as a partial replacement of natural aggregates (NA) on the terrestrial ecosystem was assessed using a battery of plant-based bioassays. Leaching tests were conducted on four concrete mixtures and one mixture containing only NA (reference concrete). Leachates were tested for phytotoxicity using seeds of Lepidium sativum, Cucumis sativus, and Allium cepa. Emerging seedlings of L. sativum and A. cepa were used to assess DNA damage (comet test). The genotoxicity of the leachates was also analyzed with bulbs of A. cepa using the comet and chromosome aberration tests. None of the samples caused phytotoxic effects. On the contrary, almost all the samples supported the seedlings; and two leachates, one from the SS-containing concrete and the other from the reference concrete, promoted the growth of C. sativus and A. cepa. The DNA damage of L. sativum and A. cepa seedlings was significantly increased only by the reference concrete sample. In contrast, the DNA damage in A. cepa bulbs was significantly enhanced by the reference concrete but also by that of a concrete sample with SS. Furthermore, all leachates caused an increase in chromosomal aberrations in A. cepa bulbs. Despite some genotoxic effects of the concrete on plant cells, the partial replacement of SS does not seem to make the concrete more hazardous than the reference concrete, suggesting the potential use of SS as a reliable recycled material. Environ Toxicol Chem 2023;42:2193-2200. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Ecotoxicity Evaluation of Industrial Waste and Construction Materials: Comparison Between Leachates from Granular Steel Slags and Steel Slags-Containing Concrete Through a Plant-Based Approach

Steel slags, the main waste product from the steel industry, may have several reuse possibilities. Among others, building applications represent a crucial field. However, the potential impact of harmful substances on the environment should be assessed. The aim of this study was to assess the phytotoxicity of steel slags (SS) and concrete mixtures cast with a partial replacement of SS (CSS). Leaching tests were carried out on four SS and four CSS according to EN 12457-2 and UNI EN 15863, respectively. Each leachate was assayed using root elongation tests on 30 seeds of Allium cepa, Cucumis sativus, and Lepidium sativum, respectively, and on 12 bulbs of A. cepa. The latter also allowed the analysis of other macroscopic parameters of toxicity (turgidity, consistency, colour change and root tip shape) and the evaluation of the mitotic index on 20,000 root tip cells per sample. None of the samples induced phytotoxic effects on the organisms tested: all samples supported seedlings emergence, verified by root elongation comparable to, or even greater than, that of the negative controls, and did not affect cell division, as evidenced by mitotic index values. The absence of phytotoxicity demonstrated by the leachates allows SS and SS-derived concrete to be considered as reliable materials suitable for use in civil constructions or in other engineering applications, with economic and environmental advantages, such as the reduction of the final disposal in landfills as well as the consumption of natural resources.

Cytogenetic effects of β-particles in Allium cepa cells used as a biological indicator for radiation damages

Analysis of cytogenetics effects of ionizing radiation for flora and fauna is essential to determine the impact on these communities and may produce an efficient warning system to avoid harm to human health. Onion (Allium cepa) is a well-established in vivo standard model, and it is widely used in cytogenetics studies for different environmental pollutants. In this work, onion roots were exposed to 0.04-1.44 Gy of β-particles from a ⁹⁰Sr/⁹⁰Y source. We investigated the capacity of brief external exposures to β-particles on inducing cytogenetic damages in root meristematic cells of onion aiming to verify if onion can be used as a radiation-sensitive cytogenetic bioindicator. A nonlinear increase in the frequencies of chromosomal aberrations and cells with micronuclei was observed. Onion roots exposed to doses 0.13 Gy or higher of β-particles showed a significant difference (p<0.05) in these frequencies when compared to the unirradiated group. The frequencies of these endpoints showed to be suitable to assess the difference in the dose of beta radiation received from 0.36 Gy. Our research shows the potential of using cytogenetic effects in Allium cepa cells as a biological indicator for a first screening of genotoxic damages induced by brief external exposures to β-particles.

Air pollution in Sarajevo, Bosnia and Herzegovina, assessed by plant comet assay

Bosnia and Herzegovina (B&H) is among the European countries with the highest rate of air pollution-related death cases and the poorest air quality. The main causes are solid fuel consumption, traffic, and the poorly developed or implemented air pollution reduction policies. In addition, the city of Sarajevo, the capital of B&H, suffers temperature inversion episodes in autumn/winter months, which sustain air pollution. Human biomonitoring studies may be confounded by the lifestyle of subjects or possible metabolic alterations. Therefore, this study aimed to evaluate Ligustrum vulgare L. as a model for air pollution monitoring by measuring DNA damage at one rural and two urban sites. DNA damage was measured as tail intensity (TI) in L. vulgare leaves, considering seasonal, sampling period, leaf position and staging, and spatial (urban versus rural) variation. Effects of COVID-19 lockdown on TI were assessed by periodical monitoring at one of the selected sites, while in-house grown L. vulgare plants were used to test differences between outdoor and indoor air pollution effects for the same sampling period. Significantly higher TI was generally observed in leaves collected in Campus in December 2020 and 2021 compared with March (P < 0.0001). Outer and adult leaves showed higher TI values, except for the rural site where no differences for these categories were found. Leaves collected in the proximity of the intensive traffic showed significantly higher TI values (P < 0.001), regardless of the sampling period and the stage of growth. In regards to the COVID-19 lockdown, higher TI (P < 0.001) was registered in December 2020, after the lockdown period, than in periods before COVID-19 outbreak or immediately after the lockdown in 2020. This also reflects mild air pollution conditions in summer. TI values for the in-house grown leaves were significantly lower compared to those in situ. Results showed that L. vulgare may present a consistent model for the air pollution biomonitoring but further studies are needed to establish the best association between L. vulgare physiology, air quality data, and air pollution effects.

Toxicogenetic of tebuconazole based fungicide through Lactuca sativa bioassays

The rampant use of pesticides can cause serious environmental problems. They can be contaminating surface water and groundwater, affecting the surrounding micro and macro biota. In this sense, this work aimed to evaluate the effects of a tebuconazole-based fungicide through endpoints accessed in Lactuca sativa bioassays. Germinated-seeds with roots upon 2 mm were treated with a fungicide containing Tebuconazole (TBZ) as active compound. The final concentration of TBZ in the tested solutions were 0.025 (C1); 0.05 (C2); 0.1 (C3); 0.2 (C4) and 0.4 g/L (C5). L. sativa roots were exposed for 24 h to these solutions and Petri dishes containing the treated seeds were kept in incubation chamber at 24 °C. Two positive controls (PC,) the herbicide trifluralin (0.84 mg/L) and Methanesulfonate (4 ×10-4 mol/L), were applied. Distilled water was negative control (NC). The following endpoints were analyzed: root growth (RG), cytogenotoxic potential by cell cycle analysis, induction of DNA damage through TUNEL and comet assays. The obtained data were submitted to one-way variance analysis (ANOVA) and then to Tukey or Kruskal Wallis (P < 0.05) tests. The concentrations (C1, C2, C4 and C5) affected negatively the RG of L. sativa, in comparison with the NC. The mitotic index was reduced by 25% from NC to C1 and in the rest of treatments it did not present significant modifications. However, from C3 to C5 great amount of chromosome alterations were observed, in comparison with the NC. TBZ-based fungicide also induced DNA fragmentation as measured by TUNEL and comet assays. Thus, TBZ-based fungicide in some concentrations can have phytotoxic, cytotoxic and genotoxic effects in roots and meristematic cells of L. sativa.

Graphene oxide exposure suppresses nitrate uptake by roots of wheat seedlings

Despite the large number of studies reporting the phytotoxicity of graphene-based materials, the effects of these materials on nutrient uptake in plants remain unclear. The present study showed that nitrate concentrations were significantly decreased in the roots of wheat plants treated with graphene oxide (GO) at 200-800 mg L^-1. Non-invasive microelectrode measurement demonstrated that GO could significantly inhibit the net NO₃^- influx in the meristematic, elongation, and mature zones of wheat roots. Further analysis indicated that GO could be trapped in the root vacuoles, and that the maximal root length and the number of lateral roots were significantly reduced. Additionally, root tip whitening, creases, oxidative stress, and weakened respiration were observed. These observations indicate that GO is highly unfavorable for vigorous root growth and inhibits increase in root uptake area. At the molecular level, GO exposure caused DNA damage and inhibited the expression of most nitrate transporters (NRTs) in wheat roots, with the most significantly downregulated genes being NRT1.3, NRT1.5, NRT2.1, NRT2.3, and NRT2.4. We concluded that GO exposure decreased the root uptake area and root activity, and decreased the expression of NRTs, which may have consequently suppressed the NO₃^- uptake rate, leading to adverse nitrate accumulation in stressed plants.

Investigating arsenic toxicity in tropical soils: A cell cycle and DNA fragmentation approach

Arsenic (As) is a metalloid and a toxicant that is found naturally in many environmental compartments, soils included. Soils with high levels of As occur worldwide and might pose a threat not only to humans, but also to many ecosystems. Considering the scarcity of studies regarding cytogenotoxic effects of model plants in As-contaminated soil, mainly in tropical areas, this study proposes the use of Allium cepa root tip bioassays for a fast-track assessment of As toxicity in tropical soils. For this end, root tip cells of A. cepa were exposed to an Oxisol, an Inceptisol and a Tropical Artificial Soil (TAS) contaminated with increasing doses of As (0, 8, 14.5, 26, 46.5, 84, 150, and 270 mg kg^-1). The effects of As on cell cycle, micronucleus formation, and DNA fragmentation were evaluated. In general, root tip cells exposure to As increases the frequency of chromosome abnormalities and micronucleus, in turn, decreasing the frequency of mitotic index. As-treated cells also presented an increase in the percentage of DNA damage observed in comet assay. Overall, the effects of As in TAS were more pronounced, than in the Oxisol, being the Inceptisol the less toxic. A discussion of each As effect in cells and the link with the soil type is presented and reveals that clastogenic effects of As in A. cepa cells seemed to be the mode of action of this soil contaminant.

Phytotoxicity and cytogenotoxicity of hydroalcoholic extracts from Solanum muricatum Ait. and Solanum betaceum Cav. (Solanaceae) in the plant model Lactuca sativa

Plants are rich in biologically active compounds. They can be explored for the production of bioherbicides. In this context, the present work aimed to evaluate the allelopathic effect of hydroalcoholic extracts from two Solanaceae species: Solanum muricatum Ait. and Solanum betaceum Cav. For this end, we conducted phytochemical screening and biological assays, determining the effects of the extracts on germination, early development, cell cycle, and DNA fragmentation in plantlets and meristematic cells of the plant model Lactuca sativa L. (lettuce). The percentage of seeds germinated under effect of S. muricatum extract did not differ from the control, but plantlet growth was reduced at the highest concentrations. For S. betaceum extract, dose dependence was observed for both germination and plantlet development, with the highest concentrations inhibiting germination. The growth curves revealed the concentrations of 2.06 and 1.93 g/L for S. muricatum and S. betaceum extracts, respectively, as those reducing 50% of root growth (RG). At these concentrations, both extracts presented mitodepressive effect, besides inducing significant increase in the frequency of condensed nuclei, associated to DNA fragmentation and cytoplasmic shrinkage. The frequency of chromosome alterations was not significant. We further discuss the mechanisms of action related to the chemical composition of the extracts, which presented organic acids, reducing sugars, proteins, amino acids, and tannins, besides catechins and flavonoids, only found in the extract of S. betaceum.

Spent pot liner from aluminum industry: genotoxic and mutagenic action on human leukocytes

Spent pot liner (SPL) is a toxic solid waste generated in the aluminum mining and processing industry. SPL is considered as an environmental pollution agent when is dumped on environment. Thus, it is important to access its toxicological risk for the exposed organisms. The comet assay and micronucleus test are efficient tests to detect genotoxic/mutagenic compounds by DNA damage observation. Therefore, in the present study, the genotoxic potential of SPL was evaluated through the micronucleus and comet assay on human leukocytes. After ethics committee approval (COEP-UFLA n°. CAAE 11355312.8.0000.5060), blood aliquots collected from healthy volunteers were exposed to increasing concentrations of SPL (from 0.1 to 80 g L^-1). All SPL treatments, including the lowest concentration applied (0.1 g L^-1), significantly increased the micronucleus frequency. The frequency of DNA damage was determined by visual scores (from 0 to 4) and the results were expressed on percentage of damage and arbitrary units (AU). CaCl₂ (0.01 M) was applied as negative control (NC) and doxorubicin (10 μg mL^-1) as positive control (PC). It was observed a dose-dependency between SPL treatments: as SPL concentration for cell incubation increases, the frequency of damage on DNA also increases. Cells incubated on the NC presented nucleoids class 0 to 2, while those exposed to SPL presents nucleoids class 0 to 4. SPL-incubated cells increasing significantly the frequency of nucleoids class 4. For the PC, the UA of damage was 267.74, which is lower than the one observed for the treatments with high doses of SPL (40-287.40 g L^-1 and 80-315.30 g L^-1). Thus, it was demonstrated that the SPL is a genotoxic agent that induces DNA damage on exposed organisms.

Loss of genetic integrity in artificially aged seed lots of rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.)

Loss of genetic integrity can occur during the long-term conservation of seeds. We have studied these effects in seeds of rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.) exposed to accelerated aging (elevated temperature and moisture) conditions. Tests of first count, germination, and germination speed index were performed to measure physiological quality; cytogenetic tests and comet assay were used to evaluate genetic integrity. With aging, we observed a decrease in mitotic index and an increase in the frequency of chromosomal alterations in root cells of imbibed seeds, as well as increased DNA damage (comet assay) in dry and imbibed seed embryos of both species. The comet assay can be a useful technique for measuring genetic integrity in seed conservation programs.

Polybia occidentalis and Polybia fastidiosa venom: a cytogenotoxic approach of effects on human and vegetal cells

The venoms of wasps are a complex mixture of biologically active compounds, such as low molecular mass compounds, peptides, and proteins. The aim of the study was to evaluate the action of wasp venoms, Polybia occidentalis and Polybia fastidiosa, on the DNA of human leukocytes and on the cell cycle and genetic material of the plant model Lactuca sativa L. (lettuce). The cultured leukocytes were treated with the venoms and then evaluated by the comet assay. On another assay, seeds were exposed to a venom solution; the emitted roots were collected and the occurrence of cell cycle alterations (CCAs) and DNA fragmentation were evaluated by agarose gel electrophoresis and TUNEL assay. The results demonstrated that the venom of both wasps induces several CCAs and reduces the mitotic index (MI) on treated cells. They induced damage on human leukocytes DNA. High frequencies of fragments were observed in cells exposed to P. occidentalis venom, while those exposed to P. fastidiosa showed a high frequency of non-oriented chromosome. Both venoms induced the occurrence of various condensed nuclei (CN). This alteration is an excellent cytological mark to cell death (CD). Additionally, CD was evidenced by positive signals in TUNEL assay, by DNA fragmentation in agarose gel electrophoresis with vegetal cells, and by DNA fragmentation of the human leukocytes evaluated. Furthermore, human leukocytes exposed to the venom of P. fastidiosa had high rate of damage. The data demonstrate that both vegetal and human cells are adequate to evaluate the genotoxicity induced by venoms.

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.

Mutagenic effects of spent potliner and derivatives on Allium cepa L. and Lactuca sativa L.: A molecular approach

Spent potliner (SPL) is a solid residue generated by the aluminum industry. Its composition is variable and complex, containing fluoride and cyanide salts as well as aluminum, which contributes to its toxicity. SPL is sometimes released directly into the soil, where it is prone to leaching and has the potential to cause alterations and damage to DNA. Considering that polymorphism analysis of simple sequence repeat (SSR) and inter-simple sequence repeat (ISSR) DNA markers is an interesting tool to determine the mutagenicity of an environmental pollutant, the present study adopted this approach to verify the mutagenic potential of SPL and its main toxic components (aluminum, fluoride, and cyanide) on root tip cells of Lactuca sativa and Allium cepa. Alterations in ISSR and SSR regions were identified by DNA fingerprinting (gain and loss of bands and changes in band intensity). The estimated dissimilarities indicated differences between treatments and the negative control. Furthermore, the relationship between the amplification profile of the markers and alterations in cell mitosis was discussed.

Genotoxicity of spent pot liner as determined with the zebrafish (Danio rerio) experimental model

Spent pot liner (SPL) is a solid waste generated during the primary smelting of aluminum, and its toxicity is attributed to the presence of fluoride, cyanide, and aluminum salts, which can be leached into aquatic ecosystems. Since the effects of this waste on aquatic life forms have not yet been investigated, the objective of our study was to evaluate the toxicity of simulated leachates of SPL on zebrafish (Danio rerio). Animals were exposed to 0 (control), 0.32, 0.64, or 0.95 g L^-1 of SPL for 24, 72, and 96 h, and genotoxicity was accessed through micronucleus and comet assays. All of the tested treatments induced DNA fragmentation, and the observed frequency of micronuclei and damaged nucleoids generally increased with increasing SPL concentration. The highest frequency of micronuclei (3.3 per 3000 erythrocytes) was detected after 96 h of exposure with 0.95 g L^-1 SPL. In the comet assay, nucleoids classified with highest level of damage in relation to the control were observed principally after 24 and 96 h of exposure. The data obtained in this study confirm the genotoxicaction and mutagenic potential of SPL and indicate that open-air deposits of the waste material could represent a health risk to humans and ecosystems alike.