Studies that help understand the mechanisms of action of environmental pollutants are extremely important in environmental toxicology. In this context, assays using plants as models stand out for their simplicity and low performance cost. Among the plants used for this purpose, Allium cepa L. is the model most commonly applied for cytogenotoxic tests, while Lactuca sativa L., already widely used in phytotoxic investigations, has been gaining prominence in cytotoxic analyses. The present study aimed to compare the responses of A. cepa and L. sativa via macroscopic (root growth) and microscopic analyses (cell cycle and DNA fragmentation via TdT-mediated deoxy-uracil nick and labeling (TUNEL) and comet assays) after exposure of their roots to environmental pollutants with known cytogenotoxic mechanisms. Both species presented sensitive and efficient response to the applied tests after exposure to the DNA-alkylating agent Methyl Methanesulfonate (MMS), the heavy metal Cadmium, the aluminum industry waste Spent Potliner (SPL) and the herbicide Atrazine. However, they differed regarding the responses to the evaluated endpoints. Overall, A. cepa was more efficient in detecting clastogenic changes, arising from DNA breakage, while L. sativa rather detected aneugenic alterations, related to chromosome segregation in mitosis. In the tests applied to verify DNA fragmentation (comet and TUNEL assays), A. cepa presented higher sensitivity. In conclusion, both models are efficient to evaluate toxicological risks of environmental pollutants.

Spent pot-liner (SPL) is a hazardous solid waste produced by the aluminum industry. Although its composition may vary, fluoride and cyanide salts as well as aluminum are predominant components. A seed-germination and root-elongation test was performed with Lactuca sativa seeds as a test system. SPL induced decrease of seed germination rate and root elongation. The concentration of 26.5g/L SPL was established from a regression curve as the IC50 (inhibition concentration 50%). Through chemical analyses, the concentrations of fluoride, cyanide and aluminum in SPL solutions of 26.5g/L (IC50), 39.75g/L (1.5IC50) and 13.25g/L (0.5IC50) were determined. Further, a cell-cycle test was conducted with root tips of L. sativa exposed to these same SPL solutions. All test chemicals presented toxic effects on meristematic cells of L. sativa. Aluminum was identified as the SPL component mainly responsible for reduction of the mitotic index. Chromosomal alterations resulted from the interactions among the three main chemical components of SPL, without a clear predominantly responsible agent. Induction of condensed nuclei was mainly due to effects of aluminum and fluoride, and may serve as an indicator of induced cell death.

Jatropha curcas L. (Euphorbiaceae) is important for biofuel production and as a feed ingredient for animal. However, the presence of phorbol esters in the oil and cake renders the seeds toxic. The toxicity of J. curcas oil is currently assessed by testing in animals, leading to their death. The identification of toxic and nontoxic improved varieties is important for the safe use of J. curcas seeds and byproducts to avoid their environmental toxicity. Hence, the aim of this study was to propose a short-term bioassay using a plant as a model to screen the toxicity of J. curcas oil without the need to sacrifice any animals. The toxicity of J. curcas oil was evident in germination, root elongation and chromosomal aberration tests in Lactuca sativa. It was demonstrated that J. curcas seeds contain natural compounds that exert phyto-, cyto-and genotoxic effects on lettuce, and that phorbol esters act as aneugenic agents, leading to the formation of sticky chromosomes and c-metaphase cells. In conclusion, the tests applied have shown reproducibility, which is important to verify the extent of detoxification and to determine toxic doses, thus reducing the numbers of animals that would be used for toxicity tests.

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Spent potliner (SPL) is a solid waste generated in the aluminum mining and processing industry. It is sometimes dumped into the environment and leach in contact with water, thereupon affecting living beings, which are likely to be exposed to the waste for long periods. Considering this, we aimed to evaluate the effects of extended exposure to SPL through bioassays using Allium cepa as plant model system. Seeds of A. cepa were either directly exposed to SPL (continuous exposure) or first germinated in water and then exposed to SPL (discontinuous exposure). The germination rate was determined from 24 to 192 h of exposure. The maximum effects of SPL on germination were observed after 96 h in both exposure approaches. For the parameter root elongation, the discontinuous treatment was more efficient in demonstrating differences among the applied SPL concentrations (60% of reduction). Microscopic analysis was carried out in root tip cells discontinuously exposed to SPL for 96 h. A mitodepressive effect was observed (above 50%), as well as increased rate of chromosome abnormalities (up to 100-fold) and induction of cell death. The consequences of exposure to SPL for longer periods are discussed.

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Infusions of the leaves and seeds of Annona crassiflora Mart. are commonly employed in the treatment of diarrhoea, snakebites, tumours and disorders of the hair and scalp. The aim of the present study was to investigate the cytotoxic and genotoxic properties of ethanolic extracts of A. crassiflora by evaluating their effects on germination, root elongation, chromosome structure and the cell division of Lactuca sativa (lettuce). The experiment followed a randomized design involving the treatment of L. sativa seeds with ethanolic extracts from leaves and seeds of A. crassiflora applied at ten concentrations (0.0125, 0.025, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mg/L) and with five repetitions per treatment. Seeds of L. sativa exposed for 48 h to A. crassiflora leaf extract at concentrations ≥ 0.1 mg/L, or to seed extracts at concentrations ≥ 0.2 mg/L, showed germination percentages that were significantly (p < 0.05) lower than those of seeds exposed to aqueous ethanol control. Exposure of L. sativa seedlings to leaf (but not seed) extracts of A. crassiflora produced significant (p < 0.05) reductions in the mitotic indices of root meristem cells of lettuce and induced chromosome and nuclear abnormalities in the root cells. The presence of chromosome stickiness, bridges, fragments, laggard chromosomes and nuclear condensation were also observed. The cytogenetic effects observed suggest that folkloric medicines prepared with extracts of the leaves or seeds of A. crassiflora should be employed with caution.