Avaliação toxicológica da fitorremediação, extratos e óleo essencial de Plectranthus neochilus

Abstract

The plant Plectranthus neochilus (boldo gambá) is a herbaceous, creeping species and its leaves and flowers have a strong aroma. In traditional medicine, its tea is used for stomach pain and liver problems. Furthermore, research has shown different biological activities of its extracts in different models. This species promoted the phytoremediation of the herbicide 2,4-D from water and showed changes in phenolic metabolism and antioxidant activity after this remediation. For this reason, the present study evaluated whether the metabolism of volatile compounds is also affected by exposure to 2,4-D and the possibility of using essential oil and tea from the plant, also after phytoremediation. Due to the strong odor of its leaves and the use of tea from the plant, the repellent and insecticidal effect of the leaf, tea, and essential oil of P. neochilus was verified. Finally, the toxicity of its tea was evaluated in biological models. The results showed that the metabolism of volatile compounds (trans-tujene and alpha-pinene) and essential oil content (1-octen-3-ol) is minimally affected by exposure to 2,4-D. The aqueous medium became less toxic through the lower detection of 2,4-D in the phytoremediation water (5.18 μg/mL without the plant and 4.42 μg/mL with the plant), and for the biological models Artemia salina (no mortality in both groups) and Allium cepa (greater toxicity and cytotoxicity of the roots in the group without the plant). Regarding the use of the plant after phytoremediation, its essential oil can be used as an antimicrobial (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumonie, Acinetobacter baumannii, and Enterococcus faecalis), as there was no significant difference in the concentration range of the minimum inhibitory growth of the plant exposed and not exposed to 2,4-D. However, its tea showed greater toxicity in plants exposed to 2,4-D (100% mortality of D. melanogaster after ingestion). Regarding the repellent and insecticidal effect (distance and death of D. melanogaster), both the leaf and the tea of the plant presented an attractive effect for the flies. Only the essential oil showed such activities, which were confirmed by its chemical constitution, with caryophyllene, 1-octen-3-ol and linalool as the main compounds with such effects. Furthermore, the essential oil of P. neochilus showed a greater insecticidal effect (90 minutes of exposure) compared to other oils that also have these characteristics: P. neochilus > L. angustifolia > F. vulgare > C. paradisi. Finally, the tea presented alkaloids, flavonoids, tannins, glycosides, saponins, phenols and terpenoids in its constitution. The antioxidant activity reached 71.48% of DPPH radical inhibition (15 mg/mL) and there was a linear increase of phenolic compounds and flavonoids (243.53 μgGAE/g and 103.16 mgRE/g, up to 21 mg/mL) . Tea toxicity occurred only at excessively high concentrations in the experimental models A. cepa (24 mg/mL), A. salina (4.94 mg/mL) and D. melanogaster (6.93 mg/mL). This study obtained valuable data from the P. neochilus plant that could still be explored in the following areas: environmental, through phytoremediation and insecticidal effect (the main novelty of the work); traditional medicine, for the properties of its tea.