Single and mixture toxicity evaluation of three phenolic compounds to the terrestrial ecosystem.

Endocrine-disrupting chemicals (EDCs) are primarily studied regarding endocrine-mediated effects in mammals and fish. However, EDCs can cause toxicity by mechanisms outside the endocrine system, and, as they are released continuously into soils, they may pose risks to terrestrial organisms. In this work, the plant Allium cepa and the earthworm Eisenia foetida were used as test systems to evaluate the toxicity and cyto-/geno-toxicity of three environmental phenols known as EDCs (Bisphenol A - BPA, Octylphenol - OP, Nonylphenol - NP). The tested phenols were evaluated in environmentally relevant concentrations (µg/L) and in single forms and mixture. BPA, OP, and NP did not inhibit the seed germination and root development in A. cepa in their single forms and mixture. However, all single forms of the tested phenols caused cellular and DNA damages in A. cepa, and although these effects persist in the mixtures, the effects were verified at lower levels. These phenols caused acute toxicity to E. foetida after 48 h of exposure and at both conditions evaluated (single forms and mixture); however, unlike A. cepa, in earthworms, mixtures and single forms presented the same level of effects, indicating that interspecies physiological different might influence the mixture toxicity. In summary, our results suggest that BPA, OP, and NP are toxicants to earthworm and cyto-/geno-toxicants to monocotyledonous plants at low concentrations. However, interaction among these phenols reduces the magnitude of their individual effects (antagonistic effect) in the plant test system. Therefore, this study draws attention to the need to raise knowledge about the ecotoxicity of phenolic compounds to help predict their ecological risks and protect non-target terrestrial species.

Thymol-Loaded Biogenic Silica Nanoparticles in an Aquatic Environment: The Impact of Particle Aggregation on Ecotoxicity.

Thymol, a monoterpene phenol, is used as a natural biocide. To circumvent its chemical instability, we propose use of thymol-loaded biogenic silica nanoparticles (BSiO2 #THY NPs); however, the toxicity of this system for aquatic organisms is unknown. Thus, the present study aimed to evaluate the toxicogenetic effects induced by thymol, BSiO2 NP, and BSiO2 #THY on Artemia salina and zebrafish (Danio rerio) early life stages. We also investigated the impact of BSiO2 aggregation in different exposure media (saline and freshwater). Based on the median lethal concentration at 48 h (LC5048h ), BSiO2 #THY (LC5048h = 1.06 mg/L) presented similar toxic potential as thymol (LC5048h = 1.03 mg/L) for A. salina, showing that BSiO2 had no influence on BSiO2 #THY toxicity. Because BSiO2 aggregated and sedimented faster in A. salina aqueous medium than in the other medium, this NP had lower interaction with this microcrustacean. Thus, BSiO2 #THY toxicity for A. salina is probably due to the intrinsic toxicity of thymol. For zebrafish early life stages, BSiO2 #THY (LC5096h = 13.13 mg/L) was more toxic than free thymol (LC5096h = 25.60 mg/L); however, BSiO2 NP has no toxicity for zebrafish early life stages. The lower aggregation of BSiO2 in the freshwater medium compared to the saline medium may have enhanced thymol's availability for this aquatic organism. Also, BSiO2 #THY significantly induced sublethal effects as thymol, and both were genotoxic for zebrafish. In conclusion, although BSiO2 #THY still needs improvements to ensure its safety for freshwater ecosystems, BSiO2 NP seems to be a safe nanocarrier for agriculture. Environ Toxicol Chem 2021;40:333-341. © 2020 SETAC.