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- Ecotoxicity of oxidative stress effectorsPublication . Pais, Ricardo Teles; Pastorinho, Manuel Ramiro Dias; Sousa, Ana Catarina AlmeidaIn a state of redox homeostasis, an oxidative challenge initiates a stress response, executed through molecular redox switches, activating gene expression counteracting the challenge. Levels of oxidants and antioxidant species are balanced at a physiological level permitting redox signaling and redox regulation. However, certain stressors can elicit a response that unbalances this homeostatic state, inducing an imbalance between oxidants and antioxidants in favor of the oxidants, and leading to the prevalence of supraphysiological oxidative stress, disrupting redox signaling and/or damaging biomolecules, which may ultimately lead to the onset of disease. When the damaged biomolecules are lipids, the phenomenon is termed lipid peroxidation. The main target of lipid peroxidation are polyunsaturated fatty acids that, when oxidized, generate non-enzymatically biomolecules called isoprostanes. Thus, isoprostanes are considered final products of lipid peroxidation and, therefore, possible indicators of the existence of a state of oxidative stress associated with several pathologies. Given that isoprostanes are excreted through urine, they can be detected in effluents from wastewater treatment plants and therefore be used as indicators in the assessment of the health status of a population. However, the fact that isoprostanes are detected in effluents can raise concern for the aquatic environment as their potential toxicity to aquatic species remains to be explored. Thus, we suggest the hypothesis that isoprostanes can initiate a phenomenon of circular toxicity: humans, when in a state of oxidative stress, will excrete isoprostanes through urine that is discharged in the sewage system and will reach WWTPs. Because most WWTPs lack the technology to completely remove or degrade these contaminants they will enter the aquatic ecosystem where they can interact with several species that have receptors that recognize them. To test this circular toxicity hypothesis, the toxicity of effectors of oxidative stress (sodium hypochlorite and isoprostanes) was evaluated using standard acute and chronic toxicity tests performed using the model organism Daphnia magna. Furthermore, multigenerational and transgenerational tests were also performed to understand if these compounds induce effects in generations that aren’t chronically exposed to them. From the obtained results it is possible to conclude that when daphnids were chronically exposed, both to sodium hypochlorite and isoprostanes, reproductive success was dependent on the concentration. However, only sodium hypochlorite affected the size of daphnids, suggesting that the mechanism of action of these two compounds is different. In addition, it was also possible to conclude that both compounds are capable of inducing multigenerational and transgenerational effects on reproductive success, thus backing up our initial hypothesis of circular toxicity.