Most of the world´s population live in urban areas, and this has a profound impact in the natural environment. Urban centers are generally located close to waterbodies, hence ecological research on urban aquatic ecosystems has received special interest in recent years. Multiple stressors such as light pollution and chemical contamination impose novel challenges on species living in urban/suburban areas. Evaluating how these multi-stressor scenarios shape biodiversity loss, shifts in species occurrence, rapid adaptive evolution and ecosystem functioning is a must research priority. Light pollution and especially Artificial Light At Night (ALAN) have become emergent issues of environmental concern given the human health and ecological detrimental effects recently identified. Studies dealing with anthropogenic-induced changes to light conditions show that ALAN disrupt biological rhythms and also reduce biological fitness through changes in melatonin levels. This time-keeper hormone plays a pivotal role of relaying information about changes in day-length and modulate circadian responses in physiology, metabolism and behavior of organisms. Assessing the role of light pollution as an environmental endocrine disruptor is of pivotal importance. We argue that this should focus on the mechanistic links between ALAN, physiology and biological fitness, and in addition must include more realistic, multi-stressor conditions. Besides light pollution, urban aquatic ecosystems are usually recipients of hospital, municipal and industrial discharges resulting in increased concentrations of human pharmaceuticals with potential adverse environmental consequences. With the rise of cancer incidence worldwide, the number of prescribed chemotherapeutic drugs has also increased exponentially. These drugs are not efficiently removed by wastewater treatment and are now commonly detected in urban surface waters, being considered emerging contaminants of special interest having limited information regarding their ecotoxicological profiles and environmental risk. Given the ubiquity and co-occurrence of light pollution and antineoplastic drugs, it is critical to evaluate their combined impacts on urban aquatic ecosystems particularly in light of possible synergistic effects. The mechanistic links dictating how shifting light conditions influence fitness and tolerance to antineoplastic drugs are currently not understood. This limitation needs to be addressed given the central role that melatonin plays. Besides regulating circadian rhythms, melatonin also regulates antioxidant activity, immunity and metabolism as well as behavior and reproductive processes. Moreover, this hormone exerts antineoplastic action due to antiproliferative, cytostatic, antimetastatic and proapoptotic effects against tumor cells. Melatonin is now being tested and co-administered in chemotherapeutic treatments, to increase efficacy of antineoplastic drugs and because it reduces their toxicity and collateral side effects due to its potential to downregulate cellular inflammation and oxidative injury while stimulating cellular repair and defense mechanisms in healthy cells. LED will thus focus on the general work hypothesis that light pollution, ALAN in particular, is a pervasive endocrine disruptor[8] that can mediate the ecological effects of antineoplastic drugs in urban aquatic ecosystems. Through a combination of ecotoxicological approaches where we will manipulate both ALAN (by using light emitting diodes) and exogenous melatonin (to counter the ALAN-induced reduction of internal melatonin), we will investigate: i) to what degree ALAN affects melatonin levels and biological fitness in Daphnia magna and Danio rerio (zebrafish); ii) how ALAN and the expected change in melatonin levels influence the toxicity of antineoplastic drugs that are nowadays emerging contaminants of urban aquatic ecosystems; and iii) the ecological consequences of ALAN and of antineoplastic drugs for microevolutionary responses and for species interactions in aquatic environments. Relying on the strong expertise of the research team in working with the aquatic model species (Daphnia magna; Danio rerio) in freshwater ecology and ecotoxicology, ecophysiology, environmental transcriptomics and lipidomics, mixture toxicity assessment and analytical chemistry, results from this project will increase knowledge and awareness on light pollution and provide scientific support for better urban environmental planning policies towards the protection and conservation of biodiversity and ecosystem services provided by urban freshwater ecosystems. The LED project will also clarify mechanistic pathways of toxicity of antineoplastic compounds that are essential for the development of Adverse Outcome Pathways (AOPs), the interpretation of their ecological effects and effective environmental risk assessment.
