Is UV radiation changing the toxicity of compounds to zebrafish embryos? Ana Rita Almeida a,n , Thayres S. Andrade a , Viktoriia Burkina b , Ganna Fedorova b , Susana Loureiro a , Amadeu M.V.M. Soares a,c , Inês Domingues a a Department of Biology & CESAM (Centre for Environmental and Marine Studies), University of Aveiro, Portugal, Campus Universitário de Santiago, 3810 Aveiro, Portugal b University of South Bohemia in Ceske Budejovice, Faculty of Fisheries and Protection of Waters, South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses, Zatisi 728/II, Vodnany 389 25, Czech Republic c Programa de Pós-Graduação em Produção Vegetal, Universidade Federal do Tocantins, Campus de Gurupi, Rua Badejós, Zona Rural, Cx Postal 66, CEP 77402-970 Gurupi, TO, Brasil article info Article history: Received 18 February 2015 Received in revised form 17 July 2015 Accepted 20 July 2015 Keywords: UV radiation Triclosan Prochloraz Chromium Danio rerio Combined effects abstract At ecosystems level, environmental parameters such as temperature, pH, dissolved oxygen concentration and intensity of UV radiation (UVR) have an important role on the efficiency of organisms’ physiological and behavioral performances and consequently on the capacity of response to contaminants. Insignif- icant alterations of these parameters may compromise this response. In addition, these parameters can additionally alter chemical compounds by inducing their degradation, producing thereafter other me- tabolites. Understanding the combined effects of chemicals and environmental parameters is absolutely necessary for an adequate prediction of risk in aquatic environments. According to this scenario, this work aims at studying the combined toxicity of UVR and three xenobiotics: the biocide triclosan (TCS), the metal chromium (as potassium dichromate, PD) and the fungicide prochloraz (PCZ). To achieve this goal zebrafish (Danio rerio) embryos (3 h post fertilization (hpf)) were exposed to several concentrations of each chemical combined with different UV intensities; mortality and eggs were recorded every 24 h for the all test duration (96 h). Results showed different response patterns depending on the toxicant, stress levels and duration of exposure. The combination of UVR and TCS indicated a dose ratio deviation where synergism was observed when UVR was the dominant stressor (day 2). The combination of UVR and PD presented a dose level dependency at day 3 indicating antagonism at low stress levels, changing with time where at day 4, a dose ratio deviation showed statistically that synergism occurred at higher PD concentrations. Finally, UVR combined with PCZ indicated a dose ratio at day 3 and dose level de- viation at day 4 of exposure, suggesting a synergistic response when PCZ is the dominant stressor in the combination. The obtained results in this study highlighted the importance of taking into account the possible interaction of stressors and time of exposure to better predict environmental risk. & 2015 Elsevier Inc. All rights reserved. 1. Introduction Recent scientific evidences have shown that climate change – mainly driven by anthropogenic activities – is causing extensive alterations on ecosystems with drastic consequences to the en- vironment (IPCC et al., 2013; Schiedek et al., 2007). In aquatic environments where organisms are exposed to environmental contamination, the fluctuation on these environmental parameters (such as temperature, pH, dissolved oxygen concentration and UV radiation) may act as co-stressors and should be taken into account to assess the overall ecosystem health (Barata et al., 2007; Ferreira et al., 2010; Holmstrup et al., 2010). In the last decades, the increased levels of ultraviolet radiation (UVR) reaching the earth surface have received attention. After noticing the depletion of stratospheric ozone layer, more than 30 years ago, a great effort has been made by both scientific com- munity and authorities to minimize the emissions of ozone de- pleting substances. Although the Montreal Protocol is being fol- lowed, it will take several decades for ozone layer to return to pre- 1980 values (Weatherhead and Andersen, 2006). UVR is known to cause severe damage to aquatic life. Exposure to UVR has shown to decrease feeding rate and reproduction in water flea (Ribeiro et al., 2011), to cause DNA damage, reduce hatching success, and to in- crease deformities and mortality in zebrafish embryos (Behrendt Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety http://dx.doi.org/10.1016/j.ecoenv.2015.07.021 0147-6513/& 2015 Elsevier Inc. All rights reserved. n Corresponding author. Fax: þ351 234 372 587. E-mail address: rita.almeida@ua.pt (A.R. Almeida). Ecotoxicology and Environmental Safety 122 (2015) 145–152