Metabolic effects in the freshwater fish Geophagus iporangensis in response to single and combined exposure to graphene oxide and trace elements Aline Maria Zigiotto de Medeiros a , Francine C ^ oa a , Oswaldo Luiz Alves b , Diego St  efani Teodoro Martinez c , Edison Barbieri a, * a Instituto de Pesca-SP-APTA-SAA-Governo do Estado de S~ ao Paulo, Av. Prof. Besnard s/n, CEP.11990-000, Canan eia, SP, Brazil b Laborat orio de Química de Estado S olido (LQES), Instituto de Química, UNICAMP, Campinas, SP, Brazil c Laborat orio Nacional de Nanotecnologia (LNNano), Centro Nacional de Pesquisa em Energia e Materiais (CNPEM), Campinas, SP, Brazil highlights graphical abstract  The metabolic rate reveals that com- bined exposure (GO þ trace element) potentiates the effects of trace ele- ments on fish.  The increase in hydrodynamic diam- eter with zinc is probably a result of interaction between the trace element and GO.  The interaction between Cd and GO did not affect hydrodynamic size within 24 h.  The exposition to Cd only revealed differences between single and com- bined exposure only at metabolic rate. article info Article history: Received 30 August 2019 Received in revised form 17 October 2019 Accepted 4 November 2019 Available online 5 November 2019 Handling Editor: Jim Lazorchak Keywords: Metabolic rate Oxygen consumption Ammonia excretion Trojan horse abstract Graphene oxide (GO) is part of a new set of nanomaterials with particular characteristics related to its nanoscale size. Due to this feature, it presents high reactivity and other contaminants present in the environment could bind to them and affect its intrinsic toxicity. The metabolic effects of such nano- materials and their combination with two common pollutants, zinc and cadmium, on the freshwater fish Geophagus iporangensis are analyzed. Moreover, metabolic rate and ammonia excretion were used as bioindicators to measure metabolic changes. Fishes were exposed for 24 h in filtered tap water to different concentrations of GO (0.5; 1.0; 2.0 and 4.0 mg L 1 ), Zn (0.5; 1.0; 2.0; 4.0 and 10.0 mg L 1 ) and Cd (0.1; 0.5; 1.0; 2.0 and 4.0 mg L 1 ). Combined effects were verified using the same concentrations of trace elements added to 1.0 mg L 1 of GO. Exposure to GO and Cd resulted in a decrease of metabolic rate in G. iporangensis, by about 30% compared to control means, in the highest concentration tested (4.0 mg L 1 ). However, zinc exposure in the highest concentration (10 mg L 1 ) raised metabolic rate to around three times that of the control group. Ammonia excretion was not affected by exposure to GO and Cd. In contrast, exposure to Zn at 10 mg L 1 raised the rate to around 47%. The combined exposure of GO and Zn intensified the effects of the trace element, inducing responses in both biomarkers at lower concentrations and demonstrating that the interaction between elements increases zinc’s effects. The * Corresponding author. E-mail address: ebarbieri@pesca.sp.gov.br (E. Barbieri). Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere https://doi.org/10.1016/j.chemosphere.2019.125316 0045-6535/© 2019 Elsevier Ltd. All rights reserved. Chemosphere 243 (2020) 125316