Efeito do material particulado atmosférico (MPA) sedimentável proveniente da atividade siderúrgica sobre a função cardíaca de tilápia, Oreochromis niloticus

Abstract

The industrial activity for obtaining and processing metal alloys, iron and steel result in the emission of Sedimentable Atmospheric Particulate Material (SAPM). Mining-steel industries located in the “Complexo do Tubarão”, in Metropolitan Region of Vitoria (MRV), Vitoria – ES, emit a metal smoke commonly called "black powder" that contains a varied composition of metals and metal nanoparticles that are deposited in aquatic environments. Faced with a scenario that seeks to produce information that can help the sustainable management of water resources, the objective of this study was to evaluate the possible effects of acute exposure (96 hours) of sublethal concentrations of 0.01 g.L-1, 0.1 g.L-1, and 1.0 g.L-1 of SAPM on myocardial contractility of Nile tilapia, Oreochromis niloticus. The group exposed to 1.0 g.L-1 of SAPM showed significantly higher values of contraction force (Fc) and cardiac pumping capacity (CPC) at all stimulation frequencies. In the exposed animals, time-dependent parameters (TPT = time to peak tension, and THR = time to 50% of relaxation) were lower, while contraction and relaxation rates were higher. All groups exhibited a Fc decay after the non-physiological diastolic pause of 300 seconds, which was more conspicuous in the exposed groups, suggesting a prominent role of the Na +/Ca2+ (NCX) exchanger in calcium extrusion. As the 1.0 g.L-1 concentration of SAPM showed pronounced effects on cardiac contraction, we also investigated the effects of this exposure on hematological parameters and plasma biomarkers of stress response and oxidative stress. Alterations in myocardial contractility in MPAS-exposed fish were associated with a stress response characterized by significant increases in plasma cortisol and glucose levels. Tilapia exposed to SAPM also showed a significant reduction in hemoglobin content indicating a possible hypoxemia state, which may require adjustments in cardiac output, with increased Fc to increase systolic volume. The exposed fish showed higher values of hepatosomatic index and relative ventricular mass, probably associated with the overload of activity of the heart and liver. Additionally, SAPM exposure induced significant increases in plasma levels of lipid peroxidation and protein carbonylation, indicating oxidative stress and reflecting an imbalance of redox homeostasis. NCX protein expression showed no significant difference between the groups, indicating that the positive inotropic and lusitropic effects are associated with β-adrenergic responses during stress situations. Thus, the effects of SAPM may negatively affect the adaptation, survival and reproductive success of tilapia, as the energy requirement to maintain the physiological patterns of the cardiovascular system and the detoxification processes demanded by SAPM exposure is high.