Interactive Effects of Cadmium and Microplastics on Oxidative Stress and Digestive Physiology in the Male Euryhaline Species Poecilia sphenops

Abstract

The estuarine and coastal regions of India and Taiwan are under increasing threat from pollutants such as microplastics (MPs) and heavy metals including cadmium (Cd). These contaminants are known to have adversely affect biodiversity and water quality. In this study, the combined toxic effects of polyethylene microplastics (PE-MPs) and Cd were evaluated using Poecilia sphenops, a euryhaline fish species, selected for its adaptability to varying salinity conditions. P. sphenops were exposed to Cd (20, 40, and 60 mu g/L), MPs (8, 16, 24 mg/L), and co-exposure combinations ranging from Cd 5 mu g/L + MPs 4 mg/L to Cd 20 mu g/L + MPs 16 mg/L Results showed significant (p < 0.05) negative effects on growth parameters including body weight gain, specific growth rate (SGR), and survival rate. Hematological analysis revealed significant (p < 0.05) decreases in hemoglobin (Hb), red blood cells (RBCs), and white blood cells (WBCs), indicating impaired oxygen transport and compromised immune function. Elevated blood glucose levels indicated physiological stress, while reduced total protein levels suggested a compromised nutritional status. Antioxidant enzyme activities, including catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx), were significantly (p < 0.05) decreased in the toxicant-treated groups compared with the control. Digestive enzyme activities (proteases, amylases, and lipases) were also reduced, suggesting impaired digestion and nutrient assimilation. The study also included a comparative assessment of water quality between the exposed and control tanks. Water quality parameters such as turbidity, salinity, hardness, alkalinity, chloride, fluoride, and total suspended solids (TSSs) were elevated in the toxicant-treated media, accompanied by a notable decline in dissolved oxygen (DO) levels. These findings highlight the urgent need for integrated pollution control and water quality monitoring, particularly in coastal regions vulnerable to desalination discharges and plastic contamination. Sustainable management strategies must address these complex interactions between multiple pollutants to protect aquatic ecosystems.