Cytotoxic impacts of treated electroplating industrial effluent and the comparative effect of their metal components (Zn, Hg, and Zn+Hg) on Danio rerio gill (DrG) cell line.

Effluent produced during the electroplating process can contain high concentrations of heavy metals that can enter the environment and induce toxicity to aquatic organisms. Relatively high concentrations of zinc (Zn) and mercury (Hg) have been detected in treated electroplating industrial effluent (TEPIE), though the cytotoxic potential of these compounds has not been well assessed in fish gills. A novel cell line, Danio rerio gill (DrG), were exposed to TEPIE and concentrations of Zn, Hg, and Zn + Hg previously measured in treated effluent to evaluate the use of the DrG cell line following exposure to environmental pollutants. Several cytotoxic assays were employed to assess the effect of TEPIE, Zn, and Hg on this cell line. The percent cell viability was significantly reduced in a concentration-dependent manner following exposure to TEPIE, Zn, Hg, and Zn + Hg (p < 0.05) for 24 h, with additional morphological changes observed in exposure treatments relative to controls. Additionally, there was a significant induction of DNA damage detected in all exposure treatments determined through comet assay tail length. An increase in intracellular ROS generation was also observed in cells exposed to TEPIE, Zn, Hg, and Zn + Hg, corresponding to dose-dependent increases in apoptosis. Our study confirmed that TEPIE and the metals present in it induced cytotoxicity in the DrG cell line, demonstrating its usefulness as a model to explore relationships between pollutants and fish gills.

Effects of zinc and mercury on ROS-mediated oxidative stress-induced physiological impairments and antioxidant responses in the microalga Chlorella vulgaris.

The rapid growth of industrialization and urbanization results in deterioration of freshwater systems around the world, rescinding the ecological balance. Among many factors that lead to adverse effects in aquatic ecology, metals are frequently discharged into aquatic ecosystems from natural and anthropogenic sources. Metals are highly persistent and toxic substances in trace amounts and can potentially induce severe oxidative stress in aquatic organisms. In this study, adverse effects of the two metal elements zinc (maximum concentration of 167.25 mg/L) and mercury (104.2 mg/L) were examined using Chlorella vulgaris under acute and chronic exposure period (48 h and 7 days, respectively). The metal-induced adverse effects have been analyzed through photosynthetic pigment content, total protein content, reactive oxygen species (ROS) generation, antioxidant enzymatic activities, namely catalase and superoxide dismutase (SOD) along with morphological changes in C. vulgaris. Photosynthetic pigments were gradually reduced (~32-100% reduction) in a dose-dependent manner. Protein content was initially increased during acute (~8-12%) and chronic (~57-80%) exposure and decreased (~44-56%) at higher concentration of the two metals (80%). Under the two metal exposures, 5- to 7-fold increase in ROS generation indicated the induction of oxidative stress and subsequent modulations in antioxidant activities. SOD activity was varied with an initial increase (58-129%) followed by a gradual reduction (~3.7-79%), while ~1- to 12-fold difference in CAT activity was observed in all experimental condition (~83 to 1605%). A significant difference was observed in combined toxic exposure (Zn+Hg), while comparing the toxic endpoint data of individual metal exposure (Zn and Hg alone). Through this work, lethal effects caused by single and combined toxicity of zinc and mercury were assessed, representing the significance of appropriate monitoring system to trim down the release of metal contaminants into the aquatic ecosystems.