| dc.description.abstract | Pollutants and other forms of environmental stress (lifestyle and social behaviour) are of global concern due to significant adverse effects on human health. The term "exposome" has emerged as a concept in environmental health sciences, including environmental epidemiology, exposure science, and toxicology. It is the composite of an individual's lifetime exposures and how those exposures relate to health. A major source of individual exposure to the external environment, either directly or indirectly, is via drinking water since most pollutants in the air and soil end up in water bodies, including rivers. In India, one of the major rivers that receive different wastes is the Cauvery River (CR). The Cauvery River, an interstate river, flows eastward from Karnataka through Tamil Nadu and drains into the Bay of Bengal, providing potable water for over 150 million humans and animals and has long-sustained fishing and irrigation. However, indiscriminate discharge of waste into the river water causes unexplained health hazards to human and other animal species, like skeletal deformity and dwindling numbers of fish species in the river. However, in detail, the health hazard impacts of the Cauvery water have not been investigated so far. To investigate this phenomenon, we analyzed the biological, physical, and chemical parameters as well as microplastics present in the CR water and then evaluated the toxicity effects on the zebrafish (Danio rerio) model.
Zebrafish offers many advantages as a research model, including rapid development, optical transparency, a large number of offspring, and an excellent vertebrate model for toxicological research. We treated the zebrafish with KRS-CR water samples collected from three stations (fast-flowing water [X], slow-flowing [Y], and stagnant [Z] water), before and after filtration.
Firstly, we detected microscopic organisms (MO) such as Cyclops, Daphnia, Spirogyra,
Spirochaeta, and total coliform (Escherichia coli), which are bioindicators of water pollution present in the samples. All physicochemical parameters analyzed, including heavy metals before and after filtration of the water with Millipore filter paper (0.45 μm), were within the acceptable limits set by standard organizations, except for decreased dissolved oxygen (DO), and increased biochemical oxygen demand (BOD), and chemical oxygen demand (COD), which are indicators of hypoxic water conditions. We also identified the presence of microplastics (polybutene (≤ 15 μm), polyisobutene (≤ 20 μm), and polymethylpentene (≤ 3mm) as well as cyclohexyl functional group in CR water samples. Zebrafish embryos treated with the water samples, both before and after filtration, exert the same cytogenotoxic effects by inducing increased reactive oxygen species (ROS) production, which triggers subcellular organelle dysfunctions, DNA damage, apoptosis, pericardial oedema, skeletal deformities, and increased mortality. As a result, we observed that both water samples and zebrafish larvae had significantly less oxygen availability, due to the presence of plastic materials (polyisobutylene).
Plastic pollution has become a serious global concern. The plastic waste is broken down into minute particles known as microplastics (MPs) and released as granules, pellets, and/or powders, influencing biosystems. 'Microplastic' is a term for plastic particles without a universally established definition. In the literature, microplastic is often defined as plastic particles up to 5 mm in dimensions with no defined lower size limit. Among the three types of MPs observed in this study, we discovered that the concentration of polyisobutylene (PIB) (<10 μg/mL) was higher than that of the other MPs particles identified in the CR. Since the mechanism of polyisobutylene's toxicological effects is unknown, we synthesized, characterized, and determined the toxicity effects and accumulation of polyisobutylene (PIB) in zebrafish. Using the solvent evaporation method, we synthesized pristine and fluorescence PIB-MPs with particle sizes of < 2-10 μm. The PIB Raman peak (715.942 cm-1) and FTIR characterization tests showed that the samples have notable peaks at 1366 and 1388 wavenumber (cm-1), and zeta potential of approximately -40mV to -60 mV, indicating the inherent stability of the suspensions. Zebrafish larvae exposed to various concentrations (low and high concentrations) of PIB-MP showed reduced swimming and hyperactivity, delayed hatching, increased ROS, and changes in mRNA levels of genes (mnsod, cu/znsod, gsr, and gstp1) encoding antioxidant proteins. Interestingly, we observed that the PIB-MP accumulated in all three gut regions (proximal intestine, middle intestine, and distal intestine) of both larvae and adult fish within 7 to 21 days, respectively. Histopathological examination of the gut revealed increased vacuolation as well as damage to the intestinal mucosa. The immunohistochemistry results showed an enhanced expression of two proinflammatory cytokines (TNF-α and IL-18) in the gut and tail regions of treated fish, which ultimately led to an increase in apoptosis. The build-up of these PIB particles generates adverse consequences in zebrafish larvae and adults. The most frequent phenotypic manifestation we found was skeletal abnormalities, which ultimately led to higher mortality. Our findings show that KRS-CR water can cause cytogenotoxic and embryotoxic defects in zebrafish due to hypoxic water conditions triggered by the PIB microplastic influx. The present study, with its comprehensive analysis of biological and physicochemical parameters in Cauvery River water, offers valuable insights for the evaluation of environmental health hazards. By identifying the presence of microplastics in the river, the study highlights the potential risks posed by this specific microplastic (PIB-MP) to the environment and human health. The cytogenotoxic and embryotoxic effects observed in the zebrafish highlight the potentially hazardous nature of the water, indicating a need for further investigation and implementation of appropriate mitigation measures. Such information is crucial for policymakers, regulatory bodies, and/or environmental agencies as it provides a scientific basis for developing effective strategies and interventions to mitigate the adverse impacts of microplastics in river water. The findings can help in designing targeted and efficient river water treatment strategies, aiming to reduce microplastic contamination and ensure the provision of safe and clean water resources for communities and ecosystems in other to protect the health of both aquatic organisms, animals, and human populations dependent on the river water for various purposes. | en_US |
