Abstract
Diazinon exposures have been linked to the onset of toxic pathways and adverse outcomes in aquatic species, but the ecological implications on model species are not widely emphasized. The objective of this study was to determine how the organophosphate pesticide diazinon affected hematological (hemoglobin, total red blood count, total white blood count, and mean corpuscular hemoglobin), growth (condition factor, hepatosomatic index, specific growth rate), biochemical (total serum glucose, total serum protein), and endocrine (growth hormone, tri-iodothyronine, and thyroxine) parameters in Clarias batrachus after chronic exposure. Diazinon was administered at predefined exposure doses (0.64 and 1.28 mg/L) and monitored at 15, 30, and 45 days into the investigation. Observation for most biomarkers revealed patterns of decreasing values with increasing toxicant concentration and exposure duration. Correlation analysis highlighted a significant inverse relationship between variables (mean corpuscular hemoglobin, condition factor, specific growth rate, tri-iodothyronine, thyroxine, and total serum protein) and elevated chronic diazinon exposure concentrations. The integrated indices (IBR and BRI) indexes were used to provide visual and understandable depictions of toxicity effects and emphasized the relativity of biomarkers in terms of sensitivity and magnitude or severity of responses under graded toxicant exposures. The significant damage reflected by evaluated parameters in diazinon exposure groups compared to control portends risks to the health of local fish populations, including Clarias batrachus in aquatic systems adjacent to agrarian landscapes.
Highlights
Pesticides, otherwise referred to as plant protection products (PPPs), by deliberate use and applications in pest control and crop protection have recorded elevated occurrences in the environment [1,2,3]
Compared to the control fish, the exposed fish showed a significant reduction in Hb, TRBC, TWBC, and MCH values in groups with higher exposure concentrations (Figure 1)
The decrease in Hb and TRBC levels observed in diazinon exposure groups could be related to the disrupted function of the hemopoietic system, erythrocyte destruction, or reduced synthesis in bone marrow [56,57]
Summary
Pesticides, otherwise referred to as plant protection products (PPPs), by deliberate use and applications in pest control and crop protection have recorded elevated occurrences in the environment [1,2,3]. Though integrated systems require fewer pesticides than the conventional ones, they are used lavishly in co-culture farming techniques [5], the eventual contamination of aquatic ecosystems with PPPs either due to spray-drift, leaching, runoff, and/or accidental spills and from aquacultural applications [6,7,8] could culminate into risks of debilitating effects and mass mortalities of non-target species [9,10,11,12,13,14,15]. Diazinon (dimpylate) is an organo-thiophosphate derivative used widely as an agricultural and household insecticide. It is inactivated by photochemical oxidation and expected not to be persistent, it has an estimated moderate to high toxicity to freshwater fish, estuarine, and marine fish and potential high toxicity to birds [20]. In vitro studies on cell lines suggest that it causes oxidative stress through free-radical generation and promotes DNA fragmentation [31,32]
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