Toxicological and Genotoxic Effects of Used Drilling Fluid: Histopathology and Genotoxicity Assessment

During the process of extracting crude oil from the subsurface of the earth, drilling fluids play a crucial role. To evaluate the toxic and genotoxic characteristics of used oil-based drilling fluid, experiments were conducted using Clarias gariepinus (a type of fish) and Allium cepa (an onion). Prior to the experiments, the test subjects were acclimatized and stored for a period of 14 days. Following acclimatization and storage, test solutions were prepared in different concentrations based on the results of a range-finding test. After 96 hours of exposure, the LC50 values for the drilling fluid were determined as follows: 71.589% at 24 hours, 96.052% at 48 hours, 96.052% at 72 hours, and 59.508% at 96 hours. The mortality rate was recorded, revealing a direct relationship between the concentration of the drilling fluid and the mortality of the test subjects. The EC50 values also indicated a correlation between root tip-growth inhibition and increased toxicant concentration. Furthermore, histopathological studies conducted on the gills and livers of Clarias gariepinus after 96 hours of exposure revealed noticeable alterations. To analyze the content of polycyclic aromatic hydrocarbons (PAHs) present in the oil-based drilling mud, substances such as Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenathrene, Anthracene, Fluoranthene, Benzo (K), Pyrene, Benz (a) anthracene, Chrysene, Benzo (b) fluoranthene, Benzo (k) fluoranthene, Benzo (a) pyrene, Indeno (1,2,3-cd) pyrene, Dibenz (a,h), anthracene, and Benzo (g,h,i) perylene were analyzed using GC-MS mode S4 = 71096. These parameters are believed to be responsible for the toxic effects observed in fish and onion root tips. Considering the toxic effects and alterations observed, it is crucial to closely monitor the disposal of drilling fluids after the recovery of crude oil. Compliance with the necessary regulatory standards established by regulatory bodies should be ensured to prevent adverse environmental impacts.