Waste engine oils are hazardous waste oils originating from the transportation sector and industrial heavy-duty machinery operations. Improper handling, disposal, and miscellaneous misuses cause significant air, soil, sediments, surface water, and groundwater pollution. Occupational exposure by prolonged and repeated contact poses direct or indirect health risks, resulting in short-term (acute) or long-term (chronic) toxicities. Soil pollution causes geotoxicity by disrupting the biocenosis and physicochemical properties of the soil, and phytotoxicity by impairing plant growth, physiology and metabolism. Surface water pollution impacts aquatic ecosystems and biodiversity. Air pollution from incineration causes the release of greenhouse gases creating global warming, noxious gases and particulate matter eliciting pulmonary disorders. The toxicity of waste engine oil is due to the total petroleum hydrocarbons (TPH) composition, including polycyclic aromatic hydrocarbons (PAHs), benzene, toluene, ethylbenzene, xylene (BTEX), polychlorinated biphenyls (PCBs) congeners, organometallic compounds, and toxic chemical additives. The paper aims to provide a comprehensive overview of the ecotoxicological effects, human and animal health toxicology and exposure to waste engine oils. It highlights the properties and functions of engine oil and describes waste engine oil generation, disposal and recycling. It provides intensive evaluations and descriptions of the toxicokinetics, metabolism, routes of exposure and toxicosis in human and animal studies based on toxicological, epidemiological and experimental studies. It emphasises the preventive measures in occupational exposure and recommends risk-based remediation techniques to mitigate environmental pollution. The review will assist in understanding the potential risks of waste engine oil with significant consideration of the public health benefits and importance.
The research aimed to determine the influence of endophytic fungi on tolerance, growth and phytoremediation ability of Prosopis juliflora in heavy metal-polluted landfill soil. A consortium of 13 fungal isolates as well as Prosopis juliflora Sw. DC was used to decontaminate heavy metal-polluted landfill soil. Enhanced plant growth (biomass and root and shoot lengths) and production of carotenoids, chlorophyll and amino acids L-phenylalanine and L-leucine that are known to enhance growth were found in the treated P. juliflora. Better accumulations of heavy metals were observed in fungi-treated P. juliflora over the untreated one. An upregulated activity of peroxidase, catalase and ascorbate peroxidase was recorded in fungi-treated P. juliflora. Additionally, other metabolites, such as glutathione, 3,5,7,2',5'-pentahydroxyflavone, 5,2'-dihydroxyflavone and 5,7,2',3'-tetrahydroxyflavone, and small peptides, which include Lys Gln Ile, Ser Arg Ala, Asp Arg Gly, Arg Ser Ser, His His Arg, Arg Thr Glu, Thr Arg Asp and Ser Pro Arg, were also detected. These provide defence supports to P. juliflora against toxic metals. Inoculating the plant with the fungi improved its growth, metal accumulation as well as tolerance against heavy metal toxicity. Such a combination can be used as an effective strategy for the bioremediation of metal-polluted soil.