ABSTRACT:
The disposal of Used Lubricating Oil (ULO) is an emerging global environmental issue, especially in developing nations where waste management systems and regulatory frameworks are weak. ULO is a complex mixture of toxic heavy metals coming from wear and additive breakdown, which can have detrimental effects on soil and water quality. In this research, the levels and sources of heavy metals in ULO from four typical vehicles in Quetta City, Pakistan, were studied using energy-dispersive X-ray Fluorescence (XRF) spectroscopy. Nine elements (Pb, Sn, Cu, Ni, Cr, Mn, Zn, P, and S) were measured, with high levels of Tin (50,000-117,800 mg/kg) and Copper (11,100-31,600 mg/kg) suggesting significant wear. Zinc (777-867 mg/kg) and phosphorus (908-1,046 mg/kg) exhibited minimal variations, indicating uniform additive compositions. Principal component analysis (PCA) revealed two major sources of variability (91.2% variance explained), including wear contaminants (bearings, bushings, and unburnt fuel) and additives, Zinc Dialkyldithiophosphate (ZDDP-based additives). Compared with international soil quality guidelines, the levels of Tin (Sn), Copper (Cu), Nickel, and Chromium (Cr) are well above the recommended limits, suggesting environmental concerns associated with improper ULO disposal. While Lead concentrations were found to be low due to the success of lead-free fuel policies, the study highlights the importance of collecting ULO, enforcing regulations, and undertaking environmental surveillance. This research provides a baseline assessment of ULO contamination in Pakistan and contributes to international knowledge of ULO contamination, thereby aiding the establishment of sustainable waste-oil management practices.
Keywords: XRF; Used lubricating oil, Heavy metals; Source apportionment; Environmental risk; Quetta

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