The toxic effects of spent crankcase oil exposures; systematic review and meta-analysis

The study sought to execute a systematic review and meta-analysis to describe the toxicological implications associated with exposures of humans and laboratory animals to Spent Crankcase Oil (SCO). Databases like PubMed, Scopus, Science Direct, Google Scholar, Web of Science, and PlosOne were searched systematically for all data that assessed the effects of SCO on humans and animals. For each parameter involved in the meta-analysis (those with extractable data), mean, standard deviation, the sample size was extracted for both exposure groups and control. This was then used to compute the standardized mean difference (SMD). Statistical analysis and forest plots were done with RevMan 5.3 software. Twenty-eight (28) studies fulfilled the pre-specified criteria for eligibility. Fourteen (14) of the studies were used for the meta-analysis, which included a total of 1243 subjects from different human epidemiological occupational exposure studies and animal experimental studies. The meta-analysis revealed that SCO exposure caused a significant reduction in the body weight of animals (n = 5, SMD; - 1.2; 95% CI; (- 1.78, - 0.67), p = 0.0001, I² = 22%), and in the red blood cell count (n = 5, SMD; - 1.28; 95% CI; (- 2.18, - 0.38, p = 0.02); I² = 78%) and haemoglobin (n = 4, SMD; - 1.12, 95% CI; (- 2.71, 0.46); p = 0.16; I² = 89%) in animal models. While there was a significant elevation of the aspartate amino transferase (AST) (n = 6, SMD; 0.76; 95%CI; (0.41, 1.11), p = 0.0001, I² = 89%), alkaline phosphatase (ALP) (n = 5, SMD; 1.92; 95% CI; (0.02, 3.83), p = 0.05, I² = 92%), and creatinine (n = 4, SMD = 1.56; 95% CI; (0.05, 3.07), p = 0.04, I² = 90%) concentrations in comparison to the control. On the other hand, there was a non-significant effect on the alanine amino transferase (ALT) (n = 5, SMD; 1.13; 95% CI; (- 0.37, 2.62); p = 0.14; I² = 92%), urea (n = 4, SMD; 1.23; 95% CI; (- 1.18, 3.65), p = 0.32, I² = 94%), packed cell volume (PCV) (n = 5, SMD; 0.10; 95% CI; (- 0.36, 0.56), p = 0.67; I² = 47%); and the haemoglobin (n = 6; SMD; - 0.74; 95% CI; (- 1.73, 0.26), p = 0.15; I² = 89%) concentrations. Oxidative stress, heavy metals bioaccumulation, immunotoxic, genotoxic, and carcinogenic effects were also in the list of findings. The toxicological implications associated with SCO exposure points to the need for immediate establishment of policies that regulate the disposal of spent crankcase oil in the environment.

The online version contains supplementary material available at 10.1007/s43188-021-00093-2.