Environmental impact of crude oil on the phytochemical constituents of some selected medicinal plants in Nigeria

Purpose: To investigate the effect of crude oil exploration on secondary metabolites of Magnifera indica, Ficus exasperata, Mallotus oppositifolius, Millettia aboensis and Newbouldia leavis. Methods: The leaves of the plants were collected from Ogoni (oil-producing area) referred to as test samples, and Awka (non-oil-producing area) referred to as control, in Nigeria. Methanol and dichloromethane extracts of the leaves of the plants, harvested from both regions, were subjected to phytochemical analyses and gas chromatography/mass spectrometry (GC-MS) analysis. Quantification of the phytochemicals was done spectrophotometrically and expressed as equivalent to their respective standards. Results: Extraction yield ranged from 4.4 to 10.4 %w/w. Phytochemical analysis showed that all the test phytochemicals, except cyanogenic compounds, were detected in both test and control samples. Steroids and alkaloids were significantly higher in test samples compared to control samples (p < 0.05). Furthermore, terpenoid was significantly lower (p < 0.05) in test samples (F. exasperate and M. oppositifolius) than in control samples. The GC-MS analysis revealed that only M. indica contained 1,3-diazocane-2-thione and 5-methyl-1,2-oxazol-3-amine were present in both the test and control samples, while the other samples contained diverse alkaloidal chemotypes. Conclusion: The multifactorial nature of oil exploration may affect plant phytochemicals via chemical transformation, depletion or accumulation. This provides valuable insights into the need for environmental conservation.