Assessment of the concentrations and human risk of polycyclic aromatic hydrocarbons in stem bark samples of Psorospermum febrifugum and soil from Nsukka area in eastern Nigeria

Psorospermum febrifugum (P. febrifugum) is an active anti-inflammatory medicinal plant and for the treatment of various illnesses [7]. The presence of 16 EPA priority polycyclic aromatic hydrocarbons (PAHs) was investigated in the plant stem bark extract and soil. The plant samples were extracted with ethanol while the soil samples were extracted with hexane-dichloromethane (3:1) mixture according to the Association of Official Analytical Chemist (AOAC) method. Gas chromatography-mass spectrometry (GC-MS) was used for the determination. Recovery experiments were carried out to validate the accuracy of the analytical methods employed. Carcinogenic equivalent potency of PAHs was determined according to EPA method on the basis of Benzo[a]pyrene equivalent (B[a]peq). Pearson correlation coefficient was employed to measure the strength of association between the concentration of the PAHs in the plant and the soil. Bioaccumulation factor (BAF) of the contaminants was carried out. Source of PAHs was derived from diagnostic concentration ratios which were calculated using the concentration of specified PAHs or as a common group from a common source. The recoveries for PAHs were between 82.58 and 99.85%. The concentrations of PAHs in P. febrifugum stem bark ranged from (0.089 +/- 0.145-0.370 +/- 0.354 mu g/kg) to soil (0.060 +/- 0.050-0.716 +/- 0.119 mu g/kg). The diagnostic ratio values of PAHs were in this order: Phen/Anth < 10, Anth/ (Anth + Phen) > 0.1, Flu/ (Flu + Pyr) > 0.4, Pyr/Bap < 50 and Bbf/Bkf < 3.9 indicating pyrolysis as the major source of PAHs in the studied area. The B[a]P eq concentrations of PAHs in the analyzed plant samples varied between 0.00175 and 0.22 mu g/kg, while in soil samples 0.0358 and 0.486 mu g/kg. The BAF values of PAHs ranged from 0.14 to 4.85. Although, the concentrations of PAHs detectable in P. febrifugum stem bark and soil samples were far lower than the permissible limits for medicinal plants and soil set by FAO/WHO [9]. The data showed that there is no potential health danger of PAHs contamination to the consumers of P. febrifugum from the study area. However, assessment of medicinal plants for possible contaminants is necessary for safe consumption.