Assessment of exposure to polycyclic aromatic hydrocarbons and heavy metals in suspected contaminated groundwater of two localities in Enugu Metropolis of Nigeria

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are common pollutants associated with anthropogenic groundwater pollution. In this study, exposure risks to PAHs and heavy metals in hand-dug well waters (groundwater) used for the purposes of cooking, bathing and washing by residents of two localities in Enugu Metropolis of Enugu State, Nigeria, were assessed. The study was motivated by the suspicion that the well waters were polluted by hydrocarbons about 7 years ago following complaints from the residents of these areas of oil sheen in the well waters. The indiscriminate disposal of wastes around the two localities necessitated the inclusion of heavy metals in this study. The PAHs were measured using gas chromatography-mass spectrometry (GC-MS), whereas the heavy metal concentrations were measured using atomic absorption spectrometry (AAS). Obtained results indicate that the only PAHs detected in the well waters were acenaphthylene and benzo(k)fluoranthene. Acenaphthylene occurred at an average concentration range of 0.4–0.6 mg/L in the well water samples of Nkpologwu and Ekulu, whereas benzo(k)fluoranthene occurred at 0.2–0.4 mg/L in the water samples of Nkpologwu but undetected in Ekulu. Among the analyzed heavy metals, arsenic and aluminium were not detected but copper, zinc, lead, cadmium and chromium VI were detected. The non-carcinogenic health risks associated with exposure to the PAHs by the residents were not significant given that the hazard index (HI) for all the samples varied from 0.002 to 0.005 (less than 1). However, the exposure risks to the non-carcinogenic health effect of cadmium and chromium VI were significant as these two heavy metals especially chromium VI had hazard quotients (HQ) more than unity for all the well waters. Employing a cancer threshold risk of one in a million, the cancer risk index (RI) of the PAHs in this study varying from 1.5×10 −5 to 3.1×10 −5 was considered significant. Also, the excess lifetime cancer risk (ELCR) of the heavy metals in the water indicated that lead, chromium and cadmium posed high carcinogenic risks especially cadmium with ELCR of 7.7×10 −3 . These well waters were therefore not fit for the purposes they had been used till now and should be discontinued. There is an urgent need for the remediation of the groundwater towards the removal of the heavy metals mainly cadmium, chromium and lead.