Assessment of radioactivity and polycyclic aromatic hydrocarbon levels in ground waters within the bitumen deposit area of Ondo State, Nigeria

ABSTRACT

The quality of groundwaters within Nigerian bitumen deposit area was investigated with a view to providing valuable information on the radioactivity and organic parameters associated with the contamination of the groundwaters by bitumen deposit. This will also provide baseline data required for the assessment of future environmental impact during the development of the natural resource. Two-season groundwater samples were collected and analyzed for the radioactivity levels using a well-calibrated gamma-ray spectrometer, while samples were collected in separate amber glass bottles for polycyclic aromatic hydrocarbons (PAHs) analysis. The extraction, cleanup, and concentration of the PAHs were done using certified analytical methods. Quantitative determination of the PAHs was made using Agilent 7890A Gas chromatography. The radionuclides obtained with reliable regularity are associated with the decay series of ²³⁸U and ²³²Th as well as the non-decay series ⁴⁰K. The specific activities of the groundwaters were found to vary between N.D - 5.24 ± 1.66 Bq/L for ²²⁶Ra, ²²⁸Ra (N.D - 2.00 ± 0.87 Bq/L), and ⁴⁰K (N.D - 9.54 ± 2.75 Bq/L) during the dry season and between N.D - 2.23 ± 1.02 Bq/L for ²²⁶Ra, ²²⁸Ra (N.D - 2.41 ± 0.91 Bq/L), and ⁴⁰K (17.06 ± 9.15 - 44.62 ± 16.60 Bq/L) during the rainy season. The mean absorbed dose rates of the water samples were found to be higher than the recommended limit (0.1 mSv/yr) for drinking water. Sixteen priority pollutants PAHs were identified, and their concentrations were determined. The study revealed that the total average PAHs in the water samples ranged from 0.607 ± 0.065 to 3.983 ± 0.098 mg/L for dry season and 0.072 ± 0.050 to 1.467 ± 0.130 mg/L for rainy season. These were higher than the control for dry season (0.071 ± 0.052 mg/L - 0.444 ± 0.166 mg/L) and rainy season (0.067 ± 0.042–1.092 ± 0.084 mg/L). During both seasons, the PAH concentrations were higher than 0.000005 mg/L recommended for uncontaminated groundwater and 0.000001–0.000011 mg/L for drinking water. Total risks of 19.5E-03 and 4.7E-03, which exceeded the 10⁻⁵ risk limit specified by the USEPA, were established for the dry and rainy season samples, respectively. The radioactivity and PAH levels observed were an indication of their contamination from the bitumen deposit by the groundwaters within the study area.

KEYWORDS:

• Bitumen
• gamma-ray spectroscopy
• GC
• groundwater
• PAH
• radioactivity