Bitumen Seepage: Impact and Interaction on Heavy Metal Concentrations in Surface Water

Abstract

The association and interaction among metals in bitumen-polluted water may affect the availability of the metals 
even at toxic levels to the surrounding environment and biota that are dependent on such water. This study 
was carried out at Ode-Irele in Ondo State bitumen belt, Southwest of Nigeria, where there are bitumen 
seepages and at Ebute-Irele where there are no records of seepages to serve as a control. Composite samples 
of surface water were collected to a depth of 30 cm midstream in the sites and heavy metals- manganese, 
iron, copper, zinc, lead, chromium, cadmium, nickel, vanadium and arsenic, and alkali metals- calcium, 
magnesium, potassium, and sodium were determined using standard methods. The data of metal 
concentrations were analyzed using descriptive statistics and t-test at p < 0.05. The associations that exist 
among metals of surface water were determined using regressive correlation. The concentrations of the metals 
were compared with standards in the Federal Environmental Protection Agency and World Health Organisation 
Guidelines. The results show that nickel, calcium, magnesium, and sodium were higher in the seepage site 
than in the control, with only nickel in the seepage sites (0.40 ± 0.00 mg L-1) significantly different from the 
control (0.30 ± 0.00 mg L-1). Manganese, iron, copper, zinc, chromium, cadmium, nickel, vanadium, arsenic, 
and calcium concentrations were higher than the guideline levels. The correlation coefficients were positive 
and significant between iron and copper, manganese and vanadium, iron and sodium, calcium and magnesium, 
and between magnesium and sodium while the negative correlation between lead and zinc was significant. The 
metals whose concentrations were higher in the surface water of the seepage site and exceeded the guideline 
values, especially the component elements of bitumen (nickel, iron, manganese, vanadium, calcium, and 
sodium), would have toxic effects on the environment if not closely monitored during the bitumen development 
phase.