Abstract
The prevalence of heavy metal pollution in oil and gas producing areas, Niger-Delta Nigeria, due to drilling activities in some oil and gas sites has resulted in the pollution of an immeasurable area of land and water. This study appraised the level of environmental menace caused by heavy metals in water-based drilling fluid waste. It involved an oil and gas site where drilling activities were taking place and settlement with no record of drilling activities served as control. In the drilling sites, two composite drilling fluid waste samples were collected before and after treatment and analyzed for cadmium, chromium, iron, nickel, lead, and zinc using flame atomic absorption spectrophotometry. The measured concentrations of the heavy metals in drilling fluid wastes were then used to determine the pollution and ecological risk posed by heavy metals. The thermal desorption treatment method was used. Their concentrations before and after treatment of the drilling fluid wastes were in the order Fe > Cr >Zn > Cd > Ni > Pb and Fe > Cr > Ni > Zn > Pb > Cd respectively with Cr, Fe, Ni, and Pb having their concentrations higher than permissible levels in water after treatment and responsible for most of the total potential ecological risk. The PLI (Pollution Load Index) before and after treatment were 0.0463 and 0.0017 respectively. There was a drastic decrease in potential pollution levels after treatment. Also, all the several pollution indices studied revealed that the drilling sites were contaminated with Cd and Cr. This reveals that drilling sites cause further risk of heavy metal pollution. The correlation analysis of heavy metals assessed is between 0.9 - 1.0 suggesting that all the heavy metals assessed showed high positive correlation coefficients at (p < 0.05) and likely originated from the same source of drilling activities in the study area.

Key words: Water Based drilling Fluid, Drilling Waste, Pollution Load Index, Drill Waste Management, Heavy Metals