Source determination of tar balls on Ibeno beach, Niger delta region of Nigeria using Pristane/Phytane ratio

The appearance of tar balls on the coastline is an indication of oil spill although natural seeps also contributes to this. Problems do ensue between the host communities and the oil producing companies as a result of this. Tar balls picked from Ibeno Beach, Akwa Ibom State in the Niger Delta Basin of Nigeria were analyzed to trace their origin using GC/FID. The parameter used was pristane/phytane ratio, (Pr/Ph), The results obtained from the tar ball analyses revealed that in most of the tar balls analyzed, pristane and phytane were absent as a result of extensive weathering; however, in those tar balls that still contained some amount of pristane and phytane there was a predominance of pristane over phytane giving a pr/ph ratio of more than unity (>1). Comparing this result with those obtained from the unaltered crude oil sourced from some selected oil wells in the Niger Delta which were also analyzed, revealed that the tar balls could be from Niger Delta oil wells. These oil wells Idoho Bravo, W/24, EST. 25, Soku FS, Utorugu 55 and Umuechem Pumpline. However, in four tar ball samples, a predominance of phytane over pristane was observed; an indication that such tar balls are foreign to Niger Delta environment. This study revealed that, Pr/ph ratio cannot be conveniently used to trace tar balls back to their origin because during weathering most of the isoprenoids especially pristane and phytane are altered; some even completely disappear with extensive weathering. However, the pr/ph ratio of some of the tar balls did not match those of the Niger Delta oil wells analyzed. They are suspected to be from neighboring West African countries like Gabon and Congo Brazzaville etc which may have been transported by ocean currents and left stranded on the Nigerian coast line. The significance of these study is that pristane/phytane ratio alone cannot be used to trace petroleum residue back to its source.