Fugro received 36 spill samples on January 10, 2012 in the form of free oil, soils/sendiments and waters.
The samples were provided from various sample locations offshore and on stretches of the Nigerian coastline following an accidental release of crude oil from the Bonga FPSO while loading a tanker.
On January 20th 2012, a further sample arrived of Bonga crude oil for use in comparative analysis, a further two samples arrived on 24th January 2012, one of Bonny light crude and an absorbent pad from the sea near the Bonga FPSO.
On 9th February 2012 a further six samples were received and the analysis immediately commenced. The Analysis was carried out in accordance with the CEN method CEN/TR 15522-2-2009 which was developed in large by SINTEF of Norway, FUGRO ERT, ( formerly ERT Scotland limited) and various European Union government laboratories involved in oil spill analysis.
The CEN method was developed as an update to the NORDTEST method.
The first stage (level 1) of the analysis was carried out by GC-FID to examine the hydrocarbon profile of the samples and establish the general oil type, degree of weathering, e.t.c. Results from this step in the analtycal process informative though inconclusive as the majority of the spill sample chromatogram revealed a hydrocarbon profile typical of lightly to heavily weathered crude or fuel oil.
A few sample GC-FID chromatograms revealed only very low levels of hydrocarbons suggesting no significant input of oil. Comparisons of the spill samples against the Bonga crude by means of visual assessment bar graphs and PW plots produced many similarities in the distributions of n-alkanes, isoprenoids and UCM when weathering is taken into account.
Being unable to conclude clear and definitive match/ non- matches by the GC-FID (level 1) analysis alone, further investigation was carried out by GC-MS (level 2). The first step in the level 2 analysis by GC-MS was the visual assessment of the various biomarker and PAH ion chromatograms for any totable differences or distinguishing features.
Several significant differences were observable in key ion chromatograms (ho panes- m/2 191 etc) with more obvious differences in the compounds affected by weathering ( sesquiterpanes-m/2 123 and PAHS) The visual assessment of the various biomarker and PAH ion chromatograms by GC-MS were inconclusive for a large number of the samples thus further investigation was neccesary. Significant visual differences were however, observed for a number of the samples analyzed, predominantly those in laboratory batches C, D and E.
The major visual differences to note were in the ion chromatograms for the hopanes/tarpanes (m/2 191) particularly for 17 (H) 21, B (H)-25 norhopane (25nor30ab) and 18 (H)-Oleane (300). These components are resistant to sustained weathering and differences here typically indicate true compositional differences between samples.
Where the visual assessment proved inconclusive the biomarker and PAH compounds analyzed where quantiated and a suite of diagonistic ratios generated.
A similar step was also performed for those samples that did show significant visual differences in order confirm and reinforce the findings of visual assessment.
The evaluation of the diagonistic ratios was carried out in accordance with the instruction in CEN/TR 15522-2-2009 utilizing a calculation worksheet used to submit round-robin proficiency testing results to the BONN Agreement OSINET group.
The samples found to exhibit significant differences in their visual assessment were confirmed as non- matches to the sample of Bonga crude through evaluation of their diagonistic ratios. Those samples found to be inconclusive under visual assessment were almost all identified as a positive match to the Bonga crude sample after comparison of the diagnostic ratios.
Two samples (A11 and D13) were found to be inconclusive following visual and quantitative evaluation due to an insufficient amount of oil present.
Further statistical investigation of the samples was undertaken to find any similarities between the Bonga crude oil and the spill samples analyzed and also highlight any similarities between those samples and Bonny or forcados crude.
Statistical evaluation revealed of the three crude oils, the sample of Bonga crude exhibited the greatest similarity to many of the spill samples.
This Series is from the stable of the Oil spills victims Vanguard a non- governmental organization(NGO) incorporated with the corporate affairs commission, OSPIVV is an initiative whose main object is dedicated to fight for compensation for victims of oil spills, health hazards of gas flaring, transparency and accountability in the Extractive industries in Nigeria. HARRISON JALLA
is an Executive Director (OSPIVV)

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