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Public Lab Research note


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[Reference] Characterization of Chronic sources and Impacts of Tar along the Louisiana Coast

by eustatic |

What I want to do

Link to a reference from Ed Overton, Paulene Roberts, and Charles Henry Jr, concerning the study of "mystery" tar balls suspected to come from the Mega Borg Spill of 1990. It's OCS Study MMS 93-0046.

Henry, C B, P O Roberts, and E B Overton. 1993. Characterization of Chronic sources and Impacts of Tar Along the Louisiana Coast. US Dept of the Interior, Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, LA. OCS Study MMS 93-0046, 64pp.

Currently, the grey lit is hosted on the BOEM site http://www.data.boem.gov/PI/PDFImages/ESPIS/3/3606.pdf

Why I'm interested

Tar balls are weathered crude oil from many sources, and have an array of impacts. Generally, they come in an array of shapes and appearances, but the aromatic hydrocarbons, such as benzene and napthalene, have dissolved or evaporated. Other, larger ring hydrocarbons are present--Hopanes are commonly referred to as characteristic hydrocarbons in weathered tar. The tar is not acutely harmful unless ingested; but unfortunately creatures like young sea turtles do ingest them.

There are still lots of tar balls washing up on Louisiana beaches, and it's a far question from which spill they came. Dr. Overton is still in the business of using chemical tests to 'match' tar balls to sources.

[note to GG: the Guardian uses the term 'fingerprint']

The paper classifies tar balls by pliability, color, morphology and by Gas Chromatography / Mass Spectrometry. It classifies tar balls into 9 categories (#9 is 'unclassifiable') and determines sources by a principal component analysis. There were 66 sources identified for less than 120 samples. Many 'sources' were found to match tar across wide geographic range of the study (which only included the Louisiana coast).

This is a reality check for trying to determine a method for identifying remnant Macondo tar vs serial tar balls in Louisiana in years to come. Certain oil types are described in the paper, but on the level of comparing Louisiana 'sweet' crude to say, Crude from the North Slope.

A second paper is

OCS Study MMS 2000-086

Studying and Verifying the Use of Chemical Biomarkers for Identifying and Quantitating Oil Residues in the Environment

Analytical chemistry and instrumentation provides environmental scientists with the ability to identify and track the fate of spilled oil residues in the marine environment Compounds commonly used for the identification of spilled oil to a source are called biomarkers. Biomarker compounds are universal in crude oils and petroleum products and are generally more resistant to environmental weathering than most other oil constituents. The distribution of biomarker compounds is unique for each oil and different sources of petroleum exhibit different oil fingerprints. Self-normalizing fingerprint indexes (SF1) calculated from the oil fingerprints provide a stable and useful tool for determining a match or nonmatch for different oil residues present in some environmental samples. A combination high-resolution gas chromatography and mass spectrometry, visual comparison and self-normalizing fingerprint indexes (SF1) were utilized to establish eight petroleum biomarkers for oil spill identification and assessment. The eight petroleum biomarkers chosen for detection and analysis were determined through a literature search and previous research. SF1 calculated from GC/MS analysis of tarballs and an oil degradation study validated the use of the eight biomarkers chosen.

Of the eight SF1, four remain stable over an extended period of time and laboratory simulated weathering. Visual comparison of biomarker fingerprints played an important role in distinguishing gross, and in some cases subtle, differences between unknown environmental samples. Double SF1 scatterplots were also utilized as a screening tool for source matchlnonmatch determinations.



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