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THE GREEN DETECTIVES

TECHNICAL NOTE

Environmental forensics experts, just like their counterparts in the police, can determine what has happened where, when and by who by examining the evidence. Hazel Davidson reports.

The science of environmental forensics is a relatively new discipline but it is gaining recognition. Graduates are appearing on the job market with degrees in the subject more regularly, several conferences are now held throughout the year on the subject and Alcontrol laboratories (Hawarden) now has a small department concentrating on this field.

So what is environmental forensics- It covers a wide range of analytical instruments and specialist subjects. But it is driven by increasing legislation and in particular, the Environmental Liability Directive, which will come into force from the EU next year.

The 'polluter pays principle' has been the driver of much SI and clean up work in the UK for some years, but with the added impetus of EU legislation, more cases could be heading for litigation in the near future.

Environmental forensics involves a series of analyses, often performed on a tiered basis, from simple product analysis to high level mass spectrometry ratio techniques.

There is also interpretation and comparison of the data to provide a conclusion or recommendation based on all the results.

Tier one is a qualitative assessment to obtain a 'fingerprint' of the product(s), using gas chromatography or liquid chromatography.

Tier two is a quantitative assessment involving the targeting of specific compounds (usually those less resistant to biodegradation) by GCMS (gas chromatography / mass spectrometry), with the possible use of biomarkers and thin layer chromatography or carbon isotopes to verify or identify a source.

Tier three is a diagnostic interpretation that uses data from tiers one and two to produce a full forensic report to possibly include an ageing profile, the degree of weathering or biodegradation, CORAT (compound ratio technique), whether the source is petrogenic (petroleum derived) or pyrogenic (coal derived) and source identification.

Examples of where this approach is useful include:

Characterising new or historical petroleum spills. What is it- How old is it- Where did it come from?

Who was responsible?

Differentiating petroleum hydrocarbons from those derived from coal or naturally occurring hydrocarbons.

Analysis of contaminants in marine cargoes, bunker oils and other products.

Determining sources of complex mixtures of hydrocarbons.

Petroleum products in particular are complex mixes of compounds and can vary enormously in composition.

They may be light, straw coloured condensates or black, virtually solid, bituminous materials, depending on the environment in which they were produced and the processes they have subsequently undergone.

Crude oils are composed mainly of hydrocarbon compounds (carbon and hydrogen only), plus other heterocompounds incorporating nitrogen, sulphur and oxygen (NSO compounds) combined in various ways with the carbon and hydrogen. The two main classes of compounds are aliphatics (straight chain, branched and cyclic alkanes) and aromatics (mono and poly) based on the benzene ring structure.

Asphaltenes (high molecular weight NSO containing compounds) are also common in crude oils.

The degree and rate of weathering and biodegradation which these compounds undergo varies signifiantly depending on conditions, and comparison of the ratios of the more recalcitrant compounds (cyclic compounds, higher molecular weight compounds, etc) can be used to identify sources or determine the age of a spill.

Conclusion

These examples show the wide range of applications for environmental forensics, and there are far more techniques and ratios which can be deployed, depending on the nature of the problem and the composition of the products.

This is a rapidly expanding science, and the industry is likely to become involved in more and more of these complex and interesting cases.

Hazel Davidson is policy and communications manager for Alcontrol Laboratories.

Further information of these types of analyses (and seminars on this subject) can be obtained by contacting the author, email: hazel. davidson@alcontrol. co. uk

REFERENCES

PAH Double Ratio Plot Yunker M B , Macdonald R W, Vingarzan R, Mitchell R H, Goyette D, and Sylvestre S, (2002). PAHs in the Fraser River basin: a critical appraisal of PAH ratios as infi cators of PAH source and composition.

Organic Geochemistry 33, 489-515.

www. elsevier. com Costa H J , and Sauer T C Jr, (2005).

Technical Note Forensic Approaches and Considerations in Identifying PAH Background. Environmental Forensics, 6:9-16. Taylor & Francis.

ISSN 1527-5922 (print), 1527-5930 (online).

PAH Histograms Boehm P D, Douglas G S, Burns W A, Mankiewicz P J, Page D S, and Bence A E, (1997). Review Application of Petroleum Hydrocarbon Chemical Fingerprinting and Allocation Techniques after the Exxon Valdez Oil Spill. Marine Pollution Bulletin, Vol 34, No. 8, pp599-613. Elsevier Science.

CORAT Scally K, Farrell-Jones J, Keogh M, Keaveney G, (2004). Forensic Polycyclic Aromatic Hydrocarbon Fingerprint Interpretation and Source Characterisation Using Compound Ratio Analysis (CORAT). SCI/RSC Conference: Contaminated Land - achievements and aspirations 1215 September 2004, Loughborough, UK. EPP Publications Ltd. ISBN: 1 900995 01 8.

EU Policies Summaries of legislation, including the Environmental Liability Directive, are available at europa. eu/ scadplus/scaden. htm

Case study

1 A farmer was being taken to court for an undisclosed diesel and lube oil spill on his land. He sent samples to Alcontrol Laboratories, which on superficial analysis did appear to give diesel and lube oil fingerprints by GC/FID (gas chromatography/flame ionization detector).

However, the use of thin layer chromatography and CORAT (compound ratio technique) enabled Alcontrol to prove the hydrocarbons were derived from tarry fragments associated with hardcore the farmer had spread on his land to improve drainage, and not from a spill.

The high percentage of asphaltene in the sample was not compatible with lube oil or diesel, but was symptomatic of a bituminous or tarry material. This was confirmed by using CORAT analysis, which assesses whether two or more products correlate by comparing the relative abundance of selected compounds obtained from the chemical fi ngerprint and ratioing them to each other. The ratios are overlaid to produce a star plot, clearly demonstrating the close correlation between the sample extract and a road tar extract.

Case study 2

A tanker of oil arrived at its destination in the USA where the oil was found to have formed a semi-solid slurry, too thick to pump out. A large insurance claim followed and Alcontrol analysed samples of the oil fraction and waxy fraction to determine what had happened. Using GCMS and isotopic analysis, it was concluded the oil was the correct cargo (from the North Sea), but that a high asphaltene containing oil (from a Middle East field), had not been completely cleaned out from a previous cargo and had caused a seeding effect, producing the precipitation of wax from the more recent cargo.

Although only a small proportion of the asphaltene remained, flocculation of asphaltene will occur in high concentrations of high alkane hydrocarbons (the newer cargo). These asphaltene flocs will grow in size, and so larger and larger steric-colloids will be formed, eventually resulting in their precipitation to form the semi-solid slurry seen in the tanker. The ratios between peaks 1 and 2, and also between peaks 3 and 5 are quite distinctive, and are used to confirm the oil source.

Case study 3

The owner of a site where degraded hydrocarbons were present was attempting to prove these were derived from a petrol station close to the site. However, analysis of the PAHs (polyaromatic hydrocarbons) proved these were derived from coal products rather than petroleum products, due to the differing ratios of the 16 PAHs.

If the differing ratios of the individual PAHs, for example fluoranthene/ pyrene against benzo(a)anthracene/chrysene, are plotted onto a double ratio plot, distinctive areas of the plot will be identifi ed which are relevant either to petroleum (petrogenic) sources, or to coal (pyrogenic) derived products.

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