Background
Background - Following concerns about the differences in extraction procedures and analytical techniques for the analysis of Totals Petroleum Hydrocarbons (TPH), a working group was established in the U.S called the Total Petroleum Hydrocarbons Criteria Working Group or TPHCWG.

It was reconised that the current methods and regulatory levels are not based on scientific assessment of human health so the committee set out to develop a set of documents and procedures outlining a scientifically defensible risk based approach for the assessment and remediation of hydrocarbon contaminated sites.

The overlying theme of the document is "exposure potentials" and the approach is based on "fate and transport" and toxicological properties of petroleum hydrocarbon classes of compounds. The Working Group believes that "If this approach is not considered, unrealistic human health risks could be calculated, resulting in misinformed decisions about site cleanup".

The Working Group selected the American Society for Testing and Materials (ASTM) Risk Based Corrective Action (RBCA) framework as an example of how these elements can be used to calculate risk-based screening levels driven by non-cancer human health risk for petroleum contaminated sites.

The Procedure
Separates Total Petroleum Hydrocarbon into aliphatic and aromatic fractions and delineates them into equivalent carbon number fractions based on fate and transport considerations. The Working group has selected toxicity criteria (e.g. Reference Doses) for each of the fate and transport fractions. The range of hydrocarbon products covered include petrol, kerosene, diesel, fuel oils, some lubricating oils, and portions of other heavier oils.

The Laboratory Method is considerably more involved than the traditional TPH analysis. Soil samples are extracted with n-pentane and the solvent extract is fractionated by solid phase separation. This is performed using open column chromatography with an alumina column. Once the soil extract has been separated into aliphatic and aromatic fractions the extracts are analysed by Gas Chromatography.

The Report
Details Matrix Type, Date Sampled, Date Extracted, Date Analysed, Soil Moisture, and the calculated concentration of Aliphatic and Aromatic compounds in each fraction of TPH from C6 to C36. Chromatograms and all Quality Control Data are included in the report.

The fractionation results are used as a basis for a human health risk assessment (HRA). The analytical method, fate and transport considerations, and toxicity criteria are the technical elements which fit into a risk-based framework for determining human health based criteria at petroleum hydrocarbon contaminated sites.

References:
Total Petroleum Hydrocarbon Criteria Working Group (TPHCWG) - Volume 3 : Fate and Transport.
Proceedings of the Fourth National Workshop on the Health Risk Assessment & Management of Contaminated Sites - Contaminated Sites Monograph Series # 7 1998 : ANZECC & SA Health Commission.