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When oils ain’t oils – understanding hydrocarbon contamination

When oils ain’t oils – understanding hydrocarbon contamination

Date Published: 31-Oct-16

Commonly used methods can’t determine the type of hydrocarbon contamination, which can potentially create inaccuracies in applying national guidelines, according to ChemCentre’s Lead Petroleum Chemist, Leif Cooper. This concept was a central theme in a presentation Leif gave to the Society of Environmental Toxicology and Chemistry conference in Hobart this month.
“The National Environment Protection Measures (NEPM) guidelines for assessing petroleum hydrocarbon contamination provide levels for different hydrocarbon fractions in different soil types or groundwater situations,” Leif said. “These levels rest on a set of assumptions, and presume that the contamination is from a ‘typical’ hydrocarbon; that is, petrol or diesel.

“The method most commonly used to assess hydrocarbon contamination levels is gas chromatography-flame ionization, which is a non-specific method that cannot determine the type of contamination. The results shown in the chromatograph will not show whether the contamination comes from petrol or diesel, or from the breakdown of plastics in a landfill site, or even from eucalyptus oil from gum trees.”

For his conference presentation, Leif collated a series of case studies collected from actual contaminated samples and assessed them.

“We took any unusual chromatographic profiles and further analysed them using mass spectrometry to determine exactly what compounds were present, and assessed how applicable the NEPM guidelines were to the data,” he said.

“We found that the assumptions behind the levels set under NEPM are robust enough for most contaminated sites, but there are times when blindly applying these assumptions without a deep knowledge of the type of contamination could lead to incorrect actions being taken.

“The raw data that comes from the chromatography needs to be interpreted so a decision can be made as to whether or not it is a typical hydrocarbon. The presence of hydrocarbon contamination will mean that some sort of action needs to be taken, so that doesn’t change. But the type of hydrocarbon will dictate what sort of action needs to be taken, for how long, and the potential risk to people’s health and the environment. The hydrocarbons may still be toxic, but if they are different to what is expected, then the toxicity changes, and therefore the risk to human health changes, and the appropriate response changes as well.”

Leif added that the fault is not in the NEPM Guidelines but is rather due to people making an overly simplistic interpretation of their application.

“The NEPM guidelines clearly state that expert analysis is required for site specific assessment,” he said.

Leif’s presentation received a very positive response at the Hobart conference, with delegates appreciating the detailed analysis and chemistry involved.

ChemCentre provides industry and regulatory clients with timely testing of hydrocarbon contamination in soil and water. For more information, contact Leif Cooper on 08 9422 9933 or enquiries@chemcentre.wa.gov.au.

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