Independent Consultants in Environmental and Forensic Chemistry
Volume 2, Issue 2, Spring 1998
Is Age-Dating a Petroleum Middle Distillate Junk Science?
At the American Academy of Forensic Sciences meeting in San Francisco in February, 1998, a case study was presented regarding the age-dating of a release of #2 fuel oil. As a Halloween prank on October 31, 1993, a valve inside a fenced heating oil storage facility in southeastern Pennsylvania was partially opened allowing approximately 800 gallons of home heating oil to be released. In August, 1996, a petroleum expert studied the analytical data from more than 20 contaminated soil samples collected from the site. The expert=s opinion was that the home heating oil was greater than 15 years old and most likely greater than 20 years old. Was the 1993 release superseded by another much older release?
Monitoring well MW-2 was in place prior to the 1993 release. Quarterly monitoring of the groundwater from this well prior to the heating oil release did not show any petroleum product. In the sampling which occurred in November, 1993, immediately after the release, there were 18 inches of free product. The petroleum GC/FID fingerprint of this free product showed the material to be Afresh@ home heating oil. The pattern of chemical compounds was consistent with a standard of Afresh@ home heating oil. A year later in November, 1994, there was still no noticeable change in the petroleum Afingerprint@ chromatogram. However, by March, 1995, there was an obvious change in the relative concentrations of the compounds. By August, 1995, a dramatic change in the relative concentrations of the compounds was observed.
Based on changes in the relative concentrations of compounds in the soil samples, the petroleum expert estimated the age of the release of heating oil to be 15 to 20+ years old. However, only two years had elapsed since the release. He used the method published by Christensen and Larsen* (see President=s Corner, Winter 1998) to estimate the age. This release to the soil was similar to those described by Christensen and Larsen except that the average soil temperature in Pennsylvania is approximately 2.5 to 3°C warmer than the average soil temperature reported for Denmark and the Netherlands where the authors gathered their data.
Many factors affecting the relative rates of biodegradation of petroleum meddle distillates must be identical to those studied by the authors to be able to utilize their findings empirically. Since this is highly improbable, the findings by Christensen and Larsen cannot be universally applied. Any application of the Christensen and Larsen method to age-date releases of petroleum middle distillates is a journey into the realm of junk science.
* Christensen, L.B. and T.H. Larsen, "Method for Determining the Age of Diesel Oil Spills in the Soil," GWMR, Fall 1993, pp 142-149.
Book Review: The Demon-Haunted World - Science as a Candle in the Dark, Carl Sagan
Carl Sagan takes us on a historical and cultural journey examining witch hunts, myths, frenzies, and other bump-in-the-night practices and beliefs thrust upon the public as early practices of pseudo science. While, today, we wonder how so many could be duped for so long, Sagan points out that, in these technologically enlightened times, similar unfounded beliefs and theories continue to exist and propagate. He offers the scientific method as a means to distinguish the scientist from the charlatan, fact from fiction, and the truth from the untruth not only in science but in everyday life.
Chapter 12 offers a Abaloney detection kit@ that contains the techniques for skeptical thinking which allow one to recognize a fraudulent argument by pointing out the faculty logic commonly used to advance fallacious arguments.
Conclusions must be derived from all of the facts and sound logic, not from preconceived or desired outcomes, fear or dislike of the alternatives, or ignorance (i.e., if
it can=t be proved false, it must be true). The kit can be used to discriminate between reality and the zeal of advocates to prevail in litigation. A tendency exists to select the facts that support a client=s position instead of developing opinions based on all of the data. Legal professionals should be particularly watchful of
the phrase AIn my experience..@ This phrase usually precedes an untested, unsupported, and unverifiable statement or series of statements. Such statements challenge the unbelievers with AIf you can=t prove me wrong, I must be right@ and exemplify one of the basic approaches to the propagation of junk science.
This book is a must read for everyone in the legal profession, particularly judges, that interacts with scientists as expert witnesses. Since the United States Supreme Court ruling Daubert v. Merrell Dow Pharmaceuticals in 1993, judges have been placed in a position of gatekeeper. They must determine whether the conflicting opinions from expert witnesses are based on science or on junk science. Likewise, attorneys should be aware of the strengths and weaknesses of the expert opinions from both sides in preparation of their cases. To assist in this discrimination between facts and fantasy, Carl Sagan offers this candle in the dark.
False Positives in Metals Analyses ... or when is a trace not traceable?
For years, you've been monitoring the ground water at a closed landfill site on a quarterly basis. Total and dissolved metals concentrations, analyzed and validated according to EPA Contract Laboratory Program (CLP) procedures, have been very consistent. All is right with the world. Then one quarter, the results show selenium at concentrations up to 45 parts per billion in the dissolved, but not the total, fractions of all of the samples. Selenium has never been detected at this site before. Closer examination of the metals results reveals that the problem is not limited to selenium. Similar, though less dramatic, discrepancies are observed in some samples for arsenic, lead, and thallium. What happened??
You note that this is the first time the laboratory used trace inductively coupled plasma (Trace ICP) rather than traditional ICP and graphite furnace atomic absorption (GFAA) to analyze the samples from this site. Interestingly, the affected analytes were the very four that were previously analyzed by GFAA. None of the positive results for selenium was confirmed upon re-analysis by GFAA. Apparently, the change in instrumentation to the newer, more technologically advanced, Trace ICP had an unexpected - and undesirable - effect on the accuracy of at least some of the sample results.
But why would an instrumentation change cause a difference in results? In this case, another factor was found to be part of the equation. The samples for dissolved metals analyses were acidified in the field after filtration but (consistent with CLP specifications) were not digested prior to analysis. One of the dissolved sample fractions was re-analyzed by Trace ICP after digestion. Selenium, thallium, and lead (which were originally detected in the undigested, dissolved sample analysis but not in the total fraction) were not detected after digestion. Apparently, organic compounds present in the undigested sample interfered with analyses by Trace ICP; digestion of the sample destroyed these compounds and allowed accurate analyses.
So, what is the moral of the story? There are several. First, all analytical methods are not created equal. Second, don't automatically believe everything you see on a Form I even if the results are generated using an Aapproved@ analytical method. Third, always be aware of exactly what the laboratory is doing or have your sampling and analysis program coordinated and your data validated by someone who will. Fourth, don't be afraid to modify an analytical method to solve a site-specific problem.
It's your site, your data, your responsibility. Get it right!
Are Analytical Blanks Reliable?
Various types of field and laboratory blanks may be employed in a sampling and analysis program. Blanks are intended to monitor the amount and type of contamination introduced at various points during the sampling and analysis process. Contamination found in a blank indicates that similar contamination found in associated field samples may have been introduced artificially and may not represent the environmental condition of the matrix that was sampled. In order to provide meaningful information, blanks must be prepared properly and at appropriate frequencies.
Blanks must also be appropriate for your sampling and analysis program. Although prepared and analyzed according to approved protocols, blanks are not necessarily appropriate or useful. Most analytical methods for volatile organic compounds specify that no contamination should be found in method blanks. To achieve this goal, many laboratories purge helium through their blank water supplies prior to analyses. Contaminants which may be present in the water supply are removed with the helium; therefore, the laboratory can report a clean blank. Some laboratories perform multiple analyses of a blank until no contaminants are detected and report only the analysis in which no contamination was found. These practices defeat the purpose of including blanks in the analytical process. While the laboratory is now method-compliant, low level concentrations of common laboratory contaminants in your field samples appear to be real when they may not be.
EPA-approved methods sometimes specify the use of water matrix blanks in association with solid matrix field samples. However, water matrices are poor indicators of artificially-introduced contamination in solid matrix samples. A water matrix does not have the same surface area or the ability to adsorb contaminants at the same rate as a solid matrix. As a result, if a water blank and a solid matrix sample were placed next to each other and were contaminated by the laboratory environment, contamination could be detected in the water blank at only parts per billion levels but contamination could be detected in the solid matrix sample at much higher parts per million levels. Since the level of contamination in the water blank would be considered insignificant compared to that in the solid sample, the contribution by background contamination would be ignored. Based on current validation guidance, the contamination in the solid matrix sample would then be considered real.
Blanks can provide very important information regarding the sampling and analysis of your field samples. However, they must be properly planned and processed to perform their intended monitoring function. When designing your sampling and analysis program, careful consideration must be given to selecting the types and matrices of blanks to be included in order to provide the desired reliable information.
Are Your Tentatively Identified Compounds Still Tentatively Identified?
The US Environmental Protection Agency (EPA) popularized the phrase Atentatively identified compounds@ or ATICs.@ TICs are compounds detected by gas chromatography/mass spectrometry (GC/MS) analyses but are not on one of the EPA Ahit@ lists of compounds of concern. Up to 30 TICs are required to be reported for each volatile and semivolatile organic compounds analysis.
Although often not scrutinized, TICs can provide valuable information about the physical and chemical origins of contamination, fate of compounds in the environment, etc. Correct identification of TICs is essential to understanding the contamination present at the site.
The ability to identify a compound by its mass spectrum can be difficult. TICs are identified by matching the mass spectrum of a compound against a library of mass spectra of authentic compounds through a series of computerized steps that depend on the software developer. The compound of interest must be in the library. Potential matches are listed and often reported without further review or review by an experienced chemist. Consequently, correct identifications of TICs are limited by the computer software, size of the mass spectral library, and the knowledge of the reviewer.
One of the most extensive mass spectral libraries available at a single location is held by Bruce E. Wilkes at Environmental Analytical Consulting, Inc. in Scott Depot, West Virginia. Bruce has all of the major commercially available databases as well as his own library of over 50,000 compounds not contained in any of the major databases. With over 34 years in interpreting mass spectra, Bruce provides a powerful combination of references and experiences to quickly, accurately, and inexpensively identify TICs. If your TICs are still TICs, you need to give Bruce a call at (304) 757-2499.