Independent Consultants in Environmental and Forensic Chemistry

Volume 2, Issue 3, Summer 1998

President's Corner - James S. Smith, Ph.D., CPC, President/Chemist

Does Advanced Chemical Fingerprinting Work?

Numerous papers in the literature address the presence of polynuclear aromatic hydrocarbons (PNAs or PAHs) in petroleum products and crude oils that have been released to soils, sediments, and the oceans. Investigations following the Exxon Valdez release increased the level of interest in using PAH analyses to identify and differentiate various sources of petroleum products and crude oils. Several EPA methods such as 625, 1625, 525, 8270, and 8310 are capable of detecting and measuring PAHs in environmental samples and sixteen specific PAHs are identified as target analytes.

"Advanced chemical fingerprinting" (ACF) is a recently reported approach to the identification of mixed and/or biodegraded petroleum products in the environment using routine analytical methods. Ratios of the concentrations of the more biologically resistant PAHs and their alkyl derivatives have been used to differentiate crude oil sources. By using basic EPA methods with larger sample sizes and smaller final extract volumes, PAHs are measured in the low parts per billion range. However, these types of method modifications only lower the measurement range of the method; they do not increase the accuracy. At the low parts per billion range, accurate measurements must be obtained for the PAHs before any serious consideration can be given to using the results in calculating a ratio. Routine analytical methods do not generate data amenable to this type of calculation.

By using EPA method 1625, an isotope dilution approach, accurate identification and quantification of PAHs can be accomplished; this is not necessarily the case for the non-isotope dilution GC/MS methods. Method 1625 can accurately identify and determine benzo(a)pyrene in the presence of benzo(e)pyrene. This method has been successfully used for the determination of PAHs in petroleum products, contaminated soils, pyrogenic soots, and CERCLA investigations and should also be considered as the preferred method to accurately identify and quantify PAHs in highly biodegraded petroleum products. If PAH data are required for site characterization and/or risk assessment, particularly if the expected concentrations are near the detection limit, the use of method 1625 is necessary for accurate quantitative determinations.

If the ACF approach is to be used to generate reliable conclusions, accurate measurements of PAH concentrations at low concentrations are essential, and isotope dilution GC/MS analysis is the best way to obtain reliable parts per billion level data.

 

Research Corner

But who wants a holy wall?

Permeable barriers are a rapidly growing field and are anticipated to be a major cost effective groundwater remediation technology in the near future. In the 1990s, numerous authors (available upon request) showed that zero-valent iron can remediate groundwater contaminated with hexavalent chromium. This passive remediation technology, consisting of a permeable reactive wall of zero-valent iron, was successfully demonstrated in situ at several sites. Although groundwater monitoring is required to verify the continued effectiveness of the remediation, few operating and maintenance costs exist after the reactive wall is installed.

Zero-valent iron, in a particle size suitable for a permeable reactive wall, costs approximately $400 a ton. For a large volume wall, the cost can be considerable. Recent research conducted by Trillium and International Mill Service, Inc., strongly suggests that the same results can be obtained

when steel slag is substituted for zero-valent iron. Steel slag has several advantages: it is plentiful, readily available in most areas of the United States, requires no additives or other preparation, and (the best part) costs about $10 a ton.

Steel slag reduces hexavalent chromium to trivalent chromium in groundwater. Various types of steel slag, steel mill producers, and particle sizes are currently being tested to determine the most effective material for use in a permeable reactive wall application. Flow rates of groundwater are being studied to determine the amount of slag needed to treat a given amount of hexavalent chromium under real-life groundwater flow conditions. These experiments will also serve to verify the sustained permeability of steel slag during the treatment process.

Initial experiments with a mixture of chromium ore process residue (COPR) and steel slag indicate that a significant reduction in leachable hexavalent chromium is obtained. When mixed with a contaminated soil, steel slag may reduce or eliminate the leaching of hexavalent chromium from the soil to groundwater. Application of steel slag on top of hexavalent chromium contaminated soil may also prevent environmental exposure to hexavalent chromium.

A permeable zero-valent iron reactive wall has been shown to cause the destruction of chlorinated organic solvents in groundwater. Initial experiments with steel slag also show a significant reduction of trichloroethene (TCE) and chloroform indicating that steel slag can be substituted for zero-valent iron to remediate chlorinated alkanes and alkenes.

The use of steel slag is being explored as a cost effective alternative for groundwater and soil remediation. Low cost, availability in bulk, and chemical properties make it a good choice for a multipurpose remediation material for many organic and inorganic pollutants.

[Presented at the 30th Mid-Atlantic Industrial and Hazardous Waste Conference, Philadelphia, PA, July 15, 1998]

 

Guest Corner - Denise Shepperd

Do you know your laboratory?

So you think you've found a pretty good lab to analyze your samples. Their documentation looks good, and their prices are terrific. You can get your data on hardcopy, diskette, or electronically. PE sample results are all acceptable. Your audit looks good. The lab is certified in many states and even has a CLP contract. But what if there are things you don't know?

Like... those prices are good because the lab recently got rid of their highest salaried (i.e., most experienced) personnel; many of the bios in their SOQ represent people who no longer work there; the QA Officer is only employed part-time.

Like... Several of the GCs, the LC, and at least one of the GC/MSs you were shown during the audit are not functioning properly and haven't run a sample in more than a year.

Like... Some of the analyses you requested will be subcontracted to other laboratories; you won't know because the results will be reported on your lab's stationary as if they analyzed the samples.

Like... Some of the state certifications are actually only applications to be mailed if the contract is awarded, and other certifications involve nothing more than filling out a lab identification form and paying a fee.

Like... the EPA CLP contract was awarded based on letters of intent to employ experienced analysts, but none were hired.

Like... PE samples were actually analyzed at another lab.

Like... SOPs are not current and their updates are in a constant state of work in progress.

Like... although the organizational chart says the QA Officer does not report to the lab manager, in reality he does and, consequently, has little or no authority.

Don't assume anything. If you aren't familiar with laboratory operations, find someone who is and get his/her help.

In an ideal world, we could believe everything we're told. We wouldn't need to audit and validate and read between the lines. But, in this world, we need to determine for ourselves "Is my lab reputable? Are they honest? Can I trust them?"

 

Detection Limits  -  Part 1 of 3  -  Are you confused yet?

Historically, when someone asked an analyst what the lowest concentration he could observe was, the answer was usually preceded with "about" or "around." With the growing awareness of environmental problems and potential liabilities, "about" or "around" were no longer acceptable adjectives. Exact values needed to be determined and documented with little regard to whether inherent imprecision prohibited such numbers from being real. Over the last decades, a myriad of terms have arisen in an attempt to describe the lowest concentration that could be observed: MDL, PQL, IDL, LOQ, etc. What are they talking about?

The US Environmental Protection Agency (EPA) has defined a Method Detection Limit (MDL) as "the minimum concentration of an analyte that can be measured and reported with 99% confidence that the analyte concentration is greater than zero." In other words, at and above the MDL concentration, the observation of an analyte in a sample was not due to instrumental noise but due to the presence of the analyte with 99% confidence.

To obtain an EPA MDL, a solution containing the analytes of concern at an estimated MDL was analyzed seven times. The standard deviation of the seven determinations was calculated and multiplied by three to yield the MDL. For example, assuming concentrations of 5.0, 4.8, 5.3, 5.1, 4.9, 4.8, and* 5.0 g/L were obtained from the analyses of a 5.0 g/L solution, the resulting calculated MDL would be 0.5 g/L. In this case, the MDL is ten times less than the concentration of the solution and much less than the tested concentration.

Using the EPA method, the MDL of 0.5 g/L was never actually measured and was based on the analyses of a solution at a significantly greater concentration. There is no certainty that the laboratory can accurately determine the concentration of analytes close to the MDL with any confidence. In addition, MDLs are based on the precision of a measurement at a higher concentration, not on any measurement of accuracy. There is no provision in the calculation of the MDL for how close the results are to the true value. A low MDL means only that the results are closely clustered, not that the actual concentration can be accurately measured. Moreover, the measurements were taken in a pristine solution; any interferences in natural samples may further complicate the ability of the analyst to accurately measure at the calculated MDL.

The manner of determining the EPA MDL generated serious questions as to the accuracy and reliability of quantitative measurements near the MDL. To counter these reservations, the practical quantitation limit (PQL) was introduced.

 

Book Review:  Our Stolen Future, Are We Threatening Our Fertility, Intelligence, and Survival? - A Scientific Detective Story,
                            
Theo Colborn, Dianne Dumanoski, and John Peterson Myers

Endocrine disruptors are simply defined in Our Stolen Future as chemicals that disrupt the normal functioning of hormones. The foreword by Al Gore, scientific reports, and authoritative writing are used by the authors to provide credibility to the book's frightening tale of endocrine disruptors in our food, water, air, and soil causing deformity, infertility, lowered intelligence, cancer, sickness, and even death. The authors prophesize an infertile human race whose minds, numbed by endocrine disruptors, are unable to wake in time to be rescued from extinction.

In the same way that a good science fiction writer mixes fact with fiction to develop a believable story, the authors of Our Stolen Future mix scientific fact, theory, and innuendo to support their conclusion that endocrine disruptors are threatening our very survival. In one instance, the authors recount a seminal scientific report suggesting a link between a chemical spill and dramatic reduction of fertility in Lake Apopka alligators. The report is held up as an example of the ability of endocrine disruptors to cause adverse effects in wildlife and in humans. The authors, however, fail to provide critical analyses of the report's findings. Instead, they race forward to the next case, apparently hoping that the weight of such observations is convincing evidence of our worst fears. Recent scientific research, however, has shown that reduced alligator fertility in Lake Apopka is not correlated with exposure to man-made chemicals.

Don't read Our Stolen Future if you are looking for an unbiased look at endocrine disruptors. The authors conclusions are flawed by a lack of critical analyses and the selective use of scientific research. Unfortunately, Our Stolen Future is likely to have a profound effect on environmental policy well into the next millennium