Effectiveness of Purge-and-Trap for Measurement of Volatile Organic Compounds in Aged Soils

Abstract

The U.S. EPA-recommended method for measurement of trace levels of volatile organic compounds (VOCs) in soil, purge-and-trap, measures the readily desorbable organic contaminants from soil pore spaces and external soil surfaces. It does not, however, measure contamination that has diffused into internal micropores of soil matrix. Thus, the purge-and-trap method measures only a small fraction of total soil contaminants, especially in long-contaminated soils, where ∼90-99% of contamination may be in the interior of the soil matrix. We compared three methods for determination of VOCs in aged field samples: purge-and-trap, methanol immersion, and hot solvent extraction. Hot solvent extraction proved to be much more effective than the U.S. EPA-approved purge-and-trap technique. For three long-contaminated soils containing such VOCs as trichloroethene, benzene, toluene, chloroform, methylene chloride, and cis-1,1-dichloroethylene, recovery from purge-and-trap ranged between 1.5 and 41.3% that of hot solvent extraction. Our data show that purge-and-trap may not be the best methodology for measuring soil VOCs concentrations, particularly in aged soils. It is clear from this and previous studies that the best overall choice for soil VOCs measurements is hot solvent extraction. These results also indicate the inefficiency of purge-and-trap as a method for evaluating vapor extraction remediation technology. Our results suggest that the EPA should review the use of the purge-and-trap method for measuring VOCs concentrations in soils.

Enhanced electrokinetic dissolution of naphthalene and 2,4-DNT from contaminated soils

“…It has been also reported that the extraction efficiencies of methanol depends on the octanol-water partition of VOCs, soil organic carbon content as well as duration of methanol extraction. Although, elevated temperatures speed up the release of VOCs especially high octanol-water partitioning compounds from soil with high organic content, 1 day MeOH extraction was long enough to get maximum release of tested compounds used in this study and was much longer than that of hot MeOH extraction at 40 • C in an ultrasonic water bath for 30 min [18].…”

Solid-phase microextraction gas chromatography/mass spectrometric analysis of volatile organic compounds in water

“…The purge and trap (P&T) method for the analysis of VOCs has been widely described in the literature. [6][7][8][9] Solid phase microextraction, SPME, despite its name, is not only another useful extraction tool, but is an innovative and complete sample preparation technique, which was first developed in 1989 by Pawliszyn and his group.…”

Microwave-assisted extraction of trichloroethylene from clay samples

“…Both methods are not useful for volatile contaminants that have diffused into internal micropores of soil (the usual case for sites that were contaminated for a long time) and/or are strongly sorbed by the matrix [8,9]. In the investigations reported in this article, soil samples were obtained from a site where the VOC contamination has been in the ground for a few decades, so aging had to be considered an important factor.…”