Final Decision to Certify Hazardous Waste Environmental Technology
EnviroGard™ Petroleum Fuel in Soil Test Kit (Total BTEX)
Certification No: 95-01-018
The technology is based on the principle of enzyme-linked immunosorbent assay (ELISA). It differs from other systems in that polyclonal antibodies are bound to the interior walls of polystyrene test tubes. Soil samples are extracted with methanol using the EnviroGard Field Soil Extraction Kit. The assay is carried out with a diluted methanol extract of the soil. After the analyte and a competing enzyme conjugate have been allowed to bind to the antibody and excess reagents have been removed, an enzyme-mediated color reaction is initiated and the intensity of the resulting yellow color determined in a photometer.
While the components of BTEX respond differently to the assay, contamination of the soil is indicated in terms of a manufacturer-supplied BTEX calibration standard which consists of equal parts of benzene, toluene, ethylbenzene, o-, m-, and p-xylene. The assay detects gasoline by virtue of its BTEX content; the detection level of diesel fuel is somewhat higher. The assay cannot be recommended for the detection of polynucleated aromatic hydrocarbons (PAHs). For results to be expressed in terms of specific petroleum fuel present at a site, calibration can be performed using such a product; calibrations may be related to each other by the use of appropriate conversion factors. Three concentration levels of standard calibrator are provided with the test kit.
The assay is semi-quantitative in that it is intended for the detection and quantification of BTEX in relation to the supplied calibrator levels of 2, 10, 50, and 300 ppm, or intermediate levels available from the manufacturer. Higher concentrations can be assayed after diluting the extract. The assay does not respond to n-alkanes. It responds only poorly to benzene. Non-BTEX compounds that show a positive reaction in the assay are other methylbenzenes, naphthalene, acenaphthylene, acenaphthene, and to a small extent the higher polynucleated aromatic hydrocarbons. While these cross-reactants do not interfere with the assay’s ability to detect petroleum fuels and may even enhance it, not all matrix effects may yet be known, and confirmatory analysis by approved methods such as U.S. EPA Method 8020/8021 or 8240/8260 is necessary to identify and quantify individual BTEX compounds, to confirm positive results in site characterizations, and to decide on site closure after cleanup.
The assay is designed to have a slight positive bias which reduces the probability of false negative results at the expense of obtaining false positive results in the order of 7 to 15 percent, depending on the site; bias is determined by the relationship between calibration and target levels selected. Soils with up to 20 to 25 percent water content can be tested; extraction efficiency is reduced at soil water content over 30 percent.
Great care is required in soil sampling and sample handling to reduce losses of the volatile BTEX compounds. As with similar assays, certain temperature controls are required for reagent storage and for carrying out the assay. The assay should be used only by trained individuals to reduce operator caused variability.
A copy of the published Certification Notice may be obtained by contacting us at:
File last updated: October 9, 1996