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Final Decision to Certify Hazardous Waste Environmental Technology


(For Total Petroleum Hydrocarbons in Soil)

Certification No: 95-01-012

Technology Description:

The immunoassay test kit is suitable for fast, semi- quantitative field measurements of petroleum hydrocarbons in soil. The system uses enzyme-linked immunosorbent assay (ELISA) technology. An antibody is bound to the walls of small polystyrene test tubes. The reaction is performed on a methanol extract of a small sample of the soil. Antibody that has not reacted with hydrocarbons in the methanolic extract is detected by a color reaction; less color develops as hydrocarbon concentrations increase. The semi-quantitative results are obtained by comparing optical densities obtained with a standard and with the soil extract in a differential photometer which is suitable for field use. The EnSys system offers one or more detection levels which can be customized for each project.

The antibody reacts primarily with lower aromatic hydrocarbons and some aliphatics in the C6 to C9 range. The total response is the sum of the responses of these hydrocarbons. The calibrating solution is supplied by the manufacturer; assay results are in terms of a specified gasoline or diesel fuel. Detection levels are 10 ppm for gasoline and 15 for diesel fuel, #2 fuel oil, jet fuel A, and kerosene. This was determine by comparison with the California gas-chromatographic method for the Leaking Underground Fuel Tank (LUFT) Program (U.S. EPA SW-846, Method 8015, modified).

As gasoline and other fuel formulations change, and as petroleum hydrocarbon mixtures discharged to soil change as a result of volatilization, solubilization, chemical and microbial degradation, it is the user's responsibility, when assaying hydrocarbon mixtures, to establish the relationship between the immunoassay response and the applicable regulatory laboratory reference methods. The manufacturer provides instruction in the use of the testing system.

The assay is applicable to testing of soil or soil-like material which is not highly contaminated with oil or other non- aqueous phase liquids (NAPLs). The efficiency of the test depends on the extraction of petroleum hydrocarbons from the test soil into a methanol solution. The efficiency of extraction is reduced in excessively moist soils and may be affected by high clay or organic content of the soil. It is recognized that the calibration is biased so as to minimize the probability of false negative results. The DTSC's findings are described in greater detail in an evaluation report.

Issued to:
EnSys, Inc.
P.O. Box 14063
Research Triangle
Park, NC 27709
(919) 941-5509
Effective Date:
July 3, 1995
Expiration Date:
July 3, 1998
EnSys, Inc.
432 Villa Point Drive
Newport Beach, CA 92660
Dwight Denham,
Southwest Regional Manager
(800) 242-7472 Ext. 173
(714) 644-8650
DTSC Contact:
Dr. Wolfgang Fuhs
(510) 540-3076

A copy of the published Certification Notice may be obtained by contacting us at:

Department of Toxic Substances Control
Office of Pollution Prevention and Technology Development
P.O. Box 806
Sacramento, California 95812-0806
Phone: (916) 322-3670
Fax: (916) 327-4494
e-mail: techdev@dtsc.ca.gov

File last updated: October 9, 1996

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