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EnSys, Inc.-PETRO RISc Soil Test System-For Total Petroleum Hydrocarbons in Soil

Final Decision to Certify Hazardous Waste Environmental Technology

Published Weekly by the Office of Administrative Law
Register 95, No.22-Z
June 2, 1995
pp 876-877

The California Environmental Protection Agency, Department of Toxic Substances Control (Department) has made a final decision to certify the following company’s hazardous waste environmental technology listed below:

EnSys, Inc.
P.O. Box 14063
Research Triangle Park, NC. 27709

PETRO RISc™ Soil Test System
(Rapid Immunoassay Screen)
for Total Petroleum Hydrocarbons
in Soil

Chapter 412, Statutes of 1994, Section 25200.1.5, Health and Safety Code, enacted by Assembly Bill 2060, Weggeland 1993, authorizes DTSC to certify the performance of hazardous waste environmental technologies. Only technologies that are determined not to pose a significant potential hazard to the public health and safety or to the environment when used under specified operating conditions and which can be operated without specialized training and with minimal maintenance may be certified. Incineration technologies are explicitly excluded from the certification program.

The purpose of the certification program is to provide an in-depth, independent review of technologies at the manufacturer’s level to facilitate regulatory and end-user acceptance and to promote and foster growth of California’s environmental technology industry.

DTSC makes no express or implied warranties as to the performance of the manufacturer’s product or equipment. The end-user is solely responsible for complying with the applicable federal, state, and local regulatory requirements. Certification does not limit DTSC’s authority to require additional measures for protection of the public health and the environment.

By accepting certification, the manufacturer assumes, for the duration of certification, responsibility for maintaining the quality of the manufactured equipment and materials at a level equal or better than was provided to obtain certification and agrees to be subject to quality monitoring by DTSC as required by the statute under which certification is granted. DTSC’s notice of intent to certify was published on April 14, 1995, in the California Regulatory Notice Register Volume 95, No.15-Z, p.633-641. Written comments in relation to the proposed certifications received during the public review and comment period have been duly considered in the final certification as presented here. DTSC’s final certifications shall become effective on Monday, July 3, 1995.

Additional information supporting DTSC’s final certification decisions is available for review at:

California Environmental Protection Agency
Department of Toxic Substances Control
Office of Pollution Prevention and Technology Development
P.O. Box 806
301 Capitol Mall, 1st Floor
Sacramento, California 95812-0806
(916) 322-3670

A description of the technology to be certified, the final certification statement and the certification limitations for the technology follows:

EnSys, Inc.
PETRO RISc™ Soil Test System
for Total Petroleum Hydrocarbons
in Soil

Certification Statement and Technology Specification

Under the authority of Section 25200.1.5 of the California Health and Safety Code, DTSC hereby certifies the PETRO RISc™ Soil

Test kit manufactured by EnSys, Inc. as a Measurement Technology, with the specifications and under the conditions described in this certification.

The immunoassay system uses enzyme-linked immunosorbent assay (ELISA) technology. An antibodywith affinity to certain petroleum hydrocarbons 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 in crease. The semiquantitative 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 test kit is suitable for fast, semiquantitative field measurements of petroleum hydrocarbons in soil. The EnSys system offers one or more detection levels which can be customized for each project.

The affinity of the antibody to hydrocarbons varies; it reacts primarily with lower aromatic hydrocarbons and also with some aliphatics in the C6 to C9 range. The total assay 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 determined by comparison with the California gas-chromatographic method for the Leaking Underground Fuel Tank (LUFT) Program (U.S.EPA SW-846 8015 method, 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 testing reagents and utensils, including a sample weighing balance and a photometer for field use, a user manual, material safety data sheets, field data recording forms, and instruction in the use of the testing system.

The technology is applicable to testing of soil or soil-like material which is not highly contaminated with oil or other nonaqueous 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 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 possibility of false negative results; other limitations are set forth below. DTSC’s findings are described in greater detail in an evaluation report.

Limitations of Certification

DTSC makes no express or implied warranties as to the performance of the manufacturer’s product or equipment. DTSC has not conducted any bench or field tests to confirm the manufacturer’s performance data. Nor does DTSC warrant that the manufacturer’s product or equipment is free from any defects in workmanship or material caused by negligence, misuse, accident, or other causes.

DTSC believes, however, that the manufacturer’s product or equipment can achieve performance levels set out in this Certification. Said belief is based on a review of the data submitted by the manufacturer and other information, and is based on the use of the product in accordance with the manufacturer’s specifications.

This Certification is issued as part of a pilot project to expedite the California Environmental Technology Certification Program. As a result, this Certification is subject to the conditions set out in the regulations to-be-developed, such as the duration of the Certification, the continued monitoring and oversight requirements, and the procedures for certification amendments, including decertification. By accepting this Certification, the manufacturer assumes, for the duration of the Certification, responsibility for maintaining the quality of the manufactured materials and equipment at a level equal or better than was provided to obtain this Certification and agrees to be subject to quality monitoring by DTSC as required by the law under which this Certification is granted.

Specific Conditions

  1. EnSys, Inc. shall inform the user that the detectable concentrations apply to specified hydrocarbon mixtures, that the sensitivity of the assay to the various petroleum hydrocarbons does vary, and that it is important for the user to correlate immunoassay results with regulatory and other reference methods, particularly if the type of contamination is unknown and the petroleum hydrocarbon mixture at the site is weathered.
  2. EnSys, Inc. shall keep users abreast of known interferences and matrix effects. As a minimum, users should know that the assay is not suitable for oily matrices and soils containing 1 to 10% or higher levels of petroleum hydrocarbons; also organic solvents may affect recovery. Users should be aware of unacceptably low extraction efficiency in wet soils (water content of 30% or higher); for consistent results, soils should be dry and results expressed per gram of dry or dr;ed soil.
  3. EnSys, Inc. shall furnish the product with Material Safety Data Sheets for the instruction of users in the safety aspects of the product and its application.
  4. User’s Guide shall state under “Important Notice” that the manufacturer recommends that the user attend an eight-hour training/certificate course given by an EnSys, Inc. trainer or be trained by an experienced user.
  5. The User Guide shall contain a clear indication of the shelf life of the reagents and a warning on the deterioration of reagents at high temperatures as may be encountered in transit and in field use.
  6. A warning that the false negative rate could increase with high assay temperatures should be included in the User’s Guide.
  7. The User’s Guide calls for “critical timing and care” in “following printed instructions,” but should specifically call for adherence to the instructions in mixing the contents of the antibodycoated tubes. Excessive mixing may increase the number of false negative results.
  8. The user should never become uncritical on the matter of extraction times with regard to both minimum and maximum period of extraction. Incomplete recovery and matrix effects can occur with some soils as was the case with a particular silty loam which gave a false positive rate of 25%. DTSC agrees with the manufacturer that sitespecific background samples be tested at every site to identify potential matrix problems. Therefore, manufacturer should include the requirement for site-specific background samples in the QC section of the User’s Guide.
  9. Documentation available to DTSC is consistent with a 90%, not a 95% probability that a petroleum-free soil is correctly identified as such.

Basis for Certification

This Certification is based on the evaluation of documents provided by the manufacturer and on independent evaluations which support performance claims consistent with this Certification. A listing of these documents is contained in the evaluation report. The manufacturer has declared that certain submitted materials contain proprietary information and should not be subject to public disclosure.

Recommended Applications

The immunoassay is for the semiquantitative determination of “total petroleum hydrocarbons (TPH)”, a term of convenience which is defined in terms of one or several laboratory methods with results read either in terms of “gasoline” or “diesel fuel” and certain options for analysts in the interpretation of the raw data. The PETRO RISC Soil Test System by EnSys, Inc. responds mainly to low molecular hydrocarbons (such as toluene, xylenes, naphthalene; the response to benzene is weak) and to aliphatics in the range from pentane to octane. Additionally, the validations, which are reviewed in this report, document the response of the immunoassay to specified gasoline and other fuel products and allow to establish predictable relationships between the immunoassay and reference methods for these products. In the case of TPH immunoassays, the correlation between the immunoassay results and laboratory reference testing results can change for three reasons:

(a) Petroleum fuels are reformulated from time to time to reduce air pollution, either by region, season, or on a national scale. Reformulation may include the addition of non-hydrocarbon chemicals which may or may not react in the assay.

(b) Laboratory reference methods may be revised, resulting in an altered response relative to an immunoassay.

(c) In water and soil, the composition of a petroleum product will change as a result of solution, volatilization, chemical oxidation, and biological degradation. Especially the lower alkanes and benzene may be lost through volatilization. In the presence of water, benzene is lost by solubilization; aromatics and linear alkanes are potentially lost or modified through biodegradation.

Therefore, unless the product and the response of the assay to the product are known, immunoassays for TPH need to be recalibrated by parallel testing with the applicable regulatory laboratory method and an appropriate correction factor determined. Without such an adjustment, results can be either high or low, depending on the affinity for the assay’s antibodies for the unknown target mixture.

A semiquantitative determination will provide a response, interpreted as either positive or negative, at one or several predetermined detection or target levels. Target levels are usually chosen to have relevance to a specific situation.

In each application of the assay, the probability of false negative and false positive results disclosed by the manufacturer should be noted. A low false-negative rate is important in site investigations. In site remediations, however, the false-positive rate may be of greater interest.

A comprehensive process of developing data quality objectives (DQC)) was published by U.S. EPA under the U.S. Superfund Program. It provides guidance for analytical method QA/QC as applied to field investigations for contaminated soils. The process is intended for site-specific sampling plans. The immunoassay would generally qualify as a Level 2 (field analysis) method, subject to confirmation by a Level 3 method (California LUFT TPH) applied predominantly to positive results. DTSC recommends that minimum quality control should include method blanks and duplicates at 5 percent, or one per batch or per matrix, whichever is the more frequent, in addition to the samples required for confirmation. The use of proficiency evaluation and spiked samples should depend on project-specific needs.

The California LUFT TPH Method (a modification of U.S. EPA Method 8015, gas-chromatography with flame ionization detection) is presently the approved method for Leaking Underground Fuel Tank (LUFT) investigations in California.

“Screening” and Preliminary Site Investigations.

The immunoassay can assist in preliminary site investigations, if there are compelling historical data to indicate the presence of petroleum hydrocarbons. If used on samples of largely unknown composition, without prior characterization by an approved, fully qualitative and qualitative laboratory method, confirmatory analysis is needed for every positive immunoassay result. No negative determinations can be made without taking into account the specificity of the assay and its possible susceptibility to interferences and matrix effects.

In the absence of other regulations and guidelines, DTSC recommends that assay results be confirmed in the following manner:

(a) For the delineation of petroleum hydrocarbon contamination in a coherent mass of soil, the required frequency of confirmation by an approved method resulting in identification and quantification is one of every ten samples, or a fraction thereof, of the samples testing positive at the target or action level applicable at the site.

(b) One of every ten, or fraction thereof, of all negative results should be confirmed.

If appropriate protocols are followed, the immunoassay can be used to great advantage to classify contaminated soils as to low, medium, or high contamination and to determine which samples would provide the most information from laboratory analysis.

Site Investigations and Remedial Actions.

Here the testing is expected to proceed under a site-specific Quality Assurance Project Plan (QAPP). Immunoassay and other field measurements will be “bracketed” in time and space by qualitative and fully quantitative analyses. Generally, a site is first characterized by the use of approved, fully qualitative and quantitative analytical methods as to the nature and level of contamination in key sampling locations and as to the presence of substances that may interfere with the use of the immunoassay. After such initial characterization, the immunoassay can be used in the comprehensive mapping of the site with respect to identified contaminant(s) to which the immunoassay responds. The percentage of samples that would be confirmed by another approved, fully quantitative method would be as stipulated in the QAPP; the project manager could call for additional confirmatory testing if such a need is indicated in the course of the investigation. During site cleanup, the QAPP would provide for use of the immunoassay to monitor progress. Confirmatory laboratory testing would occur before a decision on site closure is made.

Regulatory Implications

This immunoassay has been accepted as a Draft Method by the U.S. EPA Office of Solid Waste (SW-846 Collection of Methods, Method 4030, Revision Draft 1, October 1992, 7p.). DTSC’s Certification is based on the technology’s performance and by itself does not change the regulatory status of TPH testing; it should, however, facilitate and encourage the acceptance of this technology where a project’s data quality objectives can be met by its use. To this end, DTSC’s findings should contribute to a consideration of this technology in regulated activities, depending on each regulated program’s objectives and constraints.

State certification does not imply certification by the U.S. Government for use at federal Superfund sites and other facilities under the jurisdiction of the U.S. Government for which state authorization for administrative oversight has not been granted. Under state implementation of the U.S. Resource Conservation and Recovery Act (RCRA), Treatment, Storage, and Disposal Facilities may contact state permitting agencies for use of the immunoassay for operational monitoring as part of a waste analysis plan.

For more information, contact 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

File last updated: October 9, 1996