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Sample Holding Time Re-Evaluation

Abstract

Holding times are the length of time a sample can be stored after collection and prior to analysis without significantly affecting the analytical results. Holding times vary with the analyte, sample matrix, and analytical methodology used to quantify the analytes concentration. Maximum holding times (MHTs) have been established by the U.S. Environmental Protection Agency (EPA) and have been presented in the Code of Federal Regulations (CFR) and SW-846 methods manual. Holding times can be extended if preservation techniques are employed to reduce biodegradation, volatilization, oxidation, sorption, precipitation, and other physical and chemical processes. Under this task, samples will be collected, held, and analyzed after specific time periods (fractions or multiples of the MHTs) to determine the validity of the existing current holding times.

Objective

The overall objective of this task is to provide EPA with independent scientific data on contaminant concentrational changes through time to allow for the reevaluation of the current holding times presented in the current regulations.

Approach

U.S. EPA is concerned about the holding times and preservation techniques for semi-volatile organics, pesticides, PCBs, volatile organic compounds (VOCs), total organic carbon, nutrients and chlorophyll in water (fresh and saline), sediment, and tissue samples. In discussion with the Regions, the following general approach will be taken:

1) identify CERCLA or other contaminated sites (a minimum of two) with multiple contaminants present. Sites will be selected such that have a range in contaminant concentrations (one near the regulatory threshold value and the other notably higher) and site conditions. CERCLA sites will be selected since all inherent matrix interactions will have had sufficient time to occur. Initial emphasis will be placed on organic contaminants including the semi-volatile compounds, PCBs, pesticides, and TOC.

Note: VOCs will not be examined in this RMI proposal since a current research effort is currently underway examining numerous preservation techniques in soils.

2) concurrently, develop quality assurance project plan (QAPP) for project starting with sediments as the first matrix to be examined and a different matrix selected each year.

3) collect bulk samples. It is anticipated that 6-9 soils will be collected for the semi-volatile analyses, 2-4 soils for the metals analyses, and 4-6 soils will be collected for the chromium VI analyses.

Note: Additional bulk samples will be collected and maintained at 4 deg. C for inorganic analyses until needed.

4) homogenize, preserve, and bottle samples on-site. Preservation techniques to be included, but not limited to, cooling to 4 deg. C and freezing at -20 deg. C with the addition of SW-846 required chemical preservants.

5) perform analyses following standard SW-846 methods.

- analyses to be performed on day 0 to establish baseline contaminant concentrations, at 0.5 MHT; MHT; 2 MHT; 3 MHT; 6 MHT, and 12 MHT for the semi-volatile organics; 0.5 MHT; MHT, and 2 MHT for metals; and 0.5 MHT, MHT 2 MHT, 4 MHT, and 8 MHT for chromium 6 analyses.

6) process resultant data.

7) prepare report(s) and journal article(s).

Initial emphasis will be placed on organic contaminants since inorganic contaminants are not subject to degradation. Steps 3 through 6 will be repeated as necessary to cover the range in organic contaminant classes (e.g., semi-volatiles, PCBs, and pesticides) and for the inorganic contaminants.

Relevance/Significance/Impact

The research to be conducted under this task is in direct response to two Regional Methods Initiatives requests.

Holding times are the length of time a sample can be stored after collection and prior to analysis without significantly affecting the analytical results. Holding times vary with the analyte, sample matrix, and analytical methodology used to quantify the analytes concentration. Maximum holding times (MHTs) have been established by the U.S. Environmental Protection Agency (EPA) and have been presented in the Code of Federal Regulations (CFR) and SW-846 methods manual. Holding times can be extended if preservation techniques are employed to reduce biodegradation, volatilization, oxidation, sorption, precipitation, and other physical and chemical processes.

While holding times may appear adequate to protect sample integrity and provide sufficient time for laboratory analysis, relevant data is sparse on individually defined holding times and, thus, some of the holding times appear to be arbitrary and/or politically driven. Holding times appear to be arbitrary when a single value is applied over a large general class of compounds (e.g., pesticides or polyaromatic hydrocarbons); when the holding time was originally "established" for aqueous media and then blindly applied to other media (e.g., sediments and tissues); or when a contaminant is known to be chemically highly stable and will still be present in the sample even if the sample is not extracted in the regulatory time frame. For example, if PCBs significantly degraded after 7 days, then there would not be an environmental problem with PCBs today.

Holding times may appear politically driven to speed commercial laboratories in sample analysis and report production. While holding times tend not to be a major concern for large commercial laboratories, they may be especially harmful for non-production-based analytical laboratories, such as EPA Regional laboratories. The primary concern of both government and private laboratories occurs when their sample load is heavy or excessive, instruments break down, or extraction difficulties occur due to matrix complications and the holding times are, thus, exceeded. If the holding times are exceeded, even if only by 1 day, the data must be flagged and is often declared invalid or are reported as "estimated," and the data are then called into question, especially if the data are to be used in a court of law. Once declared invalid, the time and expense associated with the sample collection and processing is forfeited even though, in truth, the analytical result may be perfectly accurate (i.e., sample integrity is maintained). The potential for missing holding times often causes a laboratory to charge extraordinary fees to pay for overtime, or in many cases, to simply turn away work for fear of having data rejected should it not meet the arbitrary holding times. From the Agency's point of view, holding times are particularly objectionable when they cause data to be rejected, delay projects, and cost the government money for rework that is unnecessary.

The results from this study will be used by EPA to assess the validity of currently recognized holding times in 40 CFR and will provide a scientific basis for changes that may be necessary to the current regulations.

Staffing

Task Manager/Principal Investigator
Brian Schumacher, Supervisory Physical Scientist

Characterization and Monitoring Home Page
Environmental Sciences | Research & Development
National Exposure Research Laboratory
Send questions or comments to Steve Gardner
Email: gardner.steve@epa.gov


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