Guidance for Sampling of and Analyzing for Organic Contaminants in Sediments
Since May 1985, the Criteria and Standards Division of the U.S. Environmental Protection Agency has been pursuing the development of a method for establishing numerical sediment quality criteria. In anticipation of such a method for nonpolar organic contaminants, this report describes recommended procedures for sample collection, preservation, preparation, and analysis to obtain consistent and comparable data for validating and exercising this method. To ensure that the samples are of high quality, pre-collection planning and preparation are critical. Among the pre-collection activities are preparing the sampling plan, including quality assurance/quality control (QA/QC) plan; choosing the appropriate sampling device; choosing the appropriate method for locating the sampling station; and collecting and preparing the sampling equipment and containers. During collection, accurate and detailed records must be kept of all activities and deviations from those described in the sampling plan. Two types of samples are collected; one for organic carbon and dry weight analysis and the other for contaminant analysis. All samples must be refrigerated or frozen until analyzed. Analysis of the samples should be conducted only by laboratories that are experienced in applying analytical methods that meet minimum QA/QC requirements. All measurements are to be reported on a dry weight basis by drying the sample for at least 16 hours at 70 degress celcius. The method recommended for total organic carbon analysis is dry combustion, using an inductive furnace. Sample preparation and analysis involve Soxhlet extraction of the sediment, cleanup of the extract, and subsequent analysis by gas chromotography/mass spectrometry and/or gas chromatography equipped with electron capture, halogen-specific, or flame ionization detectors. The choice of system depends on instrument available, individual preference, and class(es) of compounds targeted. Cleanup procedures are described for removing paraffinic, polar, and biogenic materials and sulfur that could interfere with the analysis. Data derived from implementing the above approaches can then be used to calculate the organic carbon normalized concentration of the contaminant for comparison with the sediment criterion value.