Determinacion De Carbono Organico

NCEA-C- 1282 EMASC-001 April 2002

METHODS FOR THE DETERMINATION OF TOTAL ORGANIC CARBON (TOC) IN SOILS AND SEDIMENTS

Brian A. Schumacher, Ph.D. United States Environmental Protection Agency Environmental Sciences Division National Exposure Research Laboratory P.O. Box 93478 Las Vegas, NV 89193-3478

Ecological Risk Assessment Support Center Office of Research and Development US.Environmental Protection Agency

ACKNOWLEDGMENTS

This document was prepared by Brian Schumacher of EPA*s National Exposure Research Laboratory, Office of Research and Development (ORD) in response to a request received by ORD*s Ecological Risk Assessment Support Center. Peer review of the document was conducted by Peter Landrum of the National Oceanographic and Atmospheric Administration, and RobertOzretich of ORD*s National Health and Environmental Effects Research Laboratory. Bruce Duncan, EPA Region 10, and Sharon Thorns, EPA Region 4, provided helpful insights and comments during the preparation of the document. Programmatic review of the document was conducted by the Trichairs of EPA*s Ecological Risk Assessment Forum: Steve Wharton, EPA Region 8; Bethany Grohs, Office of Solid Wasteand Emergency Response, Office of Emergency and Remedial Response (OSWER/OERR); and Brenda Jones, EPA Region 5. Finally, we would like to acknowledge the efforts of Mark Sprenger, EPA/OSWER/OERR, in initiating the original request.

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1. INTRODUCTION

Organic matter in soils and sediments is widely distributed over the earth*s surface occurring in almost all terrestrial and aquaticenvironments (Schnitzer, 1978). Soils and sediments contain a large variety of organic materials ranging from simple sugars and carbohydrates to the more complex proteins, fats, waxes, and organic acids. Important characteristics of the organic matter include their ability to: form water-soluble and water insoluble complexes with metal ions and hydrous oxides; interact with clay minerals and bindparticles together; sorb and desorb both naturally-occurring and anthropogenically-introduced organic compounds; absorb and release plant nutrients; and hold water in the soil environment. As a result of these characteristics, the determination of total organic carbon (a measure of one of the chemical components of organic matter that is often used as an indicator of its presence in a soil or sediment) isan essential part of any site characterization since its presence or absence can markedly influence how chemicals will react in the soil or sediment. Soil and sediment total organic carbon (TOC) determinations are typically requested with contaminant analyses as part of an ecological risk assessment data package. TOC contents may be used qualitatively to assess the nature of the sampling location(e.g., was a depositional area) or may be used to normalize portions of the analytical chemistry data set (e.g., equilibrium partitioning). The purpose of this document, as defined by the Ecological Risk Assessment Forum, is to answer the question of “What is the most appropriate method for soil and/or sediment TOC analyses and what factors should be considered when selecting the method?”

2.SOURCES AND FORMS OF CARBON IN SOILS AND SEDIMENTS

In soils and sediments, there are three basic forms of carbon that may be present. They are: (1) elemental C, (2) inorganic C, and (3) organic C. The quality of organic matter in sediments is critical to the partitioning and bioavailability of sediment-associated contaminants. For example, Talley et al., 2002, demonstrated that although themajority of PAHs in a dredged sediment were found preferentially on coal-derived particles, the PAHs on the clay/silt sediment fraction were more mobile and available, and thus potentially of greater concern.
2.1. ELEMENTAL CARBON FORMS

Elemental carbon forms include charcoal, soot, graphite, and coal. The primary sources for elemental carbon in soils and sediments are as incomplete combustion...