Ecological Soil Screening Levels for Polycyclic Aromatic Hydrocarbons (PAHs) Interim Final OSWER Directive 9285.7-78 U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response 1200 Pennsylvania Avenue, N.W. Washington, DC 20460 June 2007 This page intentionally left blank TABLE OF CONTENTS 1.0 INTRODUCTION .......................................................1 2.0 SUMMARY OF ECO-SSLs FOR PAHs......................................1 3.0 ECO-SSL FOR TERRESTRIAL PLANTS....................................4 5.0 ECO-SSL FOR AVIAN WILDLIFE.........................................8 6.0 ECO-SSL FOR MAMMALIAN WILDLIFE..................................8 6.1 Mammalian TRV ...................................................8 6.2 Estimation of Dose and Calculation of the Eco-SSL ........................9 7.0 REFERENCES .........................................................16 7.1 General PAH References ............................................16 7.2 References Used for Derivation of Plant and Soil Invertebrate Eco-SSLs ......17 7.3 References Rejected for Use in Derivation of Plant and Soil Invertebrate Eco-SSLs ...............................................................18 7.4 References Used in Derivation of Wildlife TRVs .........................25 7.5 References Rejected for Use in Derivation of Wildlife TRV ................28 i LIST OF TABLES Table 2.1 PAH Eco-SSLs (mg/kg dry weight in soil) ..............................4 Table 3.1 Plant Toxicity Data - PAHs ..........................................5 Table 4.1 Soil Invertebrate Toxicity Data - LMW-PAHs ...........................6 Table 4.2 Soil Invertebrate Toxicity Data - HMW-PAHs ...........................7 Table 6.1 Mammalian Toxicity Data Extracted for Wildlife Toxicity Reference Value (TRV) - LMW - PAHs.............................................10 Table 6.2 Mammalian Toxicity Data Extracted for Wildlife Toxicity Reference Value (TRV) - HMW - PAHs ............................................12 Table 6.3 Calculation of the Mammalian Eco-SSL for LMW-PAHs ................13 Table 6.4 Calculation of the Mammalian Eco-SSL for HMW-PAHs ................13 LIST OF FIGURES Figure 6.1 Mammalian TRV Derivation for LMW - PAHs .........................14 Figure 6.2 Mammalian TRV Derivation for HMW - PAHs .........................15 LIST OF APPENDICES Appendix 2-1 Summary of Peer Review Appendix 5-1 Avian Toxicity Data Extracted and Reviewed for Wildlife Toxicity Reference Value (TRV) - LMW - PAHs Appendix 5-2 Avian Toxicity Data Extracted and Reviewed for Wildlife Toxicity Reference Value (TRV) - HMW - PAHs ii Appendix 6-1 Mammalian Toxicity Data Extracted and Reviewed for Wildlife Toxicity Reference Value (TRV) - LMW - PAHs Appendix 6-2 Mammalian Toxicity Data Extracted and Reviewed for Wildlife Toxicity Reference Value (TRV) - HMW - PAHs iii 1.0 INTRODUCTION Ecological Soil Screening Levels (Eco-SSLs) are concentrations of contaminants in soil that are protective of ecological receptors that commonly come into contact with and/or consume biota that live in or on soil. Eco-SSLs are derived separately for four groups of ecological receptors: plants, soil invertebrates, birds, and mammals. As such, these values are presumed to provide adequate protection of terrestrial ecosystems. Eco-SSLs are derived to be protective of the conservative end of the exposure and effects species distribution, and are intended to be applied at the screening stage of an ecological risk assessment. These screening levels should be used to identify the contaminants of potential concern (COPCs) that require further evaluation in the site-specific baseline ecological risk assessment that is completed according to specific guidance (U.S. EPA, 1997, 1998, and 1999). The Eco-SSLs are not designed to be used as cleanup levels and the United States (U.S.) Environmental Protection Agency (EPA) emphasizes that it would be inappropriate to adopt or modify the intended use of these Eco-SSLs as national cleanup standards. The detailed procedures used to derive Eco-SSL values are described in separate documentation (U.S. EPA, 2003, 2005). The derivation procedures represent the group effort of a multi-stakeholder group consisting of federal, state, consulting, industry, and academic participants led by the U.S. EPA Office of Solid Waste and Emergency Response. This document provides the Eco-SSL values for polycyclic aromatic hydrocarbons (PAHs) and the documentation for their derivation. This document provides guidance and is designed to communicate national policy on identifying PAH concentrations in soil that may present an unacceptable ecological risk to terrestrial receptors. The document does not, however, substitute for EPA's statutes or regulations, nor is it a regulation itself. Thus, it does not impose legally-binding requirements on EPA, states, or the regulated community, and may not apply to a particular situation based upon the circumstances of the site. EPA may change this guidance in the future, as appropriate. EPA and state personnel may use and accept other technically sound approaches, either on their own initiative, or at the suggestion of potentially responsible parties, or other interested parties. Therefore, interested parties are free to raise questions and objections about the substance of this document and the appropriateness of the application of this document to a particular situation. EPA welcomes public comments on this document at any time and may consider such comments in future revisions of this document. 2.0 SUMMARY OF ECO-SSLs FOR PAHs Polycyclic aromatic hydrocarbons (PAHs) (CASRN: 130498-29-2) constitute a class of organic substances made up of carbon and hydrogen atoms grouped into at least two condensed aromatic ring structures. These are divided into two categories: low molecular weight compounds composed of fewer than four rings and high molecular weight compounds of four or more rings. PAH derivatives are PAHs having an alkyl or other radical attached to a ring. Heterocyclic aromatic compounds (HACs) include PAHs having any one carbon atom in a ring replaced by a Eco-SSL for PAHs 1 June 2007 nitrogen, oxygen, or sulfur atom PAHs are also referred to as polynuclear hydrocarbons, polynuclear aromatic hydrocarbons, or polycyclic organic matter (HSDB). Polycyclic aromatic hydrocarbons (PAHs) are found throughout the environment in air, soil, water, and sediment. PAHs enter the environment from both natural and anthropogenic sources. Natural sources include volcanic eruptions and forest fires (ATSDR, 1995). Primary anthropogenic sources are from the extraction, transport, and refining of petroleum products and combustion products resulting from their use (International Labor Office, 1998). Other industrial sources include machine lubricating and cutting oils, and color printing oils (WHO, 2002). PAHs are also found in creosote (NTP, 2003), coal tar, roofing materials, and surface coatings. PAHs are not currently produced for commercial use in the United States, although several compounds are distributed for research purposes by specialty chemical companies (NTP, 2003) (HSDB). The primary mode of toxicity for PAHs in soil dwelling terrestrial invertebrates is non-specific, nonpolar narcosis (Sverdrup et al., 2002a). The uptake of PAHs by earthworms occurs primarily by direct contact with the soluble phase of the soil solution (interstitial porewater) (Fairbrother, 2005). Soil porewater concentrations of PAHs are more predictive of biological responses (toxicity and/or bioaccumulation) in soil organisms than are bulk soil concentrations. Several studies show a relationship between bioaccumulation of or toxic effects of PAHs and soil porewater concentrations. The relationships are more predictable for low molecular weight compounds and show significant variability for high molecular weight PAHs (Ma et al., 1998) (Fairbrother, 2005). The bioavailability of PAHs in soils is influenced by organic carbon quality and quantity, aging and weathering, microbial action, methylation/hydroxylation, adsorption/desorption hysteresis and ultra-violent light interaction (Fairbrother, 2005). The soil organic carbon-water partition coefficients (Koc) for PAHs vary depending on the size of associated soil particles with the highest values in silt (fine particles) followed by sand and clay (Krauss and Wilcke, 2002). Microbial degradation of PAHs is a key process in environmental fate in soils. The rate of biodegradation is dependant on the nutrient content and bacterial community in the soil. PAHs in soils undergo a weathering process such that the lighter chain fractions are removed (primarily by volatilization). Heavier fractions bind more readily to the soil organic matter and remain behind in the top soil horizon. As the mixture of PAHs age, bioavailability changes as the fraction remaining bind more tightly (Fairbrother, 2005). Aging reduces the bioavailability of PAHs in soils (Johnson et al., 2002). Chemicals in soils “age” by becoming incorporated inside the crystal lattice structure of the soil particle, or partitioning onto organic matter or soil nanopores (Nam et al., 1998), so they are no longer available for uptake by organisms. Bulk sediment chemistry methods can measure PAHs sequestered in this manner but it is not biologically available to organisms. Aging is, however, influenced by biodegradation and soil characteristics and is not a linear predictive relationship (Sverdrup et al., 2002b). PAHs that result from combustion processes are inserted into particulate