Site Mitigation & Restoration Program

We protect and maintain California’s land and places
by setting strict standards for land restoration and cleanup

Human and Ecological Risk Office

Ecological Risk Assessment

Guidance | Tools

Preliminary Endangerment Assessment Guidance Manual (PEA Guidance Manual) (January 1994. Revised October 2015).

This manual provides guidance on the basic information needed to determine if a release of hazardous substances to the environment presents a risk to human health or the environment. It explains how a PEA ties into the cleanup process and provides technical recommendations for conducting a PEA site investigation and human health and ecological screening evaluations. The manual also makes recommendations on how a PEA report should be organized and what information should be included in the report.

Ecological Risk Assessment Guidance

Guidance for Ecological Risk Assessments – Part A

OVERVIEW.PDF is an Adobe Acrobat file containing the document titled Guidance for Ecological Risk Assessments at Hazardous Waste Sites and Permitted Facilities, Part A: Overview, dated July 4, 1996. This document contains the description of the DTSC-recommended phased method for conducting an ecological risk assessment. Outlined are the contents of a Scoping Assessment, a Phase I Predictive Assessment, a Phase II Validation Study and a Phase III Impact Assessment. More detailed guidance for each of these components will be available in a series of additional documents. Also included are flow charts describing the process with a text description of the decision points and work products contained in the flow charts. A response to comments section contains written responses to more than 100 written comments received after public notice of this document.

Guidance for Ecological Risk Assessments – Part B

SCOPE.PDF is an Adobe PDF file containing the document titled Guidance for Ecological Risk Assessments at Hazardous Waste Sites and Permitted Facilities, Part B:Scoping Assessment, dated July 4, 1996. This document contains the more detailed description of the contents of the initial Scoping Assessment with example tables, exposure route diagrams and conceptual site model diagrams.

HERD EcoNOTES outline specific issues which have arisen subsequent to the release of the Department of Toxic Substances Control Guidance for Ecological Risk Assessment in 1996. These EcoNOTES are meant to provide clarification for specific issues not directly addressed in the 1996 guidance documents or to supersede any previous departmental guidance. EcoNOTES should be reviewed prior to preparation of an Ecological Risk Assessment.

EcoNOTE-1 Depth of Burrows for Burrowing Mammals

HERD typically recommends a soil interval of surface to 10 feet to estimate the soil exposure point concentration (EPC) for human health risk assessments. This EcoNOTE1 recommends a default soil interval of surface to 6 feet for burrowing mammals in an ecological risk assessment. Literature sources are provided and several examples are provided for implementation. This EcoNOTE has been reviewed by and incorporates the suggestions of the U.S. EPA Region IX Biological Technical Assistance Group (BTAG).

EcoNOTE-2 Intake Calculation for Vertebrate Receptors

Calculation of intake for vertebrate receptors in a Phase I Predictive Assessment. A two phase methodology is recommended. Individual sample concentrations should be used to detect areas of elevated concentration (i.e., ?hot spots?). The 95th upper confidence limit on the mean should be used to calculate a generalized intake for the site. Ingestion, inhalation and dermal absorption (where applicable) should be related to body size. A range of adult and juvenile intake and hazard calculation is recommended. A recommendation for development of a more extensive range of intake and hazard based on individual vertebrate body weights is outlined. This EcoNOTE has been reviewed by and incorporates the suggestions of the U.S. EPA Region IX Biological Technical Assistance Group (BTAG).

EcoNOTE-3 (Revised) Dibutyltin

Calculation of an action level/preliminary cleanup goal for dibutyltin (DBT) in surface, ground, and sediment interstitial water for protection of saltwater aquatic life. HERD recommends an action level/preliminary cleanup goal for DBT in surface, ground, and sediment interstitial water that is equal to 0.1 µg/L [100 times more than the proposed U.S. EPA Ambient Water Quality Criterion of 0.001 µg/L for tributyltin (TBT) in saltwater]. The HERD recommended DBT action level/preliminary cleanup goal should only apply in situations where DBT is detected in water (i.e., surface water or sediment interstitial water), but not TBT. In situations where both DBT and TBT are detected in water, HERD recommends that a toxic equivalency factor (TEF) approach be used.

EcoNOTE-4 BTAG TRVs in Ecological Risk Assessment

This EcoNOTE encompasses many topics related to the use of Navy/Biological Technical Assistance Group (BTAG) Toxicity Reference Values (TRVs) in ecological risk assessment. HERD presents rationale and/or recommendations for the following:

  • The Navy/BTAG TRVs should be used during the predictive phase of the ecological risk assessment.
  • Updates to the Navy/BTAG TRVs can be proposed based on more recent toxicological or physiological experiments following consensus procedures outlined by the BTAG.
  • The ecological risk assessment should include supporting evidence necessary to substantiate the conclusions of the predictive assessment.
  • When lead is a contaminant of ecological concern, bioavailability must be assessed on a site-specific basis.

This EcoNOTE has been reviewed by and incorporates the suggestions of the U.S. EPA Region IX Biological Technical Assistance Group (BTAG).

EcoNOTE-5 (Revised) BTAG Mammalian TRV for Lead

Revised U.S. Environmental Protection Agency (USEPA) Region 9 Biological Technical Assistance Group (BTAG) Mammalian Toxicity Reference Value (TRV) for Lead: Justification and Rationale. HERD and the BTAG have reviewed the request and submittal of the U.S. Army for reconsideration of the current mammalian BTAG TRV for lead (Pb). After consideration of the endpoints, dosing information, evaluation of the experimental results, and limitations of the experiments, the BTAG has agreed to set the mammalian Pb NOAEL (TRV-Low) at 1 mg/kg BW/day, based primarily on the kidney toxicity data contained in Fowler et al. (1980) and supported by at least 19 other studies suggesting that a 1 mg/kg BW/day Pb dose would be protective of bone, behavioral, immune, reproductive, embryonic, renal, and ocular effects seen at doses within one order of magnitude higher. The decision to alter the BTAG TRV is based on the best available data developed after the initial determination of the BTAG mammalian TRV-Low in 1997. As new information becomes available, this TRV, or others, may be revised. The BTAG will not consider revising other TRVs without sufficient scientific justification and documentation, as provided in this EcoNOTE.

EcoNOTE-6 Avian TRV for Cadmium

Revised Avian Toxicity Reference Value for Cadmium: Justification and Rationale.  This document represents a revision to the cadmium toxicity reference value (TRV) for birds used by regulatory agencies and resource trustees in California for predictive ecological risk assessments. Our review focused on evaluating TRVs between the currently used TRV and the Eco-SSL TRV, considering the application of an updated ingestion rate model and uncertainty factors. After consideration of the endpoints and evaluation of the experimental results, we propose an ecologically protective NOAEL TRV based primarily on the kidney toxicity data in wood ducks, but supported by other studies that indicate the kidney is a critical target organ for cadmium toxicity. This TRV is also protective of reproductive effects, another sensitive endpoint for cadmium toxicity. In addition, a lowest observable adverse effect level was identified based on kidney nephrosis in mallards. Overall, these updated TRVs incorporate more recent studies and reviews on cadmium toxicity in birds while establishing thresholds based on ecologically relevant endpoints.

EcoNOTE 7 – Sampling Updates for Ecological Risk Assessment

This EcoNOTE includes updated recommendations for discrete sampling approaches for ecological risk assessment, as well as for incremental sampling methodology (ISM). Recommendations in this note supersede the recommendations made in previous HERO ecological risk assessment notes.

Ecological Risk Assessment Tools

For additional Ecological Risk Assessment Tools and Resources, see the Other Risk Assessment Tools and Resources Page.

Recommended Sources of Media Screening Levels for Ecological Risk Assessment

This list is provided as an aid to those preparing ecological risk assessments for submittal to the Department of Toxic Substances Control’s Site Cleanup Program. The list contains sources of DTSC accepted screening levels for ecological risk evaluations. If a screening value is not presented for a constituent in these sources, or an alternative screening level or source is to be proposed, please consult in advance with the DTSC ecotoxicologist assigned to the project. If you have questions, please contact the DTSC project ecotoxicologist or ERAS Unit Chief Brian Faulkner at brian.faulkner@dtsc.ca.gov.

Recommended Guidance Documents for Ecological Risk Assessment of Per- and Polyfluoroalkyl Substances (PFAS)

ERAS recommends that the development of ecological risk assessments for PFAS utilize the following guidance documents and that development of PFAS risk assessments be conducted in consultation with a DTSC ecotoxicologist:

ECO Checklist

This checklist is provided as an aid to those preparing ecological risk assessments for submittal to the Department of Toxic Substances Control’s Site Cleanup Program. This check list contains the elements of an ecological risk assessment the Department feels are necessary to provide adequate data to regulating agencies.

BTAG Mammalian and Avian TRVs, 2/24/09

Currently Recommended U.S. Environmental Protection Agency (USEPA) Region 9 Biological Technical Assistance Group (BTAG) Mammalian and Avian Toxicity Reference Values (TRVs)  Revision Date February 24, 2009.

This file includes listings of the most current mammalian and avian BTAG TRVs, including the recent change to the cadmium avian TRV, and supercedes listings provided in EcoNOTE4. When a chemical of potential ecological concern is present at a site as a result of a release to the environment, and a corresponding BTAG TRV exists, the BTAG TRV must be used in predictive and validation study phases of the ecological risk assessment. Ecological risk assessments submitted to DTSC for technical review that do not include consideration of the BTAG TRVs will be rejected. Alternate TRVs may be proposed and supported, however they must be evaluated in conjunction with the BTAG values. A BTAG TRV-Low represents a lowest credible no adverse effect level; a BTAG TRV-High represents the mid-point of a variety of adverse effects levels and therefore is not necessarily a lowest adverse effect level (LOAEL). A TRV-Low dose would not be expected to produce an adverse effect and is protective of an individual or population of organisms; a TRV-High dose would be expected to produce an adverse effect to an individual or population of organisms. In the first iteration of the predictive risk assessment, a TRV-Low hazard quotient or index less than one suggests de minimus ecological risk. A TRV-High hazard quotient or index greater than one suggests unacceptable ecological risk, which can be confirmed or determined to be not applicable to the specific site by the validation study. A chemical with a TRV-Low hazard quotient or hazard index greater than one and TRV-High less than one (i.e., the “gray area”) suggests further site-specific information (e.g., to refine exposure and bioavailability assumptions) should be collected to reduce the uncertainty and obtain a more site-specific estimate of the potential for ecological risk. As new information becomes available, BTAG TRVs may be revised. The BTAG will not consider revising a TRV without sufficient scientific justification and documentation, as outlined in EcoNOTE4 and demonstrated in EcoNOTE5.

Page last updated January 19, 2022

HERO Links

HERO Quick Links

HERO Quarterly Updates

Whats New at HERO

Risk Assessment News:

Site Mitigation & Restoration Program Links

Site Mitigation & Restoration Program Related Links