Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 21.1

21.1 Framework for Ecological Risk Assessments

An ERA is a qualitative and/or quantitative appraisal of the actual or potential effects of one or more chemicals on plants and animals in the wild. At its simplest, risk can be defined as a function of the overlap in space and time of a stressor (a chemical) and a living organism (a receptor) where the stressor causes some adverse effect on the receptor. The process of risk assessment is designed to (1) identify the distribution and magnitude of chemical stressors; (2) identify the locations of living organisms that are sensitive to the chemical stressor; and (3) quantify the probability that the receptor will be exposed to the stressor and experience adverse effects related to the exposure.

This simple model of spatial and temporal overlap of a chemical and an organism is rarely encountered in the field, however. Instead, ERAs must often address sites where multiple chemicals have been released into several media (soil, groundwater, sediment, surface water) and numerous receptors are potentially exposed during all or part of their complex life cycles. Chemicals may be present but physically bound to media so that they do not exert a toxic effect on organisms. Concentrations of chemicals in background/ambient/reference samples may confound the interpretation of risk at the site. Information on the sensitivity of local organisms to the chemicals at the site may be unavailable. These and other difficult issues make the ERA process complex and add to the uncertainty of decisions based on ERA results.

In an effort to strengthen and streamline the ERA process, USEPA published an 8-step framework for ERAs that has been widely adopted, with modification, by national and state programs around the world (USEPA 1992e). Steps 1and 2 of the USEPA framework, generally referred to as the SLERA, are primarily based on limited site-specific sediment data and default assumptions about exposure and effects. Oftentimes, the SLERA incorporates the initial part of Step 3 (commonly referred to as Step 3a) in which the conservative default assumptions of Steps 1 and 2 are refined to focus the ERA process on the chemicals and receptors of greatest concern at the site. This HEER Office guidance includes Step 3a in the SLERA.

In addition to the USEPA framework, information and technical advances from the Australian/New Zealand Environment and Conservation Council / Agriculture and Resource Management Council of Australia and New Zealand (ANZECC/ARMCANZ) Guidance on ERAs will continue to be evaluated as they pertain to tropical marine sediments. Tables and data in the HEER Office TGM will be updated periodically as new information becomes available from sources relevant to tropical marine environments.

The risk assessor should realize that preparing an ERA is seldom a simple or linear process. More often, the risk assessor will work with data from many disciplines, including geologists, hydrologists, toxicologist, ecologists, and chemists to develop an understanding of the unique situation at the site. Some of the required elements may be available to the risk assessor from the start, while others may prove to be unobtainable within the time frame of the investigation. The steps and tasks can be approached in a different order; some processes may run concurrently and some may be repeated as the need for additional information becomes apparent. The risk assessor should maintain communication with the HEER Office and seek confirmation and clarification on the chosen approach whenever necessary.