PRINCIPLES OF ENVIRONMENTAL TOXICOLOGY AND CONTAMINATION (PART III)

Table of Contents

1. Index
2. UNIT 9 - Environmental risk assessment
   1. Introduction
   2. Problem formulation
   3. Analysis Phase
   4. Risk characterization
   5. Risk management and assessment
   6. Human health risk assessment
3. UNIT 10 - Environmental risk communication
4. UNIT 11 - Modelling in Ecotoxicology
5. UNIT 12 - Legislation
6. Glossary of key terms associated with environmental toxicology

Introduction

The overall goal of risk assessment is to establish chemical concentrations values that can be present in the environment without compromising humans or wildlife species. There are two main branches of risk assessment related to chemical exposure: 

• Human health risk assessment
• Ecological risk assessment

Additionally, risk assessment is the process of assigning probabilities and magnitudes to adverse effects associated with an event. The development of risk assessment methodology focused on accidental events (e.g., a maritime accident such as an oil spill) and specific environmental stresses to humans (exposure of humans to chemicals). Therefore, most risk assessment approaches are characterized by discrete events or stresses affecting well-defined endpoints (e.g., incidence of human death or cancer). This single stress-single endpoint relationship allows the use of relatively simple statistical and mechanistic models to estimate risk and is widely used in human health risk assessment. However, this simple paradigm has only partial applicability to ecological risk assessment because of the inherent complexity of ecological systems and the exposure to many chemical, physical, and biological stresses that have both direct and indirect effects on a diversity of ecological components, processes, and endpoints. So, ecological risk assessment must consider effects at the population, community, and ecosystem levels as well as at the individual species level. For example, there is a tremendous number of different species with different sensitivities to chemicals. Thus and also due to the fact that relevant assessment endpoints are not universally accepted, ecological risk assessment process is generally more complex and protracted than most human health risk assessments (only one species). Less information regarding the toxicity of chemicals and exposure patterns is available for the great majority of species found in the environment than for humans. In addition, although the roots of ecological risk assessment can be found in human health risk assessment, the methodology for ecological risk assessment is not well developed and the estimated risks are highly uncertain. Despite these limitations, resource managers and regulators are looking into ecological risk assessment in order to provide a scientific basis for prioritizing the problems that pose the greatest ecological risks and to focus research efforts in areas that will yield the greatest reduction in uncertainty.

To this end, the United States Environmental Protection Agency (EPA) has issued guidelines for planning and conducting ecological risk assessments. Because of the complexity and uncertainty associated with ecological risk assessment, the EPA guidelines provide only a loose framework for organizing and analyzing data, assumptions, information, and uncertainties to assess the likelihood of adverse ecological effects. Nevertheless, the guidelines represent a broad consensus of the present scientific knowledge and experience on ecological risk assessment. Many other countries in Europe have adopted the same general approach for improving the quality, consistency, and applicability of assessments of the impact of environmental stressors on components of an ecosystem.

Ecological risk assessment - is defined as the process that evaluates the likelihood¹ that adverse ecological effects²may occur or are occurring³as a result of exposure to one or more stressors⁴.

¹Estimating the likelihood can range from qualitative judgments to quantitative probabilities, though quantitative risk estimates are still rare in ecological risk assessment.

²Adverse ecological effects - are changes that are considered undesirable because they alter valued functional or structural characteristics of ecological systems and generally include the intensity, type, and scale of the effect as well as the potential for recovery.

³The statement that effects may occur or are occurring refers to the dual prospective and retrospective nature of ecological risk assessment.

⁴The inclusion of one or more stressors is a recognition that ecological risk assessments may address single or multiple chemical, physical, and/or biological stressors.

Note: Risk assessment is conducted to provide input to management decisions and for this reason, most risk assessments focus on stressors generated or influenced by anthropogenic activity. Nevertheless, natural phenomena also can induce stress that results in adverse ecological effects and cannot be ignored.

The overall ecological risk assessment process is illustrated in figure 1.

Figure 1 - The ecological risk assessment framework as set forth by the U.S. Environmental Protection Agency (EPA).

This continuous process involves three primary phases:

• Problem formulation
• Analysis (of exposure and effects)
• Risk characterization