U.S. Environmental Protection Agency


Document Type


Date of this Version



Published in Cyanobacterial Harmful Algal Blooms: State of the Science and Research Needs, ed. H. Kenneth Hudnell (Springer, 2008).


Risk assessment is a four–stage process used in evaluating the impact of contaminants on the well being of individuals, populations and/or the physical environment. As defined by the National Academy of Sciences (1983), the four components are as follows: hazard identification, dose– response assessment, exposure assessment and risk characterization.
The goal of a risk assessment is to utilize existing information coupled with site specific data to quantitatively characterize the potential risk of a stressor to an identified receptor(s). Quantitative, risk–based estimates of dose–response relationships integrated with exposure scenarios and information on environmental conditions often become the basis for regulatory measures or management policies to protect the population or physical environment from harm. The precision of the guideline value is impacted by the quantity and quality of scientific data available because uncertainty factors are applied in its derivation to compensate for deficiencies in the database. The more comprehensive the database, the lower the uncertainty in the risk assessment and the more precise the value generated.
Risk assessments are one tool used by risk managers when choosing between various options for protecting human health and the environment. They play a significant role in risk management decisions. However, the physical and societal environment is complex. It includes a multitude of receptors, each of which may be impacted by any risk management decision. Management decisions almost always involve considerations of a variety of risk factors, competing priorities, societal value systems, and resource limitations. In addition, the decision process may need to consider balancing risks.
The Risk Assessment Work Group was given the overall charge to identify the research needs for both cyanobacteria and their toxins. In order to provide context and focus to their deliberations, the work group addressed the following six charge questions:

• What data are available to derive health–based guideline values (TDI’s, RfD’s) for cyanobacterial harmful algal blooms (CHABs)?
• What research is needed to reduce uncertainty in health based guidelines?
• What research is needed to minimize the cost and maximize the benefits of various regulatory approaches?
• What are the exposure pathways for the receptors of concern?
• What are the ecosystem–services we want to protect?
• How can regulators best devise a framework for making risk management determinations that incorporates consideration of the characteristics of CHABs, the risk to human health and ecosystem sustainability, and the costs and benefits of CHABs detection and management?
The report that follows will address each of the stated charge questions in sequence culminating with a management framework that integrates concerns for human health protection with those for environmental ecosystems.