US EPA

The National Center for Environmental Assessment has prepared the Toxicological Reviews of Cyanobacterial Toxins: Anatoxin-a, Cylindrospermopsin and Microcystins (LR, RR, YR and LA) as a series of dose-response assessments to support the health assessment of unregulated contaminants on the CCL. The purpose of these documents is to compile and evaluate the available data regarding toxicity of these toxins to aid the Office of Water in regulatory decision making.

The Safe Drinking Water Act (SDWA), as amended in 1996, requires the EPA to publish a list of contaminants that, at the time of publication, are not subject to any proposed or promulgated national primary drinking water regulations, are known or anticipated to occur in public water systems, and may require regulations under SDWA. This list, known as the Contaminant Candidate List (CCL), was first published in 1998 and then again in 2005. The 1998 and 2005 CCLs include cyanobacteria (blue-green algae), other freshwater algae, and their toxins as microbial contaminants.

In 2001, a meeting was held among EPA, researchers from the drinking water industry, academia and government agencies with expertise in the area of fresh water algae and their toxins. The goal of this meeting was to convene a panel of scientists to assist in identifying a target list of algal toxins that are likely to pose a health risk in source and finished waters of the drinking water utilities in the U.S. Toxin selection was based on four criteria: health effects, occurrence in the United States, susceptibility to drinking water treatment and toxin stability. Anatoxin-a was identified at this meeting as being a toxin of high priority based on those criteria.

NCEA then prepared the document, Toxicological Review of Cyanobacterial Toxins: Anatoxin-a as one in a series of dose-response assessments to support the health assessment of unregulated contaminants on the CCL. The purpose of this document is to compile and evaluate the available data regarding Anatoxin-a toxicity to aid the EPA/Office of Water in regulatory decision making. It is not intended to be a comprehensive treatise on the chemical or toxicological nature of Anatoxin-a.

Cyanobacteria, commonly referred to as blue-green algae, are found in freshwater, estuarine and marine environments. Cyanobacteria, other freshwater algae, and their toxins are included as microbial contaminants on EPA’s Office of Water (OW) Contaminant Candidate List (CCL). These draft assessment documents discuss potential human health effects of exposure to these cyanobacterial toxins for four durations-- acute, short-term, subchronic and chronic-- focusing on noncancer effects due to oral exposure.

Following the public comment period and external peer review, EPA will incorporate the comments in a Final report to be released in 2007.

US EPA. Toxicological Review of Cyanobacterial Toxins: Anatoxin-a (External Review Draft). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-06/137, 2006.

In Section 6, Major Conclusions in the Characterization of Hazard and Dose Response, EPA has characterized its overall confidence in the quantitative and qualitative aspects of the hazard and dose response by addressing knowledge gaps, uncertainties, quality of data and scientific controversies. The discussion is intended to convey the limitations of the assessment and to aid and guide the Office of Water in the ensuing steps of the human health risk assessment of anatoxin-a.