Risk Assessment Workgroup Report

Abstract

The Risk Assessment Work Group focused on six charge questions related to CHABS, cyanobacteria and their toxins. The charge questions covered the following topics: Research needed to reduce uncertainty in establishing health based guidelines. Research that minimize the cost and maximize the benefits of various regulatory approaches. Exposure pathways for receptors of concern. Data available to support the derivation of health-based guideline values for harmful cyanobacterial algal blooms. Ecological services that guidelines or regulations should protect? A framework for making risk management determinations that incorporates consideration of the characteristics of CHABs, the risk for human health, ecosystem viability, and the costs and benefits of CHABs detection and management? The Work Group concluded that there is a considerable amount of human case-study data and information from animal studies to demonstrate that cyanobacterial toxins pose a hazard to humans, domestic animals, wildlife, and the ecosystem. However, the data on dose-response are limited and confounded by a lack of sufficient pure toxin to conduct most of the toxicological studies that will be needed in order to answer remaining questions on risk, and to provide the data for quantitative dose-response analysis. The Work Group recommended that research on purification or synthesis of pure toxin must be accomplished before the large scale studies to establish dose-response relationships will be possible. As the necessary-pure toxins become available, the Work Group recommended that studies be prioritized by the impact that they will have on reducing the uncertainty in the risk assessment in order to minimize the research costs and maximize the risk assessment benefits. Use of quantitative structure activity relationships (QSAR) and toxicity equivalency factor studies are also recommended as approaches for filling dose-response data gaps. The Work Group recognized that CHABs rarely introduce single toxins into the water supply. Under CHAB conditions, affected water is likely to contain a variety of toxins in varying concentrations that may change over the duration of the bloom. Accordingly, research on cyanotoxin interactions is needed, along with the development of risk assessment approaches for CHAB mixtures. The development of simple, accurate analytical methods that can be utilized by most analytical laboratories or used in the field was recognized as a major data need for establishing exposure potential and monitoring bloom conditions. Most currently available methods are time-consuming and/or costly. Human exposure to cyanobacterial toxins can occur through ingestion of contaminated drinking water, plus dermal contact and/or inhalation of aerosols while bathing and showering in tap water. Treatment can reduce the concentrations of both the toxins and the bacteria in the treated water but there is still much to be learned about the effectiveness of most treatment technologies on cyanobacteria and toxin removal. Human exposure to cyanobacteria and their toxins also occurs through incidental ingestion, dermal contact, and inhalation of aerosols during recreational use of surface waters, ingestion of contaminated fish and other foods of aquatic origin, and/or BGAS supplements. Establishing intakes and duration parameters for these exposure scenarios will facilitate the application of risk assessment approaches to these situations.