CRITICAL REVIEW Neurobehavioral effects of harmful algal bloom (HAB) toxins: A critical review MELISSA A. FRIEDMAN 1 and BONNIE E. LEVIN 2 1 The NIEHS Marine and Freshwater Biomedical Sciences Center, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Florida 2 Department of Neurology, University of Miami School of Medicine, Florida (Received February 27, 2004; 1st Revision October 29, 2004; Accepted December 30, 2004) Abstract Human exposure to naturally occurring marine toxins has been associated with a range of neurobehavioral abnormalities. The toxins are produced by harmful algal blooms (HABs) and are typically contracted through seafood consumption. The primary target of many of the HAB toxins is the neurologic system, and the neurobehavioral symptoms associated with the HAB illnesses have influenced public health policy. The HAB-related illnesses most frequently linked to neuropsychological disturbance are Amnesic Shellfish Poisoning, Ciguatera Fish Poisoning, and Possible Estuarine Associated Syndrome, which is associated with exposure to the Pfiesteria piscicida organism. Although the neurophysiologic mechanisms underlying many of the HAB illnesses have been well delineated, the literature examining the neuropsychological impairments is unclear and needs to be defined. This review is intended to introduce an emerging area of study linking HAB illnesses with neuropsychological changes. ( JINS, 2005, 11, 331–338.) Keywords: Marine toxins, Neurotoxins, Neuropsychology, Pfiesteria piscicida, Ciguatera poisoning, Amnesic shellfish poisoning, Domoic acid, “Delirium, dementia, amnestic, cognitive disorders” INTRODUCTION This review examines the neurobehavioral consequences of exposure to Harmful Algal Bloom (HAB) toxins, which are naturally occurring toxins produced by microalgae in marine, freshwater, or brackish estuarine water environments. Many of the HAB toxins are highly potent neurotoxins linked to serious human health effects. The neurobehavioral symp- toms associated with HAB-related illnesses have been the subject of public concern and have influenced public policy decisions. In 1997 in Maryland, for instance, concern about the human health and neuropsychological effects of expo- sure to the Pfiesteria piscicida organism led to the closure of the Maryland waterways (Griffin, 1997) and the enact- ment of new water quality legislation (Simpson, 1998). The term, HAB, refers to a proliferation or “bloom” of certain microalgae in the water, which can lead to massive fish kills, the deaths of birds and marine mammals, and seafood contamination. HABs have been known to cause changes in the color of marine water (e.g., red tides). HABs can deplete oxygen or block sunlight necessary for the sur- vival of other organisms (Centers for Disease Control and Prevention, 2004). In addition, during HABs some micro- algae, such as dinoflagellates, diatoms, and cyanobacteria, produce toxins. The toxins accumulate in digestive organs and soft tissues of fish and shellfish via feeding, and become bioconcentrated as they move up the food chain, ultimately affecting the humans who consume them. Human consump- tion is particularly problematic because the toxins are gen- erally tasteless, odorless, and heat- and acid-stable, rendering Dr. Friedman is now affiliated with Carlos Albizu University, Miami, Florida 33172. Reprint requests to: Melissa A. Friedman, Ph.D., Carlos Albizu Univer- sity, 2173 NW 99thAve., Miami, FL33172. E-mail: melissafried@yahoo.com Journal of the International Neuropsychological Society (2005), 11, 331–338. Copyright © 2005 INS. Published by Cambridge University Press. Printed in the USA. DOI: 10.10170S1355617705050381 331