LEARNING AND MEMORY DIFFICULTIES AFTER ENVIRONMENTAL EXPOSURE TO WATERWAYS CONTAINING TOXIN-PRODUCING PFIESTERIA OR PFIESTERIA-LIKE DINOFLAGELLATES

Background At the beginning of autumn, 1996, fish with ''punched-out'' skin lesions and erratic behaviour associated with exposure to toxins produced by Pfiesteria piscicida or Pfiesteria-like dinoflagellate sp ecies were seen in the Pocomoke River and adjacent waterways on the ea stern shore of the Chesapeake Bay in Maryland, USA. In August, 1997, f ish kills associated with Pfiesteria occurred in these same areas. Peo ple who had had contact with affected waterways reported symptoms, inc luding memory difficulties, which raises questions ia about the human- health impact of environmental exposure to Pfiesteria toxins. Methods We assessed 24 people who had been exposed. We collected data on expos ure history and symptoms, did a complete medical and laboratory assess ment (13 people), and carried out a neuropsychological screening batte ry. Performance on neuropsychological measures was compared with a mat ched control group. Results People with high exposure were significant ly more likely than occupationally matched controls to complain of neu ropsychological symptoms (including new or increased forgetfulness); h eadache; and skin lesions or a burning sensation of shin on contact wi th water. No consistent physical or laboratory abnormalities were foun d. However, exposed people had significantly reduced scores on the Rey Auditory Verbal Learning and Stroop Color-Word tests (indicative of d ifficulties with learning and higher cognitive function), and the Groo ved Pegboard task. There was a dose-response effect with the lowest sc ores among people with the highest exposure. By 3-6 months after cessa tion of exposure, all those assessed had test scores that had returned to within normal ranges. Interpretation People with environmental exp osure to waterways in which Pfiesteria toxins are present are at risk of developing a reversible clinical syndrome characterised by difficul ties with learning and higher cognitive functions. Risk of illness is directly related to degree of exposure, with the most prominent sympto ms and signs occurring among people with chronic daily exposure to aff ected waterways.