Fishermen exposed to the toxic microorganism Pfiesteria developed problems detecting visual patterns, according to preliminary findings from a federal study.
The Environmental Protection Agency study of North Carolina fishermen released Thursday is the first to suggest a chronic health effect from contact with Pfiesteria piscicida, a marine organism fatal to fish.
Previous studies suggested Pfiesteria can cause temporary learning or short-term memory loss, confusion and other cognitive impairment.
Researchers warned that the new findings are not definitive proof that the organism harms humans.
"Further research is needed before definitive conclusions can be made as to whether Pfiesteria may adversely affect vision or pose other human health risks," said Kenneth Hudnell, a neurotoxicologist at the EPA's National Health and Environmental Effects Research Laboratory.
Pfiesteria is a harmless one-celled organism unless something triggers it to change form and emit a poison that attacks fish, allowing the organism to feed on them until they die.
The fishermen exposed to Pfiesteria experienced a 30 percent reduction in sensitivity to visual patterns. People with visual sensitivity problems may perform tasks more slowly and run a higher accident risk, Hudnell said.
He said fishermen's eyes may be especially vulnerable to Pfiesteria toxins because they are exposed to mist and water from contaminated waterways.
"It may pass right through the eye into the retina," Hudnell said.
Hudnell administered a test to two groups of fishermen. Twenty-two fished in estuaries where there had been Pfiesteria-related fish kills and 20 others operated in coastal waters where exposure was unlikely.
The test measured the amount of contrast needed between dark and light bars for a person to see a pattern. The results showed a drop in the exposed fishermen's ability to detect the visual patterns. Their ability to focus on objects appeared unaffected.
Hudnell said it is too soon to say whether the visual problems are reversible.
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