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During red tide outbreaks, people often report upper respiratory
problems, including coughing, itchy and tearing eyes, runny nose,
headache and shortness of breath. But no one has ever proved
scientifically that red tide is the cause of these symptoms, so scientists
from Mote Marine Laboratory and 12 other agencies, research centers,
hospitals and universities have embarked on a five-year, $6 million
study to determine the effects of red tide toxin on human health. The
scientific team has been using test subjects who are most often exposed
to red tide: lifeguards.
Red tide is caused by the single-celled alga Karenia brevis, that
contains a powerful neurotoxin called brevetoxin. K. brevis occurs
naturally in sea water, and at normal concentrations, about 10 cells per
liter, it causes no problems. But occasionally, for reasons unknown to
scientists, the organism undergoes a population explosion, or bloom,
and the toxin kills fish and makes shellfish poisonous to humans. Mote
scientists have proved that breaking waves during red tide rupture _K.
brevis_ cells, and the toxin becomes airborne.
The study was started in September [2001], during a serious red tide
outbreak; air and water samples were taken, and 40 lifeguards
underwent a series of tests. The study continued this week with no red
tide present so scientists can compare results from the red tide period to
a period without red tide.
During both test periods, lifeguards were tested before and after their
daily shifts. First, they answered a series of questions. "We ask things
like whether they've ever been in a red tide, and if so, what their
symptoms were," said Mote scientist Barbara Kirkpatrick. "In
September [2001], a lot of them reported upper respiratory symptoms.
One guy sneezed a lot, so we tried to get him to count how many times
he sneezed every hour."
Each day, mucus from nasal and throat swabs was put on slides, which
were sent to the University of Miami to check for brevetoxin.
Lifeguards also underwent spirometric tests -- the subject takes a deep
breath and blows as hard as he can into a tube; a computer measures
lung capacity and how well the subject empties his lungs. "We don't
know the effects of brevetoxin on the lungs," Kirkpatrick said. "The
nose and throat are designed to be filters: 70 percent of the toxin
should be filtered out by the nose and throat. But 30 percent of red tide
toxin is small enough to penetrate into the lungs."
Scientists have studied the effect of brevetoxin on dogs, guinea pigs,
and sheep and discovered the toxin causes asthma-like reactions in
animal subjects. But testing human lungs is completely different, said
Lora Fleming, associate professor in the University of Miami's
Department of Epidemiology & Public Health. "Humans get a lower
dose than animals: We're going to get out of an area where there's red
tide," she said. "And with animals, we can measure the toxin by
looking at the lung cells."
With baseline work done on lifeguards, the red tide team is waiting for
fall and hoping for a red tide so they can begin the next phase of the
study. Volunteers with asthma or chronic lung disease will sit or walk
on the beach and take the same tests as the lifeguards. "Based on
animal models, we think people with lung disease are at higher risk
from red tide, but that hasn't been proved," Kirkpatrick said. "Our
results could be a big benefit for the tourist industry. A lot of tourists
have never even heard of red tide before. Having good, accurate
information regarding health effects will relieve a lot of people's minds
- -- people who don't have asthma and lung disease, who'll know that the
tickle in the throat is nothing serious, and people with lung disease who
do have to be cautious."
The red tide team hopes to have its results ready for the International
Conference on Harmful Algal Blooms meeting in October [2002].
[By Kevin Kollar]
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