RIO DE JANEIRO, Brazil - When patients at a dialysis clinic in the northeastern Brazilian city of Caruaru began dropping dead of seizures and liver hemorrhage, health authorities blamed an overdose of chlorine.
The tanker driver who transported water from the city's reservoir to the clinic told investigators he routinely added a bit of chlorine "when (the water) didn't look so good" because of algae that formed a thick green scum on the reservoir.
But Sandra Azevedo, a biologist and algae neurotoxins expert at the Federal University of Rio de Janeiro, watched news reports of the rising death toll with an uneasy sense of familiarity.
"What was happening to the patients was just the same as what I see in my lab," she recalled.
Today, she and Wayne Carmichael, a Wright State University biologist considered the world's top expert on cyanobacteria, know the outbreak for what it was: the first conclusive evidence of human deaths from pond scum or, more scientifically, blue-green algae, tiny cousins of the better known saltwater "red tide."
For centuries, people have known that eating shellfish when reddish algae build up in saltwater oyster and mussel bays can bring about an agonizing death. Until recently, little was known about similar neurotoxins released by blue-green algae, the greenish scum that, usually in a nontoxic variety, can clog freshwater lakes and reservoirs from Illinois to Antarctica.
Only some forms of it are toxic, but the toxins are deadly. Over the past 100 years, thousands of migrating ducks and geese in the Midwest have died after drinking water contaminated by the algae. Deer, horses and cattle also have succumbed.
Water contaminated by blue-green algae neurotoxins undoubtedly has killed people as well, Carmichael said, though in modern times such deaths are rare or little noticed because freshwater shellfish are rare and because few people drink scummy pond water.
However, people now are being exposed to cyanobacteria in ways unknown in the past, the Ohio-based researcher said.
Fertilizer runoff to blame
Water sources throughout the world are increasingly polluted with fertilizer runoff, which provides the nutrients for luxuriant blooms of blue-green algae, he said.
Dialysis, a treatment that puts human blood in direct contact with up to 100 gallons of water a week, also is growing more common.
People are even eating a form of blue-green algae known as spirulina, which has gained a popular following since the late 1970s as a health-food diet additive and purported miracle treatment for everything from Alzheimer's disease to leukemia.
Algae have been used for thousands of years as an important protein supplement in countries from Mexico to Chad, researchers say. Long before the Spanish conquest, Peru's Incas made algae flour and carried dried algae cakes while traveling.
There might be something to the medical claims. Algae neurotoxins, while deadly, may have anti-bacterial and anti-fungal properties, early research shows. The compounds also allegedly act as carcinogens. Families in parts of China where blue-green algae contamination of water is common show high rates of liver cancer, Carmichael said.
Informed decision on spirulina
The potential risks make the current spirulina craze worrisome, Carmichael said. Health officials in Oregon, where most U.S.-sold spirula is harvested from lakes, have for three years required testing for neurotoxins in algae products. Other states do not have similar laws. Spirulina products are not required to carry labels warning of potential neurotoxin hazards.
That might cause problems, Carmichael said, because potentially deadly algae and nontoxic algae are virtually indistinguishable, except through sophisticated biochemical testing.
"There's nothing wrong with eating algae. People have done that for thousands of years," Carmichael said, "but people need to make an informed decision."
69 dialysis patients died
Just how deadly blue-green algae can be was made clear for the first time in Caruaru, where 69 people died after undergoing dialysis treatment with contaminated water over four days in February 1996.
After treatments in which their blood was filtered through an average of 30 gallons of contaminated water, more than 100 patients reported visual disturbances, nausea and vomiting. Within days, many began to die as their livers hemorrhaged and failed.
Blue-green algae neurotoxins have no antidote.
Carmichael, who is in Brazil this week to testify in civil trials surrounding the deaths, said the clinic allowed toxins into the patients' dialysis process by using poorly filtered reservoir water treated with chlorine. Blue-green algae secrete toxins only when they are dead or dying, and the chlorine treatment killed the algae, breaking them down and spreading toxins in the water.
Inspection records show that the clinic had not performed mandatory water analysis testing for more than two years and that filters designed for use by eight patients were being used for as many as 60.
Chlorine the wrong strategy
If the water had not been treated with chlorine, filtration might have safely removed the living algae, sparing lives, Carmichael said. While most water-purification systems focus on removing bacteria and viruses, almost none look for neurotoxins.
That presents a potential problem even for the United States, where water filtration is much more advanced than in Brazil but where few municipal treatment plants monitor for water-borne algae neurotoxins.
"Five years ago, we wouldn't have figured out what happened," Carmichael said. "But the toxin is much more potent intravenously, and here people were exposed to lots of contaminated water through dialysis."