Garimpeiros are responsible for just three percent of the mercury found in the Brazilian Amazon, because "the region is rich in natural mercury," says Reinaldo Peleja, a biologist at the Federal University of Pará (UFPA), based on the cooperative efforts of Brazilian and Canadian scientists who studied the soil of the Amazon River basin.

The natural origin is verified in the contaminated fish found far from the 'garimpo' gold mining areas and in reservoirs with no obvious human sources of the metal, said Peleja. In the Rio Negro, where there is little mining activity, there is almost twice as much mercury as in the Rio Tapajós, whose basin is a large source of gold.

Contamination of mining areas and rivers has been a concern since the boom in Amazonian gold began in the 1980s. The garimpeiros use mercury to collect gold particles dispersed in the soil into amalgam, and then heat it to high temperatures to evaporate the mercury, which contaminates the people nearby and the environment in general.

When mercury remains in the soil, it is maintained in its less toxic inorganic form, but once it filters to the rivers as a result of rains and floods, it becomes part of the food chain in fish, and turns into methylmercury, which when concentrated in the human body can cause serious neurological problems.

"I already feel one symptom: trembling in the hands. I knew the risks, but I burned a lot of amalgam," says Ivo Lubrina, 57, a garimpeiro since age 31 and currently president of the Tapajós Association of Gold Miners.

Working in the Garimpeira Reserve of the Tapajós Basin, which covers 23,000 square km in the west of the northern state of Pará, are around 70,000 miners, and another 20,000 people that provide services, Lubrina estimates.

A local investigation by the mineral technology center of the Ministry of Science and Technology (under the auspices of the Global Mercury Project of the United Nations, underway in six countries), found fish with up to 40 times the accepted level of mercury in their systems. Plants and the soil were also found to be highly contaminated.

Now a campaign is being launched to convince the garimpeiros to work in a safer way, using cleaner technologies already in existence.

Mercury use has been banned in Brazil since 1989, by a law that is rarely heeded. "We must demonstrate the advantages of the alternatives, with immediate daily benefits, not just benefits for some distant future," stressed Zuleica Castilho, an expert in environmental risk assessment and campaign coordinator.

The garimpeiros "are not ignorant," they are aware of the dangers and know they should use protective equipment, but "because of the culture of kill or be killed and the haste to go on binges (after work)," they abandon the safety measures, lamented the miner Lubrina.

On the positive side, most of these informal miners come from northeast Brazil, where they were accustomed to eating beef, so they generally escape one factor of mercury contamination because they don't eat nearly as much fish as people from the Amazon do, he added.

Little is known about the biological damage that mercury causes in humans or in fish, said UFPA biologist Peleja in Santarém, where the Tapajós flows into the Amazon River. The recommended limit for humans is 50 parts per million (ppm) of the metal in the blood, but he said he knew of a case of a man with 176 ppm, and his health was "apparently normal."

It is a "silent, chronic problem, that progresses to a serious situation in 20 to 30 years," he predicted.

"There won't be an epidemic of neurological illnesses" in the Amazon, says Sandra Hacon, a biologist with a doctorate in geochemistry, who argues that mercury is released in "homeopathic doses" and that many of the symptoms being attributed to contamination are confused with other diseases common to the region, like malaria, or even epilepsy.

Tests that are valid in Europe and the United States are not appropriate for the Amazon reality, where it is necessary to distinguish between "subtle symptoms" and to focus the tests on children, to detect difficulties in learning and concentration, maintains Hacon, researcher for the National School of Public Health, in Rio de Janeiro.

The biologist is taking part in drafting a plan of action that the Amazon Cooperation Treaty Organization aims to promote in its eight member countries (Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname and Venezuela), and is slated to be ready in September.

The first step is to set up a database and systematize the approximately 400 studies published on this matter, she explained. The eight countries are producers of gold through artisanal mining. There could be as many as 100,000 or 200,000 garimpeiros in Colombia, a similar number in Peru, and twice that in Brazil.

Colombia is attempting to disseminate pollution-reducing technologies in a participatory way, with help from mining cooperatives, and in Peru there are some interesting studies about the Iquitos region, according to Hacon.

But some of these studies have not been published, and there is scant information, even for Brazil, which has "an enormous environmental liability" with mercury, she said.

In the opinion of Julio Wasserman, oceanographer and expert in heavy metals and geochemistry, broader studies are needed by experts who live in the Amazon, who can work there for extended periods. But such scientists are in short supply and there are few resources to support them.