Is it the mercury or the malaria?
Or maybe it's something else entirely that's making people sick in the Peruvian Amazon.
Those questions are bedeviling researchers from Duke University who have been studying gold mining in the region. Illegal mining has exploded in the area in the past decade, and the people living downriver have a variety of medical issues, from malaria to anemia to high blood pressure.
Researchers have documented that mercury used in illegal gold mining ends up hundreds of miles downstream from the mines, and it eventually ends up in fish — a major local source of protein.
But you can't see or smell mercury in fish.
So it's hard to measure the impact on residents. One of the main effects of mercury is that it causes developmental delays in children. Toxic exposure can cause severe fatigue, headaches and vomiting. Those symptoms could be the result of mercury. Or not. There's very little data on all the other things that could be responsible for health issues in the area.
To try to determine the possible health effects of the mercury, this year the researchers launched a massive survey that stretches from the Eastern slope of the Andes down into the plains of the Amazon basin.
The researchers are based in the sleepy little town of Salvacion, six hours east of Cusco when the roads are open. Mudslides often block the road during the rainy season, so Salvacion feels even more cut off than it already is.
At a simple, wood plank house in Salvacion, Dr. Ernesto Ortiz and two of his colleagues are about to start interviewing the family of Valentino Escobar Gutierrez. The entire health survey of Escobar's family will take two to four hours to complete.
"We're going to sample for malaria and for dengue," Ortiz says. "We are also testing for tuberculosis. Also testing for chronic diseases, diabetes, hypertension, kidney function, nutritional status, so we are going to have a big picture of how things are going."
Escobar, 45, wants to know why they need to take so much blood.
Ortiz explains with a laugh that each tube of blood will be used to test for a different disease or health condition. And he assures Escobar they're taking only a tiny portion of all the blood in his body.
"With one glass of water, you'll replace all of this," Ortiz assures him.
This study is all about gathering lots and lots of data. Ortiz and his colleagues at Duke plan to enroll 5,000 people. At each house they'll take medical histories. They'll ask about diet, income, education and past illnesses. They'll get blood, urine and hair samples to check a range of health conditions.
They're also testing for mercury exposure.
Ortiz says it's particularly important to understand how mercury from the gold mines could be affecting children.
"If [a child] is exposed to mercury for a long time, you get problems with brain development. They won't be able to have good attention, to learn things," Ortiz says. Sometimes they won't even be able to finish school. If that happens during early childhood, there's no return, they won't be able to heal from that damage."
So people have no idea whether they or their kids are consuming dangerous levels of the heavy metal. This study could flag that potential health threat.
Dr. Fernando Medieta, who's in charge of the local health district, is excited about the Duke survey for other reasons. He sees the study as a way to get data about his community that he would never have the time or the resources to collect on his own.
"This study is important because it's going to allow us to see the health of the whole population," he says. "And allow us to come up with ways to make things better.
This study is funded by Texas-based Hunt Oil Co., which is exploring for natural gas in the region. The researchers stress that their survey is an independent, academic project controlled by Duke.
Medieta runs a small hospital in Salvacion. He also oversees 15 small, bare-bones clinics scattered through the jungle. Ten of the posts are accessible only by river and the most distant one takes at least four days to reach by canoe.
For him mercury isn't his most pressing issue. In some of the villages he serves, half the children are malnourished. Water and mosquito-borne diseases are major problems. And chronic diseases like diabetes and hypertension are on the rise.
Down the road all the data collected by the Duke team might help show how climate change, new roads, new vaccination campaigns or environmental toxins like mercury affect disease rates in this part of the Amazon Basin.