For 13 years Sofia Gatica has organized opposition to the aerial spraying of agrochemicals that threaten human health and the environment in Argentina -- and for almost as long, she and her children have faced physical threats from anonymous agents.

Gatica, who lives in a working-class neighborhood of 6,000 in central Argentina surrounded by soy fields, began organizing against Monsanto after she noticed a disturbingly high rate of cancer and birth defects in her community. Her own 3-day-old daughter died of kidney failure in 1999, and a neighbor had a baby die of the same uncommon birth defect.

Editor's Note: This story contains explicit language.

"I started seeing children with mouth covers, mothers with scarves wrapped around their heads to cover their baldness, due to chemotherapy," she told Grist in an interview, explaining what inspired her to co-found Mothers of Ituzaingó. The efforts of those half-dozen mothers, who began going from door to door collecting information on health problems in their community, led to the first epidemiological study that showed cancer rates in Gatica's hometown of Ituzaingó were 41 times the national average, with high rates of birth defects and infant mortality as well.

Within a few years of the study's publication, and as her advocacy work gave her a higher profile, Gatica began to receive death threats, culminating in an incident in late 2007.

"I had just come back from the corner store, and I never lock my door," she told HuffPost through a translator. "I always just come and go in our neighborhood, and I came in and he followed behind me and put the gun against my head in my kitchen and said that I needed to 'stop fucking with the soy.'"

Gatica said she held perfectly still and complied with the gunman's wishes. "He made me sit down in a chair," she said. "He said not to leave, and so I didn't leave. I waited until he drove away and then I went to the police."

Despite her careful description, the police were unable to identify the man, and Gatica continued to receive threatening phone calls.

"I was living with my heart in my mouth," said Gatica, after an anonymous caller told her she would soon have "two children instead of three." She asked the police to tap her line and trace the callers, and while they told her they had opened an investigation, she's been told the file is secret.

Other threats, she said, came from neighbors who were angry that the value of their homes had gone down because of her work.

"In one case a woman got on the bus and was yelling at me, saying I had lowered the price of her house and that who was I to be telling people if they were sick or not, if my neighbors were sick or not? She was insulting me personally to the point I got off the bus and walked to my office, and when I got there, I found out where she lived and called the police to get a restraining order. It turned out later that that woman had cancer," Gatica said, "so she was likely having some kind of an emotional reaction."

Gatica said that same woman had threatened her youngest daughter, now 14 years old, when her daughter was riding her bicycle in the neighborhood, and that her other children, a 19-year-old daughter and a 23-year-old son, had also been targeted at school.

Farmers and others in Argentina use weedkiller primarily on genetically modified Roundup Ready soy, which covers nearly 50 million acres, or half of the country's cultivated land area. In 2009 farmers sprayed that acreage with an estimated 200 million liters of glyphosate, the active ingredient in Roundup and other herbicides used around the globe, which critics have argued for decades poses a serious threat to public health.

The Argentine government helped pull the country out of a recession in the 1990s, in part by promoting genetically modified soy. Though it was something of a miracle for local farmers at the time, residents in areas nearby the crops began a few years later to report health problems, including high rates of birth defects and cancers, as well as the losses of crops and livestock.

Gatica said that after she began reporting those problems on local radio in 2006, she was hassled by the local police. "At one point they actually knocked on my door and made me come out on the street," she said through a translator. "The street was filled with maybe 30 patrol men asking her to stop 'lying' about her neighborhood."

"It was very intimidating," she told HuffPost, but she stood by her statements. The police actually took her to the house of a local soy farmer who had been spraying Roundup and asked the farmer to tell Sofia that he hadn't hired them. Then, she said, "they left me there in the farm and I had to walk back and the farmer was letting his dogs out and they were barking at us."

Still, she says, she doesn't blame the police for these actions. "I feel like they were following orders," she said.

While Monsanto avers that glyphosate poses no risk to humans, the work of activists like Gatica and Argentine government scientist, Andres Carrasco, suggest a different story. Carrasco conducted a study in 2009, "Glyphosate-Based Herbicides Produce Teratogenic Effects on Vertebrates by Impairing Retinoic Acid Signaling," which found that glyphosate causes malformations in frog and chicken embryos at doses far lower than those used in agricultural spraying. It also found that malformations caused in frog and chicken embryos by Roundup and its active ingredient glyphosate were similar to human birth defects found in genetically modified soy-producing regions.

"The findings in the lab are compatible with malformations observed in humans exposed to glyphosate during pregnancy," wrote Carrasco, director of the Laboratory of Molecular Embryology at the University of Buenos Aires. "I suspect the toxicity classification of glyphosate is too low.”

“In some cases this can be a powerful poison," he concluded.

Another pesticide Gatica has targeted of late, endosulfan, has been banned in 80 countries, and in May of 2011 the Stockholm Convention, an international treaty, added the pesticide to their list of persistent pollutants to be eliminated. Her group's press conferences, demonstrations and data-gathering efforts have yielded some success in recent months, and a countrywide ban of endosulfan will go into effect in July 2013.

Gatica has also succeeded in passing a municipal ordinance prohibiting aerial spraying 2,500 meters from people's homes, and in 2012 she was awarded the distinguished Goldman Prize for environmentalists in South and Central America. She's currently working on a campaign to create buffer zones for agrochemicals throughout all of Argentina, protecting residential areas and waterways.

Her next project, she says, will be pushing for a countrywide ban on glyphosate.

Gatica notes that she's made a lot of enemies, even if she isn't sure who they are.

"I don't know if it's the soy farmers, or the soy industry, or the government because they're all so linked -- and they're all angry about the work I've been doing."