Paraquat: A controversial chemical's second act

(This story accompanies a Special Report: “Why Brazil has a big appetite for banned pesticides”)

April 2 (Reuters) - One of the oldest and most widely used pesticides in the world is also one of the most toxic and controversial.

Paraquat, a herbicide used to control weeds since the 1950s, was banned in the European Union in 2007. It is restricted for use only by licensed technicians in the United States and, since 2012, many of its formulations in China are being phased out.

Known for its toxicity to vital organs, including the liver, kidneys, heart and respiratory system, it is deadly if ingested and has long been criticized by public health experts. They say farm workers, especially in less educated and less regulated markets, are at risk if they use the chemical improperly.

“It’s terribly toxic,” says Mark Davis, senior officer for pesticide management at the Food and Agriculture Organization of the United Nations. “Once it is in your body there is no antidote.”

Paraquat caused a public health scare in the United States in 1970s: Mexican drug enforcement authorities, with funding from the U.S. government, sprayed the chemical on marijuana that later crossed the border. In the 1980s, paraquat was the agent in suicide and murder scares in Japan.

Paraquat is still widely used across much of the developing world, especially in Asia and Latin America. It is popular because it kills weeds on contact and breaks down fast once it enters the soil.

The chemical is also increasingly used to complement other popular herbicides, such as glyphosate, more commonly known by its original brand name, Roundup.

That product, developed by U.S.-based Monsanto Co but now also made by generic manufacturers, is the world’s most widely used herbicide. It is commonly applied to genetically modified strains of soybeans, corn and other produce engineered to withstand glyphosate and grown on the massive, single-crop farms that dominate global agriculture today.

But glyphosate itself is controversial. Last month, the World Health Organization said glyphosate is “probably carcinogenic to humans,” prompting the U.S. Environmental Protection Agency to say it will seek new rules for its use.

And after years of exposure to glyphosate, many weeds have developed resistance, leading to renewed use of paraquat and other complements.

Global sales of paraquat, according to a study commissioned by the Australian unit of Syngenta AG, one of the many manufacturers of the chemical, totaled $640 million in 2011. The global market for all pesticides in 2013 totaled $54.2 billion, according to market researcher Phillips McDougall. (Edited by Michael Williams)