Two common Big Agriculture production practices -- feeding antibiotics to livestock and spraying herbicides on conventional crops -- each face condemnation from the environmental community. And there's been plenty of new fodder in the last week: One study predicted that antibiotic use in livestock will soar by two-thirds globally from 2010 to 2030, and another declared that Monsanto's popular Roundup herbicide is "probably carcinogenic to humans."
The latest research may merge the herbicide and antibiotic battle lines. The use of common herbicides, such as Roundup, Kamba and 2,4-D, according to a study published on Tuesday, may help drive antibiotic resistance.
Antibiotic-resistant infections take the lives of more than 23,000 Americans every year. The World Health Organization and the U.S. Centers for Disease Control and Prevention are among major groups warning of the dire threat posed to public health. Antibiotic resistance stemming from overuse in livestock also is the target of a bill re-introduced in Congress on Tuesday.
Environmental health advocates predict the use of herbicides will continue to rise as farmers plant more genetically modified seeds engineered to survive weedkillers. The U.S. Environmental Protection Agency recently approved Enlist seeds, which are designed for use with a mix of 2,4-D and glyphosate, the chief ingredient in Roundup.
In some cases, combinations of herbicides and antibiotics in the new study made bacteria more susceptible to antibiotics, or had no effect. But more often, it had the opposite effect. If the disease-causing bacteria -- E. coli and salmonella -- were exposed to high enough levels of herbicide, the researchers found that the microbes could survive up to six times more antibiotic than if they hadn't been exposed to herbicide. They studied five common classes of the drugs: ampicillin, chloramphenicol, ciprofloxacin, kanamycin and tetracycline.
"In a sense, the herbicide is 'immunizing' the bacteria to the antibiotic," said Jack Heinemann, lead author of the study and researcher at the University of Canterbury in New Zealand. He noted that the levels of herbicide tested in the study were above legal limits for residues on food, but lower than what's commonly applied to commercial crops.
The new finding builds on emerging evidence that multiple environmental contaminants may play a role in the rise of antibiotic resistance. Swedish researchers reported in September that antibiotic residues and heavy metals in the environment -- even at "infinitesimally low" concentrations -- may team up to drive the growth of antibiotic resistance. In addition to metals potentially leaching into the environment from other industries, construction or health care facilities, some farmers use arsenic in animal feed and as a pesticide. Mercury can also contaminate fish meal, while copper is common in swine fodder.
"This could be an important contributor" to antibiotic resistance, Dan Andersson, lead author of that study and a microbiologist at Upsalla University in Sweden, told The Huffington Post in October.
Mark Silby, a biologist at the University of Massachusetts, Dartmouth, noted an "important parallel," between the heavy metal and herbicide studies. "Low-level antibiotics can be of considerable importance in the evolution of antibiotic resistance, by means which we may not be very good at anticipating," he said.
Most research in the past has looked at chemicals or other contaminants in isolation, rather than as the cocktail that typically lingers in the environment -- especially near farms -- and is enlisted in modern agricultural practices. Livestock feed, and the fields on which animals graze, may contain traces of antibiotics, herbicides and heavy metals.
Heinemann, too, emphasized that "combinations of exposures to what we think of as different kinds of chemicals can matter."
He also pointed to the core issue of the overuse of antibiotics in both medicine and agriculture. His team's study was published the same day that Rep. Louise Slaughter (D-N.Y.) re-introduced the Preservation of Antibiotics for Medical Treatment Act. The bill has the support of 50 city councils and more than 450 medical, consumer advocacy and public health groups.
"Right now, we are allowing the greatest medical advancement of the 20th century to be frittered away, in part because it's cheaper for factory farms to feed these critical drugs to animals rather than clean up the deplorable conditions on the farm," Slaughter, the only microbiologist in Congress, said in a statement Tuesday. "My legislation would save eight critical classes of antibiotics from being routinely fed to healthy animals, and would reserve them only for sick humans and sick animals."
The U.S. Food and Drug Administration offers voluntary guidance to the pharmaceutical industry on the use of antibiotics in livestock, including a request that drugmakers change their labels by December 2016 to exclude uses for growth promotion. The FDA hasn't imposed a ban or mandatory restrictions. Advocates are not impressed, pointing to potential loopholes in the voluntary guidance.
Slaughter's bill has faced steep opposition since its first iteration in 1999. In the last Congress, according to a press release from her office on Tuesday, 82 percent of lobbying reports filed on her bill came from “entities hostile to regulation.”
Slaughter is among experts and advocates who largely blame the pressing public health problem on the routine administration of low doses of antibiotics to cattle, swine, chickens and other livestock. Just as an incomplete course of antibiotics can result in the rise of a more virulent infection in a person, this use in animals -- often to prevent the spread of disease or to simply promote growth -- means bacteria that can withstand the drugs will survive, reproduce and pass on their resistance to the next generation of bugs on the farm.
Food animals receive about 80 percent of the antibiotics sold in the U.S. Livestock antibiotics are thought to affect human health via multiple pathways: direct or indirect contact with food, water, air or anywhere urine or manure goes.
While some fast food brands and retailers have begun eliminating medically-important antibiotics from their supply chains, the agriculture industry maintains that its practices are critical for livestock health and not a significant contributor to the rise of antibiotic resistance. The Animal Health Institute, which represents pharmaceutical companies, suggested that the herbicide and heavy metal studies further support their case.
"These studies are further indications that antibiotic resistance is a very complex issue and there are non-antibiotic compounds that can select for resistance," Ron Phillips, vice president of legislative and legal affairs with the group, told HuffPost in an email. "That's why simple solutions will only waste resources while not addressing the real issue. We must address the issue of antibiotic resistance with careful, science-based" approaches.
Charla Lord, a spokeswoman for Monsanto, added that her company was taking a closer look at the "very complicated" study. She said more research is needed to identify what components in the herbicide may be linked to any effects.
Amy Pruden, an expert on antibiotic resistance at Virginia Tech, agreed that the studies "definitely complicate things" and add evidence that "it's not just antibiotics that contribute to the problem."
Pruden emphasized the need for "a really broad management plan that thinks comprehensively about all the things that contribute to the failure of antibiotic treatment." She noted that antibiotic overuse, including in livestock, is far from off the hook. "It's common sense that antibiotics themselves are the core issue," she said. "It's just that even if we cut way back on them, we still might have work to do and other things to think about."
Silby agreed. "Obviously, sick animals should be looked after appropriately, but the large-scale use of antibiotics as growth enhancers has almost certainly been a significant driver of antibiotic resistance."