Concerns cited in two studies on antibiotic levels in manure

By CELESTE BAUMGARTNER

Ohio Correspondent

BUFFALO, N.Y. — Antibiotic resistance has been called one of the world’s most pressing public health problems, according to the U.S. Centers for Disease Control and Prevention.

It can cause illnesses that were once easily treatable with antibiotics to become dangerous infections. And a couple of studies are raising concerns about how agriculture may be contributing to the problem.

Diana Aga, Ph.D. at the University of Buffalo, found that both advanced anaerobic digestion and reverse osmosis filtration – two of the most elite waste treatment systems available on farms – leave behind concerning levels of residue. Meanwhile, Holly Dolliver, University of Wisconsin-River Falls, looked at a variety of composting techniques and found not all of the antibiotics degrade in the same ways – and some don’t degrade at all.

“Neither of the two treatment systems we studied was designed to remove antibiotics from waste as a primary goal,” Aga said. “Anaerobic digestion is used to reduce odors and produce biogas.”

Reverse osmosis filtration is advertised to convert animal wastewater into drinking water, she said. It makes the water clear, but instrumental analysis detected some residues of antibiotics remaining in the water.

“That was a surprise to us,” Aga explained.

With both processes, when the manure was separated into liquids and solids, most of the antibiotics preferred to remain in the solid portion so the antibiotics become more concentrated in the solid than the liquid part, Aga said. The simplest way to remove the antibiotics is composting with high temperature and aeration. Just putting it in a pile is not effective.

“We have a new USDA project where we are looking at spreading the manure in buffer strips and some other technologies that would be effective,” Aga said. “We want the manure in the soil, but how do we prevent the antibiotics from persisting in the environment?”

Dolliver’s research looked at a variety of composting techniques and how antibiotics degrade during that process. It focused on small-scale organic farmers.  Using turkey manure, the researchers studied four antibiotics that spanned across a wide range of antibiotic classes.

“We found that all of them did degrade at least to some extent,” she noted. “The time frame was maybe a day, all the way up to 20 days. We were trying to get very controlled conditions, which is not practical on farms.”

The researchers evaluated three manure composting treatments: a control treatment (manure pile with no disturbance or adjustments after initial mixing), a managed compost pile (weekly mixing and moisture content adjustments) and vessel composting.

Despite significant differences in temperature, mass and nutrient losses between the composting treatments and the experiment control, there was no difference in antibiotic degradation among the treatments, Dolliver said. Chlortetracycline concentrations declined rapidly during composting, whereas monensin and tylosin concentrations declined gradually in all three treatments. There was no degradation of sulfamethazine in any of them.

In another study, she looked at how plants uptake antibiotics, specifically sulfamethazine. The scientists found that corn, lettuce and potatoes were all taking up the antibiotic, which was in the water.

“This uptake was in the raw material,” Dolliver said. “Corn is heavily processed; we don’t know the fate of sulfamethazine or any antibiotic in processing. I also did lettuce and potatoes because lettuce is directly consumed. I was looking at how much was ingested in a salad, and it was a small amount. But the point is that it is there.”

“Antibiotic resistance is a global problem,” Aga said. “The United Nations, World Health Organization, Bill Gates Foundation – they are all supporting this type of research because antibiotic resistance is probably going to be one of the top two killers in 2020. We are running out of effective antibiotics that will kill pathogens.

“It doesn’t matter who is to blame, but in the end, we are all responsible. There is animal contribution, there is human contribution and there are also manufacturing contributions, especially in India and China where they are not regulated.”