Crops absorb livestock antibiotics, science shows

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Crops absorb livestock antibiotics, science shows

<http://www.environmentalhealthnews.org/ehs/news/antibiotics-in-crops>

http://www.environmentalhealthnews.org/ehs/news/antibiotics-in-crops

 

Consumers have long been exposed to antibiotics in meat and milk.

Now, new research shows that they also may be ingesting them from

vegetables, even ones grown on organic farms.

 

By Matthew Cimitile Environmental Health News January 6, 2009

 

For half a century, meat producers have fed antibiotics to farm

animals to increase their growth and stave off infections. Now

scientists have discovered that those drugs are sprouting up in

unexpected places.

 

Vegetables such as corn, potatoes and lettuce absorb antibiotics when

grown in soil fertilized with livestock manure, according to tests

conducted at the University of Minnesota.

 

Today, close to 70 percent of the total antibiotics and related drugs

produced in the United States are fed to cattle, pigs and poultry,

according to the Union of Concerned Scientists. Although this

practice sustains a growing demand for meat, it also generates public

health fears associated with the expanding presence of antibiotics in

the food chain.

 

People have long been exposed to antibiotics in meat and milk. Now,

the new research shows that they also may be ingesting them from

vegetables, perhaps even ones grown on organic farms.

 

The Minnesota researchers planted corn, green onion and cabbage in

manure-treated soil in 2005 to evaluate the environmental impacts of

feeding antibiotics to livestock. Six weeks later, the crops were

analyzed and found to absorb chlortetracycline, a drug widely used to

treat diseases in livestock. In another study in 2007, corn, lettuce

and potato were planted in soil treated with liquid hog manure. They,

too, accumulated concentrations of an antibiotic, named

Sulfamethazine, also commonly used in livestock.

 

As the amount of antibiotics in the soil increased, so too did the

levels taken up by the corn, potatoes and other plants.

 

" Around 90 percent of these drugs that are administered to animals

end up being excreted either as urine or manure, " said Holly

Dolliver, a member of the Minnesota research team and now a professor

of crop and soil sciences at the University of Wisconsin-River Falls.

" A vast majority of that manure is then used as an important input

for 9.2 million hectares of (U.S.) agricultural land. "

 

Manure, widely used as a substitute for chemical fertilizer, adds

nutrients that help plants grow. It is often used in organic farming.

 

The scientists found that although their crops were only propagated

in greenhouses for six weeks--far less than a normal growing

season--antibiotics were absorbed readily into their leaves. If grown

for a full season, drugs most likely would find their way into parts

of plants that humans eat, said Dolliver.

 

Less than 0.1 percent of antibiotics applied to soil were absorbed

into the corn, lettuce and other plants. Though a tiny amount, health

implications for people consuming such small, cumulative doses are

largely unknown.

 

" The antibiotic accumulation in plants is just another negative

consequence of our animal agriculture industry and not surprising

given the quantity fed to livestock, " said Steve Roach, public health

program director for the non-profit Food Animal Concerns Trust.

 

For highly processed plants such as corn, the drugs would most likely

be removed, added Dolliver. But many food crops such as spinach and

lettuce are not processed, only washed, allowing antibiotics to

remain.

 

" Nobody particularly eats corn or soybean directly, " said Satish

Gupta, a University of Minnesota professor of soil science and study

leader. " But there are crops I am much more worried about, like

cabbage and lettuce, because these are leaves we eat directly and

consume raw. "

 

One finding that particularly worries food scientists is the

accumulation of antibiotics within potato tubers. Tubers are an

enlarged, underground stem that uptake and store nutrients from the

soil. In crops like potatoes, carrots and radishes, it is the part

humans eat.

 

" Since these tubers and root crops are in direct contact with the

soil they may show a greater propensity for (antibiotic) uptake, "

said Gupta.

 

Health officials fear that eating vegetables and meat laced with

drugs meant to treat infections can promote resistant strains of

bacteria in food and the environment.

 

Roach said " the clearest public health implication " from treating

livestock with antibiotics is the development of resistant bacteria

that reduces the effectiveness of human medicine. Past studies have

shown overuse of antibiotics reduces their ability to cure

infections. Over time, certain antibiotics are rendered ineffective.

 

Scientists believe antibiotics also may have contributed to the

explosive rise in asthma and allergies in children over the last 20

years. Researchers at Henry Ford Hospital in Detroit, following 448

children from birth for seven years, reported that children who

received antibiotics within their first six months had a higher risk

of developing allergies and asthma.

 

Such health concerns led the European Union in 2006 to ban antibiotic

use as feed additives for promoting livestock growth. But in the

United States, nearly 25 million pounds of antibiotics per year, up

from 16 million in the mid 1980s, are given to healthy animals for

agriculture purposes, according to a 2000 report by the Union of

Concerned Scientists.

 

Livestock producers contend that the spread of resistant strains of

bacteria stems from the overuse of all medicines to treat infectious

diseases in both humans and animals. Removal of antibiotics, they

say, would only lead to increased disease in animals and reduction in

food safety.

 

Tainted manure can impact more than just the soil. Once applied to

the land, antibiotics can infiltrate water supplies as it seeps

through the soil into aquifers or spills into surface water due to

runoff, explained Dolliver.

 

" The other thing to remember is that the field is not a sterile

environment. Mice, rabbit and foxes traverse farmland while other

animals graze, all with the potential to become vectors for the

resistant bacteria organisms and spread it throughout different

animal populations, " said Pat Millner, a U.S. Department of

Agriculture microbiologist based in Maryland.

 

The presence of antibiotics within the food chain is likely to

increase as the U.S. Food and Drug Administration has permitted

greater use of controversial drugs on farm animals. For example, this

past October, the FDA dropped plans to halt use of cefquinome, a

potent antibiotic, after it said in July it would push against its

use in animals.

 

While there are restrictions on use of raw manure in U.S. organic

farming because of concern over bacteria, no such rules are in place

regarding antibiotics or hormones. Not all organic growers use manure

with antibiotics, but many do, said Gupta. Even if a product has the

USDA organic label, it still might harbor traces of antibiotics.

[Correction 1/6/09: FDA was changed to USDA]

 

High-temperature composting of manure, designed to kill pathogens, is

required for crops certified under the USDA organic label. That could

eliminate some antibiotics. But others are resistant, according to a

study by Dolliver and Kupta published last year. Growers are not

required to monitor crops for the drugs.

 

" Antibiotic uptake by plants may be of particular concern to organic

crop producers....To our knowledge, there is no current plan or

standardized methodology for monitoring antibiotics in animal manure,

which is often obtained from nonorganic farms where antibiotics are

commonly used, " Dolliver said in the 2007 study.

 

Added Gupta, " We urgently need to find some way to put guidelines in

place on organic food regarding these chemicals. "

 

Gupta said all growers should be told that composting manure can

help reduce antibiotics. Composting decays piles of food or manure as

microbes decompose organic matter using oxygen to survive, grow and

reproduce. Heating up the material creates conditions conducive for

bacteria to break down antibiotics and pathogens.

 

A pilot study by USDA scientists in Maryland added straw to a beef

cattle manure pile, heating up the dense material while allowing

spaces for air to penetrate. The higher temperatures sped up the

decaying process of harmful substances.

 

" The process happens very rapidly, in this study it took about 10

days, " said Millner. " This is not too surprising since antibiotics

are not a thermally stable chemical compound. "

 

In another study, the same researchers who discovered the uptake of

antibiotics by plants tested four of these drugs to determine how

effective composting would be in reducing harmful chemicals in turkey

manure. After 25 days using a combination of natural heat generated

by microbial activity, three of the four antibiotics broke down under

the high energy conditions created, said Dolliver.

 

Composting reduced concentrations of three antibiotics by 54 percent

to 99 percent, although one drug, sulfamethazine, did not degrade at

all, according to their study, published in May in the Journal of

Environmental Quality.

 

" These findings suggest manure management can be an important

strategy for reducing the overall impact for these compounds making

their way into the environment, " said Dolliver.

 

Many questions still remain. Currently, projects are underway to grow

crops for a full season in antibiotic laced manure, to grow them in

fields rather than greenhouses and to analyze the concentrations and

locations of the antibiotics within the plants. Researchers also want

to determine which antibiotics are more likely to be picked up, which

plants are more prone to uptake, what composting methods are most

effective in reducing harmful material in manure and what antibiotics

may be resistant to composting.

 

There are serious societal implications regarding the discoveries

already made and the questions yet to be answered, Gupta concluded.

 

" We are a chemical society and humans are the main user of

pharmaceutical products, " said Gupta. " We need a better understanding

of what takes place when chemicals are applied to sources of food and

must be more vigilant about regulating what we use to grow food and

what we put in our bodies. "

 

Cimitile, a second-year graduate student at Michigan State

University's Knight Center for Environmental Journalism, is an intern

at Environmental Health News. He can be reached at

<mcimitile%40gmail.com>mcimitile.