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Study finds little dairy antibiotics in groundwater

September
2, 2010, Davis, CA – In the first large study to track the fate of a wide range
of antibiotics given to dairy cows, University of California, Davis scientists
found that the drugs routinely end up on the ground and in manure lagoons, but
are mostly broken down before they reach groundwater.


September
2, 2010, Davis, CA – In the first large study to track the fate of a wide range
of antibiotics given to dairy cows, University of California, Davis scientists
found that the drugs routinely end up on the ground and in manure lagoons, but
are mostly broken down before they reach groundwater.

The
findings should help alleviate longstanding fears that dairy farms, and the
fields fertilized with their waste, might lead to large-scale groundwater contamination.

Researchers Mike Mata of UC Davis, left, and Brian Bergamaschi of the US Geological Survey drill core samples from the ground under a dairy freestall. (Thomas Harter/UC Davis photo)

“What
we found is that antibiotics can frequently be found at the manure-affected
surfaces of the dairy operation (such as corrals and manure flush lanes) but
generally degrade in the top 12 inches of soil,” said Thomas Harter, an expert
on the effects of agriculture on groundwater quality and the Robert M. Hagan Chair for Water Management and Policy at UC Davis.

“A
very small amount of certain antibiotics do travel into shallow groundwater.
Our next task is to determine whether these particular antibiotics are further
degraded before reaching domestic and public water wells.”

Harter
said the study findings should be particularly useful to people who get
drinking water from wells (such as water companies and homeowners), dairy
producers and policymakers. It provides the first comprehensive data set to
assess and compare potential local impacts to groundwater from the wide variety
of antibiotics in use on “freestall” dairy farms, where cows are free to enter
and leave resting cubicles rather than being confined in stanchions or pens.

California
is the nation’s largest producer of milk and cheese, with 1.8 million milking
cows. More than 90 percent of those are housed in freestall operations.

California
dairies typically administer antibiotics to young cows (calves and heifers,
which are cows that have not had a calf), and to nonlactating adult cows, but
not to lactating, or “milking,” adult cows.

Health
officials are concerned that antibiotics could travel from cows’ urine and
feces into the groundwater that supplies drinking water to people and
livestock, potentially fostering antibiotic resistance in disease-causing
bacteria.

Harter
said the health effects of antibiotics in drinking water at the low levels he
detected are not known.

The
new UC Davis study looked at two large freestall operations in the San Joaquin
Valley, in a region with highly vulnerable groundwater due to its shallow depth
and sandy soils. The two dairies had a total of more than 2,700 milking cows
and 2,500 heifers.

Soil
and water samples were collected from the ground surface under the animals;
surfaces such as flush lanes, which carry waste; manure lagoons, where feces
and urine are collected; farm fields where lagoon contents were spread for
fertilizer; the first 12 inches of soil immediately below the surface of
various sections in the dairy operation; and from groundwater 10 to 30 feet
beneath the animal areas, adjacent to the lagoons, and beneath the manured
fields.

(The
study did not test surface water, such as creeks. Dairies are not permitted to
discharge waste-containing runoff to surface water.)

Harter
and colleagues from UC Davis and the U.S. Geological Survey’s Water Science
Center in California conducted the fieldwork in 2006 to 2008, with analytical
support from the U.S. Geological Survey’s Water Science Center in Kansas. The
research was funded with $568,000 from the CALFED Bay-Delta Authority Drinking
Water Program, which is administered by the California State Water Resources
Control Board, and $65,000 from the California Department of Food and
Agriculture, using funds collected from dairy producers to support research and
marketing.

The
study was published in the online version of Environmental Science &
Technology, a journal of the American Chemical Society.