From: Andy Soos, ENN
Published August 30, 2010 01:41 PM

The Fate of Dairy Antibiotics in Ground Water

There are a lot of things that can go into the ground water. The key is whether what goes in will readily biodegrade and if not can it harm you or the environment. In the first large study to track the fate of a wide range of antibiotics given to dairy cows, University of California (UC) 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. Note that antibiotics are given to sick cows who are isolated from the regular milking herd until the antibiotic is absent from their system.


Dairy cows may be found either in herds on dairy farms where dairy farmers own, manage, care for, and collect milk from them, or on commercial farms. Dairy cow herds range in size from small farms of fewer than five cows to large herds of about 20,000 with the average dairy farm having a few hundred.

Cows get sick just like any other animal or human. Sick cows are no good for milk production and it is not right to let them suffer either. So these cows will be treated with antibiotics.

Health officials are worried that even if the sick cow is not producing milk for production, that the antibiotic will be released to the environment in urine or feces. When this happens, it may be transferred to the ground water and be ingested by others in their drinking water. The antibiotic, if ingested in this way, may cause increased antibiotic resistance in disease causing bacteria.

“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."

Antibiotics are commonly used in food animal production to treat illness, promote growth, and ward off disease. These drugs and their metabolites appear in animal wastes and can eventually enter ground and surface waters following the common practice of applying manure to agricultural fields. Given that low levels of antibiotics can promote the development of microbial drug resistance, their presence in ground and surface waters constitutes an environmental health concern.

This study provides the first comprehensive data set to assess and compare potential local impacts to groundwater from the wide variety of antibiotics in use on dairy farms.

The new UC Davis study looked at two large 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 was published in the online version of Environmental Science & Technology, a journal of the American Chemical Society.

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