The fate of farm antibiotics

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  • Published: Sep 20, 2010
  • Author: Steve Down
  • Channels: HPLC
thumbnail image: The fate of farm antibiotics

The wide-ranging prescription of antibiotics has had an unquestionable effect on the health of humans and farm animals alike, but at an environmental cost. The sheer volume of antibiotics taken has led to a marked increase in the amount of parent drugs and their metabolites that are excreted. For humans, wastewater treatment plants remove most of the compounds before the water is released, although increasing levels of antibiotics are being found in waters, so the treatment process is not ideal.

For animal waste from farms, water quality control is more difficult to achieve and there is increasing concern over antibiotics from concentrated animal feeding operations as a source of environmental contamination. Antibiotics are used not only for medicinal purposes, but also to promote growth and productivity.

In the US, for instance, 12,600 metric tons of antibiotics were sold for animal use in 2007, with 13% intended for animal growth and efficiency. The largest concentration of milking cows in the US is in the San Joaquin Valley of California, and this is where a group of scientists have focused their study on the fate of antibiotics in dairy operations.

Thomas Harter and colleagues from the University of California, Davis, and the U.S. Geological Survey examined two farms containing 1450 lactating cows, 1400 heifers and 250 dry cows, and 1340 lactating cows, 1240 heifers and 470 dry cows, respectively. Samples were collected from calf hutches, hospital pens, liquid manure storage lagoons, manure applied fields and corrals. In addition, soil litter, loose soil, wastewater and shallow groundwater were collected over 18 months, covering all of the seasons.

All samples were analysed by liquid chromatography-tandem mass spectrometry following on-line solid-phase extraction for liquid samples or accelerated solvent extraction for solid samples. The antibiotics were measured by multiple reaction monitoring with electrospray ionisation in alternating positive- and negative-ion modes.

There were notable differences between the types and amounts of antibiotics found at each farm. Penicillin, procaine G, monensin and acetylsalicylic acid were the most abundant at each location at several hundred g/day, followed by ampicillin, ceftiofur, sulfonamides and tetracyclines.

Despite their heavy use, the antibiotics were retained within the farm boundaries, not even escaping through the groundwater. Different levels were found at different locations around each site but release into the subsoils and shallow groundwater was minimal.

For instance, in the first farm, all antibiotics were below the detection limits in samples from lactating cow freestall soils and lactating cow exercise yards, even though several were detected in surface samples. Some were detected in soils at low levels in the second farm. The results illustrated the differential mobility of antibiotics in the subsurface and showed that the production areas of dairies could not be discounted as a potential source of antibiotics in groundwater.

Analyses of shallow groundwater from wells near animal production areas confirmed the presence of sulfamethazine, with two other antibiotics sporadically detected.

Still, the calculated total masses of the antibiotics in the different environmental compartments revealed that the amounts in groundwater were small compared to the other areas.

Tetracyclines accumulated mostly in the lagoon sediments and surface layers, whereas sulfonamides were found mainly in the lagoon water.

So, in a well-managed farm, the antibiotics were commonly found in surface soil but did not accumulate extensively in the subsurface. Even after decades of use, they were not generally transported beyond the farm boundaries.

However, the results from this study indicate that samples should be taken from many different areas in the vicinity of a dairy farm to acquire a clear picture of the antibiotic distribution.

The researchers declared that more work should be carried out to determine the effects of the continual presence of antibiotics at the farm surface on the local ecosystem and also to assess airborne concentrations of antibiotics in dust emissions from the farm.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.



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