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Updated 11 September 2013

Recycled wastewater safe for crop irrigation

Recycled sewage water can safely be used for crop irrigation, according to new research.

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In what's thought to be the first study conducted under realistic field conditions, researchers found that crops irrigated with the water discharged from sewage treatment plants contains only low levels of prescription drugs and ingredients commonly found in antibacterial soaps, make-up, shampoos and other personal care products.

"The levels of pharmaceuticals and personal care products that we found in food crops growing under real-world conditions were quite low and most likely do not pose any health concern," study leader Jay Gan, from the University of California-Riverside, said in a news release from the American Chemical Society.

"I think this is good news. These substances do not tend to accumulate in vegetables, including tomatoes and lettuce that people often eat raw. We can use that information to promote the use of this treated wastewater for irrigation," Gan said.

Recycled water often safe

Water flushed down toilets or drained in sinks enters sewage treatment plants and is processed to remove contaminants and disease-causing microbes. Although this treated water is considered safe enough to drink, it's typically released into rivers and streams as it may still contain traces of the ingredients found in medications and personal care products.

In the southwestern United States and other parts of the world that face droughts or water shortages, however, recycled sewage water is the only way to irrigate food crops.

To address concerns about the health and environmental effects of using treated sewage water for crop irrigation, the researchers examined 20 different pharmaceuticals and personal care products under realistic field conditions to determine if they could accumulate to potentially dangerous levels in a number of foods, including carrots, bell peppers, tomatoes, cucumbers, lettuce, spinach, celery and cabbage. The researchers specifically chose foods that are often eaten raw, because cooking can destroy certain contaminants.

Although all the crops absorbed the ingredients from medications and personal care products -- such as an epilepsy medication, the antibacterial agent triclosan, a tranquiliser and caffeine -- the levels of these contaminants were "reassuringly low," the investigators found.

The study revealed, however, that leafy vegetables absorbed the highest levels of contaminants. The researchers also noted that young children, older people and those with chronic diseases may be more susceptible to even low levels of these trace ingredients from drugs and personal care products.

Although the United States only recycles about 2% to 3% of its wastewater, predicted water shortages could substantially increase the use of recycled sewage water around the world, the researchers say.

The study was scheduled to be presented  at the American Chemical Society meeting in Indianapolis. The data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

The U.S. Environmental Protection Agency has more about crop irrigation.

 
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