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Why We Shouldn’t Worry About Growing Plants With Recycled Water

Trace amounts of common pharmaceuticals show up in crops grown with recycled water, but not as much as you’d think

(Jim Craigmyle/Corbis)
smithsonian.com

Using recycled water to irrigate crops is becoming a common occurrence in drought-stricken areas of the world, including California. But scientists are still trying to figure out the implications of using water that has passed through human infrastructure (and also humans) on crops. 

Though wastewater goes through several levels of treatments, there are some things that don’t get filtered out, like the remnants of drugs that humans take. The painkillers, caffeine, birth control and other products that we inadvertently flush down the toilet or rinse off in the shower end up in wastewater, where conventional treatment methods do not remove the drugs from the water completely.   

So, what effect does that have on crops? For a new study in the journal Environmental Science and Technology, researchers grew crops like carrots, lettuce, celery and peppers in fields irrigated with treated wastewater. The researchers found that while the vegetables did accumulate commonly occurring pharmaceutical and personal care products (PPCPs)—including antidepressants, DEET, triclosan and caffine—they were present only in very small amounts. 

From the study:  

[T]he accumulation of 19 frequently occurring PPCPs in 8 common vegetables irrigated with tertiary treated wastewater was limited under field conditions, and that human exposure to PPCPs through daily consumption of these PPCP-contaminated vegetables was likely to be small. This finding may help to promote the implementation of agricultural irrigation with disinfected, tertiary treated wastewater in arid and semi-arid regions. The use of treated wastewater in agriculture may further allow the allocation of fresh water for more crucial purposes (e.g., drinking) and concurrently reduce the contamination of aquatic ecosystems from the discharge of treated wastewater into these systems. 

Other studies that have looked specifically at using wastewater to irrigate crops have also found few harmful effects. In a study in 2012, researchers in Israel (which uses recycled water to irrigate over half of its crops) found that contrary to assumptions, using recycled wastewater on crops wasn’t spreading antibiotic-resistant bacteria into the environment. 

That’s good, but it’s hardly the final word.  In 2008, a report by the Associated Press found that there were a wide range of pharmaceuticals found in trace amounts in the drinking water supply of 41 million Americans. As the human population grows, and along with it, the amount of pills and drugs consumed, scientists are taking a close look at how inadvertent ingestion of drugs can effect people and the environment, whether through crops, drinking water, or a combination of the two. 

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