Irrigating crops with recycled water can leave dinner salads laced with small amounts of drugs and personal care chemicals. But researchers disagree on whether the contaminated produce is likely to harm people.
In a new study, researchers irrigated eight vegetable crops with treated wastewater that carried 19 drugs and chemicals. These included the antimicrobial triclosan, cholesterol drugs such as gemfibrozil, the anticonvulsant drug carbamazepine and caffeine. All are commonly found in wastewater and are difficult to filter out. Eight of the chemicals made it into the edible portions of the crops, researchers report September 11 in Environmental Science & Technology.
But the researchers, led by environmental chemist Jay Gan of the University of California, Riverside, say the concentrations were so low that that they probably wouldn’t harm people. “I don’t think we should say that we’re totally free of risk,” Gan says. “But the risk should be very small.”
Recycling water is becoming a popular way to conserve. Dry U.S. states such as California reuse treated wastewater for agriculture, as do arid countries such as Israel, Jordan, Peru and Saudi Arabia. But earlier studies, mainly done in indoor labs, have found that plants can take up trace contaminants in the recycled water.
To test typical farm conditions, Gan and colleagues grew eight vegetables, including lettuce, tomatoes, carrots and cucumbers, and watered them with either a standard treatment of recycled water containing 19 common pharmaceutical and personal care compounds or recycled water spiked with extra doses of those chemicals to mimic maximum levels recorded in wastewater elsewhere. The latter represents the worst-case scenario, Gan explains.
At the end of the growing season, eight of the chemicals had made their way into the plants at levels in the range of nanograms per gram of dried produce. These included triclosan, caffeine, carbamazepine and the insect repellent DEET. Of the vegetables grown with spiked water, 91 percent of produce tested contained at least one of the chemicals; 64 percent of the vegetables given recycled water carried at least one.
Using estimates of how much produce U.S. consumers eat, Gan and his colleagues calculated the average yearly dose of the compounds that a person might ingest. Carrots, which contained the highest chemical concentrations, would deliver just over 2 micrograms.
Overall, in a year, a person would eat on average about 3.7 micrograms of the 19 chemicals combined, the researchers estimate. Since common medical doses of a single chemical are at least 1,000 times as high, that amount is probably harmless, Gan says.
But others disagree, saying that medical doses aren’t a relevant comparison. After all, says environmental chemist Benny Chefetz of the Hebrew University of Jerusalem in Rehovot, no one intends “to replace pills with cucumbers.” Medical dosages are designed for sick people, Chefetz says. Researchers should instead assess the risks to healthy adults and children.
In a study in the Aug. 19 Environmental Science & Technology, Chefetz and colleagues did just that and found potential harms. The researchers grew carrots and sweet potatoes in farm conditions irrigated with recycled water. They found chemicals in the plants at levels similar to those found by Gan’s group, but Chefetz and his team calculated exposure risks using thresholds under which compounds are considered to be safe. The researchers reported that children who ate half of a carrot every day would ingest possibly unsafe levels of the anticonvulsant lamotrigine.
Other factors are also troubling, says environmental toxicologist Ryan Prosser of the University of Guelph in Canada. Some of the chemicals can build up in the soil, possibly increasing risks over time. Also, he adds, a consumer isn’t eating just one of the chemicals at a time but rather a cocktail of multiple contaminants. “It’s very difficult to assess the risk of that mixture,” Prosser says.
Still, Prosser sides more with Gan about whether the results raise concern. The concentrations reported are so small that they seem to pose little risk, particularly compared with the levels of some of these compounds in everyday commercial products, he says. “It’s not, in my mind, a concern for human health.”