Study: Vegetables Irrigated With Human Wastewater Can Absorb Drugs

A study of vegetables irrigated with treated human wastewater has revealed that some vegetables may build up drug concentrations that exceed safe exposure levels, according to Chemical and Engineering News.

The study, conducted by soil scientists at Hebrew University, showed that carrots and sweet potatoes in particular can accumulate an anticonvulsant drug and a drug metabolite at potentially unsafe concentrations.

About half of Israel’s agriculture relies on irrigation with treated wastewater, and the practice is gaining ground in Africa, Asia, Mexico and in parts of the US, according to Tomer Malchi, one of the soil scientists who conducted the study. In specific, California is one state that is currently considering recycling wastewater for human consumption.

In addition, the World Health Organization released a study earlier this year warning of the potential problems of irrigating with wastewater.

For the Hebrew University study, Malchi and his colleagues tracked 14 common pharmaceuticals and two metabolites of one drug in irrigation water and then in the edible parts of crops. The scientists grew sweet potatoes and carrots outdoors in plots irrigated with the same treated wastewater used by local farmers from the city of Kiryat Gat, Israel.

The scientists measured concentrations of the compounds in the irrigation water, soil, and plant tissue using liquid chromatography/mass spectrometry. In the two vegetables, the scientists did not detect any drugs except for caffeine and the epilepsy drugs lamotrigine and carbamazepine. However, they also found 10,11-epoxycarbamazepine, a metabolite of carbamazepine.

The scientists then determined the threshold of toxicological concern, a method used by the European Food Safety Authority.

On the basis of the concentrations detected in the vegetables, an adult would have to consume hundreds of kilograms daily of sweet potatoes or carrots from the study to reach the TTC level for caffeine or carbamazepine, Malchi said. For 10,11-epoxycarbamazepine, a child would need to eat 90 grams a day of sweet potato leaves to exceed the TTC level. However, that same child could surpass the TTC level for lamotrigine by eating just half a carrot in one day.

The study is likely the first time that the TTC has been used to assess health risks from pharmaceuticals in food crops, according to Chad A. Kinney, an analytical chemist at Colorado State University, adding that the study also suggests the need to look at metabolites — not just parent compounds — when determining the risks of using treated wastewater in agriculture.

Photo Credit: Tomer Malchi