As climate change intensifies droughts and disrupts rainfall patterns, freshwater supplies are becoming increasingly strained in many parts of the world. As a result, some farmers are turning to treated wastewater to irrigate their crops. While this approach helps conserve water resources, it also raises some concerns. Even after treatment, wastewater can contain trace amounts of various substances, including psychoactive medications used to treat mental health conditions.
New research from scientists at Johns Hopkins University examined how irrigating three crops - tomatoes, carrots, and lettuce - with treated wastewater affects plant chemistry.
In the study, which was recently published in the journal Environmental Science and Technology, the researchers grew these crops in controlled conditions and introduced small amounts of four psychoactive pharmaceuticals commonly detected in treated wastewater (carbamazepine, lamotrigine, amitriptyline, and fluoxetine). After several weeks, the scientists investigated different parts of the plants to see where the compounds wound up.
The results show that as water moves through a plant, it carries these substances from roots to stems to leaves. As the water evaporates, the pharmaceutical compounds are left behind, resulting in higher concentrations in the leaves. In fact, tomato leaves contained more than 200 times the concentration of these compounds compared with the tomato fruit. In carrots, the leaves had about seven times the levels found in the edible roots.
The researchers emphasize that these findings should not be interpreted as a health warning, but rather a step toward better understanding how plants distribute chemical compounds that enter through wastewater irrigation.
