Wastewater-Irrigated Crops Store Pharmaceuticals in Leaves

As global freshwater supplies face increasing pressure from droughts, the agricultural sector is turning toward treated wastewater as a sustainable alternative for irrigation. A new study from Johns Hopkins University, published in Environmental Science and Technology, provides key insights into how food crops process trace pharmaceuticals found in this recycled water.

The research focused on how common medications—including antidepressants and seizure drugs like carbamazepine and fluoxetine—interact with tomatoes, carrots, and lettuce. The findings suggest that while these plants do absorb the chemicals, they primarily store them in their leaves rather than the parts typically consumed by humans.

The study indicates that the distribution of these compounds is driven by the plant’s natural water transport system. As water moves upward from the roots to the leaves, it eventually evaporates through the stomata (tiny leaf pores). However, the pharmaceutical compounds are left behind.

Because plants lack an excretory system similar to animals, these substances become trapped within leaf cell walls or storage compartments called vacuoles.

The researchers found significant disparities in drug concentrations between the edible and non-edible portions of the plants:

• Tomatoes: Leaf tissue contained over 200 times the concentration of pharmaceutical compounds compared to the fruit.
• Carrots: Concentrations in the leaves were roughly seven times higher than those found in the edible roots.
• Lettuce: As the leaves are the primary edible portion, these plants store the compounds directly in the harvested product, though levels vary by medication.

The research team, led by doctoral student Daniella Sanchez and Associate Professor Carsten Prasse, emphasizes that these findings are not a direct health warning. Instead, the data serves as a map for regulators to understand which compounds pose the highest potential for accumulation.

While most drugs appeared at low levels, carbamazepine (an epilepsy medication) showed a higher tendency to accumulate across all tissues, including tomato fruits and carrot roots.

“To continue to use wastewater safely, we need a more sophisticated understanding of where and how crop species metabolize agents in the water,” Sanchez stated. The study highlights the importance of monitoring not just the original drugs, but the byproducts created as the plants break them down, ensuring that future irrigation regulations are rooted in precise chemical data.

Photo credit: Daniella Sanchez, Johns Hopkins University

Source: Science Daily

Daniella A. H. Sanchez, Carsten Prasse. Accumulation and Metabolism of Wastewater-Derived Psychoactive Pharmaceuticals in Edible Crop Plants. Environmental Science, 2026; DOI: 10.1021/acs.est.5c14903