Scientists have discovered where pharmaceutical residues end up inside crop plants when they are exposed to treated wastewater used for irrigation. The new research shows that most of these drug compounds accumulate in the leaves of plants rather than in the parts people usually eat.
The study was conducted by researchers at Johns Hopkins University and published in the journal Environmental Science & Technology. The findings could help scientists better understand the safety of using treated wastewater in agriculture, particularly in regions where freshwater supplies are limited.
Across many parts of the world, farmers are increasingly turning to recycled wastewater to irrigate crops. This practice helps conserve freshwater resources, especially in areas facing drought or water shortages. However, treated wastewater can still contain very small amounts of pharmaceutical chemicals that pass through treatment plants.
These chemicals often come from medications used by people and eventually enter water systems through sewage. Among the most common drugs detected in wastewater are medications used to treat depression, bipolar disorder, and epilepsy.
To understand how crops respond to these substances, the research team led by doctoral student Daniella Sanchez designed a controlled experiment. The scientists grew tomato plants, carrots, and lettuce in a laboratory environment and exposed them to water containing small amounts of four commonly detected medications.
The drugs studied included Carbamazepine, Lamotrigine, Amitriptyline, and Fluoxetine. These medications are widely prescribed to treat conditions such as seizures, depression, and mood disorders.
During the experiment, the plants were grown for up to 45 days while receiving a nutrient solution that contained water, salts, nutrients, and one of the pharmaceuticals. After the growth period, researchers collected samples from different parts of the plants and analyzed them using advanced chemical detection methods.
The results revealed that most pharmaceutical compounds accumulated in the leaves rather than in edible plant parts. Tomato leaves contained more than 200 times the concentration of pharmaceutical residues compared to the tomato fruits. Similarly, carrot leaves had about seven times higher levels of the compounds than the edible carrot roots.
These findings suggest that plants tend to transport and store these chemicals primarily in their leaf tissues. Scientists believe this happens because water moving through the plant carries the compounds upward from the roots toward the leaves.
As water reaches the leaves, some of it evaporates through microscopic openings known as stomata. When this evaporation occurs, the water leaves the plant while many of the chemical molecules remain behind, causing them to accumulate inside leaf tissues.
According to Sanchez, plants do not have an efficient way to remove these chemical substances once they enter their system. Unlike animals or humans, plants cannot easily eliminate waste products. Instead, the compounds often become trapped inside cellular structures such as vacuoles or embedded in plant cell walls.
Over time, this process can cause drug residues and their chemical byproducts to build up inside the leaves.
The study also showed that different pharmaceuticals behave differently inside plants. Some drugs appeared at relatively low levels across plant tissues. For example, lamotrigine and its breakdown products were detected in much smaller concentrations throughout the plants.
In contrast, carbamazepine was more persistent and accumulated at higher levels across several plant parts, including tomato fruits, carrot roots, and lettuce leaves. This suggests that certain pharmaceuticals may move more easily through plant systems than others.
The researchers emphasize that the study does not indicate that eating these crops is harmful. Instead, it provides important scientific information about how plants absorb, process, and store chemical compounds that enter through irrigation water.
Co-author Carsten Prasse, an environmental health and engineering expert at Johns Hopkins University, explained that understanding how plants metabolize pharmaceuticals is important for evaluating future environmental and food safety risks.
Scientists say the research will help regulators identify which chemicals should be studied more closely when evaluating the safety of wastewater irrigation.
The findings may also guide future policies on water reuse in agriculture, which is expected to become increasingly important as climate change and population growth place greater pressure on global freshwater supplies.
As countries search for sustainable ways to manage water resources, studies like this highlight the importance of understanding how modern chemicals interact with food crops and ecosystems.