In regions where freshwater is scarce, farmers sometimes use treated wastewater to irrigate their fields. This approach helps conserve water resources, but it raises concerns among regulators and consumers due to the possible presence of trace amounts of various substances in the wastewater, including psychoactive drugs used to treat mental health disorders.

Study of Substance Accumulation in Plants

A recent study conducted at Johns Hopkins University found that certain crops, such as tomatoes, carrots, and lettuce, can accumulate chemical compounds primarily in their leaves. This is important for consumers, as typically the edible parts are fruits and roots, not leaves. The research, published in the journal Environmental Science and Technology, is part of a broader investigation into the safety of using treated municipal wastewater for irrigating crops. In most cases, such water undergoes preliminary treatment at specialized facilities.

How Plants Absorb Pharmaceuticals

The experiment examined four psychoactive drugs commonly found in treated wastewater: carbamazepine, lamotrigine, amitriptyline, and fluoxetine. These medications are used to treat depression, bipolar disorder, and epilepsy. To study their interaction with plants, tomatoes, carrots, and lettuce were grown under controlled conditions using a nutrient solution containing one of the drugs for 45 days. Afterwards, various plant parts were analyzed using advanced chemical methods to determine the distribution and accumulation of the drugs and their breakdown products.

Concentration of Substances in Leaves

The results showed that the drugs and their metabolites mainly accumulated in the leaves. In tomato leaves, the concentration of these compounds was more than 200 times higher than in the fruits, while in carrot leaves it was about seven times higher than in the edible roots.

Mechanisms of Movement and Accumulation

The movement of water through the plant explains this pattern: water carries nutrients and other molecules from the roots up the stem to the leaves, where it evaporates through the stomata. The remaining compounds become concentrated in the leaf tissues. Plants lack developed mechanisms to eliminate such substances, so they can accumulate inside cells, including in cell walls and vacuoles.

Differences Between Drugs

The study also revealed that different drugs are absorbed by plants in different ways. For example, lamotrigine and its breakdown products were found at relatively low concentrations in all plant parts, while carbamazepine accumulated at higher levels, including in edible parts such as carrot roots, tomato fruits, and lettuce leaves.

Implications for Regulation

The study's findings help us better understand how plants distribute chemical compounds absorbed from irrigation water. Identifying drugs that tend to accumulate in edible plant parts can be useful for assessing potential health risks and developing future regulatory standards. The research also highlights the importance of studying not only the original drugs but also their breakdown products in plants.