Farmers in many parts of the world struggle with limited freshwater. Because of this shortage, some of them use treated wastewater to irrigate their crops. Treated wastewater is water that has gone through cleaning processes at treatment plants so it can be reused. However, this practice raises concerns among regulators and consumers. Many people worry that chemicals commonly found in wastewater, including medicines used to treat mental health conditions, could enter crops and eventually reach the food people eat.
A new study from researchers at Johns Hopkins University offers helpful details about this issue. Scientists found that some vegetables, such as tomatoes, carrots, and lettuce, can absorb chemicals from wastewater.
Most chemicals remain in the leaves and are typically not present in the parts that humans eat. This finding helps scientists better understand how chemicals travel inside plants. It also shows which parts of crops are more likely to contain higher levels of these chemicals. The study was published in the journal Environmental Science & Technology.It looks at whether treated wastewater is safe for farming. Freshwater is becoming scarce because of drought and climate change. Therefore, using treated wastewater may become more important for agriculture.
According to Daniella Sanchez, a doctoral student involved in the research, agriculture places a large demand on freshwater resources. She explained that with growing water shortages around the world, farmers may have to rely more on treated wastewater in the future. For that reason, scientists need a more profound understanding of how plants interact with the chemical substances that may be present in reused water.
The researchers concentrated on four psychoactive medications frequently found in treated wastewater. These medicines are commonly prescribed for conditions such as depression, bipolar disorder, and epilepsy. The drugs studied were carbamazepine, lamotrigine, amitriptyline, and fluoxetine. These pharmaceuticals can enter wastewater when people take them, and traces of them pass through the body and into the sewage system.
To study how plants absorb these compounds, the researchers grew tomatoes, carrots, and lettuce in a controlled environment. Instead of soil, the plants were given a liquid solution containing purified water, nutrients, salts, and one of the medications. The plants were exposed to this mixture for up to 45 days. During the experiment, scientists collected samples from different plant tissues, including roots, leaves, and fruits.
Using advanced chemical testing methods, the team measured how much of each medication the plants absorbed and where those chemicals ended up inside the plant. They also looked at how the plants changed the drugs by breaking them down into different chemical byproducts.
The results indicated that most of the pharmaceutical compounds collected in the leaves. In tomato plants, the leaves contained more than 200 times the concentration of drugs found in the fruits.
Carrot plants showed a clear difference in where the chemicals collected. The leaves contained about seven times more of the compounds than the roots that people eat. Many chemicals in irrigation water build up mainly in plant leaves, not in fruits or roots.
Scientists say this phenomenon happens because of how water moves in plants. Water enters through the roots and travels up to the leaves. It carries nutrients and other substances with it. In the leaves, water leaves through tiny openings called stomata. When the water evaporates, some chemicals stay in the leaf. Plants cannot easily remove these chemicals. Unlike humans, they do not have a waste system. They are stored in spaces called vacuoles or trapped in the cell walls. Because of this, the chemicals can slowly build up in some parts of the plant over time.
The researchers also saw that different medicines behaved in different ways. For example, lamotrigine was found in minimal amounts in the plants. But carbamazepine appeared in larger amounts. It was even detected in edible parts such as carrot roots and tomato fruits.
One of the researchers, Carsten Prasse, explained that medicines often appear in treated wastewater. However, this does not automatically mean they will harm plants or the people who eat them. He also said scientists should not focus only on the original medicines. They should also study the byproducts that form when these drugs break down. Prasse added that research like this can help identify which compounds need closer study. The findings could help guide possible regulations in the future.
