Page 23 - AWA Vol.42-No3

eduCATION IN AGrICulTure

Tomatoes, Carrots, And lettuce Store Pharmaceutical

Byproducts In Their leaves
The findings suggest some vegetables may be better
candidates for wastewater irrigation than others

In areas where freshwater is scarce, farmers often turn to
treated wastewater to irrigate crops. And many regulators
and consumers worry about exposing food to compounds
routinely found in wastewater, including many psychoactive
medications that treat mental disorders.
But new federally funded research from Johns Hopkins Uni-
versity has found that tomatoes, carrots, and lettuce store
those chemicals in their leaves—good news for tomato and
carrot lovers who eat the fruit and roots of those vegetables,
respectively. The findings could one day help regulators to
know which drugs tend to concentrate in the edible tissues said. Most water travels through the roots, through the body
of plants.
of the plant, and into the leaves. Pharmaceuticals and their
The research, published today in Environmental Science byproducts ride this wave until they hit the leaves, where wa-
and Technology, is part of an effort to explore the safety of ter molecules evaporate through pores called stomata, leav-
using municipal wastewater, most commonly after being fil- ing the drug compounds behind.
tered through treatment facilities, to irrigate crops.
"Plants don't have a well-developed mechanism to excrete
"Farming practices place a high demand on freshwater re- these drug compounds. They can't easily get rid of waste by
sources. With limited rainfall and droughts threatening global peeing, like humans do," Sanchez said.
water supplies, we're looking at a future with shortages that Instead, plants stick the compounds into the cell walls of
may only be met by repurposing treated wastewater," said leaves or in vacuoles, which act as trash bags for cells. Over
Daniella Sanchez, a doctoral student in the Whiting School time, these pharmaceuticals and their byproducts build up
of Engineering and lead author on the study. "To continue to in the plant tissue with nowhere to go, the researchers said.
use wastewater safely, we need a more sophisticated under-
standing of where and how crop species metabolize, or break Additionally, the plants were better at absorbing and metab-
down, agents in the water." olizing certain medications. All plant tissues contained low
concentrations of the epilepsy drug lamotrigine and its by-
Sanchez studied the fate of four psychoactive pharmaceu-
ticals often found in treated wastewater: carbamazepine, la- products. By contrast, carbamazepine accumulated in higher
concentrations across the plant tissues, including the edible
motrigine, amitriptyline, and fluoxetine, which treat depres- carrot roots, tomato fruits, and lettuce leaves. If, in the future,
sion, bipolar disorder, and seizures.
regulators explore risks to human health, it will be helpful to
In a temperature-controlled chamber, the researchers fed know which medications are more likely to build up in the
tomatoes, carrots, and lettuce a liquid growth solution made parts of the plants that people eat, the researchers said.
of ultrapure water, salts, nutrients, and one of the four medi- "Just because these medications are commonly found in
cations for up to 45 days. They sampled different tissues from treated wastewater doesn't mean they'll have any meaning-
each of the plants and used advanced chemical analysis to ful impact on the plant or plant consumer," said co-author
determine how the medications are absorbed by plants, what Carsten Prasse, an associate professor of environmental
byproducts the plants produce from them, and where those
chemical byproducts ultimately end up in the plant. health and engineering at Johns Hopkins who studies envi-
ronmental contaminants and wastewater.
Pharmaceuticals and their byproducts tended to accumu-
late in the leaves. Tomato leaves contained a concentration of Prasse noted that studies like this emphasize the impor-
pharmaceuticals more than 200 times higher than that of their tance of also considering byproducts and not just the origi-
fruits, while the concentrations in carrot leaves were roughly nal drugs when assessing their plant uptake. "Hopefully, this
seven-fold that of the edible roots. But the researchers cau- research will help in identifying which compounds should be
tioned those concentrations are not cause for alarm; they only assessed in more detail in order to support potential future
help to create a map of where the chemical compounds go. regulations," Prasse said.
This research was supported by funding from U.S. EPA Na-
Water, which acts like a superhighway by carrying nutri-
ents and other molecules to various parts of the plant, likely tional Priorities grant R840247.
played a role in moving the drug compounds, the researchers Circle 29 on enquiry card
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