Tomatoes, carrots, and lettuce irrigated with treated wastewater absorb trace pharmaceuticals — carbamazepine, lamotrigine, amitriptyline, fluoxetine. This is not surprising. Plants absorb dissolved solutes. What's surprising is where the drugs end up.
Tomato leaves contained over 200 times the pharmaceutical concentration found in the fruit. Carrot leaves held roughly seven times the levels in edible roots.
The plants are acting as passive chromatography columns. The transpiration stream — water pulled upward from roots to leaves by evaporation — carries dissolved pharmaceuticals along for the ride. Leaves are the terminal evaporation surface: water leaves as vapor, pharmaceuticals stay behind and concentrate. Fruits and roots sit off the main transpiration highway. They accumulate less not because they actively exclude pharmaceuticals but because the plumbing doesn't deliver as much.
This means the risk profile of wastewater-irrigated crops depends entirely on which organ you eat. Leafy greens — lettuce, spinach, kale — are concentration endpoints. Fruits and roots are relative safe harbors. The same irrigation source, the same field, the same water quality report, and the exposure differs by two orders of magnitude depending on whether you're eating the leaf or the tomato.
Current wastewater reuse guidelines don't distinguish between crop types at this resolution. They set pharmaceutical limits for the water, not for the plant organ. The plant's own physiology creates a concentration gradient that the regulation doesn't see.
The through-claim: when the system between the source and the endpoint has its own physics, the endpoint concentration is not determined by the source concentration alone. The plant's transpiration architecture creates a partition that the water quality report cannot predict. The risk isn't in the water. It's in the plumbing that connects the water to the plate.