Where Do Pharmaceuticals Go When Crops Drink Reclaimed Wastewater?

Wastewater reuse in agriculture is no longer a stopgap — it's infrastructure. And the question that keeps surfacing isn't whether reclaimed wastewater carries trace pharmaceuticals (it does, reliably), but where those residues end up once a crop takes them up. That distinction matters more than most coverage of "drugs in your food" implies, and a new study from Johns Hopkins University, published in Environmental Science & Technology, gives a tissue-resolved answer for a class of contaminants — psychoactive pharmaceuticals — that shows up consistently in crops irrigated with wastewater.

The Experiment

Researchers dosed hydroponic growth solutions — a stand-in for irrigation water carrying trace pharmaceuticals — with four psychoactive pharmaceuticals commonly detected downstream of wastewater treatment plants: carbamazepine, lamotrigine, amitriptyline, and fluoxetine. Tomato, carrot, and lettuce plants were grown for up to 45 days, with tissue sampled across roots, stems, leaves, and edible fruit. Sample preparation followed a solid phase extraction step ahead of quantification by liquid chromatography–mass spectrometry (LC-MS), the analytical method needed to resolve both parent compounds and their transformation products at trace concentrations.

That last point matters practically: at the low limits of detection and limits of quantification, these compounds are found in plant matrices, the extraction chemistry is often as decisive as the instrument itself.

The transformation-product tracking is the methodologically interesting part. Most uptake studies stop at the parent molecule. Here, the researchers explicitly mapped where transformation products accumulated — which matters, because a plant's metabolism of a pharmaceutical can produce compounds with different mobility, and potentially different toxicity, than the parent drug.

Why Leaves Become the Sink

The core finding: pharmaceuticals and their transformation products concentrated overwhelmingly across plant tissues in the leaves, not in the edible fruit or root. Tomato leaves carried more than 200 times the pharmaceutical concentration found in the fruit. Carrot leaves ran roughly sevenfold higher than the edible root — the plant leaves consistently acted as the accumulation compartment regardless of species.

The mechanism is transpiration. Water enters through the root system, moves through the plant body, and exits as vapor through stomatal pores in the leaves. Solutes carried along in that water don't evaporate with it — they get left behind at the point of water loss, which is the leaf. From there, the plant has limited options: sequester the compound in the cell wall, or shunt it into a vacuole, the cell's storage compartment for things it can't otherwise process.

That's the mechanistic bottleneck. Plants have no analog to renal clearance. There's no excretory pathway for xenobiotic compounds — once a molecule is deposited in leaf tissue, it accumulates rather than clears. It's a static endpoint, not a transit point.

Not All Compounds Behave the Same Way

The compound-specific data is where this stops being a generic "plants absorb what's in the water" story. Lamotrigine stayed low across every tissue type sampled. Carbamazepine did the opposite — it accumulated at meaningfully higher concentrations across the plant, including in the tissues people actually eat: carrot root, tomato fruit, lettuce leaf.

That's the detail that should inform any environmental risk assessment going forward. Detection of a pharmaceutical anywhere in a plant is not equivalent to detection in the fraction that reaches a plate. The relevant number is tissue-specific, compound-specific, and — based on this data — not predictable from log P or general polarity assumptions alone. Structure-dependent metabolism and transport are doing the work here, and it varies enough between four structurally similar CNS-active drugs that broad-category assumptions about psychoactive pharmaceuticals in wastewater reuse are already too coarse — and the same logic extends to the wider mix of personal care products and other trace pharmaceuticals routinely detected alongside them in reclaimed water. Some of these compound classes, and their transformation products, are also flagged for endocrine disruption potential, which is one more reason parent-compound-only monitoring understates the actual chemical landscape.

What This Means for Reuse Assessment

Under this partitioning model, fruit- and root-bearing crops irrigated with wastewater look more favorable than leafy vegetables, simply because the accumulation compartment (leaf tissue) and the harvested compartment (fruit or root) are physically separate for edible crops like tomato and carrot. Lettuce doesn't get that separation — the accumulation site is the edible tissue.

That's a useful heuristic, but it's bounded by exactly four compounds and by a study period of 45 days in a controlled hydroponic system. Field conditions, longer exposure windows, soil matrix effects, and the much wider library of compounds actually present in municipal wastewater all remain open variables. The authors are explicit that detection doesn't equal harm — the value of this work is in building the exposure map, not closing the risk question.

The unresolved piece is the metabolites. If a transformation product is more persistent, more mobile, or more bioactive than its parent compound, tracking only the parent drug — which is still standard practice in a lot of wastewater-reuse monitoring — misses the relevant hazard entirely. Analytically, that means tissue extraction protocols and LC-MS-based analytical methods for reuse-monitoring programs need to be built around metabolite libraries, not just parent-compound reference standards; gas chromatography-mass spectrometry (GC-MS) can serve as a useful confirmatory technique for select volatile or thermally stable transformation products, though it wasn't part of this particular study's methodology. Any future regulation built on contaminants of emerging concern will need that broader library to be decision-grade.

The Broader Point

This is a demonstration of why compartment-level analysis beats bulk detection every time contamination and food-chain exposure intersect. The same logic applies whether you're tracking pharmaceuticals in irrigated crops, microplastics in seafood tissue, or trace heavy metals in soil-grown produce — the aggregate concentration tells you almost nothing useful. Where the compound goes, and which biological compartment it lands in, is the number that actually drives risk assessment and regulatory decisions. It's also the framing that most contaminants of emerging concern research is converging on: wastewater treatment plants weren't designed to remove trace-level pharmaceuticals in the first place, so the relevant question downstream of the plant is always going to be fate and partitioning, not just presence.

For labs doing this kind of tissue-partitioning work, the analytical bottleneck is rarely the concept — it's reliable extraction, clean matrices, and detection sensitivity at trace concentrations across compartmentalized plant tissue, which is where instrumentation choice and reliable growth-chamber conditions for controlled dosing studies start to matter as much as the liquid chromatography–mass spectrometry method itself. On the monitoring side, utilities and research programs evaluating wastewater quality for reuse decisions are working through a similar problem to the one we covered in ensuring water quality with Water-I.D. — detection alone isn't decision-grade data without knowing where a compound ends up.

It's also worth noting that plants aren't unique in lacking a clean excretion pathway for certain waste products — we looked at a different version of that constraint in how reptiles eliminate nitrogen and salts without liquid excretion. Different biology, same underlying theme: when an organism can't clear a compound, it has to store it somewhere, and that storage location becomes the thing worth measuring.

Need equipment or reagent configurations built around a specific tissue-extraction or trace-detection workflow? MSE Supplies offers customization solutions backed by our PhD technical team. Contact us to talk through your project, or follow us on LinkedIn for ongoing research coverage like this.

Sources:

1. Sanchez, D. a. H., & Prasse, C. (2026). Accumulation and metabolism of Wastewater-Derived psychoactive pharmaceuticals in edible crop plants. Environmental Science & Technology, 60(11), 8722–8733. https://doi.org/10.1021/acs.est.5c14903

2. Wastewater-Irrigated crops store pharmaceuticals in leaves. (n.d.). Tomato News. https://tomatonews.com/wastewater-irrigated-crops-store-pharmaceuticals-in-leaves/