I have spent years studying how insects interact with chemicals. I know the power of even a small molecule. Just a few micrograms of the wrong chemical in our food can harm our health in profound ways, affecting the nervous system, disrupting hormones, or damaging organs over time. What worries me even more is that Nepal still relies heavily on a method called RBPR (Rapid Bioassay of Pesticide Residue) to test pesticide residues on vegetables and fruits sold in our markets. RBPR is cheap and fast, but it is not precise.
What RBPR Misses
RBPR(Rapid Bioassay of Pesticide Residue) tests work by checking if something in the vegetable blocks an enzyme called acetylcholinesterase, or AChE. AChE is present in nearly all animals, including humans and insects. It acts like a reset button in the nervous system, breaking down signals so that nerves can fire again. Without it, nerve signals pile up and the system malfunctions. Some pesticides work by blocking this enzyme, disrupting nerve function. So the test assumes a harmful pesticide is present when it detects that something is blocking AChE.
But here's the problem. Many natural plant compounds can also block this enzyme. For example, mustard plants (like rayo ko saag) have sharp-tasting oils called glucosinolates that help the plant defend against insects. That pungent taste you get from rayo or mustard greens (like wasabi, if you have ever had it) comes from these natural chemicals. These can confuse the test, making it seem like the vegetable has pesticide residue, even when it does not. That is a false alarm.
The reverse is also true. Many modern pesticides, such as pyrethroids and neonicotinoids, do not block this enzyme at all. Neonicotinoids are the most widely used class of insecticides globally. So even if these chemicals are present in high amounts, the RBPR test might miss them entirely. That limitation can create a false sense of safety.
Incomplete Data, Incomplete Safety
As a scientist, I find this unacceptable. And as a citizen, I find it frightening.
Nepal imports hundreds of metric tons of pesticides every year. In 2023/24, we imported over 1,660 metric tons of active ingredients, a record high.Much of this ends up on the vegetables and fruits we eat. Yet the tools we use to detect it are blind to most of these chemicals. It is like using a thermometer to guess blood pressure, the wrong tool for the job.
Pesticide residues in fruits, veg within permissible limit: Lab...
There have been many news reports where government labs found pesticide residues in produce across markets, from beans and broccoli to bitter gourd, leafy greens, and even mangoes. Some of these batches were destroyed on the spot because the residue levels were too high. These incidents make headlines every few months and paint a clear picture. The pesticide problem is widespread, not occasional.
Farmers Pay The Price
One incident hit me hard. I grew up in Terai, and I have loved mangoes since I was a child. So when I read that officials had destroyed batches of mangoes because of high pesticide residues, I felt it deeply. Mangoes are not just a fruit. They shape our summers, our childhoods, and our culture. I imagined them rotting in waste piles, not because time had spoiled them but because they carried poison. I found that devastating.
The government has set up RBPR labs in at least one location per province, with over ten sites established across the country. These labs only test for pesticide types like organophosphates and carbamates, and cannot detect other common classes of pesticides or fungicides. Crucially, RBPR cannot tell which specific pesticide is present, nor how much of it is in the sample. It only gives a vague yes-or-no answer. While the labs do their best with the tools available, this method is simply not enough.
Think about the farmers who put their energy, money, and trust into growing vegetables and fruits for us. When their produce gets flagged or destroyed based on unclear or unreliable tests, it is not just a loss. It is heartbreaking and unfair. They deserve accurate information to make better decisions, including what to spray, when to harvest, and how to meet safety standards.
Traders and shopkeepers are in the same boat. They are trying to sell what they believe is safe. But if the system cannot explain what the actual problem is, how can they fix it? Policymakers also need solid, trustworthy data if they want to build a system that protects both consumers and producers.
Pesticides Do Not Stop At The Farm
The harm goes beyond human health. Pesticides damage entire ecosystems. These chemicals do not stop working after they kill a pest. They keep moving through the soil, water, and food chain.
They poison the tiny microbes in the soil that help break down nutrients and keep the ground fertile. Over time, this weakens the very base of our farming system. They kill beneficial insects, not just pests. Pollinators like bees and butterflies, essential for many fruits and vegetables, are extremely sensitive to pesticide exposure. Pesticides also wipe out predatory insects like ladybugs, lacewings, and wasps that naturally control pest populations, leaving farmers even more dependent on chemical sprays.
Birds suffer too. Many eat insects, so when pesticide use kills off insect populations or contaminates them, birds lose their food source or ingest poison indirectly. Some pesticides also affect bird reproduction, causing thinning of eggshells or deformities in chicks.
And then there is water. Rain washes pesticide residues from fields into rivers, ponds, and wetlands. Aquatic insects and fish are highly vulnerable. Frogs and other amphibians are especially at risk because their skin absorbs chemicals directly from water.
There Is A Better Way
As a chemical ecologist, I also know that plants have their ways of defending themselves. They produce strong, bitter, or irritating compounds to keep insects away. For example, nicotine in tobacco and caffeine in coffee are not just stimulants for us. They evolved as chemical defenses to protect the plant from being eaten. In Nepal, we have timur (Sichuan pepper), which gives that sharp, numbing zing in pickles. That tingling comes from natural molecules that also deter insects. These plant-made compounds can interfere with the RBPR test and trigger false positives. That is why we need testing methods that can tell the difference between natural plant chemistry and harmful synthetic pesticides.
What we need now is real investment. Chromatography-based techniques like GC-MS (Gas Chromatography-Mass Spectrometry) or LC-MS (Liquid Chromatography-Mass Spectrometry) are the gold standard for detecting chemicals. These methods do not just guess. They separate each compound in a sample and identify precisely what it is and how much of it is there.
Think of it like this. If you squeeze many colors of ink onto a tissue, they might blur together. But chromatography separates each color so you can see what is there. In food testing, it pulls apart all the chemicals in a fruit or vegetable and shows you a detailed fingerprint, compound by compound.
These techniques are powerful because they can detect hundreds of different chemicals, even in tiny amounts. They do not get confused by natural plant compounds like RBPR does. And they give numbers, not just a yes or no. That is important for knowing whether something is just over the safety limit or dangerously high.
Trust Begins With Science
Yes, these machines are expensive and require trained people. But the technology is improving fast. Even smaller, portable devices using similar principles are becoming available. We do not need one in every ward. But we should start with at least one high-quality lab per province. Build capacity. Train scientists. Give our farmers, food sellers, and consumers the tools they need to trust the system.
Nepal must also invest in science. We need more research centers,not just for food safety, but for a broader understanding of what we eat and use. The same chromatography-based tools that detect and quantify pesticide residues can also identify nutrients, active compounds, and possible contaminants in our food, spices, and herbs. Equipped with these tools, labs can analyze what is present in gundruk, timur, besar, or any indigenous food, spice, herb, or so-called "herbal medicine" we consume. Nepal is rich in biodiversity, including a wide variety of medicinal plants, and our research system should be strong enough to explore, understand, and protect this natural wealth.
I understand the appeal of RBPR. It is fast and cheap. But if the results mislead us, what good is it? Testing must lead to trust. Right now, we do not have that. If we want safe food, informed farmers, and trust in our markets, then we need testing systems built on science, not shortcuts.
Because what is at stake is not just data. It is our health, our farmers' trust, and the safety of every bite we take.
The author is a researcher.