New tech reveals washing fruits may leave pesticide residues

Scientists in the latest edition of "Nano Letters" highlight that ordinary washing of fruits and vegetables is ineffective in eliminating potentially harmful pesticides on these products.

Pesticides, crucial in plant protection and significantly impact the food economy, can threaten human health if consumed unknowingly. Repeated studies have confirmed that pesticides can risk consumer safety. In "Nano Letters," Chinese scientists note that "Protecting human health therefore requires sensitive analytical methods that can identify even trace amounts of these potentially harmful substances."

These scientists also described an imaging method they developed, which allows for the detection of pesticide contaminants even at very low levels. Initial tests conducted using this method showed that current food safety practices may be insufficient, especially concerning fruits.

The newly developed technology is based on surface-enhanced Raman spectroscopy (SERS). This technique involves placing molecules of a substance on a special metal surface (e.g., gold or silver). When a laser light hits this surface, the metal enhances the signals from the molecules, making it easier to detect and analyse these substances. This allows for the visualization of details that might remain invisible in other tests.

To use SERS's high sensitivity for detecting pesticides, the scientists created a metal-coated membrane that can be placed on agricultural products. Initially, they used a cellulose hydrogel film, which they stretched to create nanoscale wrinkles on its surface. They then immersed the film in a silver nitrate solution to coat the resulting grooves with silver nanoparticles that enhance the SERS signals. The membrane created in this way was extremely flexible and practically transparent in visible light, essential for detecting SERS signals.

In the next step, the scientists proceeded to conduct tests. They sprayed two types of pesticides - thiram and carbendazim - on apples. After air-drying the fruits, they washed them, mimicking the everyday practices most of us use in our kitchens. After this process, they placed the membrane on the fruits.

The test results showed that pesticides were still present on all the tested apples, although in low concentrations. Traces of both thiram and carbendazim were detected, and not only were the fruits' skins contaminated but also the outer layer of their flesh. After apples, the scientists repeated their experiments on cucumbers, rice, and chillies.

According to the researchers, these test results suggest that simply washing fruits and vegetables is not enough to prevent pesticide consumption. They recommend peeling purchased fruits for greater safety.