A team of physicists in Singapore has developed an innovative way of reusing fish scale waste to remove pollution from water - and it can also be used as a material for encrypting information.

The researchers at the National University of Singapore discovered that heating fish scales at an optimal temperature transformed them into bio-adsorbents, suitable for removing the pollutant Rhodamine B from water. Rhodamine B is a pink dye commonly used in textiles, paper, paints and water-flow tracing agents.

The pollutant is associated with potential health risks including cancer and liver failure, and threatens marine ecosystems.

Fish are consumed by people all around the world, and the food processing and aquaculture sectors generate a huge amount of fish scale waste during preparation, including canning, filleting, salting and smoking. Disposal of fish scale waste in landfills can cause serious environmental pollution problems.

The scientists say that converting fish scale waste into functional materials could help reduce environmental impact and generate economic benefits.

They also found that the heat-treated fish scales emitted a vibrant cyan glow, compared to a dim royal blue fluorescence when they were untreated, under ultraviolet (UV) light. This characteristic means fish scales can be used to transmit micro and macroscopic text and imagery.

Professor Sow Chorng Haur, who led the research, said, “As the global population grows and resources become more limited, sustainability involves greater emphasis on reusing waste materials. Globally, an estimated 7.2-12 million tons of fish waste is projected to be discarded yearly.

"This makes fish scale waste an abundant resource for upcycling. By re-evaluating waste streams, fascinating properties and multifunctionalities can be discovered in materials that may have been overlooked previously.”

Multiple purposes

When in contact with Rhodamine B, the heat-treated fish scales effectively removed 91% of the pollutant within a short 10-minute contact time. Fish scales contaminated with Rhodamine B can also be reused through a simple sonication process, enhancing the sustainability of the material.

The fluorescent properties of the heat-treated fish scales under different types of light can be for steganographic purposes. Steganography is a way of hiding data within an ordinary file or message to avoid detection; the data is then extracted at its destination - acting as an extra step for protecting data.

Scales can be heated in bulk on a hotplate and arranged to convey a message, or laser-engraved with text and images on a microscopic scale.

Looking ahead, the research team will look into developing affordable and readily accessible Rhodamine B test kits for use in field detection of pollution. The approach will help minimise the risk of Rhodamine B consumption and exposure by communities relying on natural water bodies, and outfield scientists transporting contaminated water sources.

The findings were published in the journal Nature Communications. Further research is also planned to explore whether the heat-treated fish scales can adsorb other toxic chemicals.