Research finds big role for crayfish shells in water quality

After researching 300 kilograms of crayfish, Deng Hongbing and his team at Wuhan University created a material from crayfish shells that removes microplastics from water.

Filters made with the material can remove more than 99 percent of microplastics, according to the team. From May to November of this year, their research results were featured in three leading journals, including ACS Nano.

Microplastics, tiny shards of plastic smaller than 5 millimeters, are everywhere in the environment due to human activity. Once absorbed into the food chain, they pose risks to human health.

"They can originate from the fragmentation of larger plastic pieces through heat, abrasion or weathering," said Wu Yang, a member of Deng's team. "They are highly stable, toxic and difficult to degrade, making them a serious environmental issue."

While removing microplastics has become a global priority, traditional wastewater treatments often fail to capture nano-sized particles.

Deng's team turned to an unconventional solution — crayfish shells.

China produces a large amount of shrimp and crayfish shells each year, with most going to waste. By treating crayfish shells with acid and alkali, the team extracted chitin, a compound effective at trapping the shards.

"The treated shells have a natural, multilevel porous structure that resembles a finely woven net," Wu said. "The exposed chitin fibers physically intercept microplastics, including those at the nano-scale."

To collect enough crayfish shells, Deng's team once consumed 100 kg of crayfish in just two days. Over the past two years, they estimate eating around 300 kg. "It's all in the name of science," Deng said.

The team's experiments showed that crayfish shells could adsorb around 70 milligrams of polystyrene, a common plastic, per gram. The material proved effective across different water sources and particle sizes, with their findings published in ACS Nano.

Unlike traditional filtration methods, which often fail to capture nano-sized plastics and risk reintroducing pollutants when materials degrade, the team's chitin-based material offers a sustainable solution.

"The captured plastics are tightly bound to the porous crayfish shells, reducing the risk of secondary pollution," Wu said. The material can also be rinsed and reused multiple times, maintaining its performance over five cycles, while the captured plastics can be recycled.

Due to its low cost and simple production process, Deng believes the material has vast potential applications. "We've even created a water filter prototype, which works exceptionally well — not only for microplastics but also for heavy metals and microorganisms," he said.

Liu Boqianin Guiyang contributed to this story.

Contact the writers at zhoulihua@chinadaily.com.cn