Microplastics, tiny pieces of plastic less than 5 millimeters in length, are a growing environmental concern due to their persistence and potential harmful effects on wildlife and human health. While much research has focused on the smooth, spherical microplastics, a new study by researchers at Heriot-Watt University in Edinburgh, United Kingdom, and the University of California, Santa Barbara, has found that rough, irregularly shaped microplastics can be even more harmful to marine life.

The study, published in the journal Environmental Science & Technology, exposed water fleas, a type of small crustacean, to different types of microplastics, including smooth and rough particles, as well as fibers. The researchers found that the rough microplastics caused significantly more damage to the water fleas' digestive systems and reduced their reproduction rates.

"Our study shows that the shape and surface roughness of microplastics can have a significant impact on their toxicity to aquatic organisms," said lead author Dr. Laura Sadofsky, a research associate at Heriot-Watt University. "Rough microplastics may cause more damage because they can puncture or abrade the tissues of organisms, while smooth microplastics are more likely to be passed through the digestive system."

The researchers also found that the water fleas were more likely to ingest rough microplastics than smooth microplastics, which suggests that they may be more easily mistaken for food. This could lead to a greater accumulation of microplastics in the food chain and potentially harmful effects on higher trophic levels, including fish, birds, and marine mammals.

"Our findings highlight the need to consider the shape and surface roughness of microplastics when assessing their potential risks to marine life," said co-author Dr. Matthew Cole, a professor at Heriot-Watt University. "Rough microplastics may pose a greater risk than smooth microplastics, and this should be taken into account when developing policies to reduce microplastic pollution."

The study adds to the growing body of evidence on the harmful effects of microplastics on aquatic organisms. Further research is needed to understand the long-term effects of microplastics on marine life and to develop effective strategies to reduce microplastic pollution.