Until now, researchers studying microplastic pollution in the world’s oceans have focused on land-based sources, such as discarded plastic bags or water bottles.
Now, a new report appearing in ACS’ Environmental Science & Technology, has linked microplastics in China’s BeibuGulf with heavy fishing activities. Disturbingly, many of the particles were hidden in deep sediments on the ocean floor, which could have led scientists to underestimate the extent of the contamination.
Ghost fishing gear, such as nets, ropes and pots, has long been a known source of ocean plastic waste and of microplastics. However, even during use, tiny particles could be worn away from the fishing equipment used at sea.
In July 2017, Researchers Yinghui Wang and colleagues collected 52 sediment samples from Beibu Gulf and adjacent rivers, a traditional fishing ground of China and the China-Indo peninsula with little industrialisation and urbanisation. They also wanted to look for this type of contamination in deep sediments, up to 2 feet below the surface, which have not been well studied with respect to microplastic pollution.
The sediment samples analysed by the research team were found to be contaminated mainly with polypropylene (PP) or polyethylene (PE) - materials widely used in fishing nets and rope. A strong correlation was observed between the intensity of fishing activities, such as capture fishing or mariculture, and the abundance of PP and PE fibres.
The particles were detected as far down as a foot below the surface, corresponding to about the year 1913, decades before the observed plastics were invented.
The researchers theorised that these could have been transported to deep sediment layers by marine worms. As most previous studies have considered only microplastics in surface sediment, this type of pollution in ocean sediments worldwide could be greatly underestimated, they said.