Rotifers break down plastic into nanoplastics
A discarded plastic bottle is naturally broken down into smaller and smaller particles. Especially micro and nanoparticles can be dangerous for living beings. Researchers have found that some aquatic animals produce incredible quantities of such plastic particles.
PPlastic waste in bodies of water crumbles over the years into smaller and smaller pieces that are potentially more dangerous to organisms. The researchers report in the journal “Nature Nanotechnology” that small animals could play a role in this process to a previously unimagined extent. Even a single rotifer can produce more than 350,000 plastic nanoparticles every day. To illustrate the scale: In one lake included in the study, about 23,000 rotifers live in one liter of water.
Plastic waste chopped into tiny pieces is found all over the world, in arctic regions, in the depths of the sea and on mountain tops. Microplastics are particles between one and five micrometers in size, while nanoplastics are particles that measure less than one micrometer.
A smaller size means a relatively larger surface area, which makes nanoparticles more reactive and potentially more harmful to the health of people and other living things, explain researchers led by Jian Zhao of the Ocean University of China in Qingdao. Nanoplastics or the chemical additives they contain may themselves be toxic or carriers of other environmental pollutants.
Rotifers live in fresh and salt water
Fragmentation from micrometer to nanometer size usually takes hundreds of years and relies on processes such as physical wear, chemical reactions, biofouling, heat and solar radiation. Biofouling is the growth of underwater structures, such as microorganisms or algae. However, some species of aquatic zooplankton, i.e. tiny animals, can apparently greatly accelerate this process, as the research team’s laboratory study shows.
Rotifers were used, which are widespread both in the sea and in fresh water and have a strong chewing stomach. Foods such as algae or organic remains are crushed and ground by jaw-like structures made of individual hard parts. Around 2,000 species of rotifers are known in the world. According to the researchers, they live in temperate and tropical areas of the world – and therefore in places where water pollution due to microplastics is particularly high.
Jian Zhao’s team added microplastics of different sizes (5, 10, 20 and 30 micrometers) into containers with different types of rotifers. After some time, the animals were examined under the microscope and water samples were analyzed. The rotifers mainly consumed particles of five to ten micrometers, which corresponds to the size of their algae-based food.
Animals convert microplastics into nanoplastics
Animals apparently often mistake the particles for their actual food source. The researchers explain that many nanosized particles were subsequently observed in the digestive tract. Eventually, the animals expelled the fragmented microplastic; this did not accumulate in their bodies.
Due to their numbers, rotifers produce incredibly large quantities of nanoplastics worldwide. For China’s Poyang Lake, the country’s largest freshwater lake with a surface area of nearly 3,700 square kilometers, the team calculated that rotifers produce more than 13 quadrillion such particles every day. And there are many surface waters with a much higher initial concentration of microplastics than in this lake.
If you extrapolate this to all oceans and inland waters where both microplastics and rotifers are present, the number of nanoplastic particles produced each day is breathtaking. Further analyzes of conversion by other species are now needed to be able to more precisely estimate the extent of conversion of microplastics to nanoplastics by small animals.
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