Rotifers break down plastics into nanoplastics
A discarded plastic bottle is naturally broken down into smaller and smaller particles. Micro and nanoparticles, in particular, can be dangerous to living beings. Researchers have discovered that certain aquatic animals produce incredible amounts of these plastic particles.
PPlastic waste in bodies of water disintegrates over the years into smaller and smaller pieces that are potentially more dangerous to organisms. Researchers report in the journal Nature Nanotechnology that small animals could play a role in this process to a degree previously barely imagined. Even a single rotifer can produce more than 350,000 plastic nanoparticles every day. To illustrate the scale: in a lake included in the study, around 23 thousand rotifers live in one liter of water.
Plastic waste broken down into small pieces can be found all over the world, both in the Arctic regions and in the depths of the sea and on mountain peaks. Microplastics are particles that are about one to five micrometers in size, and 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 beings, explain researchers led by Jian Zhao, from Ocean University of China, in Qingdao. Nanoplastics or the chemical additives they contain can be toxic or transport other pollutants in the environment.
Rotifers live in salt and fresh water
Fragmentation from micrometer to nanometer size generally takes hundreds of years and is based 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, certain species of aquatic zooplankton – tiny animals – can apparently speed up this process immensely, as the research team’s laboratory study shows.
Rotifers were used, which are common in both sea and freshwater and have a strong chewing stomach. Food such as algae or organic remains are crushed and crushed by jaw-like structures made up of individual hard parts. About 2,000 species of rotifers are known worldwide. According to researchers, they live in the temperate and tropical zones of the world – and therefore in places where water pollution with 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 a microscope and water samples were analyzed. The rotifers mainly consumed particles measuring five or ten micrometers – which corresponds to the size of their algal food.
Animals convert microplastics into nanoplastics
Apparently, animals often mistake particles for their true food source. The researchers explain that many nanosized particles were later seen in the digestive tract. Ultimately, the animals excreted the fragmented microplastic; it did not accumulate in their bodies.
Due to their large numbers, rotifers produce incredibly large quantities of nanoplastics around the world. For China’s Poyang Lake, the country’s largest freshwater lake at almost 3,700 square kilometers, the team calculated that rotifers produce more than 13 quadrillion particles of this type every day. And there are many surface waters with a much higher initial concentration of microplastics than in this lake.
If we extrapolate the value to all oceans and inland waters where microplastics and rotifers occur, the number of nanoplastic particles produced every day is impressive. Further analyzes of conversion by other species are now needed in order to more accurately estimate the extent of conversion of microplastics to nanoplastics by small animals.
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