A study shows that the “mills of nature” also contribute significantly to the global environmental problem of plastic particle pollution: According to this, the rotifers found in water bodies around the world are very effective at converting microplastics into the even more problematic nanoplastics. The results show that a single specimen of these microscopic creatures can produce up to 366,000 such tiny particles in one day. This biological factor should now be incorporated into current research into the extent and consequences of this elusive environmental problem, say the scientists.
It is the ugly hallmark of modern civilization: humanity produces gigantic amounts of plastic products - and when they are no longer needed, they unfortunately often end up in the environment. The problem is that synthetic plastics are hardly biodegradable. Instead, the parts just break down into smaller and smaller pieces until they are referred to as microplastics and, at sizes below one micrometer, finally as nanoplastics.
This does not minimize the problem - on the contrary: the environment is teeming with these artificial particles, they penetrate into the most remote areas of the world and are absorbed by numerous living beings. They have also been detected in human tissue. While the exact significance of this pollution remains unclear, there are concerns that the particles could have complex negative impacts on human health and ecosystems.
In addition to the unclear effects of micro- and nanoplastics, there are still unanswered questions about the educational processes. It is generally known that physical and chemical factors lead to disintegration into smaller and smaller fragments: sunlight wears down plastics and water movements lead to shredding on hard surfaces. The research team led by senior author Baoshan Xing from the University of Massachusetts Amherst has now investigated the possible contribution of living beings.
On the trail of biological fragmentation
Their focus was on the rotifers, which are widespread in the world's seas and fresh waters. The over 2,000 different species of these organisms occur in some bodies of water in sometimes high population densities: one liter of water can accommodate up to 23,000 individual rotifers. At first glance, these 0.1 to 0.5 millimeter small creatures look like tiny “shredder machines”. The rotifers owe their name to the eyelashes they use to feed themselves. However, the actual mechanical unit is the chewing apparatus inside. These are hard structures that allow them to crack the shells of food particles. This led the researchers to suspect that they might also be able to scrape off microplastic particles using this chewing device.
To test this, Xing and his colleagues conducted experiments with various marine and freshwater species of rotifers. They confronted them with microplastic particles that can occur in many places in the environment today. The plastic particles were of sizes that the rotifers can absorb into their chewing and digestive systems. The scientists recorded how they handled the structures and the extent to which they transformed them into smaller fragments through microscopic examinations and by analyzing the excretions.
Crumbled by tiny “bits”.
This showed that all rotifers ingested microplastics with a size of up to ten micrometers and then “chewed” the structures with their hard “teeth”. As the analyzes showed, this led to the release of large amounts of nanoplastic particles. Each rotifer can therefore produce between 348,000 and 366,000 of the particles per day. Using Lake Poyang in China as an example, the calculations showed that the amount of microplastics and rotifers there could be 1.33 times 10 per day16 Particles are created. Looking at the world's seas and waters, the scale of production seems unimaginably large.
“We are now showing for the first time the importance of the ubiquitous fragmentation of microplastics by rotifers,” says Jian Zhao, from the Ocean University of China in Qingdao. “This is a newly discovered source of nanoplastics in both fresh and marine systems worldwide, in addition to the known physical and photochemical fragmentations. This knowledge can now help to assess the global flow of nanoplastics more precisely,” summarizes the researcher.
Xing concludes: “Our work is just the first step. We should now also explore the role of other organisms on land and in water in the biological fragmentation of microplastics. The information can then be incorporated into studies to find out what this nanoplastic plague is doing to us,” says Xing.
Source: University of Massachusetts Amherst, specialist article: Nature Nanotechnology, doi: 10.1038/s41565-023-01534-9