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Rivers and microplastics. “Objects with a very large surface area and low mass will be most susceptible to fragmentation.”

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According to the latest research, the largest amounts of microplastics are produced in rivers. – As long as we see garbage, we can remove it from the river relatively cheaply and easily. Once they turn into microplastics, the potential to remove them from the environment drops dramatically – commented one of the authors of the work, Dr. Maciej Liro from the Institute of Nature Conservation of the Polish Academy of Sciences in Krakow.

A model of the transformation of plastic garbage thrown into rivers into toxic microplastics shows that disposable polystyrene dishes, fragments of Styrofoam and pieces of foil will disintegrate the fastest. The rate of microplastic formation also depends on the climate, energy of water flow and the presence of plants.

The fragmentation of plastic garbage present in the river and the formation of microplastics from them was developed in the form of a model by Dr. Maciej Liro from the Institute of Nature Conservation of the Polish Academy of Sciences in Krakow and PhD student Anna Zielonka from the Institute of Geography and Spatial Management of the Jagiellonian University, and Dr. Tim HM van Emmerik from the University of Wageningen in the Netherlands – a world expert in the field of macroplastic pollution of rivers.

Plastic type, shape and surface

Scientists analyzed the results of experiments described in the literature. In the publication entitled “Fragmentation of macroplastics in rivers” determined when rivers are the most efficient factories of toxic microparticles.

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– Internal and external factors influence the formation of microplastics in the river. The former result from the shape and type of plastic from which macroplastics that fall into the river are made of. The second one depends on how the river flows, what the climate is like and what its bed looks like – explained Dr. Liro.

Garbage made of various types of polystyrene, such as food trays, white forks and cups, and pieces of Styrofoam, turn into microplastics the fastest. Unfortunately, this garbage is quite common in riverside areas.

It is not only the type of polymer that matters, but also the shape of the plastic waste. – The ratio of its surface to mass is important. Objects with a very large surface area and low mass, such as pieces of foil, will be most susceptible to fragmentation, Liro explained.

Water influence

The energy of water flow, the depth of the river and obstacles in the river bed influence the intensity of mechanical interactions of garbage with water and the river bottom. The type and depth of the river also influence the crumbling and fragmentation of macroplastics into smaller fragments.

– In constantly flowing rivers, and there are the largest number of such rivers in Poland, stimuli causing fragmentation occur all the time, with greater or lesser intensity throughout the year. During a flood, when the energy of the flow is several hundred or even several thousand times higher, the plastic will undergo faster mechanical fragmentation – explained the expert.

Fragmentation of macroplastics will be slightly different in periodically flowing rivers. Here, the entire riverbed zone may favor both mechanical fragmentation, caused by the flow of water and debris, and biochemical fragmentation, caused by, among others, by UV radiation.

Dr. Liro added that the hydromorphology of the river changes from section to section. That is, not only is the river uneven, but also a section of the river. Unvegetated riverbed banks, due to the availability of UV radiation and oxygen, create favorable conditions for biochemical fragmentation. Dense plant cover can limit the inflow of ultraviolet radiation (light), then less microplastics are produced in the river.

– In this work, for the first time, we noticed two things. First of all, when it comes to fragmentation, plastic is uneven. This means that different plastic trash can produce drastically different amounts of macroplastics in the river. Secondly, the type of river is an extremely important variable modifying the pace of this process. With this theoretical foundation in place, we can now formulate detailed hypotheses for field experiments with much greater precision. These, in turn, will show quantitatively – to what extent, for example, the shape of marcoplastic or the type of polymer from which it is made will increase or decrease the rate of microplastic formation in a specific river – concluded Dr. Liro.

Like a carbon footprint

Once scientists determine how much microplastic is produced from a specific type of garbage, they will be able to estimate the microplastic footprint, analogous to the carbon footprint.

– Such information obtained in field experiments could, for example, be placed on products – for example on a plastic bag in the form: “if you throw this bag into the river, it will produce 100,000 microplastic particles that will circulate in the environment for many years” – proposed the scientist .

Most microplastics in rivers are made from macroplastics, which are visible to the naked eye. – As long as we see garbage, we can remove it from the river relatively cheaply and easily. Once they turn into microplastics, the potential to remove them from the environment drops dramatically, but the cost increases, he concluded, recommending actions aimed at cleaning rivers.

Main photo source: 498456966/Adobe Stock

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