One of the main problems with plastic remaining in the ground is its environmental impact. It has been shown that the presence of these particles in the soil has negative effects.
By Virtues Martínez Hernández
United Kingdom, October 27 (TheConversation).- I still remember when I went to the playathe sand was whitish and only the particles that came from more calcareous rocks shone in the light. Today, the beaches have become a chromatic mosaic, where the plastic particles of different tones stand out against the color of the arena.
But he plastic that ends up on the beaches comes from somewhere. It has been estimated that approximately 80 percent of what is found in oceans It comes from land sources, and rivers are its main means of transportation. In the end, most of the plastics are produced, consumed and disposed of tierra firm.
In fact, some models have determined that, in addition to annual plastic emissions to the ocean, the majority of plastic waste (98.5 percent) remains trapped in terrestrial environments, where it accumulates and progressively contaminates continental aquatic ecosystems.
Therefore, solutions to address global plastic pollution lie in better understanding the sources and processes that lead to the release and transport of plastics in the terrestrial environment.
Where does the plastic that ends up in the ocean come from?
Plastics reach rivers through multiple routes. Some sources, such as agricultural and domestic activities, contribute waste to the land that moves with circulating water from precipitation.
In urban environments, plastics reach river systems primarily through discharges from wastewater treatment plants, drainage system overflows during heavy rain events, and transport by wind.
Among the point sources, wastewater has been identified as one of the main ones, despite the action of wastewater treatment plants (WWTP).
WWTPs that have primary treatment – physical removal of large and settleable solids – and secondary treatment – removal of organic matter – are capable of cleaning 75-95 percent of the microplastics identified at the inlet from the water. Most of it is retained in sewage sludge, mainly made up of a mixture of water and organic matter.
Sewage sludge is commonly reused as fertilizer on agricultural soil. Taking into account that wastewater contains a large amount of microplastics and that most of them are retained in the sludge that is subsequently applied to the land, it is likely that a greater volume of microplastics is introduced into the soil than into the water.
Specifically, it is estimated that this practice leads to a total annual contribution of between 63 thousand and 430 thousand tons of microplastics to European agricultural soils.
But it is not only sewage sludge that introduces these contaminants into the soil. Compost, a fertilizer from the decomposition of organic matter, is also an important source during soil fertilization.
Plastics used in agriculture
Furthermore, plastic is a very useful material in the agricultural environment, so there is also a direct entry through its fragmentation. A clear example is mulching, which covers the soil in order to protect it from atmospheric conditions, conserve moisture, etc. Its use has led to an improvement in production (minimizing loss due to water evaporation) and a reduction in the use of chemical herbicides (preventing the entry of light and the growth of competing species).
However, due to the difficulty involved in removing it, remains of the material used accumulate in the soil between crops. In fact, some studies show that the number of microplastics in the soil increases with successive applications.
Plastic is also used in greenhouses, pipe material, chemical product containers, encapsulated fertilizers and other commonly used parts. It is estimated that each year approximately 15 million 600 thousand tons of agricultural plastics are used on European soil.
Finally, we must also take into account the entry of microplastics through atmospheric deposition into the ground, especially in the case of bare soils. The presence of vegetation that intercepts these particles may be the reason why this source has not been identified as the most dominant.
How many microplastics are there in the soil?
Today, it is estimated that globally the contamination of agricultural soil by plastics ranges between one and 4.3 million tons for contributions from wastewater and between 5 and 2.3 million tons for those related to plastic mulch. This represents the presence of an average of 3.6 million tons.
Various environmental aspects condition the mobility of plastics present in the soil, such as the amount and intensity of precipitation, the slope of the terrain, the use and properties of the soil, and the distance to riverbeds. This makes it difficult to make an accurate estimate of the amount of microplastics that reach the river system and subsequently the ocean.
However, recently studies are being carried out that try to estimate the role of soils in the mobility of these particles. The results seem to indicate that, once they reach the ground, most of it remains. Added to this is the low biodegradation capacity of the most common polymers and their constant input.
The above implies that microplastics accumulate in the soil year after year, increasing their concentration, despite the fact that a small part is mobilized. This is the main reason why alternative materials to plastic are being developed that are biodegradable and that reduce their presence in soils in the short-medium term.
The implications
One of the main problems with microplastics remaining in the soil is their environmental impact. It has been shown that the presence of these particles in the soil has negative effects on its structure, changes the activity and functionality of microorganisms, has an influence on soil organisms and affects the growth and development of plants. Furthermore, the consumption of cultivated foods raises the level of concern about its effects on human health.
And it is no longer just that microplastics can harm our health and that of ecosystems. The smaller the particles, the greater the surface area they have together and, therefore, the greater their ability to trap environmental pollutants and release additives.
Plastic additives are the molecules that give it certain properties suitable for its use. When plastic becomes waste and is exposed to environmental conditions, it fragments, and these additives are released through its surface.
Plastic additives encompass numerous categories of chemical compounds, some of them identified as potentially toxic, persistent and mobile, which accentuate the consequences of their massive presence in soils.
Although there is progress in understanding the potential effects of microplastics, additives and other contaminants on human health, there is still a huge information gap in this regard.
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