Plastics are widely used due to their durability, versatility, and low cost. Until recently, most plastics were made from non-biodegradable polymers, and as a result of improper waste management, a significant portion of these conventional plastics ends up in the environment. Therefore, the use of plastics made from biodegradable polymers has been proposed, but their biodegradation in the environment tends to be very slow. Both conventional and biodegradable plastics can fragment into smaller particles over time due to factors such as ultraviolet radiation, waves, and mechanical abrasion. Among these fragments, microplastics (in size from 1 to 1000 μm) represent one of the most concerning forms of plastic pollution.
Microplastics represent a global environmental problem. They can affect biota and consequently the entire ecosystem directly and indirectly. So far, most research has focused on studying direct impacts on organisms from different trophic levels of the food chain, while indirect impacts, such as the impact on the physicochemical properties of water and sediments and nutrient cycling, have not yet been well studied.
Therefore, the aim of the master's thesis was to study the interactions of conventional and biodegradable microplastics with different nutrients (nitrogen and phosphorous) in the aquatic environment. In addition to pristine microplastics made of low-density polyethylene (LDPE) and polybutylene adipate terephthalate (PBAT) with added starch, we also studied the interactions with biotically aged microplastics. Such microplastics are mostly found in the environment, as upon entering the aquatic ecosystem, they are relatively quickly colonized by various microorganisms, followed by the formation of a biofilm.
As part of the master's thesis, we first developed a biofilm on microplastic surface and assessed the resulting surface changes, as well as the amount of biofilm formed. Then the quantity and strength of binding for various nutrients, namely ammonium nitrogen, nitrites, nitrates and orthophosphate, to both pristine and biotically aged microplastics were evaluated. To further investigate whether nutrient binding involved microbial uptake within the biofilm or rather surface adsorption, we also investigated nutrient interactions with aged microplastics containing either active or deactivated biofilm.
The results showed that larger proportion of nutrients adsorbed on aged microplastics compared to pristine ones. The adsorption was higher on biodegradable microplastics than on conventional ones. Due to polarity, the interactions are most likely of electrostatic nature at first, and over time, the nutrients form complexes, which represent the most common mode of binding. As observed during the adsorption experiments, this binding depends on the type of nutrient, the properties of the microplastic, and the degree of aging.
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