Plastic is widely used due to its durability, low cost and the possibility of application in many industries. The most frequently used plastic is composed of polymers that are not biodegradable and is therefore extremely persistent in the environment, and a large proportion of it is lost in nature due to improper waste disposal. It is estimated that there are 4900 million tons of plastic waste in the environment. Probably the most widespread type of plastic pollution are microplastics (MP). They are defined as plastic particles with typical dimensions of less than 1 mm. They are an extremely heterogeneous pollutant as they differ in size, colour, specific density and chemical composition. The particles are exposed to various physico chemical factors that cause the so-called aging of MP, causing their properties to change further. In addition, MP are in contact with natural suspended particles and organisms that affect the formation of biofilm on the surface of MP. The biofilm that forms on MP consists of a diverse microbial community of heterotrophs, autotrophs, predators and symbionts, called the “plastisphere”. This community is distinctive for MP and differs from that on natural substrates. The formation of biofilm on the surface of MP affects their vertical movement and long-term distribution in the aquatic environment. In addition, MP become sticky due to the biofilm and the matrix of extracellular polymeric substances, which promotes the formation of heteroaggregates from MP and microbial communities. The formation of aggregates additionally affects the mass of the particle and the resulting sedimentation.
The aim of the master’s thesis was to evaluate the changes in MP properties during their aging in surface water. Pristine MP were exposed to simulated natural conditions with a 12 week incubation in surface water containing naturally occurring microorganisms. Every 2 weeks, we checked the amount of biofilm that developed on MP, the amount of extracellular polymeric substances (EPS), the urease activity and the concentration of chlorophylls a and b. The water was replaced with fresh water every week and analysed (pH, TOC, ammonium ions, nitrite ions, nitrate ions, phosphate ions, chloride ions, number of microorganisms). Finally, we compared the properties of pristine MP and aged MP. We determined the density, the number of particles per mass and the adsorption of metals and observed the particles under an optical and scanning electron microscope. During the experiment, a biofilm developed on the MP which changed the properties of MP; the density of aged MP was higher than that of pristine MP, the number of particles of aged MP was smaller than the number of particles of pristine MP, and the aged MP adsorbed larger amounts of the metal. Therefore, when a biofilm is formed, MP’s properties change and, consequently, their behaviour and distribution in the environment are altered.
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