Investigation of the effect of microplastic concentration on cionababacteria density

In recent years, plastic has become an integral part of daily life. Millions of tons of plastic materials are produced worldwide every year. Due to the widespread application of plastic in many different sectors and its long-lasting properties, the amount of plastic garbage has increased significantly in recent times, and today plastic pollution is considered one of the most problematic issues related to the environment. When plastics are broken down in various ways and come to smaller sizes, they are called microplastics. In recent years, it is known that microplastics are frequently seen in sea, fresh water resources, land and organisms. Plastic pollution in a broad sense; It can be stated as the accumulation of plastic wastes left to nature by humans, on land and in the seas. Plastics have diversified so much with the advancement of science, pollutants that are difficult to filter as part of people's daily life. In our society, the land is polluted first, as people throw their garbage into the environment uncontrollably and use plastic excessively. The plastic wastes formed are naturally transported from the land to the aquatic environment over time. During this event, plastics break down into smaller pieces in size, forming plastics microplastics. The term microplastic was first used in 2004 by Thompson et al. was used to describe the abundance of microscopic plastic debris observed in marine environments. These substances, defined as microplastics, are plastic particles ranging in size from 1μm to 5mm, and they are present in all ecosystems and have reached everywhere from urban areas to freshwater regions, from the open seas to the great oceans. Terrestrial ecosystems play an important role in the transport of microplastics to aquatic ecosystems. Microplastics can occur in the terrestrial environment with the effect of ultraviolet rays or natural effects such as water, air, wind and sun. The first studies in this area were made in aquatic ecosystems, and microplastics are considered as serious aquatic environment pollutants. Microplastics with a density greater than water may show accumulation in the sediment. Surface microplastics in the waters may become biologically contaminated over time, absorb other pollutants, and increase in density and collapse. Microplastics that settle to the bottom can be repeatedly raised and transported to the aquatic environment by the movements of water and aquatic organisms. Microplastics are an effective pollutant for living things in the aquatic environment and pose a danger to cyanobacteria. The presence of microplastics in the aquatic ecosystem causes cyanobacteria to gradually decrease in their chlorophyll content and photosynthesis activity. The most important symptom of cyanobacteria and their toxins is organic contamination and eutrophication. Eutrophication prepares the environment for deterioration of water quality, formation and proliferation of cyanobacteria. Excessive algal growth and eutrophication cause pollution in the aquatic ecosystem, endanger usable water resources, and pose a great threat to aquatic organisms and humans. The first studies in this area were made in aquatic ecosystems, and microplastics are considered as serious pollutants of the aquatic environment. Microplastics with a density higher than water may accumulate in the sediment. Surface microplastics in waters can become biocontaminated over time, absorb other pollutants, increase in density and precipitate. Microplastics that settle to the bottom can be transported to the aquatic environment by rising repeatedly with the movements of water and aquatic organisms. In the study, polypropylene, polyvinyl chloride, polystyrene microplastics in different sizes; The effects of a single application on various cyanobacteria species such as Microcystis aeruginosa, Arthrospira platensis, and Synechocystis sp will be investigated. In this thesis, spectrophotometric cell densities, biomass amounts, chlorophyll-a amounts, and microscopic cell counts of cyanobacteria will be made and Malondealdehyde (MDA) and Hydrogen peroxide (H2O2) enzymes will be analyzed. The mode of action of microplastics against microalgae is very complex. Considering that a typical algal cell wall pore size is < 20 nm (smaller than most single microplastics), two interaction effects can be pointed out between these organisms and microplastics. The first is that microplastics can affect microalgae through their cell walls or cause membrane damage after direct contact, which may eventually lead to cytotoxic effects (Zhang et al., 2017; Liu et al., 2019), and the other effect is the shading effect of microplastics in the water column (access to light). These are the effects of being able to affect microalgae through a reduction in photosynthesis (Bhattacharya et al., 2010; Liu et al., 2019; Wang et al., 2020). Microplastics can also physically damage algal cells by increasing osmotic pressure and altering biocomponent compositions (including carbohydrate, lipid, and protein levels) (Manzi et al.,2022). Toxicity of microplastic to microalgae; It depends on many variables such as the type and size of microplastics, surface properties, concentrations and exposure time of microalgae to microplastics. During the presented 15-day study, reduction in cell density of Microcystis aeruginosa, Synechocystis sp and Arthrospiraplatensis algae greater than 100 µm in polyvinylchloride and polypropylene microplastics, reduction in cell density of less than 100 µm in polyvinylchloride and polypropylene microplastics, and polypropylene microplastics in 1 µm. not observed. It was observed that the cell density and optical density progressed in direct proportion in each experimental group. While a certain increase in the amount of chlorophyll-a was observed for each cyanobacterial culture in PP and PVC types with microplastic size less than 100 µm, a higher increase was observed in polystyrene with 1 µm size compared to other small size microplastics. This result shows us that photosynthesis may be adversely affected as the microplastic size increases in cyanobacteria. Toxicity of microplastic to microalgae; It depends on many variables such as the type and size of microplastics, surface properties, concentrations and exposure time of microalgae to microplastics. In our study, it was observed that chlorophyll-a values, cell density and cell numbers and AKM amounts were affected in different degrees in all three cyanobacteria species.