Investigation of heavy metal and microplastic effects on algae

The damage caused by heavy metal and microplastic pollution to environmental ecosystems threatens living life, and especially organisms that survive in aquatic ecosystems are more at risk due to the dissolution of heavy metals in water. Since it threatens aquatic ecosystems and reduces photosynthesis capacity, it is likely to create stress conditions especially on microalgae. In this study, the effects of Chlorella vulgaris green algae and Microcystis aeruginosa, Arthrospira platensis blue-green algae on three different heavy metals and their concentrations as a result of exposure to microplastics of different types and diameters were investigated. In the study, OD560 values, chlorophyll-a, suspended solids, cell count, malondialdehyde and hydrogen peroxide amounts were analysed to understand the responses of microalgae to metal and microplastic exposure. In the present study, Chlorella vulgaris, Microcystis aeruginosa and Arthrospira platensis were exposed to heavy metals and different concentrations (0.5-1-2.5-5-10 mg/L) of lead, copper and cadmium heavy metals were selected for Chlorella vulgaris and cadmium heavy metals for Microcystis aeruginosa and Arthrospira platensis. During the experimental period, chlorophyll-a content, OD 560 values showed serious decreases in the culture exposed to metal exposure at the highest concentration (10 mg/L), growth and development of algal cells slowed down and deaths started. Malondialdehyde and hydrogen peroxide amounts were found to be high in the cultures exposed to the highest concentration in the analyses performed due to the high toxic effect. The high amounts of malondialdehyde and hydrogen peroxide can be considered as an indication of the toxic effect and destruction in the cell due to the increase in heavy metal concentrations. In another set of experiments, Chlorella vulgaris green algae was exposed to different concentrations of copper and lead heavy metals (0.5-1-2.5 mg/L) and polypropylene, polyvinylchloride and polystyrene microplastics with diameters smaller than 100 μm. It was determined that heavy metal toxicity and microplastic effect slowed down the growth and development of microalgae cells and caused death. In the culture to which 2.5 mg/L metal and polyvinylchloride microplastics were added, decreases in chlorophyll-a and OD 560 values were determined and increases in the amount of malondialdehyde and hydrogen peroxide formed as a result of enzyme activity of the same culture were determined. In another set, Chlorella vulgaris was exposed to microplastics of different types and diameters. The microplastic type and diameter were selected as polypropylene, polyvinylchloride microplastics below and above 100 μm and 1 μm diameter for polystyrene microplastic. In this time-dependent analysis, when all cultures were compared among themselves, the best chlorophyll-a increase was detected in the culture to which 1μm sized polystyrene microplastic was added. The lowest amount of chlorophyll-a was detected in polyvinylchloride microplastic with a diameter above 100 μm. The amount of hydrogen peroxide and malondialdehyde was found to be consistent with the chlorophyll-a values analysed. A control group consisting of pure culture was formed in all of the sets carried out in the whole study. In conclusion, it is understood that heavy metals and microplastics cause serious damage to aquatic ecosystems and organisms living in these ecosystems. Exposure of organisms living in ecosystems to heavy metal or microplastic pollution and the termination of their vitality will cause the toxic effect to be carried to the upper steps of the food chain.