The influence of polypropylene- and polyethylene microplastics on the quality of Spirulina sp. harvests

Microplastics are polymer-based materials that require a variety of organic and inorganic chemical additives during the manufacturing process. These chemicals have an impact on aquatic organisms. This study aimed to quantify the impact of microplastics on the growth and quality of microalgae Spirulina sp. We studied the interaction between Spirulina sp. and 500 mg of polyethylene (PE) and polypropylene (PP) microplastics. Three glass bioreactors containing 2 L of Spirulina sp. were observed for 30 days. The first bioreactor was untreated and acted as a control. The second was treated with PE microplastic of 1 mm in size, and the third was treated with similarly sized PP microplastics. Each day, the optical density (OD) was measured to determine the rate of growth of the Spirulina sp. After harvesting, the Spirulina sp. biomass was dried in an oven at 30-35oC for 24 hrs and subsequently analyzed using Fourier transform infrared spectroscopy (FTIR). With PE treatment, the results showed a change in the organic structure on Spirulina sp., as well as a decline of polysaccharides and the loss of one peak at wave number 875.45 cm-1 . Meanwhile, in Spirulina sp. with PP treatment, two peaks that showed polysaccharides at wavelengths of 875.45 cm-1 and 1,245.67 cm-1 were lost. The results also indicated that microplastics had a significant impact on the growth and the quality of Spirulina sp., especially in decreased polysaccharide content.