Naimul Islam (MSc Thesis 2019)

Ecotoxicological Effect of Size of Microplastics Contaminated with Chemical- perfluorooctane sulfonic acid (PFOS) in the Clam Scrobicularia plana.

Microplastics (<5 mm size) are widespread in the marine environment, where organisms uptake and accumulate these tiny particles, presenting subsequent adverse biological responses. Besides, plastic debris may act as a vector of many chemical contaminants which intensify their ecological effects to marine organisms. The ecotoxicity of microplastics influenced by plastic type, size, shape and other chemical properties. In this sense, the present study aimed to assess the bioaccumulation and potential toxicity of different sized microplastic with and without adsorbed chemicals, perfluorooctane sulfonic acid (PFOS). For this purpose, a multibiomarker approach was used, including the analysis of oxidative stress (superoxide dismutase, catalase, glutathione peroxidases and glutathione-S-transferases), neurotoxicity (acetylcholinesterase activity), filtration rate and oxidative damage (lipid peroxidation) in the clam Scrobicularia plana. To mimic the natural environment, exposure aquarium was prepared with sediment to water ratio of 1:3 having continues aeration and routine water change. Clams were exposed to 1 mg L-1 of virgin and PFOS contaminated low-density polyethylene microplastics (LDPE) of two different size, 4-6 μm and 20-25 μm, over 14 days. Bioaccumulation was analysed through fluorescence microscope. Results showed an increase in accumulation of microplastics in clams with exposure time, which varied with particle size (higher accumulation of larger particles) but not the chemical, PFOS. High accumulation of particles significantly reduced the filtration rate at the end of the exposure. Results confirmed the potential generation of reactive oxygen species (ROS) in clams as a result of short-term exposure to both virgin LDPE and contaminated microplastics. Oxidative stress biomarkers showed either induction or inhibition, confirming the disturbance in the antioxidant system Larger microparticles leading to stronger impacts, when compared with smaller particles. Clams exposed to PFOS-contaminated microplastics of both sizes (higher for smaller size) indicated a higher score of the Integrated Biomarker Index (IBR), when compared with virgin LDPE. This short-term experiment confirmed the bioaccumulation and subsequent ecotoxicity of LDPE microplastics with variation in size and chemicals along exposure time. Further research with longer exposure on a variety of marine organisms is required to understand bioavailability of microplastics, adsorption and desorption of chemicals.