International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 11 Issue: 06 | Jun 2024
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p-ISSN: 2395-0072
Toxicological impacts of PLA microplastics on freshwater microalgae (Chlorella pyrenoidosa) Assale Malka Kussiaa*, Melkamu Debelo Geletaa aTongji University, College of Environmental Science and Engineering, Shanghai, 200092, P. R. China; a* Tongji University, Shanghai 200092, China.
--------------------------------------------------------------------------***---------------------------------------------------------------------------Abstract - Tiny plastic particles known as microplastics are a major environmental concern due to their wide presence and harmful Impact on aquatic ecosystems. To tackle this issue, efforts have been made to improve waste management, adjust policies, and develop new technologies. One effective solution is to use biodegradable plastics instead of traditional ones, but the environmental impact of these biodegradable microplastics needs further investigation to address potential risks. The investigation focused on studying the toxicological impact of polylactic acid (PLA) microplastics on freshwater microalgae, specifically C. pyrenoidosa. During a 96-hour co-incubation experiment, the effects of various concentrations of PLA microplastics (ranging from 0 to 100 mg/L) on the growth of C. pyrenoidosa were examined. Different concentrations of PLA microplastics had varying effects on the growth of C. pyrenoidosa over the 96-hour period. For instance, a promotion rate of 11.68% and 5.4% was observed at a PLA concentration of 100 mg/L after 72 hours of incubation. Additionally, a growth promotion effect of 5.4% was noted at a concentration of 20 mg/L during the same incubation period. The study also found that Chl-b levels decreased significantly across all incubation periods, particularly at higher concentrations of PLA, with fluctuations observed at different time points. In PLA-treated samples, there were slight increases in Chl-a levels at specific concentrations. The fluorescence efficiency of C. pyrenoidosa samples treated with PLA microplastics was notably lower compared to the control treatment, especially at concentrations of 20 mg/L and 50 mg/L. As PLA concentrations increased, protein content decreased in C. pyrenoidosa. The research highlighted the varied effects of PLA microplastics on the fluorescence efficiency of different microalgae species, with C. pyrenoidosa showing greater susceptibility. The response of nitrate concentration varied, with MDA levels decreasing as PLA microplastic concentrations increased. The diverse reactions observed among different time and concentrations underscore the necessity for further investigation in order to fully comprehend the ecological consequences of biodegradable microplastics in water environments. This highlights the pressing requirement for additional research on the environmental risks associated with biodegradable microplastics in aquatic ecosystems.
Key words: Microplastics, Biodegradable Plastics, Microalgae, Plastic pollution. 1. INTRODUCTION Plastic items are often used in human production and daily activities because of their excellent mechanical properties, light weight, strong durability, and cost-effectiveness.[1]. The most commonly used plastics, such as polyethylene, polypropylene, and polystyrene, are primarily derived from petroleum. These plastics have high molecular weights and strong chemical bonds[2]. Plastic particles originating from petroleum can persist in the environment for many centuries, or even millennia, and are recognized as emerging pollutants that pose a threat to the aquatic ecosystem[3]. Biodegradable plastics derived from sustainable sources such as starch, cellulose, bioethanol, and lignin serve as a viable substitute for conventional petroleumbased plastics[4]. These biodegradable plastics possess the ability to completely decompose into carbon dioxide (CO2) and water (H2O) within specific environments like water, soil, or compost, thereby allowing them to reintegrate into the natural cycle [5]. Polylactic acid (PLA), polybutylene adipate terephthalate, polyhydroxyalkanoates, polycaprolactone, and polybutylene succinate are the most prevalent types of biodegradable plastics. Among these, PLA stands as the most extensively utilized variant, finding applications across diverse industries including waste bags, agricultural coverings, food packaging, medical sutures, and materials for 3D printing. As reported by Zhang et al. (2021), PLA accounts for approximately 45% of the global biodegradable plastics market[6]. This study investigates the impacts of PLA microplastics on the cultivation of Chlorella pyrenoidosa, an extensively studied microalgae species that plays a pivotal role in aquatic ecosystems. Microalgae play a critical role in the global carbon cycle by absorbing carbon dioxide through photosynthesis and converting it into biomass, which supports various trophic levels in
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