Microplastics in Freshwater Ecosystems and Its Environmental Implications: The Case of the Odaw River in Ghana.

Abstract

In Ghana, escalating plastic waste has amplified microplastic pollution in the environment. The Odaw River in Accra, an urban waterway grappling with sanitation issues, has become increasingly polluted, necessitating and investigation on microplastics in this ecosystem. Despite various pollutant studies in the river, microplastics have been largely unexplored. To address these issues, this study investigates the occurrence of microplastics and their interactions (including mesoplastics) with heavy metals in the Odaw River while assessing the impact of behavior and risk perceptions regarding plastic use. Water and sediment samples were collected from 16 sites along the Odaw River. Samples were then analysed in the lab through various process; digestion, density separation, filtration and identification. Microplastics were examined under a microscope to determine their abundance, types and spatial and temporal distribution. Polymer identification was conducted through Fourier Transform Infrared Spectroscopy (FTIR) analysis, and the ecological risk of these microplastics was assessed using ecological risk indices like the pollution load index and polymer hazard index. To examine the interaction between heavy metals and microplastics, heavy metal concentrations were measured from samples of micro/ mesoplastics and sediment samples collected from seven locations along the river and analyzed for heavy metals using the aqua regia method and Atomic Absorption Spectroscopy (AAS). Ecological Risk indices were also used to assess the level of pollution of the Odaw River with heavy metals. Quantitative and qualitative survey methods were employed to gather data from respondents in four communities along the river. This data aimed to understand their behavior regarding plastic use, plastic waste management, risk perception, and knowledge about microplastics, with questionnaires serving as the primary research instrument. In the study's findings, microplastic particles were found in both water (14 - 56 items per liter) and sediment (12 - 60 items per 50 grams) at all sampling sites along the Odaw River. The highest abundance in MPs in surface water was located at Korle Gonno (Estuary) (55.33 items/l), and that for sediments was at Agbogbloshie (61.00 ±11.17 items/ 50g). The lowest concentrations of MPs were recorded at the source of the Odaw River in Brekusu (Brekusu 2) (14.00 ± 1.89 items/l; 12.00 ± 1.90 items/50g) in water and sediment samples, respectively The concentration of microplastics was more significant during the wet season compared to the dry season. Fiber-shaped microplastics were the most common, making up 73.4% of the samples, with sizes between 1000-3000 μm being the most abundant. Polyethylene was the predominant polymer, accounting for 48% of all particles. Pollution Load Index (PLI) and Polymer Hazard Index scores were remarkably high, particularly downstream. The average concentrations of heavy metals (Pb, Cu, Fe, Zn, Cr, and Hg) in meso/microplastics were higher than in the sediments. Pollution indices like Igeo, CF, and PLI were generally relatively low. The study underscores the importance of considering factors such as behavior, risk perception, plastic waste management, and microplastic knowledge in addressing excessive plastic usage. Respondents were aware of the adverse environmental and health effects of plastics, yet the use of plastics, including single-use plastics, persisted. In essence, addressing the challenges posed by plastic pollution in the Odaw River necessitates a comprehensive strategy that encompasses individual accountability, industry standards, effective monitoring, cooperative initiatives, innovation, regulatory measures, incentives, and heightened consumer awareness. By tackling each of these components, we can collaboratively strive for a future characterized by reduced plastic consumption and a diminished impact of plastic pollution on our environment.