Distribution of microplastics in shoreline water and sediment of the Ganges River Basin to Meghna Estuary in Bangladesh

Assessment and accumulation of microplastics in the Indian riverine systems: Risk assessment and implications of translocation across the water-to-fish continuum

Microplastic (MP) pollution has engulfed global aquatic systems, and the concerns about microplastic translocation and bioaccumulation in fish and other aquatic organisms are now an unpleasant truth. In the past few years, MP pollution in freshwater systems, particularly rivers and subsequently in freshwater organisms, especially in fish, has caught the attention of researchers. Rivers provide livelihood to approximately 40 % of the global population through food and potable water. Hence, assessment of emerging contaminants like microplastics in rivers and the associated fauna is crucial. This study assessed microplastics (MPs) in fish, sediment and freshwater samples across the third largest riverine system of peninsular India, the Mahanadi River. The number concentrations of MPs measured in water, sediment and fish ranged from 337.5 ± 54.4-1333.3 ± 557.2 MPs/m3, 14.7 ± 3.7-69.3 ± 10.1 MPs/kg. Dry weight and 0.4-3.2 MPs/Fish, respectively. Surprisingly, MPs were found in every second fish sample, with a higher MP number in the gut than in the gills. Black and blue coloured filaments with <0.5 mm size were the dominant MPs with polypropylene and polyethylene polymers in abundance. The Polymer Hazard Index (PHI) and the Potential Ecological Risk Index (PERI) studies revealed that the majority of the sampling sites fell in Risk category V (dangerous category). An irregular trend in the MP concentration was observed downstream of the river, though relatively elevated MP concentrations in water and fish samples were observed downstream of the river. t-Distributed Stochastic Neighbour Embedding (t-SNE) unveiled distinct patterns in MP distribution with a higher similarity exhibited in the MPs found in fish gill and gut samples, unlike water and sediment, which shared certain characteristics. The findings in the current study contribute to filling the knowledge gap of MP assessment and accumulation in global freshwater systems and highlight the microplastic contamination and accumulation in fish with its potential implications on human health.

Distribution and risk assessment of microplastics in water, sediment and brine shrimps in a remote salt lake on the Tibetan Plateau, China

Microplastics (MPs) are pervasive environmental contaminants that have infiltrated even the most remote ecosystems. Despite their widespread distribution, the transfer patterns and impacts of MPs in remote lakes remain poorly understood. This study aimed to address the knowledge gap regarding the pathways and consequences of MP pollution in these isolated environments. Focusing on Kyêbxang Co, a remote salt lake in Tibet, this study investigated the transfer patterns, sources and ecological impacts of MPs, providing insights into their mobility and fate in pristine ecosystems. Water, sediment and biota (brine shrimp) samples from Kyêbxang Co, collected during the summer of 2020, were analyzed using µ-Raman spectroscopy to determine MP abundances, polymer types and potential sources. Findings indicated significant MP contamination in all examined media, with concentrations highlighting the role of runoff in transporting MPs to remote locations. The majority of detected MPs were small fragments (<0.5 mm), constituting over 93 %, with polypropylene being the predominant polymer type. The presence of a halocline may slow the descent of MPs, potentially increasing the exposure and ingestion risk to brine shrimp. Despite the currently low ecological risk estimated for MPs, this study underscores the need for long-term monitoring and development of a comprehensive ecological risk assessment model for MPs.

The silent threat of plastics along the coastal frontiers of Bangladesh: Are we concerned enough?

Globally plastic pollution is posing a significant threat to the health and integrity of coastal ecosystems. This study aimed to provide a comprehensive overview of plastic pollution in the coastal areas of Bangladesh by examining land-based macroplastic distribution, exploring microplastic (MP) contamination in the coastal aquatic ecosystem and enhancing our understanding of the potential risks associated with MP contamination. Citizen science based monitoring approach using the android application was applied to understand the land-based plastic pollution in the coastal area of Bangladesh. From December 2022 to December 2023, a total of about 3600 photographs of plastic items from 215 citizen scientists were received from the coastal area of Bangladesh covering 580 km long coast line. Polymer Hazard Index (PHI) and Pollution Load Index (PLI) were also calculated to understand the risk of plastic pollution in sediment, water, aquatic organism, dried fish and sea salt. A total of 43 land-based plastic items reported from the coastal area of Bangladesh. Among these plastic items single use items contributed 58.2 % while disposable plastic items contributed 41.8 %. A strong spatial variability in the distribution of these plastic items was observed. PHI and PLI values suggested hazard category-I for MP contamination in sediment, sea salt, water, commercial fishery resources and dry fish. This study highlighted that coastal land area, sea salt, dried fish, water, sediment and organisms are contaminated with plastics which might have the potential threats to human health. Findings from this study will serve as reference data and also baseline for future research to combat the plastic pollution.

The deciphering of microplastics-derived fluorescent dissolved organic matter in urban lakes, canals, and rivers using parallel factor analysis modeling and mimic experiment

The aim of the study is to investigate the leaching of fluorescent dissolved organic matter (fDOM) from microplastics. In addition, this study identifies the connection between fDOM and microplastics in the aquatic environment. Three-dimensional excitation-emission matrix identified five fluorophores, that is, peak A, M, T, Tuv, and Wuv, and the parallel factor analysis modeling identified five components, that is, tryptophan-like, p-hydroxy acetophenone, humic acid (C-like), detergent-like, and fulvic acid (M-like) in the urban surface water. Mimic experiments using commonly used synthetic plastic (like microplastics) in Mili-Q water under solar radiation and dark environments demonstrate the release of fDOM from plastic. Two fluorophore peaks were observed at Ex/Em = 250/302 nm and Ex/Em = 260/333 nm for the expanded polystyrene plastic polymer and one fluorophore peak at Ex/Em = 260/333 nm for the low-density polyethylene. Fluorophore and component intensity exhibited notable associations with microplastics in the aquatic environment. These findings indicated that the characteristics and dynamics of fDOM in urban surface water are influenced by microplastics. PRACTITIONER POINTS: Fluorescent dissolved organic matters were identified in urban surface waters. Expanded polystyrene (EPS) had shown two fluorophores at Em/Ex = 250/302 and Em/Ex = 260/333. Low-density polyethylene (LDPE) had one fluorophore at Em/Ex = 260/333. Fluorophore and component intensity in the aquatic settings exhibited associations with microplastics.

Effect of tidal current on the settling and accumulation of microplastics in the Chao Phraya River estuary, Thailand

The deposition of MPs in a water column and surface sediment during a mixed spring tidal cycle of the Chao Phraya River estuary was investigated. The settling MPs during flood and ebb tides were collected by deploying traps at 3 m below the surface, while the settled MPs throughout the tidal cycle were collected by deploying traps at 1 m above the bottom. The settling rate of MPs was 2168 pieces/m2/h during highest to low tide, and 639 pieces/m2/h during high to lowest tide. The deposition rate of MPs after the end of the tidal cycle was 3172 pieces/m2/day, while the accumulation rate of MPs in the surface sediment was 1515 pieces/m2/day. The settling MPs tended to decrease inversely to the suspended solids and salinity. The major types of the deposited MPs were polyethylene (36 %) and polyamide (33 %), while that of the surface sediment was epoxy resin (80 %).