Bangladesh’s southwestern coast, especially Kuakata sea beach, is facing a severe threat from rapidly increasing plastic pollution. A recent study has, for the first time, detected microplastics up to 30 centimeters deep in the beach sediments. Researchers say the main sources are tourism, river-borne plastic waste, and the widespread use of single-use plastics.
Context of the global crisis
Due to the accumulation of plastic waste in both terrestrial and marine environments, plastic pollution has become a global ecological risk. Nearly 450 million tons of plastic are produced each year worldwide, a significant portion of which ends up in the environment. Large plastic wastes fragmented into small particles called microplastics (MPs) through physical and chemical processes, and because of wind and ocean currents, which are now found even in the most remote parts of the planet due to ocean currents and wind transport. Globally, an estimated 6.3 billion tons of plastic garbage have been produced and World Economic Forum has declared that by 2050, plastics will exceed the amount of fish in the oceans. MPs are especially hazardous because of their small size and persistence, which make them more harmful and difficult to eliminate. Bangladesh's southwestern coastal region, especially the Kuakata sea beach, is at high risk of plastic pollution.
A recent study conducted for the first time along the 18 km long Kuakata beach detected the presence of microplastics in beach sediments up to 30 centimeters depth. The research was funded by the Ministry of Science and Technology, Bangladesh under Research and Development Fellowship. The major sources include litter left by tourists, plastic waste transported by rivers, and the widespread use of single-use plastics.
Microplastics were highly persistent in all sediment layers
Sediment samples had been collected from eight locations, considering both tourist and non-tourist places to make comparisons. For sampling, three vertical layers had been considered: layer 1(0-10 cm), layer 2 (10-20 cm), and layer 3(20-30 cm). The percentages of microplastics abundance in the surface, middle, and bottom sediments were close to each other, and there was no significant difference among them. The highest concentration was observed at site S4 in layer 1, and the lowest was in sites S7 and S8 in layer 1 and layer 3 respectively.
Fragment MPs with irregular shapes were dominant in all layers, followed by fiber, microbead, and film. The highest concentration of fragments was observed in site S4 of layer 2 and the lowest was evident in layer 1.
The proportion of colorful MPs including grey, blue, green, red, yellow, and black was greater in all layers (up to 30 cm) compared to white or transparent color. As a single color, grey was the dominant one. The highest percentage of colored MPs was at site S1 of layer 1. The size of MPs ranged from 50 to 2000 μm. Large-sized MPs (>2000µm) were highest in layer 3 compared to layer 1 or layer 2. Cellophane was the dominant polymer, followed by nylon 6,6, polyamide (PA), polyethylene, and polypropylene.
Risk analysis
All the sampling sites were under category 1 of the pollution load index (PLI) for all the layers, which means low level of pollution. Though the highest condition factors (CF) had been observed at site S4 in layer 1. For the pollution hazard index (PHI), layer 1 was under category IV, which means very high hazard.
Factors affecting the vertical distribution of microplastics in sediments
Coastal beaches show dynamic environments characterized by complex hydrodynamic conditions, high biological productivity, and significant anthropogenic influence, including tourism and fishing activities. Investigations into the vertical distribution of microplastics in estuarine and coastal sediment columns have revealed significant heterogeneity, highlighting the complex interplay of physical, chemical, and biological processes that influence their deposition and vertical transport.
Site S4 was the focus point of tourist attraction because it is on the right side of zero point. Whereas site S7 is the mangrove area, and the site S8 is the sunrise point, not so popular to visitors. So, the findings of this result are reasonable. Mainly, tourism-related MPs pollution was indicated by the highest MPs abundance in the S4 site. It was also suggested that MP deposits at beaches with higher concentrations might possibly be influenced by wind-driven marine circulation. The core depth distribution can be attributed to issues like benthic organisms, which can help MPs move vertically.
Fragments of microplastic are easy to locate because of their low mass, which allows them to float on the water's surface and build up in beach sediment. The clothing of visitors, fishing lines, rope, machine filters, and tourism-related activities may also contribute to the greater percentage of fragments and fibers.
It is challenging to comment on MPs' color because bleaching processes, though the highest percentage of grey MPs may be explained by the extensive usage of grey plastic items in the packaging and fishing. Site S1 is another favorite tourist destination, the dry fish market area.
Cellophane is an organic cellulose-based polymer that is a transparent, non-toxic, and tasteless plastic that is often used as a releasing agent in fiberglass rubber production and often appears in food packaging. Kuakata beach is a tourist attraction, as a result of which it has a lot of discarded packaging bags that might be the main source of cellophane. The wide use of cellophane-based products may contribute to its high abundance.
These findings emphasize the complexity of microplastic (MP) dynamics in sedimentary environments and illustrate the influence of site-specific factors such as sedimentation rates, bioturbation, and hydrodynamic mixing. MPs typically undergo degradation through a combination of physical abrasion, photodegradation due to sunlight exposure, and biological interactions, leading to their fragmentation into smaller particles and often resulting in visible colour changes. The findings of this study suggest that the extent of weathering in these deeper layers is limited, resulting a higher proportion of larger MPs with varying colours. Additionally, biological activity tends to decrease with depth, further limiting the biodegradation of buried MPs.
Potential sustainable solution through innovation
MPs act as a unique substrate for microbial attachment due to the presence of organic compounds and enzymatic functions of microorganisms, leading to hydrolysis or oxidation-reduction reactions. To combat this growing crisis, scientists are turning to microbial solutions. Research is underway to isolate plastic-degrading bacteria from coastal plastic waste. These bacteria form biofilms on plastic surfaces and secrete enzymes that break down plastic polymers. Bacteria such as Pseudomonas, Bacillus, Rhizopus, and Ideonella sakaiensis have already shown promising ability to degrade polyethylene and polystyrene plastics. Researchers believe these bacteria can play a vital role in future eco-friendly waste management. This natural degradation process can reduce pollution without harming the environment.
Coastal beaches are dynamic environments characterized by complex hydrodynamic conditions, high biological productivity, and significant anthropogenic influence, including tourism and fishing activities. Kuakata, a prominent coastal tourist destination, generates approximately 323 kg of non-biodegradable plastic waste daily. I investigated the “Horizontal and vertical distribution of MPs along the coastline of Kuakata”. Such studies can serve as sustainable models not only for Bangladesh’s coasts but for the entire world to calculate abundance, characterize MPs, and identify their sources. In an era of rapid development and technological growth, finding scientifically sound and effective sustainable solutions for environmental protection is more urgent than ever.