Vertical distribution, accumulation, and characteristics of microplastics in mangrove sediment in China

Unveiling microplastics pollution in a subtropical rural recreational lake: A novel insight

While global attention has been primarily focused on the occurrence and persistence of microplastics (MP) in urban lakes, relatively little attention has been paid to the problem of MP pollution in rural recreational lakes. This pioneering study aims to shed light on MP size, composition, abundance, spatial distribution, and contributing factors in a rural recreational lake, 'Nikli Lake' in Kishoreganj, Bangladesh. Using density separation, MPs were extracted from 30 water and 30 sediment samples taken from ten different locations in the lake. Subsequent characterization was carried out using a combination of techniques, including a stereomicroscope, Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FE-SEM). The results showed a significant prevalence of MPs in all samples, with an average amount of 109.667 ± 10.892 pieces/kg3 (dw) in the sediment and 98.167 ± 12.849 pieces/m3 in the water. Small MPs (<0.5 mm), fragments and transparent colored particles formed the majority, accounting for 80.2%, 64.5% and 55.3% in water and 78.9%, 66.4% and 64.3% in sediment, respectively. In line with global trends, polypropylene (PP) (53%) and polyethylene (PE) (43%) emerged as the predominant polymers within the MPs. MP contents in water and sediment showed positive correlations with outflow, while they correlated negatively with inflow and lake depth (p > 0.05). Local activities such as the discharge of domestic sewage, fishing waste and agricultural runoff significantly influence the distribution of polypropylene. Assessment of pollution factor, pollution risk index and pollution load index values at the sampling sites confirmed the presence of MPs, with values above 1. This study is a baseline database that provides a comprehensive understanding of MP pollution in the freshwater ecosystem of Bangladesh, particularly in a rural recreational lake. A crucial next step is to explore ecotoxicological mechanisms, legislative measures and future research challenges triggered by MP pollution.

The path of microplastics through the rare biodiversity estuary region of the northern Bay of Bengal

Due to its harmful effects on ecosystems and human health, microplastic (MP) pollution has become a significant environmental problem on a global scale. Although MPs' pollution path and toxic effects on marine habitats have been examined worldwide, the studies are limited to the rare biodiversity estuary region of Hatiya Island from the northern Bay of Bengal. This study aimed to investigate the MP pollution path and its influencing factors in estuarine sediments and water in rare biodiversity Hatiya Island in the northern Bay of Bengal. Sixty water and sediment samples were collected from 10 sampling sites on the Island and analyzed for MPs. The abundance of MPs in sediment ranged from 67 to 143 pieces/kg, while the abundance in water ranged from 24.34 to 59 pieces/m3. The average concentrations of MPs in sediment and water were 110.90 ± 20.62 pieces/kg and 38.77 ± 10.09 pieces/m3, respectively. Most identified MPs from sediment samples were transparent (51%), while about 54.1% of the identified MPs from water samples were colored. The fragment was the most common form of MP in both compartments, with a value of 64.6% in sediment samples and 60.6% in water samples. In sediment and water samples, almost 74% and 80% of MP were <0.5 mm, respectively. Polypropylene (PP) was the most abundant polymer type, accounting for 51% of all identified polymers. The contamination factor, pollution load index, polymer risk score, and pollution risk score values indicated that the study area was moderately polluted with MPs. The spatial distribution patterns and hotspots of MPs echoed profound human pathways. Based on the results, sustainable management strategies and intervention measures were proposed to reduce the pollution level in the ecologically diverse area. This study provides important insights into evaluating estuary ecosystem susceptibility and mitigation policies against persistent MP issues.

Biodegradation of microplastics: Advancement in the strategic approaches towards prevention of its accumulation and harmful effects

Microplastics (MPs) are plastic particles in a size ranging from 1 mm to 5 mm in diameter, and are formed by the breakdown of plastics from different sources. They are emerging environmental pollutants, and pose a great threat to living organisms. Improper disposal, inadequate recycling, and excessive use of plastic led to the accumulation of MP in the environment. The degradation of MP can be done either biotically or abiotically. In view of that, this article discusses the molecular mechanisms that involve bacteria, fungi, and enzymes to degrade the MP polymers as the primary objective. As per as abiotic degradation is concerned, two different modes of MP degradation were discussed in order to justify the effectiveness of biotic degradation. Finally, this review is concluded with the challenges and future perspectives of MP biodegradation based on the existing research gaps. The main objective of this article is to provide the readers with clear insight, and ideas about the recent advancements in MP biodegradation.

Microplastics in mangroves with special reference to Asia: Occurrence, distribution, bioaccumulation and remediation options

Microplastics (MPs) are a new and lesser-known pollutant that has intrigued the interest of scientists all over the world in recent decades. MP (<5mm in size) can enter marine environments such as mangrove forests in a variety of ways, interfering with the health of the environment and organisms. Mangroves are now getting increasingly exposed to microplastic contamination due to their proximity to human activities and their position as critical transitional zones between land and sea. The present study reviews the status of MPs contamination specifically in mangrove ecosystems situated in Asia. Different sources and characteristics of MPs, subsequent deposition of MPs in mangrove water and sediments, bioaccumulation in different organisms are discussed in this context. MP concentrations in sediments and organisms were higher in mangrove forests exposed to fishing, coastal tourism, urban, and industrial wastewater than in pristine areas. The distribution of MPs varies from organism to organism in mangrove ecosystems, and is significantly influenced by their morphometric characteristics, feeding habits, dwelling environment etc. Mangrove plants can accumulate microplastics in their roots, stem and leaves through absorption, adsorption and entrapment helping in reducing abundance of microplastic in the surrounding environment. Several bacterial and fungal species are reported from these mangrove ecosystems, which are capable of degrading MPs. The bioremediation potential of mangrove plants offers an innovative and sustainable approach to mitigate microplastic pollution. Diverse mechanisms of MP biodegradation by mangrove dwelling organisms are discussed in this context. Biotechnological applications can be utilized to explore the genetic potential of the floral and faunal species found in the Asian mangroves. Detailed studies are required to monitor, control, and evaluate MP pollution in sediments and various organisms in mangrove ecosystems in Asia as well as in other parts of the world.

Microplastics leaving a trace in mangrove sediments ever since they were first manufactured: A study from Indonesia mangroves

Mangrove environments have been well recognized as marine litter traps. However, it is unclear whether mangrove sediments sink microplastics more effectively than other marine sediments due to active sedimentation. Furthermore, microplastics archives in mangrove sediments may provide quantitative data on the impact of human activities on environmental pollution throughout history. Microplastic abundance varied markedly between high and low anthropogenic activities. Both mangrove and adjacent mudflats sediments act as microplastic sequesters, despite having similar microplastic abundances and depth profiles. The decreasing trend of microplastics was observed until the sediment layers dated to the first-time plastic was manufactured in Indonesia, in the early 1950s, but microplastics remained present beneath those layers, indicating the downward movements. This discovery highlighted the significance of mangrove sediments as microplastic sinks. More research is needed to understand the mechanisms of microplastic deposition in sediments, as well as their fate and potential impact on mangrove sediment dwellers.

Stable Isotopic and Metagenomic Analyses Reveal Microbial-Mediated Effects of Microplastics on Sulfur Cycling in Coastal Sediments

Microplastics are readily accumulated in coastal sediments, where active sulfur (S) cycling takes place. However, the effects of microplastics on S cycling in coastal sediments and their underlying mechanisms remain poorly understood. In this study, the transformation patterns of different S species in mangrove sediments amended with different microplastics and their associated microbial communities were investigated using stable isotopic analysis and metagenomic sequencing. Biodegradable poly(lactic acid) (PLA) microplastics treatment increased sulfate (SO₄^2-) reduction to yield more acid-volatile S and elementary S, which were subsequently transformed to chromium-reducible S (CRS). The S isotope fractionation between SO₄^2- and CRS in PLA treatment increased by 9.1‰ from days 0 to 20, which was greater than 6.8‰ in the control. In contrast, recalcitrant petroleum-based poly(ethylene terephthalate) (PET) and polyvinyl chloride (PVC) microplastics had less impact on the sulfate reduction, resulting in 7.6 and 7.7‰ of S isotope fractionation between SO₄^2- and CRS from days 0 to 20, respectively. The pronounced S isotope fractionation in PLA treatment was associated with increased relative abundance of Desulfovibrio-related sulfate-reducing bacteria, which contributed a large proportion of the microbial genes responsible for dissimilatory sulfate reduction. Overall, these findings provide insights into the potential impacts of microplastics exposure on the biogeochemical S cycle in coastal sediments.