An overview – Fate and analysis of marine microplastics with insights into microfluidics, biofilms, and future ecological threats.

examine and analyze the available data using various established scientific parameters (Oberbeckmann et al. 2015). This paper aims to first understand the sources and transport pathways of microplastics into aquatic ecosystems such as lakes, rivers, estuaries, seas, and oceans. Once these waterways are contaminated, it is crucial to separate microplastics from other pollutants for further detection and analysis. This paper will address this issue by highlighting “Microfluidics” – a novel technique for the detection of microplastics. This paper also focuses on the biological degradation of microplastics via biofilm formation caused by characteristic microorganisms in water bodies. The types of marine bacteria and the mechanism of biofilm formation will be discussed in detail. Additionally, it is important to examine


Introduction
The first advanced plastic, Bakelite, was created in 1907.Since then, numerous cost-effective procedures have been developed for the mass production of abundant plastic polymers, which are used in various day-to-day applications.Plastics possess desirable properties such as long durability, resistance to corrosion, non-reactivity with materials, and low cost, which make them one of the most highly demanded products in the world.In 2009, it was noted that about 230 million tonnes of plastic were produced globally, accounting for approximately 8% of global oil production (Verma et al. 2016).
Plastics, after being discarded, take a significantly longer time to decompose or degrade, causing threats to ecology and environmental contamination.As a result of recent responsiveness and global concern, attempts are being made to reduce, reuse, and recycle the plastics that are used.Although these efforts seem to be succeeding for a fraction of disposed plastics, the remaining waste either goes into landfills or enters water ecosystems via multiple pathways (Lange 2021).The formation of microplastics and nanoplastics arises from the breakdown of larger plastic fragments through diverse physical, chemical, and biological processes.Plastics can decompose or degrade through a range of mechanisms, including biotic (caused by the activity of living organisms), abiotic (resulting from non-living processes), photodegradation (caused by exposure to light), thermal (induced by heat), and mechanical means (resulting from physical forces) (Dimassi et al. 2022) it takes into account the leachability of the various chemical substances (additives.In recent decades, environmental researchers have been motivated to explore micro-sized contaminants, their effects, and their fate in marine, terrestrial, and atmospheric ecosystems.Recently, microplastics, consisting of minute fragments, plastic granules, and fibers, have been classified as pollutants.The sizes of these micropollutants range from 1mm to 10 mm, but various researchers have attempted to classify them differently, such as less than 1mm, 2mm, or 2 to 6mm (Abdel-Aziz 2014a).The lack of clarity in terms of size and categorization presents a significant challenge when attempting to examine and analyze the available data using various established scientific parameters (Oberbeckmann et al. 2015).
This paper aims to first understand the sources and transport pathways of microplastics into aquatic ecosystems such as lakes, rivers, estuaries, seas, and oceans.Once these waterways are contaminated, it is crucial to separate microplastics from other pollutants for further detection and analysis.This paper will address this issue by highlighting "Microfluidics" -a novel technique for the detection of microplastics.This paper also focuses on the biological degradation of microplastics via biofilm formation caused by characteristic microorganisms in water bodies.The types of marine bacteria and the mechanism of biofilm formation will be discussed in detail.Additionally, it is important to examine the drawbacks associated with microplastic contamination and explore solutions for improving living standards and achieving a healthier environmental equilibrium.Therefore, this paper will suggest effective strategies to minimize microplastic contamination and control existing pollution conditions.

Microplastic degradation in aquatic ecosystems
Microplastic contamination can occur in both groundwater and surface water sources, making it a complicated and tedious task to trace their origin and transport mechanisms in our environment.This complexity arises because little is understood about the methods that control their transmissions within aquatic habitats.Some of the primary factors affecting their distribution and transport include the inherent physical and chemical properties, such as shape, size, density, chemical structure, and composition.Plastics are used in a diverse array of applications, and their decomposition mechanisms and subsequent pathways of transport in aquatic environments exhibit considerable variation.Moreover, there are limited methods to trace the origins and distribution of microplastics, as plastic handling and disposal protocols vary across different regions of the world.Naturally, higher amounts of plastics are used in heavily inhabited metropolitan areas, leading to more traces of microplastics observed there.
As mentioned earlier, the process of microplastic degradation can occur primarily through various abiotic and biotic mechanisms, a schematic representation of which is given in Fig 1 .Numerous researchers have investigated the decomposition and breakdown of plastics to comprehend the underlying mechanisms and modifications in polymer properties over time.The subsequent paragraphs will provide a comprehensive elucidation of the major pathways of degradation.

Abiotic degradation of microplastics
Microplastics are generally non-biodegradable in nature, as structurally plastics are complex polymers that take a lot of time to degrade naturally in the environment (Klein et al. 2018) so-called microplastics (particle size, 1-5,000 μm.Abiotic degradation usually refers to the degradation of plastic fragments under the influence of temperature, sunlight, mechanical forces, etc.The most common methods of mechanical and photodegradation are described in the following subtopics.

Mechanical degradation of microplastics
The mechanical breakdown of microplastics represents a prevailing form of degradation.This phenomenon is of utmost significance in the formation of minute plastic particles through the physical abrasion of plastic particles in aquatic environments (Corcoran 2021).The process of mechanical abrasion causes microplastics to break down into smaller fragments, and repeated abrasion can further smooth out their edges.This rounding effect is attributable to the physical characteristics of both the plastic material and the abrasive surface, as well as the duration and intensity of the abrasion process.The resulting microplastic particles with rounded edges can have significant consequences for their environmental destiny and behavior.For instance, they can be more readily transported by water or wind currents and more easily ingested by aquatic organisms.Additionally, the similarity of their morphology to natural sediment grains can make it difficult to distinguish them from natural particles, presenting a challenge for accurately quantifying their prevalence and distribution in the environment (Bremerstein et al. 2015, Mekaru 2020).

Photodegradation of microplastics
Photochemical degradation is a process that breaks down microplastics, resulting in the release of polymeric fragments, Mahima Ganguly, Jithu Valiamparampil, Divyashree Somashekara, Lavanya Mulky by-products, and chemical additives.This process involves the exposure of plastic particles to sunlight, which causes the polymer chains that make up the plastic to break down (Chen et al. 2019).Given the ubiquitous presence of microplastics and organic pollutants in natural water systems, it is likely that the photodegradation and other environmental transformations of organic micropollutants will be influenced by their adsorption onto microplastics, which may sink to subsurface sediment.Additionally, certain microplastics, such as polystyrene (PS), phenol-formaldehyde (PF), and polyethylene (PE), can absorb light energy and generate reactive radicals and/or free electrons (Zhu et al. 2019).
This interplay between microplastics and organic pollutants has significant implications for environmental and public health.It can exacerbate the persistence and toxicity of these pollutants in aquatic ecosystems.The generation of reactive radicals and free electrons by certain types of microplastics can further contribute to the degradation of organic pollutants and the formation of new, potentially harmful compounds (Osman et al. 2023).The impact of microplastics on the fate and behavior of organic pollutants in natural water systems is an active area of research.Further studies are needed to elucidate the complex interactions between microplastics and organic pollutants in aquatic environments.

Biotic degradation of microplastics
Conventional plastics are typically characterized by an extremely low bioavailability, as only a small fraction of the polymer is exposed to potential degraders due to their solid nature.Moreover, microorganisms cannot directly use macromolecule polymers; they require extracellular enzymes to break them down into smaller molecules that can be absorbed and metabolized by the cells (Battin et al. 2016).The limited bioavailability is a major factor contributing to the persistence of conventional plastics in the environment, as it restricts the ability of microorganisms to degrade them.This persistence can have significant negative impacts on the environment and human health, leading to the accumulation of plastic debris in both aquatic and terrestrial ecosystems (Zhang et al. 2021).Microbial degradation can occur under both aerobic and anaerobic conditions, depending upon the surrounding conditions and the chemical structure of microplastics (Zhang et al. 2021).The different types of microorganisms involved in the degradation of microplastics through biofilm formation in aquatic environments will be discussed in future subtopics.

Microfluidics: A novel detection technique of microplastics
Among the various organic and inorganic pollutants present in marine ecosystems, it is crucial to separate microplastics from other contaminants.Traditionally, methods such as visual sorting and scanning electron microscopy (SEM) are used for sampling and detecting microplastics, as schematically described in Fig 2 .Microfluidics is emerging as a sophisticated technology that enables high-speed, high-throughput, lowcost analysis, and high sensitivity by modifying fluids using microfabricated channel and chamber structures.Additionally, microfluidics can create a well-controlled microenvironment for fluid and particle manipulation (Farré and Barceló 2020).It is also being used in advanced chemical/biological analyses, as well as low-cost point-of-care tests, with unconventional processes appearing at the micrometer scale (Zhang et al. 2022).The surface characteristics of the device material are enhanced, which can result in unique functionalities or challenges not encountered at the macroscale.Furthermore, each material is inherently linked to specific microfabrication processes and device features.As a result, the choice of material used to make the device is crucial in microfluidic technology (Ren et al. 2013).

Chip-scale sorting, concentration, and spectroscopic analysis principle
The ample supply of the tiniest microplastic particles, sized between 1µm to 100µm, is one inspiration for conducting research in microfluidics, which particularly targets this category of particles.Microfluidics helps propose a productive methodology for their convenient quantification and identification, recognizing the type of plastic particles and determining if they might be non-plastic.The intention of these studies is to accomplish two tasks with high throughput (Regnault et al. 2018): a) to enable detailed, large-scale studies on aquatic microplastics and b) to drastically reduce the time required for analysis, which is a key factor in monitoring (Elsayed et al. 2021).
It is worth mentioning that the maximal particle dimensions analyzed using microfluidic techniques can go up to a few hundred microns or 1 mm and are not only limited to 100 µm.The suggested micro-optofluidic platform includes a microfluidic chip designed to perform a variety of activities, such as particle sorting and trapping in specialized ultracompact on-chip reservoirs (Choi et al. 2015).This allows for rapid spectroscopic examination and imaging of the particles, as well as flow cytometry, which serves as an effective reference method for the size distribution of particles.The chips are assessed using modeled plastic particles with known sizes and properties, diluted in ultra-pure water at specified proportions (Mark et al. 2010).
To substantiate and prove this concept, several demonstration projects were conducted in which particles of varying sizes were sorted and trapped in compartmentalized dedicated reservoirs, then imaged and evaluated using various spectroscopic methods such as a Raman microscope, a Raman spectrometer, and an FTIR microscope.The results obtained from these experiments were compared (Wellner 2013).The chip design includes reservoirs with lateral dimensions ranging from about 100 to 300 µm, allowing the concentration of all trapped particles in such a tiny sub-millimeter space, compared to centimeter-scale filters, which is critical for any further rapid spectroscopic analysis of the sorted particles.Furthermore, the chip reservoirs can be configured to handle particles of varying sizes (Pattanayak et al. 2021).These ultra-compact reservoirs are a significant advantage over traditional procedures that use centimeter-scale filters, which require enormous time to scan the entire surface.As a result, this approach is intended to be time-efficient and low-cost.Microfluidics provides precise readings and facilitates the coupling of optical beams for spectroscopic investigation.(Elsayed et al. 2021).
An overview -Fate and analysis of marine microplastics with insights into microfluidics, biofilms, and future ecological threats.29

Flow cytometry measurements
Flow cytometers are capable of providing precise information regarding particle shapes, sizes, and counts, along with other physical and chemical properties (Shrirao et al. 2018).Some advanced flow cytometers are equipped with highspeed cameras and a light source that can capture as many as thousands of images per second, providing detailed and crucial information about the particles in the sample used for analysis.Specialized machine-learning techniques developed for this application can be used to calculate the sizes of particles from the images obtained (Luo et al. 2020).Using image analysis, individual particle images that are successfully captured can be classified into populations of various sizes (Mauk et al. 2013).This classification procedure can accommodate particles up to a few hundred microns in size, making it quite flexible.Other variables, such as the aspect ratio of particles, can also be used to categorize particles into distinct clusters, allowing the categorization of particles of various forms, including fibers (Konry et al. 2012).It is worth noting that flow cytometry has already been used in water analysis for counting and classifying microparticles using deep learning and image processing technologies (Sgier et al. 2016).

Trapping of microplastic particles and sorting on-chip
The suggested microfluidic chips can perform at least two functions: one is to classify the particles into separate reservoirs based on their size, and the other is to trap microplastic particles in specific on-chip reservoirs.The chips are evaluated by inserting a solution of ultra-pure de-ionized water containing standard spherical plastic particles into the chips, and photographs of the trapped particles are acquired for the reservoirs.A technology called Pinched Flow Fractionation (PFF) is used for sorting the particles (Lu and Xuan 2015).
Microfluidic chips provide a novel approach to investigating the toxic effects of MPs, offering an alternative to conventional techniques for separation and detection.However, the use of microfluidic systems may have limitations in terms of sensitivity and specificity, depending on the incorporated modules, such as sensors.Despite these limitations, microfluidic systems offer advantages in the separation of various substances, including MPs, pathogenic bacteria, algae, fungi, rare metals, and proteins, all of which have a direct impact on the analysis of MPs.Thus, microfluidic chips are a promising tool for examining MPs and other substances in a range of applications.

A rising hope of plastic degradation with marine bacteria
It is a known fact that a major part of our earth is covered in a cold climate with temperatures below 50⁰C.About 70% of the earth is covered by water bodies like the deep sea, some of which are found at a constant temperature of 20⁰C.Interestingly, bacteria have been found to accommodate themselves in every possible condition, from the coldest temperatures to the hottest places, and even in environments where the presence of air and sunlight is almost nil (Russell 1990).These resilient bacteria have unique characteristics due to their habitation in rare conditions, including the ability to break down plastic waste, which has attracted researchers (Romera-Castillo et al. 2018) however, remains unknown.Here we show that plastics release dissolved organic carbon (DOC.As the amount of plastic debris disposed into the ocean increases, studies have shown that plastic can provide dissolved carbon into the oceans, acting as a substrate for benthic organisms and stimulating heterotrophic activities by microorganisms (Pauli et al. 2017).Adapting to this newly dissolved carbon substrate, bacteria may develop new characteristics, including the production of cryogenic enzymes.The distinctive abilities of microorganisms to adapt to low temperatures provide enormous opportunities for researchers and engineers working in the field of plastic waste management.
From diverse strains isolated from various species in the Arctic Sea in the Canada Basin, some were found to produce lipase.Microorganisms from the genera Shewanella, Pseudomonas, Colwellia, and Marinomonas were confirmed to display lipase activity.Of these, 20-40% of psychrophilic strains and 10-30% of psychrotolerant strains exhibited lipase activity even at temperatures as low as 0 0 C (Yu et al. 2009).Since some lipases can hydrolyze polyesters like PCL, bacterial strains with lipase activity and the ability to adapt to cold temperatures are important for the biodegradation process.It is possible that other enzymes secreted by cold climate bacteria, such as depolymerases, may also have the ability to degrade plastic (Tokiwa and Calabia 2004).Enhancing this process with additives affecting thermal stability and the capacity to absorb UV rays can further improve the microbes' ability to degrade plastic.Bacteria capable of surviving at low temperatures, such as -10 0 C, can be attached to plastic using chemically sensitive polymers.These bacteria have been observed to release protease in excess, showing the ability to produce large amounts of enzymes in polar conditions (Huston et al. 2000).This opens the field for researchers to explore and further study the opportunities hidden under the ice beds.

Biofilm Formation
Biofilms are defined by the International Union of Pure and Applied Chemistry (IUPAC) as an aggregation of microorganisms where cells cling to each other and/or to a surface, typically buried inside a self-generated matrix of extracellular polymeric substances (EPSs).Biofilms may form on both living and non-living surfaces and can be found in both aquatic and tellurian habitats.Various microscopic organisms such as protists, algae, fungi, and bacteria can easily occupy microplastic surfaces due to the large specific surface area.Biofilm formation is regarded as an essential virulence factor.The creation and growth of biofilms on microplastic surfaces An overview -Fate and analysis of marine microplastics with insights into microfluidics, biofilms, and future ecological threats.31 can alter the shape and physical and chemical characteristics of microplastics.This results in a variety of consequences, including vertical mobility, biodegradation, co-migration with chemical contaminants and pathogens, and weathering (Tu et al. 2020).

Primary Stages of Formation of Biofilm
The bacterial release of Extracellular Polymeric Substances (EPS), containing proteins, glycoproteins, and glycolipids, forms a matrix surrounding the bacteria, allowing them to connect to a range of abiotic and biological surfaces (Keswani et al. 2016).Various researchers categorize biofilm development into phases based on core flora and time series.Biofilm development is classified into three stages: the preliminary stage, lasting for about 1 to 14 weeks, the intermediary stage, lasting for about 14 to 35 weeks, and the final stage, lasting about 35 to 45 weeks, depending on alterations in the core flora of the biofilm on the surface of plastic particles exposed at the harbor's bottom.The mechanism of biofilm growth on the surface of plastic flakes in the aquatic ecosystem is wellestablished (De Tender et al. 2017).WT Wimpenny presented a brief breakdown of the traditional biofilm development process, as demonstrated in Fig. 3  Other scientists have categorized biofilm development into 4 primary stages: (1) adsorption of dissolved organic molecules (2) grouping of prokaryotes, (3) colonization by single-cell eukaryotes, and (4) colonization or grouping of invertebrate larvae and algal spores.These 4 processes might occur concurrently or independently on the surface of microplastics (Wang et al. 2019).

Factors Affecting Biofilm Formation on Microplastics
Firstly, the interaction between the surface of the plastic and the biofilm in the surrounding water takes place.After a few minutes, an adsorption layer of organic and inorganic components forms.Through attractive or repulsive interactions between the external walls of cells and the media surfaces, microorganisms come into contact with the surface.The preliminary conditioning layer might be able to influence colony formation by modifying material-specific surface features (Rummel et al. 2017).Biofilm production is a multistage process influenced by several parameters such as surface characteristics, nutritive compound mixtures, weather conditions, and pH (Sauer 2003).The conditions surrounding the matrix and cell development circumstances (such as climate, carbon supply, liquid media movement, nutritional media ingredients, and maturation characteristics) are complex factors that influence bacterial adhesion to MP surfaces (Renner and Weibel 2011).Various attachment mechanisms between bacteria and matrices promote adherence to the substrate surface through flagella, bristles, pili, and EPS production adaptation.The colonizer and initial conditioning layer modify the material's surface qualities and stimulate the colonization of additional species (Haiko and Westerlund-Wikström 2013).Based on the surface's hydrophilicity or hydrophobicity, electric charge, roughness, and functional groups, microbial cells can adhere to the surface in both general and specific ways (Rosenberg et al. 1982).The chemical characteristics of the conditioning layers are connected to the hydrophobicity or roughness of the preliminary surface of the matrix surface and are critical for biological sedimentation, emphasizing the significance of the fundamental process of adsorption (Lorite et al. 2011).Hook and his team proposed in their research that surface hydrophobicity and polymer shape have little effect on bacterial adherence to polymers (Hook et al. 2012).

Pollutants connected with plastics and their transportation via biofilms
Biofilms may influence the transfer of hydrophobic organic pollutants (HOCs) between plastic debris and water due to their ability to metabolize HOCs along with their sorptive properties (Headley et al. 1998, Paterson andAlexander 1971).Along with additives from newly released plastic waste, highly persistent pollutants can be acquired by plastic from its local surroundings and transported and released by plastic throughout its time in the sea (Teuten et al. 2016, Bakir et al. 2012).To assess the risks associated with microplastics, it is critical to understand the capacity of synthetic polymers to sorb HOCs.Thus, we must consider whether biofilms will influence thermodynamic and kinetic processes.Moreover, EPS forms a rich biological matrix containing proteins, humic acids, polysaccharides, and lipids, which can enhance the sorptive ability of biofilm-coated MP and hetero aggregates (Flemming and Wingender 2010).A wide variety of bacteria, fungi, and algae can degrade HOCs,

Reversible and irreversible attachment
Foreign species supplementation and growth Diffusion making them useful for bioremediation of surface waters in situ or as engineered bioreactors (Wu et al. 2014).This illustrates the importance of biofilms in the accumulation and/or removal of plastic-associated chemicals through metabolization, which may affect their bioavailability to consumers ingesting MP (Writer et al. 2011).The introduction of antimicrobial compounds into polymer materials to restrict microbial settlement may cause concern, as these chemicals can leak and contribute to the increase in resistance adaptations in microbial populations (Demeter et al. 2017).It can be concluded that, due to larger surface-to-volume ratios, sorptive mechanisms may result in quicker chemical absorption and release in microplastics compared to macro-plastic litter.Additionally, microbial colonization is promoted by the expanded and eroded surfaces available for colony formation, which might alter the kinetics and persistence of HOCs (Oberbeckmann et al. 2015).These bi-directional relationships, which can influence the kinetics of contaminant uptake and release into and out of the polymeric bulk phase via the active microbial interface, need further study to predict more accurately the hazards posed by microplastics as sources of HOC emission and transport in aquatic environments (Rummel et al. 2017).

Future Prospective
The trade-offs associated with microplastics are a global cause for concern.With the recent increase in awareness, there is now more scope for scientists worldwide to work on this issue.Current reviews help show a way forward in this area (Vaid et al. 2021).The two primary targets can be listed as: (a) analysis of microplastic contamination, with a particular focus on the presence, origins, and fate of microplastics in riverine systems, and (b) understanding and assessing microplastics-related toxicity in aquatic habitats, as well as a critical study of the problems and potential solutions for remediating microplastic contamination in these systems (Chaukura et al. 2021).Even though microbes may colonize any plastic introduced into the water ecosystem, few investigations have been conducted on the interactions between marine microbiota and plastics.As a result, more studies are needed to better understand the interactions between microplastics and microorganisms (Qiu et al. 2022).Humans are at serious risk of microplastic exposure and related illnesses; various scientists have observed microplastic consumption through everyday staples in their research (Lee et al. 2021, Kiran et al. 2022).Some researchers have proved that microplastic contamination via food can lead to serious health concerns, such as endocrine disruption, cancer, inflammation, and, in some cases, fatality (Barboza et al. 2018).Thus, considering the numerous prevailing and emerging hazards related to microplastics, managing them as an evolving pollutant before they become a permanent threat to humans and the environment is crucial (Yong et al. 2020).The amount of microplastics increases considerably as their size decreases (Isobe et al. 2015).According to reported studies, the average size of microplastics depends on the various sizes of the microplastics analyzed after sampling.There is a significant ongoing demand for research to describe the dynamics related to the atmospheric transport of microplastics.Thus, atmospheric particle transport modeling is an essential area of focus for future research (Zhang et al. 2020).Any correlations or links associated with the composition of atmospheric, terrestrial, and marine microplastics have not yet been given careful attention.Additionally, well-grounded research has not yet been conducted to provide sufficient evidence related to source pathways and interlinkages between freshwater, atmospheric, and terrestrial microplastics.The impact of airborne microplastics, their constituent chemical components, and the contaminants they adsorb on ecological and human health is unknown.However, the potential of nano and microplastics to affect this is a cause for concern (Wright and Kelly 2017).Though a few investigations are currently being conducted to study the sorption, toxicity, and aggregation of pollutants on microplastics in the atmosphere, significant additional research is required to fully comprehend the depth of this problem.Additionally, the interactions of microplastics with other organic toxic compounds and metals in the environment, as well as their effects on and interactions with the environment, humans, and ecosystem health, have received little attention and require further investigation (Wang et al. 2020).

Conclusion
It is commonly assumed that ocean waters serve as a major sink for microplastics, with marine and terrestrial habitats acting as significant sources and pathways for microplastics to reach the sea.In the oceans, plastic contamination primarily occurs due to the presence of large quantities of improperly managed solid waste in terrestrial environments.These wastes are typically transported through wastewater outflows, inland waterways, tidal currents, or wind advection, with rivers playing a particularly critical role.Marine ecosystems are regarded as the ultimate sinks for all plastic trash, including microplastics.Terrestrial, freshwater, oceanic, and now atmospheric habitats are understood to be interconnected through a complex network of source-pathway-sink interactions that impact the flow and accumulation of microplastics in such environmental compartments.This movement significantly influences the source-sink dynamics related to plastic pollution across various ecosystems, including the transfer between aquatic and terrestrial systems.Due to the serious and potentially lifethreatening health concerns associated with microplastic contamination, it is crucial to regulate unregulated discharge into waterways.Effective regulation involves addressing the multiple sources and sinks of microplastic particles.Control measures should include promoting sustainable and biodegradable or environmentally friendly alternatives, implementing effective legislation, advancing treatment technologies for microplastics, and upgrading or improving existing wastewater treatment technologies.These actions can contribute to more efficient management of microplastic pollution and prevent leakages.

Figure 2 .
Figure 2. Methods for detection and quantification of microplastics.

Figure 3 .
Figure 3 .Breakdown of the traditional biofilm development process.

Fig
Fig 4. Biofilm development into five s