Examining the Ecological Footprint of Microplastics: A Holistic Exploration from Genesis to Demise

Introduction

Plastic pollution has increased due to high consumption and production ratewhich has a severe effect on the ecosystem¹. Largeplastic objects break down into small pieces with time and convert into small particles which are known as microplastic (>5mm in size)². Primary and secondary are two types of microplastics which have been identified ³. Primary, such as microbeads are directly discharged into the environment while secondary microplastics are produced when major plastic products break down into smaller particles⁴. They are also classified as fibre, line, foam, fragments, nurdles, microbeads, films, and sheets according to their shape ⁵. Due to their small size and shapes, microplastics are difficult to manage and they may persist in the environment for several decades or centuries and transfer from one place to another. Plastic pellets⁶, fragmentation of large plastic debris⁷, microbeads in personal care products⁸, fibres from synthetic clothes and textiles⁹, tire wear in road dust¹⁰, paints and coatings¹¹, wastewater treatment plants¹², sludge as a fertilizer in soil¹³ and agricultural practices ¹⁴ are the main sources (Fig. 1.) of microplastics. Their ubiquitous contamination has been identified from oceans to biodiversity in the Himalayan region ¹⁵. including atmosphere¹⁶, water ¹⁷,soil ¹⁸, plants¹⁹, terrestrial ecosystem ²⁰, aquatic life such as mussels²¹, fish ²², planktons ²³ and even in the human body²⁴. Several negative impacts have identified on aquatic and terrestrial ecosystem including living beings which are described in fig 2.  Drifting of these particles causes the invasion of alien species into a particular ecosystem²⁵. Microplastic now has been declared as a ‘plastisphere’ in marine life by UNEP. and called a new marine microbial home ²⁶. However, it is becoming a serious threat to the environment day by day as it cannot be recycled and reused normally²⁷.

Figure 1: Sources, types, and effects of microplastics on different compartments of the environment. Click here to View Figure

Figure 2: Negative impacts of microplastics on plants and living beings Click here to View Figure

(Source of figure- The above data for plants is taken from references ^31–33 and forliving things is from^34–36)

Interaction of microplastics with organic and inorganic matter

Microplastics react with organic matter by hydrophobic interaction, electrostatic interactions, Van Der Wall force, H-bonding, and halogen bonding³⁷. As they have a hydrophobic surface, this large specific surface area makes it simple to interact with organic pollutants. They also interfere with the behaviour of these pollutants through the adsorption and desorption process³⁸.

Figure 3: Different ways of microplastic interaction with organic and inorganic matter. Click here to View Figure

Source of figure is reference⁵⁹(Chemosphere., 2023, 138495).

Microplastic makes a complex with the inorganic matter such as heavy metals, chloride, phosphate, nitrate etc. by surface binding, sorption and electrostatic interactions³⁹. They also interact with toxic heavy metals like cadmium and significantly increase their toxicity and accumulation properties. Microplastics act as a pathway for the movement of harmful heavy metals in different ecosystems like aquatic bodies mangroves wetlands and sediments⁴⁰

Analytical methods

Analytical methods include sampling, extraction, and characterisation procedures of microplastic which take a lot of time and patience. Although figure4shows all the steps very clearly.

Sampling and extraction in different compartments of the environment

Aquatic Environment

Water samples are collected with bottles (glass), manta nets, neuston nets, AVANI (All Purpose Velocity Accelerated Net Instrument) and trawl nets ⁴¹⁴². The collected samples are sieved or filtered with the help of different sizes of stainless-steel sieves⁴³. Acidic or alkaline digestion with H₂O₂ (30%, 15%) or HCl or KOH⁴⁴is done at 60˚C to 75˚C for 12-72hrs followed by density separation by using NaCl and NaI or another salt solution⁴⁵. The samples are filtered using filter paper or vacuum filters with aluminium oxide filters and characterised by different techniques⁴⁶.

Figure 4: Procedure for analysis of microplastic in various sectors of the environment. Click here to View Figure

Soil and Sediments

Soil samples can be collected with the help of wooden, metal frame⁴⁷spoon or shovel⁴⁸. Sediment samples are collected by using Peterson grab sampler or Van Veen sampler⁴⁵. The collected samples are dried and sieved from different sizes of sieves (5mm, 3mm, 1mm, 300µm and 63µm)⁴⁹.Density separation is performed with the help of NaCl, NaI, ZnBr₂, CaCl₂⁵⁰.H₂O₂ (30%), HCl, NaOH, KOH⁵¹ and sodium hypochlorite (>40%) are used to perform acid and alkaline digestion to remove organic matter for 5 to 6 hours⁵². After that chlorination of polymers is done byNaOClto reduce the hydrophobicity of plastics⁵³.The supernatant must be filtered after digestion with different pore-size filter papers and nylon filters⁴³. The vacuum filtration technique can also be helpful⁵².

Biota

Biological samples are mainly collected with the help of trawl nets, manta nets, fishing nets, cages, and handpicking methods⁵⁴. For a more effective investigation, freezing is an essential step right after collection and washing. After that, soft tissues of the biological sample are separated at room temperature⁵⁵. Digested by H₂O₂ (15%, 30%), and KOH (15%, 30%)⁵⁶ at temperatures of 50˚C to 75˚C for 4 to 5 hoursand stored in a petri-dish after filtration for another analysis.

Dust and Air Sample

Dust and air samples are collected with the help of a total atmospheric particulate sampler, and dust sampler. Household and indoor samples are simply collected with the help of nylon brushes by sweeping the floor. The samples are stored at low temperatures (3- 4 ˙C)¹⁶ anddensity separation isperformedusing ZnCl₂ andNaCl. The samples are digested by H₂O₂, KOH and 1-pentanol ^57,49

Quantification and Identification

In the investigation of microplastics, characterization has an essential role. Various instruments are used nowadays like Visual Sorting, Fourier Transform Infrared Spectroscopy (FTIR), SEM (Scanning Electron Microscope), Raman Spectroscopy, Gas chromatography and mass spectrometry (GC-MS)etc. These are used to identify and characterise the type of plastic polymers in various samples (solid, liquid, air). Every technique has its advantages and disadvantages which are described in Table 1.

Table 1: Instruments and their significance

NO	Instrument	Application	Advantages	Disadvantages	References
1	Visual method		Large microplastics can be detected.	Small size, type and composition of microplastic cannot be detected.	49
2	Raman spectroscopy	Chemical and spectral composition of microplastic.	Small microplastics can be detected. A small sample is required.	Detection limit 1 to 10µm Expensive instrument	58
3	SEM	Elemental interference by reflected electrons.	Clear and high-resolution image of the sample	Time-consuming Expensive method	46
4	XRF	Analyse the microplastic’s fluorescence by using X-ray.	A little sample is required.   Non-destructive method	Expensive method   Exposure to X-ray radiation   Large Sample required	59
5	FTIR	Polymeric functional group of microplastics by using IR	Determine the morphology.   Less sample required	Limit from 10 to 50µm   A specific methodology is required.	60
6	Chromatography	Analyse the type of plastic polymer.	High sensitivity and specificity	Not suitable for very small particles	61

 

Degradation of microplastic as a future perspective

The phenomenon of nanoparticle-mediated degradation held a transformative era in the domain of microplastic remediation, presenting a nuanced and eco-conscious strategy to mitigate the ubiquitous ramifications of plastic contamination on environmental ecosystems⁶². TiO₂ nanoparticles gain attention to degrade polyethylene microplastics under simulated solar irradiation, effectuated through surface adsorption and the generation of reactive oxygen species (ROS)⁶³. Fe₃O₄ nanoparticles catalyse the degradation of polystyrene microplastics via Fenton-like reactions, instigating oxidative cleavage of polystyrene chains through the generation of hydroxyl radicals (•OH) in the presence of hydrogen peroxide (H₂O₂)⁶⁴. Similarly, ZnO nanoparticles were enlisted in the degradation of polyethene terephthalate (PET) microplastics under UV irradiation, facilitating oxidative PET degradation via surface adsorption and ROS generation⁶⁵. Notably, the amalgamation of nanoparticles into bioplastic degradation paradigms represents a paradigmatic shift toward sustainable materials management. Through symbiotic engagements with microbial collectives and precise catalytic mechanisms, nanoparticles synergistically enhance the efficiency and specificity of bioplastic decomposition processes. From TiO₂ photocatalysis to AgNP-facilitated microbial consortia, nanotechnology offers a multifaceted arsenal against the intricate challenges posed by bioplastic waste. By embracing interdisciplinary cooperation and harnessing state-of-the-art nanotechnological innovations, society can aspire towards a cleaner and more sustainable future, emancipated from the perils of microplastic pollution.

Acknowledgement

The author (Pooja Yadav) is highly thankful to UGC (University Grant Commission), India under the JRF (Junior Research Fellowship) programme with ref. no. 220520732758.

Conflict of Interest

The authors declare no conflict of interest.

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