Environmental Impacts of Plastic Degradation: Toxic Byproducts, Environmental Risks, and Eco-Friendly Alternatives

Abstract

Plastics are highly persistent materials, and their environmental degradation can potentially exacerbate, rather than alleviate, pollution. The degradation of plastic materials releases toxic monomers and additives, such as bisphenol A (BPA), styrene, and dioxins, which are more reactive, harmful, and persistent than intact plastics. With half-lives ranging from weeks to decades, they bioaccumulate in food chains, disrupt ecosystems, and contribute to endocrine disruption and mutagenicity. Natural degradation pathways, like microbial metabolism and photodegradation, are slow and incomplete, often leaving toxic intermediates such as microplastics. Artificial strategies, including bioremediation and advanced oxidation processes (AOPs), show potential to address the problems of plastic pollution but face additional challenges like secondary pollution and scalability. Sustainable alternatives, including bioplastics and renewable non-plastic substitutes, present promising solutions. However, their widespread adoption is hindered by challenges such as high production costs and the need for specific conditions to facilitate degradation, necessitating further research and development. A combined approach of reducing plastic production, advancing recycling, and implementing effective remediation strategies is critical to mitigating plastic pollution’s long-term impacts on ecosystems, biodiversity, and human health. This review provides a critical analysis of the current understanding of plastic degradation processes and the toxic byproducts they generate. It highlights the paradox wherein increased degradability may exacerbate environmental hazards. Additionally, the review assesses innovative, eco-friendly alternatives designed to mitigate plastic pollution.

1. Introduction

Plastic pollution has become one of the most critical environmental challenges of the 21st century, with global plastic production exceeding 400 million tons annually, a substantial fraction of which accumulates in ecosystems across the planet [1]. While the degradation of plastics is frequently considered a viable method for managing plastic waste, the environmental breakdown of these materials often leads to the release of toxic monomers and additives [2]. As these substances are often more water-soluble than the original plastic particles, they pose a greater threat to ecosystems and biodiversity compared to the plastic particles themselves [3]. Plastics are utilized across a diverse array of applications, including food and beverage packaging, construction materials, and medical products. For instance, polyethylene terephthalate (PET) is commonly used in water and soft drink bottles, while high-density polyethylene (PE) is employed in milk jugs and pipes. Polyvinyl chloride (PVC) is used for window frames and cable insulation, and low-density PE is utilized in grocery bags and flexible films. Polypropylene (PP) is frequently used in food containers and bottle caps. Other widely used plastics include polystyrene (PS), which is found in disposable packaging and food containers, electronics casings, and medical equipment, as well as polyurethane (PU), widely utilized for its flexibility and cushioning properties in applications such as foam for furniture, bedding, and automotive seating. Polycarbonate (PC), known for its high impact strength and optical clarity, is commonly used in safety glasses, bulletproof glass, casings for electronic devices, and transparent building materials, including skylights and roofing.

Intact plastic particles primarily function as physical pollutants, often leading to notable disruptions in cellular physiology [4]. However, their breakdown products can have even more severe chemical and biological impacts, posing heightened risks to ecosystems and living organisms (

Table 1. Overview on degradation processes, toxic effects of released monomers, environmental half-life and potential removal methods.

Plastics	Degradation Processes and Byproducts	Toxic Effects of Monomers	Half-Life	Removal Methods
PE and PP	Photodegradation, oxidation and microbial degradation leads to the formation of alkanes, alkenes, and smaller hydrocarbons [11,12].	Generally less toxic; some intermediates can disrupt microbial communities in soil and water.	Decades to centuries	Biodegradation by engineered microbes (slow and inefficient).
PVC	AOPs, thermal degradation, adsorption yielding VCM, hydrochloric acid, and dioxins [13].	VCM is a known carcinogen; dioxins are highly toxic, causing endocrine disruption, immune suppression, and cancer [8].	Years to decades	AOPs and adsorption using activated carbon.
PS	Microbial degradation, pyrolysis, depolymerization contribute to the formation of styrene monomers and oligomers [14,15].	Styrene is a neurotoxin and a possible human carcinogen; it can bioaccumulate in aquatic organisms [16].	Several years	Biodegradation by specific fungi and bacteria (limited large-scale applications).
PET	Enzymatic degradation (PETase, MHETase), hydrolysis produce TPA and ethylene glycol [17,18].	TPA is relatively low in toxicity; ethylene glycol can cause kidney and liver damage in high concentrations [19].	Decades	Enzymatic degradation using PETase and MHETase enzymes.
PC	Adsorption, microbial degradation, chemical oxidation lead to the generation of BPA [20,21].	BPA is an endocrine disruptor, interfering with hormone signaling, reproduction, and development [22].	Weeks to months	Adsorption using biochar or activated carbon, as well as microbial degradation.
PU	Microbial degradation (fungi, bacteria) and hydrolysis can produce isocyanates and amines [23,24].	Isocyanates, the key chemical reactant used to create urethane linkages, are respiratory irritants and can cause asthma [25]; some amines are toxic to aquatic life [26].	Years	Biodegradation by fungi and bacteria capable of breaking down urethane bonds [23].

PE, polyethylene; PP, polypropylene; PVC, polyvinylchloride; VCM, vinyl chloride monomer; PS, polystyrene; PET, polyethylene terephthalate; PC, polycarbonate; PU, polyurethane, AOPs, advanced oxidation processes; TPA, terephthalic acid; BPA, bisphenol A; PETase, polyethylene terephthalate hydrolase; MHETase, mono(2-hydroxyethyl)terephthalate hydrolase.

). The primary reason for this is that the degradation products of plastics are often more chemically reactive and biologically harmful than the original materials, frequently exhibiting irritating or even toxic effects [5,6]. Compounding the issue, these substances are also highly persistent, with half-lives that can range from weeks to decades, depending on their chemical composition and environmental conditions. For example, bisphenol A (BPA) from PC has a half-life of weeks to months in soil and water, while styrene from PS and vinyl chloride from PVC can persist for years [7,8]. Even more stable compounds, such as dioxins formed during PVC degradation, can remain in the environment for decades due to their resistance to natural breakdown processes [9]. This persistence allows these toxic monomers to bioaccumulate in food chains, amplifying their ecological and health impacts over time [10]. This review aims to explore the environmental impacts of plastic degradation, evaluate current remediation strategies, and assess the potential of sustainable alternatives. By addressing these key aspects, the review underscores the pressing need for a comprehensive and multidisciplinary approach, given the profound and far-reaching impacts of plastic degradation on various ecosystems and human health.

2. Mechanisms and Pathways of Plastic Degradation

Plastic degradation is the process by which plastic materials break down into smaller components or lose their structural integrity. Depending on environmental conditions, the type of plastic, and the presence of specific catalysts or organisms, there are several pathways through which plastics can degrade. These include natural processes involving physical, chemical and biological mechanisms, as well as artificial strategies designed to accelerate the breakdown of plastics [27,28]. This section explores the mechanisms of plastic degradation and highlights the associated challenges (Figure 1).

2.1. Natural Degradation Processes

Natural degradation processes occur in the environment and involve physical, chemical and biological mechanisms. While these processes can break down plastics over time, they are often slow and incomplete, leaving behind harmful byproducts that can persist in ecosystems for extended periods [5,29].

Physical degradation is where plastics break down into smaller fragments due to external forces or environmental factors [30]. One of the most common pathways is photodegradation, where ultraviolet (UV) radiation from sunlight breaks the chemical bonds of polymer chains, resulting in the formation of smaller molecules [31]. This process is particularly relevant for plastics exposed to sunlight, such as polyethylene (PE) and polypropylene (PP). However, photodegradation is inefficient and often results in the formation of microplastics that persist in ecosystems and can interact with biological systems in harmful ways, potentially causing oxidative stress, DNA damage, and other cellular disruptions [32,33].

Thermal degradation, which occurs when high temperatures cause polymer chains to break down, leads to structural changes and loss of mechanical properties [34]. This process usually occurs during manufacturing or in environments with high heat [35]. Similarly, mechanical degradation involves physical forces, such as abrasion, friction or mechanical stress, that break plastics into smaller fragments. This pathway is common in environments with wind, water currents, or human activities such as agriculture, urban development, and industrial processes. However, it does not chemically degrade the material and often contributes to pollution with microplastic particles [35].

Chemical degradation occurs when plastics break down through reactions such as oxidation, hydrolysis, or depolymerization. Oxidation involves the reaction of oxygen with polymers, leading to the formation of free radicals that break down polymer chains. This process often occurs in combination with photodegradation or thermal degradation, as it requires the presence of oxygen, heat, or UV light [36,37]. Hydrolysis, on the other hand, involves water molecules breaking chemical bonds in polymer chains, particularly in plastics with hydrolyzable bonds such as polyesters (e.g., PET) and polyamides (e.g., nylon). The processes are highly dependent on environmental conditions, such as humidity, temperature, and water exposure [38].

Depolymerization is another chemical pathway, where polymers break down into their monomers or smaller molecules. This process is particularly relevant for plastics like PET, PU, PVC, PS, and PC [39,40]. While chemical degradation can effectively reduce plastics to their basic components, it often requires controlled conditions and can produce toxic byproducts [41].

The metabolism of various microorganisms can play a crucial role in breaking down plastics. Depending on the plastic and environmental conditions, certain bacteria, fungi, and algae can enzymatically degrade monomers into less harmful compounds [42]. For instance, enzymes such as polyethylene terephthalate hydrolase (PETase) and mono(2-hydroxyethyl)terephthalate hydrolase (MHETase) degrade PET into its monomers, terephthalic acid and ethylene glycol [17]. Additionally, certain microorganisms can break down urethane bonds in PU [29,38]. However, conventional plastics such as PE and PS are highly resistant to biodegradation. Even biodegradable plastics require industrial composting conditions to achieve near complete degradation. These include forced aeration at about 58 °C, high moisture, active microbes, and residence time of weeks to months. Incomplete biodegradation can result in the formation of microplastic particles or toxic byproducts, which further complicates environmental cleanup efforts [43,44].

2.2. Artificial Degradation and Removal Strategies

Artificial degradation methods are engineered processes designed to accelerate the breakdown of plastics or remove them from the environment. These strategies include bioremediation, AOPs, adsorption techniques, and thermal treatments [45,46,47]. Recently established strategies offer more targeted solutions to address the growing problem of plastic pollution and its associated monomeric decay products. These methods hold promise regarding rapid and complete plastic degradation. However, they also face critical challenges in large-scale implementation and raise concerns about potential unintended consequences.

Bioremediation employs engineered microbes or optimized enzymes such as PETase and MHETase to break down specific polymers like PET into their monomers [48]. While this approach has demonstrated success in controlled environments, it poses challenges. The release of monomers, such as terephthalic acid and ethylene glycol, into the environment can have toxic effects on aquatic and terrestrial organisms, including disruption of cellular processes and potential bioaccumulation in food chains [49,50]. Moreover, the introduction of engineered microbes into natural ecosystems must be carefully managed to avoid ecological imbalances or unintended interactions with native microbial communities [51].

AOPs, such as photocatalysis, ozonation, and Fenton reactions, use reactive species to degrade persistent compounds. For example, BPA is frequently degraded by >90% over a few hours and dioxins can be transformed into less toxic byproducts [52,53,54]. While these processes can achieve high removal rates and substantial mineralization under such conditions, they are not without risks [55]. Intermediate products generated during AOPs can sometimes be more reactive or toxic than the original compounds, posing a threat to both environmental and biological systems [56]. Additionally, the high energy requirements and chemical inputs for AOPs can limit their feasibility for large-scale applications, particularly in resource-limited settings [57].

Adsorption techniques use materials such as activated carbon or biochar to capture monomers from contaminated water and soil, reducing their bioavailability, particularly in plastics such as PC and PVC [58,59]. While this approach can temporarily mitigate the risks associated with toxic monomers, it does not eliminate them from the environment. Adsorbed compounds can be released back into ecosystems under changing environmental conditions, such as shifts in pH or temperature, reintroducing the same risks they were intended to mitigate [60]. Furthermore, the disposal or regeneration of spent adsorbent materials must be carefully managed to prevent secondary contamination [58].

Thermal treatment, including high-temperature incineration and pyrolysis, is one of the most effective methods for destroying plastics, like PE PP, PS and PVC, or converting them into fuels, oil, or smaller hydrocarbons [61,62]. However, if not carefully controlled, incineration can lead to the formation of secondary pollutants, such as dioxins, furans, polycyclic aromatic hydrocarbons (PAHs) and greenhouse gases. In the long term, these will contribute to air pollution and climate change while also posing direct risks to human health through inhalation or deposition onto soil and water [63,64]. Pyrolysis, while promising, entails high energy and infrastructure burdens (e.g., pyrolysis reactors at >300 °C, continuous feeding trains, and off-gas treatments), limiting its scalability [65].

2.3. Key Challenges of Plastic Degradation

Despite the availability of various natural and artificial degradation pathways, several challenges hinder the effective breakdown and removal of plastics. One of the primary challenges is the durability of plastics, which are designed to resist environmental degradation. As a result, natural processes are often slow and incomplete, leaving behind microplastic particles and toxic intermediates that persist in ecosystems for extended time periods [29]. Microplastic formation is a major concern, as many degradation processes, such as photodegradation and mechanical degradation, result in the fragmentation of plastics into smaller particles. These microplastics can adsorb and concentrate environmental pollutants, acting as vectors for toxins that enter food chains and bioaccumulate in organisms, including humans [66,67]. Additionally, reactive byproducts generated during degradation, such as free radicals and partially oxidized compounds, can interact with biological systems, causing oxidative stress, DNA damage, and other cellular disruptions [6,32,33,56]. Thus, the cumulative and chronic exposure to these substances raises profound concerns about their potential to disrupt biodiversity, compromise ecosystem stability, and pose risk to public health [68,69].

Another challenge is the release of toxic monomers into the environment. While adsorption techniques can temporarily sequester harmful compounds, changes in environmental conditions, such as pH or temperature fluctuations, can lead to the desorption and reintroduction of these toxic substances into ecosystems. For example, BPA, a common compound in PC plastics, has been linked to hormonal imbalances and developmental issues in wildlife and humans [70].

Finally, artificial degradation methods face limitations due to their energy and cost requirements. Processes like advanced oxidation and pyrolysis are often expensive and require high energy input, making them less feasible for large-scale applications. Additionally, inadequate waste management infrastructure and the complexity of mixed plastic waste further complicate efforts to degrade or recycle plastics effectively. To address these issues, advancements in plastic design (e.g., biodegradable plastics), improved waste management systems, and innovative technologies are essential for achieving efficient and sustainable plastic degradation and recycling [71,72,73].

The biological effects of monomers generated during the degradation of plastics represent a substantial hazard and warrant careful scientific scrutiny. Many of these compounds, including BPA, phthalates, and styrene, are well-documented for their toxicological properties, which include mutagenic effects, endocrine disruption, and other adverse biological impacts [74]. Even at low environmental concentrations, these monomers can interfere with critical physiological processes such as hormonal regulation, reproductive health, and organismal development in both wildlife and humans. The cumulative and chronic exposure to these substances raises profound concerns about their potential to disrupt biodiversity, compromise ecosystem stability, and pose risks to public health [68,69].

While artificial degradation and removal strategies, such as bioremediation, AOPs, and adsorption techniques, represent valuable tools in addressing plastic pollution, their implementation must be approached with caution. These methods should be accompanied by rigorous environmental monitoring and risk assessments to minimize unintended consequences, such as the formation of secondary pollutants or the release of toxic intermediates. A holistic and scientifically informed approach is essential to ensure that these technologies do not inadvertently exacerbate the very problems they aim to solve.

3. Ecotoxicological and Human Health Impacts of Selected Plastic Degradation Products

Plastic monomer molecules, such as styrene, VCM, BPA, TPA, ethylene glycol, and urethane, are known to exhibit toxic activities that pose significant risks to human health and the environment. The widespread use and improper disposal of plastics exacerbate these risks, leading to contamination and bioaccumulation in the environment [75].

3.1. TPA and Ethylene Glycol

These monomers can be released during the degradation of PET and have been shown to cause irritation to the skin, eyes, and the respiratory system, and prolonged exposure may result in liver and kidney toxicity [76,77]. Ethylene glycol, on the other hand, is highly toxic when ingested, inhaled, or absorbed through the skin, leading to central nervous system depression, kidney damage, and metabolic acidosis [78]. These monomers can also harm aquatic ecosystems, highlighting the environmental risks associated with improper disposal of PET-based plastics.

3.2. Styrene

These monomers are used in the production of PS and are classified as possible human carcinogens by the International Agency for Research on Cancer (IARC) (

Table 2. Compounds and their carcinogenicity; classifications follow the definitions of the IARC (2023).

IARC Group	Definition	Monomer Compounds
Group 1	carcinogenic to humans	VCM, Dioxin, Formaldehyde, Benzene, PAH
Group 2A	probably carcinogenic to humans	Styrene, Urethane
Group 2B	possibly carcinogenic to humans	DEHP, TDI, Furan, Acetaldehyde

VCM, vinyl chloride monomer; DEHP, di(2-ethylhexyl)phthalate; TDI, toluene diisocyanates; Dioxin, 2,3,7,8-TCDD, 2,3,7,8-tetrachlorodibenzo-paradioxin; PAH, polycyclic aromatic hydrocarbon.

) [79]. Exposure to styrene has been linked to an increased risk of leukemia and lymphoma [80]. Acute exposure can cause irritation of the skin, eyes, and respiratory tract, as well as symptoms such as dizziness, headaches, and fatigue due to its effects on the central nervous system [81]. Chronic exposure, particularly in occupational settings, has been associated with neurotoxic effects, including memory loss, impaired concentration, and changes in color vision [82]. Styrene, when released into the environment during production and use, poses risks to aquatic and terrestrial ecosystems due to its potential for bioaccumulation.

3.3. VCM

VCM is mainly used in the production of PVC. It is known as a highly toxic and well-documented carcinogen, and chronic exposure has been associated with an increased risk of brain and lung cancers, as well as lymphoma [83,84]. The IARC classifies vinyl chloride as a Group 1 human carcinogen, with strong evidence linking it to angiosarcoma of the liver, a rare and aggressive cancer (Table 2) [79,85]. Acute inhalation of vinyl chloride can cause dizziness, headaches, and respiratory irritation, while long-term exposure may result in liver damage, immune system suppression, and neurological effects such as memory loss and mood disturbances [86,87,88]. As a volatile organic compound, vinyl chloride can contaminate air, water, and soil, posing serious environmental and public health risks.

3.4. BPA

This chemical is used in the production of PC plastics and epoxy resins and represents a well-known endocrine disruptor [89]. BPA mimics the hormone estrogen, binding to estrogen receptors and interfering with hormonal signaling in humans and wildlife [90]. This disruption has been linked to reproductive issues, reduced fertility, developmental abnormalities, and an increased risk of hormone-related cancers such as breast and prostate cancer [91]. BPA exposure has also been associated with metabolic disorders, including obesity and diabetes, as well as potential impacts on brain development and behavior, particularly in fetuses, infants, and children [92,93,94]. When plastics containing BPA degrade in landfills, oceans, or other environments, BPA can leach into soil and water, leading to environmental contamination and subsequent bioaccumulation in organisms.

3.5. Urethane

The monomers used in the production of PU for foams, coatings, adhesives, and elastomers are also associated with toxic activities [95]. Urethane (ethyl carbamate) is classified as a probable human carcinogen (Group 2A) by the IARC, with studies linking it to an increased risk of liver, lung, and other cancers in animal models (Table 2) [75,79,96,97]. Acute exposure to urethane monomers can cause irritation to the skin, eyes, and respiratory tract, while chronic exposure may result in liver and kidney damage [98]. Improper disposal of materials containing such monomers can lead to environmental contamination, posing risks to ecosystems and wildlife.

3.6. Measured Concentrations and Bioaccumulation Metrics of BPA and Styrene

From an ecotoxicological perspective, plastic degradation products occur at measurable concentrations across diverse environmental compartments (

Table 3. Concentrations of BPA and Styrene in the Environment.

Chemical	Environment	Typical Range	PNEC (Freshwater; Marine)	BCF (L/kg)	Typical RQ vs. PNEC	Refs
BPA	Freshwater (rivers/lakes)	10–10,000 ng/L	1.5 µg/L; 0.15 µg/L	25–68 (up to ~100)	Freshwater: 0.03–0.33; hotspots (1–10 µg/L): 0.7–6.7	[99,108,109]
	Marine/coastal (offshore often <10 ng/L)	5–500 ng/L	1.5 µg/L; 0.15 µg/L	25–68 (up to ~100)	Marine: 0.03–3.3; offshore typically <0.07
	Soil/sediment (near sources)	1 µg–1 mg/kg (dry weight)	n.a.	n.a.	soil/sediment PNECs variable (consult local guidelines)
Styrene	Freshwater (rivers/lakes)	5–500 ng/L; 0.1–10 µg/L near sources	~25 µg/L; ~2.5 µg/L	13–35	Freshwater: 2 × 10−4–2 × 10−2; hotspots: 4 × 10−3–0.4	[110,111]
	Marine/coastal (offshore often <5 ng/L)	1–100 ng/L	~25 µg/L; ~2.5 µg/L	13–35	Marine: 4 × 10−4–4 × 10−2; offshore typically <0.002
	Soil/sediment (near sources)	0.1 µg–1 mg/kg (dry weight)	n.a.	n.a.	soil/sediment PNECs variable (consult local guidelines)

BPA, Bisphenol A; PNEC, predicted no-effect concentration (vary by jurisdiction and derivation method); BCF, bioconcentration factor; RQ, risk quotient (RQ < 1 generally indicates low risk; RQ ≥ 1 suggests potential ecological concern); n.a., not applicable.

) [99]. In terms of BPA, freshwater rivers and lakes generally contain 10–10,000 ng/L, with typical concentrations around 50–500 ng/L [41]. In marine and coastal waters, average levels of 5–500 ng/L are usually observed, while offshore levels are often below 10 ng/L [100]. Soils and sediments near urban or industrial sources are usually contaminated with ~1–1000 µg/kg dry weight [99]. Relative to aquatic benchmarks, widely cited predicted no-effect concentrations (PNECs) for BPA are 1.5 μg/L (freshwater) and 0.15 μg/L (marine), giving risk quotients (RQs) of about 0.03–0.33 for typical freshwater (50–500 ng/L vs. 1.5 µg/L), with hotspots at 1–10 μg/L yielding RQ~0.7–6.7. Marine/coastal waters show RQ~0.03–3.3 (5–500 ng/L vs. 0.15 µg/L), indicating generally low-to-moderate risk but localized exceedances near sources [101,102]. Bioaccumulation is limited, with BPA bioconcentration factors (BCFs) in fish or invertebrates typically being 25–68 L/kg (occasionally approaching ∼100 L/kg). Styrene exhibits similarly low BCFs of about 13–35 L/kg in fish, consistent with rapid metabolism and depuration [16,103]. Overall, risk from these plastic degradation products is usually low to moderate at background levels (RQ < 1), but can be elevated in impacted waters where BPA approaches or exceeds PNECs [104]. Caution is warranted because uptake of microplastic particles by aquatic organisms and livestock can create tissue “depots” that slowly release adsorbed additives and monomers (e.g., BPA, styrene) over time [105]. Such delayed leakage may elevate internal and downstream environmental concentrations relative to water-only exposure, potentially increasing effective RQ and cumulative risk even when ambient water concentrations appear below PNEC. This underscores the need for upstream source control and systematic monitoring of microplastic burdens. The European Commission (Joint Research Centre) risk assessment reports, the European Chemicals Agency (ECHA) registered substance dossiers and the Agency for Toxic Substances and Disease Registry (ATSDR) are the primary sources for the indicated PNECs and the toxicological profiles [106,107].

4. Innovations in Sustainable Materials

To effectively mitigate the environmental and ecological threats posed by plastic degradation products, it is imperative to integrate remediation strategies with proactive upstream measures [71]. Reducing plastic production, improving and scaling up recycling, and developing truly biodegradable alternatives are key steps. Together, these actions can reduce the release of toxic monomers into the environment [72,73]. Furthermore, combining natural and artificial degradation approaches with robust waste management systems can help address the long-term risks associated with plastic pollution. By adopting a comprehensive and interdisciplinary strategy, it is possible to safeguard ecosystems, protect biodiversity, and reduce the risks to human health posed by the persistent and toxic byproducts of plastic degradation.

4.1. Alternative Plastic Materials

This group includes a diverse range of compounds specifically engineered to mitigate the environmental challenges associated with conventional plastics. These materials may be biobased, biodegradable, or a combination of both, offering sustainable solutions to reduce plastic pollution and mitigate dependence on fossil fuel-derived polymers. Biobased plastics (

Table 4. Overview on alternative plastic materials and their advantages/disadvantages.

Bioplastic Type	Description	Advantages	Disadvantages
PLA	Sourced from renewable materials such as corn starch or sugarcane; used in packaging, disposable cutlery, and 3D printing applications [112].	Lower carbon footprint during production compared to traditional plastics. Compostable in industrial facilities.	Requires specific industrial composting conditions for effective degradation. Can contaminate conventional plastic recycling streams.
PHA	Synthesized by microorganisms through the fermentation of organic materials like food waste; fully biodegradable in diverse environments, including soil and oceans [113].	Fully biodegradable and compostable in natural environments.	Production costs can be high due to the fermentation process.
Starch-Based Plastics	Derived from plant starches and molded into various forms; commonly used for single-use items and packaging films [114].	Fully biodegradable under appropriate conditions.	Requires specialized processes for degradation. Competes with food crops for agricultural land use.
Cellulose-Based Plastics	Made from plant-derived cellulose and designed to replicate the properties of conventional plastic films [115,116].	Biobased and renewable.	Production can be expensive and energy-intensive.
Bio-PE	A biobased alternative to conventional polyethylene, produced from renewable resources like sugarcane; chemically identical to traditional PE [117,118].	Renewable resource-based. Compatible with existing recycling systems for conventional PE.	Not biodegradable. Competes with food crops for agricultural land use.

PLA, polylactic Acid; PHA, polyhydroxyalkanoates; Bio-PE, bio-polyethylene, PE, polyethylene.

) are wholly or partially derived from renewable resources such as plants.

Biodegradable and compostable plastics as described above are innovative materials that are either entirely or partially derived from renewable biological sources, such as plant-based feedstocks, instead of traditional petroleum-based resources. These plastics are designed to break down into natural components, such as water, carbon dioxide, and biomass, under specific environmental conditions [119]. Compostable plastics, a subset of biodegradable plastics, are engineered to decompose within industrial or home composting systems, leaving no toxic residues behind. An example is polybutylene adipate terephthalate (PBAT), a petroleum-based plastic that is designed to be biodegradable and used in applications like packaging films and paper cup liners [120]. Similar to PBAT, polybutylene succinate (PBS) is another fossil-based, biodegradable material used for packaging [121]. By leveraging renewable feedstocks and incorporating end-of-life strategies that minimize environmental persistence, these materials present a credible alternative to conventional plastics. Together, these approaches could promote more sustainable practices in both material production and waste management.

4.2. Innovative Non-Plastic Substitutes

Novel substitutes represent a growing field of materials and technologies aimed at reducing or eliminating the reliance on conventional plastics (

Table 5. Overview on non-plastic substitutes and exemplary fields of applications.

Category	Material	Description	Applications	Key Properties
Seaweed/Algae	Seaweed Packaging	Biodegradable, compostable, and edible material derived from seaweed extracts [126,127].	Food packaging, water spheres (e.g., Notpla products).	Biodegradable, compostable, edible.
	Algae Tiles	Sustainable bioplastics made from kelp algae [128,129].	Construction materials and food packaging.	Renewable, sustainable.
Mycelium (Mushroom-Based)	Mycocomposite	Biodegradable and compostable material made from fungal root structures (mycelium) combined with agricultural waste [130].	Packaging, insulation.	Biodegradable, compostable, renewable.
Bagasse	Sugarcane Residue	Fibrous byproduct of sugarcane juice extraction, processed into biodegradable and heat-stable materials [131].	Packaging, plates, food containers.	Biodegradable, heat-stable, renewable.
Chitosan-Based Films	Chitin-Derived Films	Biodegradable films made from chitin, a compound found in crustacean exoskeletons, with antimicrobial properties [132,133].	Food packaging, medical applications.	Biodegradable, antimicrobial, brittle.
Cork	Cork Bark	Harvested from the bark of cork oak trees; cork is a renewable and biodegradable material with excellent insulation properties [134].	Insulation, flooring, household products.	Renewable, biodegradable, excellent insulator.
Upcycled Materials	Coffee Grounds	Materials created from upcycled agricultural waste, such as coffee grounds and spent grains [135].	Packaging, construction materials.	Upcycled, renewable.
	Repurposed Cloth	Textiles upcycled into new products, diverting waste from landfills [136].	Bags, accessories.	Recyclable, reduces textile waste.
	Upcycled Tires	End-of-life tires recycled into new products [137].	Wallets, planters, industrial applications.	Durable, upcycled.
Naturally Occurring Materials	Bamboo	A fast-growing, renewable plant that is biodegradable and versatile [138].	Cutlery, stationery, household products.	Biodegradable, renewable, fast-growing.
	Wood	A natural biopolymer that is biodegradable and used for various applications.	Furniture, construction, household items.	Biodegradable, renewable, durable.
	Jute	A natural fiber known for its tensile strength, durability, and recyclability [139].	Bags, ropes, textiles.	Recyclable, durable, renewable.
	Wheat Straw	The stalks left over after wheat harvesting, used as a biodegradable alternative for various products [140].	Cutlery, packaging.	Biodegradable, renewable.
	Coconut	Nearly all parts of the coconut can be utilized to create biodegradable products [141].	Bowls, mugs, packaging.	Biodegradable, renewable, versatile.
Durable Substitutes	Glass	A safe, infinitely recyclable material that serves as an alternative to single-use plastics.	Bottles, containers.	Recyclable, durable, non-toxic.
	Stainless Steel	A long-lasting, durable material that can replace single-use plastic items.	Cups, food storage containers, utensils.	Durable, reusable, recyclable.

). These alternatives include materials derived from natural fibers, such as hemp, jute, or bamboo, which can be used in packaging, textiles, and construction [122]. Additionally, advancements in materials science have led to the development of bio-based composites, mycelium-based packaging, and edible films made from seaweed or starch. These substitutes not only reduce the environmental impact associated with plastic production and disposal but also offer unique properties, such as biodegradability and renewability [123]. By integrating these alternatives into various industries, it is possible to address the challenges of plastic pollution while fostering a transition toward more sustainable and circular material systems [124,125].

5. Recycling and the Circular Economy: Advancing Sustainability Through Plastics Recycling

The concepts of high-quality recycling and the circular economy are increasingly recognized as vital strategies for addressing global environmental challenges and resource scarcity. Circular economy aims to extend the lifecycle of materials, products, and resources within the economic system. By doing so, it reduces waste and preserves the embedded value of materials [142]. Empirical evidence shows that circular economy practices, such as plastics recycling, can substantially reduce greenhouse gas emissions. This reduction occurs because recycling generally requires less energy than linear production systems that depend on virgin resource extraction and waste disposal [143]. This improved energy efficiency and resource optimization contribute to mitigating climate change and fostering sustainable development. A key component of the circular economy is sustainable product design, which emphasizes creating products that are repairable, reusable, and recyclable [144]. This often involves using monomaterials, modular construction, and durable designs to extend product lifespans. However, the implementation of such practices is often hindered by economic barriers, a lack of standardized guidelines, and insufficient infrastructure. Deposit–refund systems and take-back programs have proven effective in creating closed recycling loops for plastics, particularly for PET packaging, by incentivizing consumers with financial rewards [145]. While these systems have increased return rates, their success depends on robust infrastructure and active consumer participation. Despite these challenges, plastics recycling and the circular economy offer numerous scientifically validated benefits [146]. Recycling reduces plastic waste in landfills and the environment, lowering disposal costs, mitigating pollution, and protecting ecosystems and biodiversity [147]. It also decreases reliance on energy-intensive virgin plastic production, enhances material efficiency, and extends the lifecycle of plastics, ensuring the sustainable use of finite resources. Additionally, recycling minimizes the formation of microplastics, which pose serious risks to ecosystems and human health [148]. While challenges remain, the advantages of plastics recycling and circular economy practices underscore their critical role in addressing environmental issues and advancing global sustainability.

6. Conclusions

The widespread issue of microplastic pollution and the release of toxic monomers from degrading plastics represents a complex challenge with wide-ranging implications for ecosystems, biodiversity, and human health. Microplastic particles not only induce physical harm but also act as carriers for environmental pollutants. Additionally, chemical byproducts resulting from plastic degradation, such as BPA, styrene, and dioxins, are toxic, with the potential to cause genetic mutations and disrupt endocrine function [149,150,151]. These compounds persist in the environment, bioaccumulate in food chains, and pose long-term risks to both terrestrial and aquatic organisms [152]. Although current remediation strategies, including bioremediation, AOPs, and adsorption techniques, show promise, they are often constrained by inefficiencies, high costs, and the potential for secondary pollution.

One key area of uncertainty lies in the degradation rates of plastics under diverse environmental conditions [153]. Our current understanding of how plastics break down in marine, freshwater, and terrestrial ecosystems is incomplete. Degradation rates vary widely based on factors such as temperature, UV exposure, and microbial activity. This variability complicates efforts to predict the long-term environmental fate of plastic materials and their byproducts [154]. Furthermore, the environmental and health impacts of the byproducts generated during plastic degradation remain poorly understood. Toxic monomers and additives released during degradation pose considerable hazards, yet there is a lack of standardized testing protocols and methods to detect and quantify these substances in water and natural environments [155]. Without such methodologies, it is challenging to assess contamination levels or develop effective mitigation strategies. While laboratory-based methods such as such as gas chromatography–mass spectrometry (GC-MS), liquid chromatography–mass spectrometry (LC-MS) or Fourier transform infrared spectroscopy (FTIR) remain the gold standard for sensitivity and compound confirmation, their high cost, infrastructure requirements, and need for trained personnel limit their applicability for routine environmental monitoring [156,157]. In the near future, novel low-technology, on-site screening devices for plastic monomer detection in resource-limited settings should reliably achieve detection limits of 1 µg/L down to 10 ng/L in water and sub-ppb in air by pairing simple preconcentration steps with handheld reader devices. Such chemical analyzers will enable rapid checks of volatile monomers, while disposable electrochemical sensors will provide targeted, low-cost assays at µg/L, improving to tens of ng/L with brief enrichment [158]. Handheld Raman/surface-enhanced Raman spectroscopy (SERS) devices will offer immediate qualitative to semi-quantitative identification of plastic degradation products on surfaces and solids [159]. To ensure practicality, workflows must remain simple, using basic field quality control and suitable reference sample materials, along with battery-powered devices. Synthetic biology-based whole-cell biosensors represent an additional, rapid detection technology for food and environmental safety and demonstrate a promising additional avenue [160]. However, for these emerging tools to move beyond proof-of-concept applications, standardized validation procedures, inter-method comparability, and demonstrated robustness under real environmental conditions are required. Together, these emerging technologies should deliver adequate sensitivity and rapid qualitative confirmation of low plastic monomer concentrations with minimal training and preparation. Addressing economic and social barriers, such as unequal access to analytical infrastructure, regulatory fragmentation, and limited technical capacity, will be essential to ensure global applicability.

Besides challenges in detection, the potential bioaccumulation of toxic monomers in food chains remains largely underexplored from the basic research perspective, leaving critical gaps in our understanding of their long-term impacts on ecosystems and human health [161]. Therefore, to effectively tackle the dual challenges of microplastic pollution and the release of toxic monomers, a comprehensive and interdisciplinary approach is essential. However, to ensure the success of reduction and recycling strategies, obvious critical research and knowledge gaps must be tackled. By prioritizing interdisciplinary research, we can address uncertainties in degradation rates and develop standardized testing protocols for monomers and additives [162]. This will prove crucial to investigate the toxicity and biological consequences of microplastics and their byproducts [163]. These efforts, combined with advancements in material science, waste management, and policy, can drive a global transition toward more sustainable and eco-friendly material systems.

Despite these challenges, there remains substantial reason for optimism. The development and adoption of alternative materials offer a transformative path forward. Biobased and biodegradable plastics, such as PLA and PHA, along with innovative non-plastic substitutes like mycelium-based packaging, seaweed-derived films, and upcycled materials, provide sustainable solutions to reduce dependence on conventional plastics. These alternatives not only degrade more readily in the environment but also align with circular economy principles by utilizing renewable resources and offering end-of-life biodegradability. Such innovations demonstrate the potential for a future where materials are designed to minimize environmental harm while meeting societal needs.