Introduction

Overwhelming environmental accumulation of plastic waste and its deleterious impacts have been underlined and validated with enough scientific evidence in the last couple of decades [1,2,3,4]. Several worldwide campaigns and perpetually increasing consumer awareness persuaded lawmakers from several countries in African, Asian and European continent to completely ban or implemented levies on the use of single-use plastic [5]. Consequently, Bioplastics (BPs) have started gaining attention as an “environment-friendly” alternative to conventional plastics with roughly a 25% growth estimated in their global market by 2023 [6]. With such a rapid growth expected, without assuming, it is critical to question if bioplastics offer a tangible solution to the global plastic waste problem and whether the rapidly growing bioplastic industry is being properly regulated.

To regulate the growing industry, a continuous emergence of bio-based, biodegradable and compostable plastic standards is taking place. However, several matters surrounding the operations and certification need immediate attention before bioplastics pollution emerges as the next environmental concern. First, “Bioplastics” is a poorly defined umbrella term creating misperception and tremendous confusion. According to European Bioplastics, a plastic is defined as a bioplastic if it is bio-based, biodegradable or features both properties [7]. The misperception originates when the connotation of “bio-based” and “biodegradable” is considered the same. “Bio-based” means that the origin of the product is either in full or partially derived from plant biomass explained frequently with a plethora of terms like ‘plant-derived’, ‘new carbon’ or ‘organic carbon’ etc. (see Table 1 for other bioplastic related terms). However, bio-based origin does not infer to the biodegradability of a material that indicates the environmental fate of a material. Therefore, a universal nomenclature for bioplastic products is the first essential step to ensure that consumers are well-informed and choose the correct waste treatment streams for bioplastic products.

Table 1 Definitions of common terms used to classify polymeric materials [7, 60]
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Bio-based plastic products are designed to meet the necessary functionalities during their use. Upon disposal, it is expected to biodegrade within a specified time frame while leaving no toxic residues. However, there is no data to support the complete biodegradation of these products within a reasonably short period [8]. If the blurred distinction between bio-based and biodegradable bioplastics is not fixed soon, more microplastics will be generated from bioplastics disregarding their original purpose as an environmentally safe alternative. Therefore, benchmarking bioplastics using a universally accepted set of biodegradability parameters is crucial.

Finally, the multifarious international bioplastic standards follow dissimilar guidelines which are highlighted and discussed for their relevance (or absence) in the natural environmental setting. Since the substantiations of biodegradability of bioplastics differ between standards, the need for stronger regulation and compliance as per their life-cycle assessment (LCA) and recycling requirements is emphasised. The review has closely looked at the factors affecting biodegradability and the possible impacts of the potential environmental accumulation of bioplastic degradation products. We have also highlighted the importance of regulating the attractive labelling of products (as “biodegradable”, “compostable”, “degradable”, “100% renewable” etc.) to ensure validity among the consumers. For the sake of clarity, different bioplastic certification standards introduced across the world are critically compared which include ISO (International organisation for Standardization), American Society for Testing and Materials (ASTM), Australian standard (AS), European Committee for Standardization (CEN), German Institute for standardization (DIN) and GreenPla (Japan).

Bioplastics: Definition and Types

The main issues encountered with the design and production of bioplastics are keeping production costs down and the optimisation of physical, chemical and mechanical properties to ensure biodegradability [9]. The lack of stringent policies and consumer awareness allows manufacturers to embellish their product names with safe words like “green” and “eco” creating a false sense of responsible behaviour among the consumers. Based on the origin of the raw material and environmental fate, all bioplastics can be assigned to the following three categories (Fig. 1).

Fig. 1
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Characterisation and examples of bioplastic materials based on their source and biodegradability (modified from EUPB [7])

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Type I: Bio-Based and Non-biodegradable

The bioplastic products such as polylactic acid (PLA), thermoplastic starches (TPS), polyhydroxyalkanoates based on natural or renewable feedstock follow the same pathway, technology, equipment and machinery as their conventional counterparts. Thus, they are essentially a “bio-similar” copy of the conventional (fossil-based) plastics and are not biodegradable or compostable [10]. They are also known as ‘drop-ins’ or ‘bio-blend’ and sometimes can contain starch or other biodegradable components in smaller amounts to only accelerate their fragmentation [11, 12]. However, once fragmented into microplastics, these bioplastics essentially have the same environmental impact as fossil-based plastics.

Drop-in bioplastics include commodity plastics like bio-based Polyethylene (PE), Propylene (PP), Polyvinyl chloride (PVC) and Polyethylene terephthalate (PET). A noteworthy example is “Plantbottle”, a material launched in 2009 by the Coca-Cola company (Fig. 2), in which the fossil fuel-based ingredient used to make a key ingredient in PET plastic, was replaced with renewable materials from plants (30% plant-based). Coca-Cola reported that “Plantbottle”, has helped prevent 365,000 metric tons of potential CO2 emissions since its introduction [13]. While the plant bottle is recyclable, the properties of the product are identical to their conventional versions (not biodegradable or compostable), though the leaf in its design suggests otherwise. The caveat here is that their success is relying on a 100% recycling rate, otherwise, plant bottles could produce microplastics similar to conventional plastic bottles. Other non-biodegradable technical/performance polymers (Fig. 1) included in this category are bio-based polyamide (PA), polyesters like poly (trimethylene) terephthalate (PTT) and polybutylene terephthalate (PBT), polyurethanes (PUR) and polyepoxides typically used as textile fibres, whose operating life lasts several years but are clearly not biodegradable [7].

Fig. 2
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PlantBottle by Coca-Cola

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Drop-ins and conventional plastic differ in their price and environmental footprint. Drop-ins are more expensive due to lower processing capacity, lower investment in research and development and higher price of raw material compared to conventional plastics. The only conceivable advantage of drop-ins is their lower environmental footprint [14]. Briefly, conventional plastic production introduces new carbon-dioxide (CO2) but the CO2 released during the manufacture of drop-ins could be captured by the plants providing the raw material, thus theoretically completing the cycle.

Type II: Bio-Based and Biodegradable

Bioplastics belonging to this category could be produced from plant biomass, microbial fermentation products and animal-derived polymers to emulate the life cycle of biomass producing CO2 and water while conserving fossil resources [7]. Plant-derived raw materials (which include vegetable oil, starch from wheat, rice, barley, oat and soy sources, fibres obtained from pineapple, jute, hemp, henequen leaves and banana stem, etc.) are used to extract thermoplastic starch, lignin, rubber, cellulose, etc. required for bioplastic production [15, 16]. Polyurethane foam with up to 50% renewable content is produced using biomass biopolyols from three residual biomass feedstocks: digested sewage sludge, hemp stalk hurds and sugar beet pulp [17]

Bioplastics derived from microbial sources are mainly polyesters [e.g. poly (3-hydroxybutyric acid)] which are storage polymers enzymatically produced by certain microbes to support their survival and growth when subjected to different nutrient and environmental stressors [18]. Given the high production and recovery cost, the use of microbial fermentation for bioplastic production is still very limited [19]. Animal-derived products such as chitin, silk, wool, casein, gelatine, gluten and fats are also be used in bioplastic production [20, 21]. Recently, collagen has been suggested as a potential source to create “bioplastic skin”, mainly derived from animal hides, to tackle the issue of waste generated in the meat and plastic industries [22]. Commercial bioplastics belonging to this category include Polylactic acid (PLA), Polybutylene Succinate (Bio-PBS), Polyhydroxy butyrate (PHB) and polybutylene adipate terephthalate (PBAT) (Fig. 1).

Type III: Fossil-Based and Biodegradable

Some fossil-based polymers used for bioplastic production inherently possess a certain amount of biodegradability including aliphatic polyesters like polybutylene succinate (PBS), poly-caprolactone (PCL), polyglycolic acid (PGA) and polyvinyl alcohol (PVOH); aromatic polyesters like polybutylene terephthalate (Fig. 1) [20, 23, 24]. Polymer degradation studies suggest that chain characteristics like hydrophilicity, reactivity, functional group stability; and mechanical properties like molecular weight (M.W.) and elasticity generally dictate biodegradability, not the origin of the raw materials [25, 26]. For instance, PCL, which is not bio-based, can completely degrade after only six weeks in compost conditions that utilise activated sludge given that no additives are present [27]. In the presence of overlapping definitions for bioplastic products, it is imperative that a detailed classification and specialized nomenclature is prepared to represent bioplastic origin and biodegradability.

Biodegradation of Polymers

Biodegradation occurs due to the action of enzymes from naturally occurring microbes (bacteria, fungi and algae) resulting in a reduced molar mass of macromolecules forming the biodegradable material [28, 29]. The process of biodegradation can be divided into (1) primary degradation and (2) ultimate degradation. During primary degradation, the material undergoes weight loss, fragmentation, reduction in M.W. and is degraded into soluble low M.W compounds. Ultimate biodegradation or mineralization leads to the conversion of low molecular weight compounds (from primary degradation) into water (in aerobic conditions), CH4 (in anaerobic conditions), CO2 and cell biomass [24, 29,30,31,32]

Compostability is a subset of biodegradability meaning that most biodegradable plastics are compostable. According to American Society for Testing and Materials (ASTM standard D6400), compostable plastic is “a plastic that undergoes biological degradation during composting to yield carbon dioxide, water, inorganic compounds and biomass at a rate consistent with other known compostable materials and leaves no visually distinguishable or toxic residues. Thus, the overall criteria of compostability of a material involve biodegradability, disintegration, non-toxic by-products and no visual distinction from the surroundings [33]. To be characterised as compostable, the following criteria must be fulfilled [34]: (a) Material/chemical characteristics: Organic and inorganic matter content, (b) Biodegradability: Extent of biodegradation or mineralization defined as the conversion of the organic carbon to CO2, (c) Disintegration: Degradation of material int visually undetectable components (< 2 mm) under controlled composting conditions and (4) Ecotoxicity: The compost obtained at the end of the composting trial, eventually containing undegraded residuals from the product, should not affect the germination and growth of plants and also earthworms in some cases. These criteria are used in the next section to discuss current global standards for biodegradable plastics and identify potential shortcomings in context to addressing critical environmental issues surrounding the use and disposal of bioplastic materials.

The biodegradability of material is greatly governed by its polymer structure [35]. Most polymer structures have either a hetero-chain or carbon backbone. Hetero-chain polymers include polysaccharides, proteins, polymers sourced from plants such as PLA, PBS and microbially-synthesized polymers like PHVB. Hetero-chain polymers degrade via enzyme-mediated or non-enzyme-mediated hydrolysis which can be influenced by factors such as thickness, chemical bonds, co-polymer type, water uptake and morphology. Polymers with carbon backbone such as natural rubber and lignin, biodegrade via oxidation or enzyme mediated (oxidative) biodegradation which may take years and slower compared to hetero-chain polymers [36]. As discussed earlier, most materials referred as biodegradable are often biocomposites which are created by blending other biodegradable materials like potato peel waste fermentation residue [37], empty fruit branch fibres [38] with the main bioplastic material to enhance their biodegradability. Consequently, the addition of such eco-friendly composites does not guarantee enhanced biodegradation as the variability in temperature and other factors in the real field conditions across the globe are arduous to address [39].

Apart from polymer properties, the rate and degree of biodegradation is dependent on various abiotic and biotic factors. For instance, in compost and soil where the higher temperature is available for degradative reactions, the rate of biodegradation is higher [40]. Similarly, the concentration and diversity of microbial communities are higher in soil and compost that supports higher rates of biodegradation (Fig. 3) [41]. In the aquatic systems, microenvironments have been shown to have a profound impact on the degradation of biodegradable plastics. Therefore, to efficiently capture the complexity of the aquatic environments, test methodology needs to account for all the habitats (supralittoral, eulittoral, sublittoral benthic, deep-sea benthic, pelagic and sediments) along with abiotic stressors (pH, salinity, temperature, UV etc.) and microbial communities influencing degradation [41, 42]. Other factors impacting biodegradation of materials include salinity, humidity, oxygen presence, pH and UV radiation [43, 44]. Major studies on biodegradation of bioplastics conducted in the laboratory and natural conditions are summarized in Table 2.

Fig. 3
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Rate of biodegradation in different environments

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Table 2 Major studies on biodegradation of bioplastics in different environments
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Global Bioplastic Standards and Certification Bodies

The major standardizing bodies creating standards are ISO International Organization for Standardization), CEN (European Committee for Standardisation) and ASTM (American Society for Testing and Materials). Also, many national standardization organizations like Australian standard (AS), German Institute for standardization (DIN) and Japan Bioplastic Association (JBPA) have created their own standards by incorporating extra testing procedures for better regulation. Standardization introduces benchmarks for desirable product quality requirements and ensures that fraudulent market behaviour is prevented. For instance, European Bioplastic association describes two systems of product evaluation: (1) use of test methods which include procedures that need to be followed using the described methodology and (2) use of a definitive set of a pass and fail criteria as the requirements that need to be met for a product or material to be compliant with the standard [45]. While these two types are often paired, the use of the second system (pass/fail) ultimately defines standard compliance. Although compliance to a standard can be voluntary or mandatory in a country, an independent standards certification of compliance obliges a product be tested and examined by an independent certification body that recruits both systems of product evaluation explained previously (Fig. 4). Since the main objective of this review is to highlight the differences in the process of product evaluation in different parts of the world, detailed information on the certification requirements by major global standardization bodies is provided in the next few sections.

Fig. 4
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Major global bioplastic standards and certification bodies

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European Committee for Standardisation

In Europe, independent certificates for biodegradable plastics are issued by DIN Certco (based on EN 14995 or ISO 17088) and Vincotte (based on EN 13432) which also certify products which can degrade in home composting, soil and water. The plastic used in packaging can provide proof of their compostability by successfully meeting the harmonised European standard, EN 13432:2000 or EN 14995:2006 which defines the technical specification for the compostability of bioplastics products.

  • Material characterization: European standard CEN/TS 16137:2011: Plastics—Determination of bio-based carbon content specifies the calculation method for determining the bio-based carbon content in monomers, polymers and plastic materials and products, based on the 14C content measurement (described in EN 15440 and ASTM D6866). It is currently the most important guideline for substantiating marketing claims regarding a material’s or product’s bio-based carbon (total and organic) content. Additionally, EN 16640:2017 and EN 16785:2018 contain methods to determine bio-based content using elemental analysis and material balance method.

  • Biodegradability: Biodegradation level of at least 90% must be reached in less than 6 months for any packaging products or biodegradable plastics, regardless of the type of polymer. The standard EN 17033 “Biodegradable mulch films for use in agriculture and horticulture—Requirements and test methods” specifies the requirements for biodegradable films, manufactured from thermoplastic materials, to be used for mulching applications in agriculture and horticulture, which are not intended to be removed. A degradation of at least 90% in two years at preferably 25 °C is required.

  • Disintegration: After 84 days in a controlled composting test, no more than 10% of the original dry mass of material should remain after sieving on a 2 mm sieve.

  • Ecotoxicity: The seedling growth test follows OECD Chemical Guidelines 208 (OECD, 2003) which involves comparing two higher plants (from Dicotyledonae and Monocotyledonae families), when one plant has added biodegraded plastics, and the other does not. The effect is observed as changes to plant germination and plant growth. The germination rate and plant biomass for both species should be 90% the same, as a minimum. The compost must not be negatively affected by control waste treatment processes and the parameters to be considered are volumetric weight, total dry solids, volatile solids, salt content, presence of nitrogen, ammonium, phosphorus and magnesium, and potassium. Acceptable heavy metal concentrations are specified (Table 3) and should not exceed the threshold.

    Table 3 A comparison of Prescribed threshold values for elements within constituents of bioplastics (EN13432 and ASTM D6400)
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International Standards organization

Currently, ISO 17088:2012 “Specifications for Compostable Plastics” specifies procedures and requirements for the identification and labelling of plastics, and products made from plastics, that are suitable for recovery through aerobic composting.

  • Material characterization: Chemical characterization of material including the analysis of organic content, nutrients and hazardous substance (organic and inorganic) is not specified in the standard.

  • Biodegradability: To meet biodegradability/mineralization requirements, 60% of organic content from a homopolymer and 90% of all other (copolymers or blends) must be converted to CO2 within 180 days.

  • Disintegration: Given in ISO 16929:2013 “Plastics—Determination of the degree of disintegration of plastic materials under defined composting conditions in a pilot-scale test”; according to which after 84 days in a controlled composting test, no more than 10% of the original dry mass of material should remain after sieving on a 2 mm sieve.

  • Ecotoxicity: Low level of heavy metal concentration based on EN 13432 and a minimum of 50% volatile solids (APHA 2504G) is specified. Volatile solids are the solids obtained by subtracting residues after incineration at 550–580 °C from total dry solids content and is an indication of the amount of organic matter in the material. For ecotoxicity assessment, the terrestrial plant test as per OECD Chemical Guidelines 208 is required.

American Society for Testing and Materials

In the USA, Biodegradable Products Institute (BPI) provides certification based on ASTM standard. As per current standard ATSM D6400-19: “Standard Specification for labelling of plastics designed to be aerobically composted in municipal or industrial facilities”, a material must biodegrade completely when exposed to an inoculum derived from a municipal waste stream. The United States Federal Trading Commission of USA requires ASTM D5338-15 as a requirement for making biodegradability claims about a product or material in which aerobic biodegradation of bioplastics for a minimum of 90 days but up to 180 days at a temperature greater than 50 °C is measured. It’s primarily used for materials that have not made it to the waste stream yet, often being used for materials intended to test food and beverage containers.

  • Material characterization: Chemical characterization of the organic constituent present more than 1% must be individually tested. Analysis of nutrients and hazardous substances (organic and inorganic) is not specified in the standard.

  • Biodegradability: For products consisting of a single polymer (homopolymer or random copolymer), 60% of the organic carbon and for products consisting of more than one polymer like copolymers, blends and addition of low molecular additives, 90% of the organic carbon must be converted to CO2 by the end of the test period within 180 days when compared to the positive control.

  • Disintegration: After 84 days in a controlled composting test, no more than 10% of the original dry mass of a material should remain.

  • Ecotoxicity: Levels of heavy metal concentration (based on EN13432) must be determined. Ecotoxicity assessment follows OECD Chemical Guidelines 208.

Standards Australia

Standards Australia is an independent, not-for-profit organisation recognized by the Australian Government as the prime non-government standards body. They adopt internationally aligned standards in Australia but are not responsible for enforcing, regulating, or certifying compliance with these standards. The Australasian Bioplastic association manages a voluntary verification scheme (https://www.bioplastics.org.au/certification/), for companies or individuals wishing to have their claims of compliance with AS verified which in turn provides the companies a competitive advantage. There are two Australian standards relating to biodegradable plastics

(a) AS 4736–2006: “Biodegradable Plastics Suitable for Composting and other Microbial Treatment”

  • Material characterisation: The constituents of the plastic and the properties for each constituent, such as thickness and visual observations are recorded (Shah and others, 2008) along with the volatile solids content which must form a minimum 50% of the plastic. The presence of metals and hazardous substances are analysed and must not exceed the standard values (Table 3). The organic carbon content and the total dry solids of the plastic are also recorded.

  • Biodegradability: Standards test is conducted aerobically over 6 months and to pass the criteria the test material must degrade at least 90% of its dry weight. All organic constituents must be analysed, including dyes, inks, and colours. Biodegradability is to be determined for the whole material and any constituent present in the plastic at a greater concentration than 1%. The constituents forming less than 1% of the plastic composition need not be tested. An alternative method to test for biodegradation is the anaerobic test, expressed as the percentage of biogas production which must be greater than 50% within two months.

  • Disintegration: A disintegration test is satisfied when there is sufficient degradation of the test material achieved within 12 weeks. No more than 10% of the dry weight of the material can fail to pass through a 2 mm fraction sieve. Also, the plastic material must not be able to be distinguished from other materials in the compost from 500 mm away.

  • Ecotoxicity: Ecotoxicity assessment follows OECD Chemical Guidelines 208 but a further test that is unique to Australian standards testing involves toxicity test for earthworms that comply with ASTM E1676. According to this, less than a 10% difference in the morbidity or mean weight of surviving worms between the treated compost and the control, needs to be achieved to pass the test.

(b) AS 5810–2010: “Biodegradable plastics suitable for home composting”

Since home composting systems vary considerably in their design, construction and operation; their performance can also vary considerably compared to commercial composting facilities. Consequently, AS 5810–2010, in comparison to AS 4736–2006, uses lower temperatures in test environments and longer test duration, to account for such variations in the performance of different home composting systems. In the case of a plastic product formed from different components, where some are compostable and others not, the product itself, cannot be designated ‘home compostable’. The plastic product or plastic component is designated as ‘home compostable’ only if all the criteria set out below are met:

  • Material characterisation: As with AS 4736–2006 above

  • Biodegradability: As with AS 4736–2006 above, except period is up to 12 months and temperature should be 25 ± 5 °C and shall be kept below 30 °C for the duration of the test)

  • Disintegration: As with AS 8746–2006 above, except period is up to 180 days and temperature should be 25 ± 5 °C)

  • Ecotoxicity: As with AS 8746–2006 above.

Japan Bioplastic Association

Japanese Institute of Standards does not provide any generalised standard for the regulation of bioplastics. In Japan, GreenPla verifies biodegradable plastics using ISO methods and evaluates based upon the pre-established criteria by Japan BioPlastic Association (JPBA). They have developed a “Green Pla” biodegradable plastics certification system which adopts a similar framework for regulation but is still unique in much of its approach to regulation.

  • Material characterization: All the constituents of material must be placed in a ‘Positive List’ provided by Green Pla (see Table 4 for details) and the constituents belonging to category A must at least form 50% of the weight or volume of a product and is biodegradable. Additionally, the upper limits are specified for metals and other elements (Table 3). However, there is no such limit to pass the test other than that it should be biodegraded by 60% of the parent material. Non-biodegradable high-polymer material can be present at concentrations less than 1% if it is proven that it serves a useful function.

    Table 4 Positive list by Japanese Green Pla bioplastic certification system
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  • Biodegradability: To meet biodegradability/mineralization requirements, 60% of organic content from a homopolymer and 90% of all other (copolymers or blends) must be converted to CO2 within 180 days.

  • Disintegration: As per ISO 16929:2013

  • Ecotoxicity: Ecotoxicity assessment follows OECD Chemical Guidelines 208 but a unique feature of the Green Pla certification system is its acute toxicity testing conducted on freshwater organisms which involve undertaking three types of tests: algal growth inhibitors, acute immobilisation tests on Daphnia, and acute toxicity tests on fish. This test records LD50 and ED50 where LD50 should be at least 2000 mg/kg.

As evident, the agreed product evaluation criteria are noticeably different for each standard which can complicate the process of benchmarking bioplastics. Particularly, the material characterization differs significantly between standards which not only can influence the life cycle of bioplastic but can significantly influence their environmental impact (discussed in the next few sections). A List of all the major published standards is provided in Table 5 and a snapshot of the significant differences between these standards is provided in Table 6.

Table 5 List of published standards for biodegradation of plastics
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Table 6 Comparative summary of bioplastic standards around the world
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Shortcomings in Bioplastics Benchmarking and Environmental Impacts

Globally, compliance to a bioplastic standard could be voluntary or mandatory which the United Nations has commented on the lack of international cohesion, stating that until there is an internationally agreed definition of biodegradability, the labelling of products as ‘bioplastics’ will not bring about a significant decrease in the amount of plastics entering the ocean [46]. The lack of regulation over what is considered ‘biodegradable’ could potentially enhance the post-disposal risks. For instance, most of the standards require that biodegradable materials must degrade (not biodegrade) by at least 90% and are not visible at a 500 mm height. No further treatment is advised once the material reaches the microscopic size. Consequently, bioplastics microparticles could remain in the environment if they do not meet optimum biodegradation conditions (heat, water and microbes). Therefore, it is quite imaginable that bioplastics will behave like conventional plastics, find their way in landfills or the ocean and do not decompose in a reasonable amount of time.

Recognisability, the final test, is a subjective, consumer-based criterion, which requires plastics entering the biowaste stream to be recognised as compostable by the end-user. The key criticism is the failure of standards in enforcing the companies to provide details on adequate waste management for their product, which in turn, brings more responsibility to consumers. Contrastingly, incorrect labelling of bioplastic products as “green’ or ‘biodegradable”, reduces the personal consumer responsibility which results in inappropriate disposal of bioplastic products. Dotted lines in Fig. 5 represent the lack of flow of appropriate information about the life-cycle and disposal of bioplastics.

Fig. 5
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Bioplastics and us- Dotted lines show the lack of consumer information surrounding the labelling, use, disposal and fate of bioplastic products

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Another discrepancy within the mentioned standards is around the characterization of biodegradable materials components. Standards follow a definite list of elements in which a product should comply to requirements for certification. However, threshold values of the elements greatly differ between all the standards (Table 3) which further complicates waste allocation and environmental impact assessment of bioplastic additives and degradation products [47]. Besides, currently, there is no standard providing clear pass/fail criteria for the degradation of plastics in seawater. ASTM D7081 “Standard Specification for Non- Floating Biodegradable Plastics in the Marine Environment” has been withdrawn without replacement and only the test methods that were referred are still in places such as ASTM D6692, ASTM D7473, OECD 306 and ISO 16221. None of these accounts for the variation between polymer types, or any variation arising from additives. Additionally, they do not account for unmanaged water systems, the dissemination of microplastics, or the overall toxicological effect of material for a complete assessment of habitat within a time frame.

The prevalent argument in support of expanding the bioplastic market is its sustainability and low carbon footprint. Detailed information on how to measure and report on the carbon footprint of products is provided in ISO 14067 “Carbon Footprint of Products”. Additionally, the two standards ISO 14040 and ISO 14044 focus on describing the principles of LCA. In Europe, the equivalent standard is EN 16760 which is based on the ISO 14040 series and EN 16751 which standardises the sustainability criteria of bio-based products and provides specific LCA requirements. However, it does not include any thresholds or limits and is unsuitable for making claims on the sustainability of products or operations. There are many other certification schemes for the sustainability of biomass, for example, ISCC PLUS, RSB (Roundtable on Sustainable Biomaterials), or REDcert but they are not based on a standard but the provisions of the EU Directive 2009/28/EC (Renewable Energy Directive).

Bioplastics in the Circular Economy

Global production capacities of bioplastics are predicted to reach about 2.62 million tonnes [6] in 2023, and this is the right time to investigate the environmental fate of so-called “Bio’-plastics” and make sure potential risks are addressed. To assess the environmental risks of bioplastics, the environmental impact of production, use and disposal of bioplastic (“cradle to grave”) needs to be determined (lifecycle of bioplastics in Fig. 6). It is also known as life cycle analysis (LCA) which is based on characterising and comparing environmental impact (Table 7) using most important indices of environmental impact detailed below [48]:

  1. (a)

    Abiotic depletion—this characterization factor considers the potential of abiotic depletion of the extraction of those minerals and fossil fuels and expressed as kg of antimony per kg of extracted material

  2. (b)

    Global warming—This determines the potential of global warming of greenhouse gas emitted to the air during the production of a material and expressed as kg of carbon dioxide equivalent per kg of emission

  3. (c)

    Human toxicity—the characterization factor is the potential of human toxicity of toxic substances emitted to the air, water or/and soil and expressed as kg of 1,4-dichlorobenzene equivalent per kg of emission

  4. (d)

    Freshwater aquatic ecotoxicology—it is the potential of freshwater aquatic toxicity of each substance emitted to the air, water or/and soil and expressed as kg of 1,4-dichlorobenzene equivalent per kg of emission

  5. (e)

    Marine aquatic ecotoxicology—is characterization factor considers the marine aquatic toxicity of each substance emitted to the air, water or/and soil and expressed as kg of 1,4-dichlorobenzene equivalent per kg of emission

  6. (f)

    Terrestrial ecotoxicology—it is the potential of terrestrial toxicity of each substance emitted to the air, water or/and soil and expressed as kg of 1,4-dichlorobenzene equivalent per kg of emission

  7. (g)

    Photochemical oxidation—it is measured as the potential of photochemical ozone formation of each substance emitted to the air and expressed as kg of ethylene equivalent per kg of emission

  8. (h)

    Acidification—the acidification potential of for each acidifying emission to the air expressed as kg of sulphur dioxide equivalent per kg of emission

  9. (i)

    Eutrophication—it is the potential of eutrophication of each eutrophying emission to the air, water and soil and expressed as kg of phosphate ion equivalent per kg of emission.

Fig. 6
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Life cycle of Bioplastics

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Table 7 Life cycle assessment of bioplastics compared to conventional plastics
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From the greenhouse gas emission and energy demand point of view, the production of bioplastics might appear advantageous compared to conventional plastics [49] but the presence of non-biodegradable polymers in drop-ins significantly increases the energy demand and CO2 emission compared to biodegradable bioplastics. The energy recovery by incineration of bioplastics is also low which can be justified due to their low calorific value compared to fossil-based plastics [50].

We are already facing a global challenge of mismanaged plastic waste due to insufficient capacity of collection, sorting and recycling which renders it difficult to transition towards a circular economy for plastic (European commission, 2019). With ever-evolving socioeconomic and material-level inventions, the bioplastic material landscape is continuously advancing. Hence, many innovative bioplastics are entering the markets, which is also the result of sustainability and circular economy influencing the bioplastics industry [51]. In 2019, the agro-based feedstock for the production of bioplastics (which is mostly 1st generation) used about 0.016 percent (0.79 million ha) of the global agricultural area which is expected to increase to 0.021% (1.00 million ha) by 2024 [6]. Although currently, the land-use for feedstock production for bioplastics is low, the increase in demand can certainly put additional pressure on limited resources, such as land, water with implications for food security and climate change [52]. Thus, an alternative means of producing bioplastics in large quantities is important for supporting a sustainable source of plastics. In this context, micro and macroalgal biomass provide a potential source for producing bioplastics, both by directly using the biomass, as well as using it as a feedstock for secondary processes [53]. Due to their biodegradability and similarity to petroleum-based plastics, bioplastics derived from microalgae provide an ecological alternative as they can be used with the existing infrastructure and applications.

Potential Negative Impacts of Bioplastics on the Environment

The current bioplastic standards allow for the inclusion of additives and heavy metals. The US standard has the highest thresholds for toxic metals in bioplastics which are known to cause a myriad of effects on organisms and the environment [54, 55]. Aside from metals and other additives, the actual constituents of the bioplastics may themselves have adverse environmental impacts. For example, PLA is derived from corn starch which emits methane, a much more potent greenhouse gas than carbon dioxide, as it decomposes in a landfill. Production of PHA requires the use of harsh chemicals like pyridine and diethyl ether which have potential occupational hazards. The data on the energy requirement of bioplastics is still controversial and the environmental impacts of the bioplastic constituents during their production could be potentially hazardous (Table 8) and warrants further research [56].

Table 8 Environmental impacts of production and/or use of commonly used bioplastics constituents modified from [56]
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Microbial communities play an essential role in regulating elemental life cycles and environmental degradation of various materials. When compared to conventional plastic bags, biodegradable bags were found to have substantially less chlorophyll on their surface in the marine environment indicating that the material type could be influencing the recruitment and/or persistence of algae. Additionally, a change in the physicochemical characteristics of marine sediments beneath plastic bags, with a linked reduction in sediment fauna abundance has been observed [57]. Bioplastics can also increase the susceptibility of coral to diseases, which subsequently has habitat implications for the marine environment [58]. More studies are warranted on the interaction of bioplastic with the microbial communities in the environment for a proper environmental assessment of bioplastics products and to avoid creating another environmental mayhem.

Bioplastics are difficult to dispose of given their longevity, toxicity, malleability, and potential to disintegrate into microplastic. The lack of bioplastic-specific recycling facilities increases the risk of degradation products getting collected through existing recovery systems for conventional plastics and contamination of the recycling stream. As a result, the mechanical properties will change significantly, and the quality of the recycled material will be low [11, 38, 59]. Contamination of the recycling stream can be minimised through improved sorting techniques, possibly using spectroscopic techniques, and by regular testing of the incoming materials [59]. Therefore, before we replace conventional plastics with bioplastics, all tiers of government must have suitable recycling policy and programs which enable bioplastics to be disposed of correctly at facilities specially designed for bioplastic waste.

Summary

Plastic pollution being a major scientific and environmental issue is likely to encourage the use of biodegradable plastics, as a suitable amelioration strategy. While we encourage research and development for better performing bioplastics, it is necessary to adopt a ‘cradle to cradle’ approach which assesses the environmental impact of bioplastic constituents and degradation products. The present disparities in bioplastic policies between jurisdictions, national, subnational and international platforms only prove that the bioplastic regulation is currently NOT on the global agenda. The common denominator for policymakers is to keep flexibility to prevent the development of intractable situations that can work against innovation. While bringing all the standard bodies together is an essential step, a policy framework which would encompass the following recommendations can be useful:

  • Creating international agreement about LCA, biodegradability, compostability

  • Introducing laws and strict policies which would relate to the standards and more closely regulate the improper use of labelling of ‘biodegradable’ to avoid doubt among the consumers

  • Revoking standards to assess the impact of plastic additives, different temperatures, and other variables known to cause different rates of biodegradation which are not currently tested

  • Utilising a broader range of testing environments to determine biodegradability under different conditions, including a range of aquatic environments present in various geographical locations

  • Harmonisation LCA procedure while involving as many indices for environmental impact as possible

  • Communicating to consumers the correct disposal methods of bioplastics through appropriate labelling, reinstating their responsibility for its right disposal

  • Introducing effective and widespread recycling services and facilities which accept bioplastics for composting purposes; and

  • Establishing additional tests and facilities so that the new researchers can quickly and easily test their products without wasting time