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Biodegradable and compostable plastics in the environment

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  • What are plastics?
    The word plastic is derived from theancient Greek term plastikós, meaning ‘shapable’ or ‘mouldable’. Plastics are made up of
    largechemical units known as polymers, which arein turn made up of repeated smaller units called monomers. Many polymers
    arecapable of being moulded into different shapes when heated, acharacteristic that has likely given this group of materials
    the name plastic. We generally think of plastics as being manufactured from petrochemical (or fossil-fuel)-based sources.3 Forexample, the gas
    ethene(ethylene) is produced by reacting fossil hydrocarbons with steam at very high temperatures and is used to create
    polythene(polyethylene), the polymer that wecommonly seein theform of plastic bags at thesupermarket. But plastics can
    also be derived from other sources, including microbes and plants. These plastics areknown as ‘bio-based’ plastics.
    Plastics often incorporateadditives that changetheir specific properties, such as their strength and durability. Theseinclude UV
    stabilisers, anti-oxidants, dyes and flameretardants. Notes
    3. Sources from oil and gas make up over 90% of thefeedstock for plastics (World Economic Forum. 2016. The New
    Plastics Economy: rethinking the future of plastics, p. 13).
  • What does it mean to say that a plastic is biodegradable?
    Biodegradable means that an item can be broken down by theaction of living organisms, typically microbes. In thecase of
    biodegradable plastics, this process is enabled byenzymes that are produced by microbes that usethe plasticas asource of
    energy – the microbes areessentiallyeating the plastic for food.
    It is important that biodegradation is not confused with other natural processes. For instance, most plastics will eventually
    break down into fragments through the weathering effects of sunlight, heat and friction if given enough time. This is
    degradation, not bio-degradation. To biodegrade, the polymers need to be broken down through theaction of living cells into
    simplechemical elements.
    Thespeed of biodegradation varies greatlyand is highly dependent on theenvironment in which the plastics end up. This will
    affect thevalue of the biodegradable product – few would consider a plastic bag to be usefully biodegradableif the process
    takes hundreds of years. Likewise, biodegradability will be of questionablevalueif the breakdown process gives riseto toxic
    products. This is wherestandards are helpful. New Zealand does not haveastandard for biodegradable or compostable plastics. However, some plastic manufacturers have
    voluntarily sought certification using some of theexisting international standards so that they can label their products
    accordingly. An industry working group has been set up to consider whether adoption of a What do biodegradable plastics break down into?
    Ultimately, a biodegradable plastic will break down into small molecules, such as carbon dioxide, methaneand water, as well as wastefrom microbial activity.
    The Organisation for Economic Co-operation and Development uses theterm ultimate biodegradability – thelevel of
    degradation achieved when thetest compound has been totally utilised by micro-organisms resulting in the production of
    carbon dioxide, water, mineral salts and new microbial cellular constituents (biomass).4
    Plastics, including biodegradable ones, often have other components mixed in as ‘additives’ for various reasons. These
    additives may bereleased when the plastics degrade.5
    The speed of biodegradation will also be important in terms of the environmental impact. standard in New Zealand would be useful.
  • What does it mean to say that a plastic is compostable?
    Composting involves the breakdown of biological material such as green wastefrom garden clippings or food scraps into
    Industrial compost facilities are designed to accelerate microbial growth by controlling moisture, airflow, microbial
    activityand the proportions of different organic wastes. As the microbes consumethe waste, they generate heat, which
    accelerates the breakdown. Theresulting product, compost, is then used to return organic matter to thesoil. Homecomposting involves asimilar process but on a much smaller scale, so it may not generateas much heat and will likely
    result in a slower breakdown process. Home composting is also much more varied depending on which method is used.
  • What does it mean to say that a plastic is certified as biodegradable?
    A product that is certified biodegradableshould meet arobust international standard. Examples of such standards include
    thosethat apply in Europeand Australia.
    Thesestandards includearange of tests for biodegradability that consider different receiving environments, such as wastewater treatment plants, freshwater or marineenvironments. Theability of plastic to biodegradespecifically in compost is
    explained further below.
    Thesetests typically includethefollowing:
    Chemical analysis of thestarting material: checking to ensurethat thecomponents do not contain unacceptablelevels of
    harmful chemicals, such as heavy metals. Biodegradation: measuring how much of thecarbon that was present in thestarting material has been consumed and
    respired by microbes. In someenvironments, microbes also produce methane, which needs to be measured. Disintegration: checking that no largefragments remain. Toxicity of the degraded material: testing whether the degraded material will havean impact on the growth of organisms
    that are commonly present in the environment where the material is intended to degrade.
  • What does it mean to say a plastic is certified as compostable?
    Products that arecertified compostable will usually have been tested in commercial composting conditions. They will not
    necessarily biodegradein a homecompost heap. Standards for homecomposting arevery different in respect to thelength of
    time over which products aretested and thetemperatures required. Few homecomposting standards exist.
    International standards for compostability (home or commercial) typically contain four tests:
    Chemical analysis of thestarting material: this involves checking thecomponents to ensurethey do not contain
    unacceptablelevels of harmful chemicals such as heavy metals. Biodegradation test: measuring how much of thecarbon present in thestarting material has been consumed and
    respired by microbes in thecompost. Disintegration: this involves checking that largefragments do not remain. Toxicity of thecompost: testing if theresulting compost will havean impacts on living organisms such as earthworms or germinating plants.
    A product that is certified as compostableshould meet arobust international standard. Examples of such standards include
    those that apply in Europe and Australia.
  • What types of plastics are biodegradable or compostable?
    Thefollowing groups of plastics areconsidered biodegradable or compostable, based on the description provided by
    European Bioplastics. Whether these plastics can becertified as biodegradable or compostable depends on whether they pass
    thetests required for certification. Whether they can be biodegraded or composted as intended depends on theconditions in
    their place of disposal.
    Biodegradable bio-based plastics: Thesetypes of plastics aresourced from biologically produced compounds and can be
    broken down by microbial action. Thefollowing examples fall into this category.
    Polylactic acid (PLA)
    PLA is madefrom lacticacid, which is usually produced by fermenting sugar or starch from vegetablesources such as corn
    and is then processed to form a polymer. Other chemicals mayalso be used in the PLA production process or introduced
    as additives. Products madefrom PLA includefood packaging and coffeecups (which may use PLA for thelid or cup
    lining). PLA also has medical uses, such as dissolvablestitches, as it breaks down into lacticacid, which is easily processed
    by the human body.
    Poly(hydroxyalkanoates) (PHAs)
    PHAs are polyesters that can besynthesised by microbes that arefed starches and cellulose. They havea widerange of
    potential uses – forexample, disposablecutlery, bags, bottles and cups.
    Thermoplastic starch (TPS)
    Starch is a polymer composed of glucose monomers that is found in many vegetableand fruit sources. Unprocessed
    starch does not generally have desirable properties (forexample, it does not flow at a high temperatureand so cannot be
    moulded easily). Therefore, it is often mixed with other plastics to form astronger and more malleable material known as
    Biodegradable fossil-based plastics: Thesetypes of plastics aresourced from petroleum-based products and can be broken
    down into simple basecompounds through microbial action. Thefollowing examples arein this category.
    Polybutylene adipate terephthalate (PBAT)
    PBAT belongs to the polyester family of polymers and is produced from petroleum-based substances. It is known for its
    flexibilityand strength, and is used to make biodegradable plastics, including plastic bags and wraps.
    Polycaprolactone (PCL)
    PCL is often mixed with starch-based polymers to producearange of products used in the packaging and biomedical
  • What types of plastics are NOT biodegradable or compostable?
    Non-biodegradable fossil-based plastics: Thereare many types of conventional, non-biodegradablefossil-based plastics. Theseareextremely durable, often taking centuries to break down depending on wheretheyend up. Oxo-degradable plastics: Oxo-degradable plastics areessentially conventional plastics such as polyethyleneand
    polypropylenethat contain additives known as ‘pro-oxidants’. Theseadditives aretypically metal salts, which areintended to
    speed up degradation of the plastics into smaller fragments without any help from microbes.
    Fragmentation is facilitated byexposureto sunlight and air, which causes oxidation – achemical reaction that leads to theloss
    of electrons and often involves oxygen – hencethe name oxo-degradable. Oxo-degradable plastics typically result in alarge
    number of micro-fragments or micro-plastic pieces. A key concern is that oxo-degradable plastics may becontributing to
    micro-plastic pollution in the marineenvironment.
    If fragmentation occurs, some biodegradation may occur in the right environment.
    Oxo-degradable plastics aresometimes marketed as biodegradable. However, they should not be unless they pass robust
    international standards for biodegradability. Beyond that, a 2018 report concluded that:
    “The evidence suggests thatoxo-degradable plastic is not suitable for any form of composting or anaerobic digestion and will not
    meet the current standards for packaging recoverable through composting in the EU.”
    Thereis alack of conclusiveevidencerelating to the benefits of oxo-degradable plastics, and restrictions on their useare being
    considered in Europe.10
    In New Zealand, two oxo-degradable bag manufacturers have been charged under theFairTrading Act for misleading claims
    regarding theenvironmental benefits of these products. Non-biodegradable bio-based plastics: Thesetypes of bio-based plastics areindistinguishablefrom conventional fossil- based plastics in terms of their chemical composition, properties and decomposition characteristics. As the namesuggests,
    theyare manufactured from at least some biologically produced compounds, typically of plant or microbial origin. However,
    theterms ‘bio-based’ or ‘plant-based’ can beambiguous as they do not convey what proportion of the plastic is bio-based. Polyethyleneterephthalate(PET) illustrates this problem.
    PET– partially bio-based but not biodegradable
    PETis a polyester that is manufactured from ethylene glycol and either dimethyl terephthalate or terephthalicacid. Ethlylene glycol comprises approximately 30% of thefinal PET material and can be madefrom plants, such as sugar cane
    or sugar beet. However, plant-based terephthalicacid is not yet available, which would berequired to make PET 100%
    bio-based. Largecompanies, including Coca-Cola, arecurrently investing in research on ways to producetheentire PET
    plastic from bio sources.
  • What happens when biodegradable or compostable plastics end up as litter?
    Whilesomecertified biodegradable or compostable products can becompletely broken down into benign molecules within a
    reasonabletimeframe, this will only occur under theright conditions. The presence of heat, moisture, and microbes would help
    createfavourableconditions. Forexample, whilea biodegradablecoffeecup may break down within several weeks in a
    carefully controlled commercial compost facility, thesamecup may take decades to break down in the ocean.12 This means
    that such products may not necessarily biodegrade– it depends on how they are disposed of.
  • Which plastics can I compost?
    Some plastic products have been tested and arecertified to break down in homecompost bins. However, therearecurrently
    no guidelines or recommended methods for homecomposting. Most certified compostable products are designed to be
    processed in industrial composting facilities at theend of their usablelife, wherethetemperature, moistureand oxygen levels
    can becarefully controlled.
    In some parts of New Zealand, organic wastesuch as garden clippings and food scraps arecollected for composting in an
    industrial composting facility. However, thesecollection schemes do not readilyaccept compostable packaging. Forexample, Christchurch has akerbsidecollection for organic waste, but packaging is not allowed.13 At someevents, compostable
    packaging material may becollected alongsidefood wasteand sent to composters, provided strict protocols arefollowed.
    Even wherecollection systems for organic wasteareavailable, composters cannot always accept compostable packaging. A
    2017 survey of 27 composting facilities found that onlyabout half would accept compostable packaging such as coffeecups
    lined with PLA.14 Composters facea number of challenges with compostable packaging, including:
    identifying and sorting compostable packaging from other packaging
    getting the proportion of food wasteto packaging material right (this may becompromised if afacility receives an influx of one particular type of packaging material) variation in theform of the material, which can influencethe process –e.g. athick plastic fork takes longer to compost
    than athin takeway food container
    the processing methods that are used in their particular composting facility – thesevary substantially, with somefacilities
    being ill-equipped to process certain items. Forexample, in open composting environments, looseitems such as plastic
    bags could blow away
    the materials that can beaccepted – many facilities accept green waste but are not consented to accept food waste or compostable packaging, and so cannot process theseitems
    the components of the packaging, some of which can affect organic certification.
    Thesechallenges need to beaddressed if genuinely biodegradable or compostable packaging is to be biodegraded as
    The Compostable Packaging Standard Adoption Working Group (CPSA-WG) has been established to pursueagreement on
    standards and labelling. This work may help resolvesomechallenges for consumers and composters around standards and
    labelling, but some of the complexities faced by composters may remain, e.g. getting the right balance of packaging to food waste, and the identification and separation of non-compostable packaging.
  • Can I recycle biodegradable plastics?
    Sometypes of biodegradable plastics can berecycled, others cannot. Biodegradable plastics can cause problems for recyclers if
    they get mixed up with plastics destined for recycling because they can render these unrecyclable.
    It all depends on thetype
    and amount of biodegradable plastic. Overseas, problems with incompatibility havesometimes resulted in mixed recyclableand compostable plastics being sent to
    landfills because of contamination with other plastics.17
    Somechallenges for recycling include:
    PLA – this is not suitablefor recycling in New Zealand and can also posechallenges for PETrecycling becauseit is
    difficult to sort without special technology (as it often resembles PET) and can reducethe quality of therecycled
    Oxo-degradable plastics – there are questions around the recyclability of these plastics as they include additives to
    mak ethem fragment, which may weaken the recycled plastic.
    Starch-based plastics – some of these plastics can berecycled, but others cannot. Starch-based polymers are
    incompatible with someconventional plastics, so they should not be mixed. Forexample, the Warehouse Group’s new
    starch-based bags will carry a warning not to recycle them
  • What happens if biodegradable or compostable plastics end up in a landfill?
    In New Zealand, municipal general waste landfills receive the bulk of domestic waste, including many types of plastics.
    Becausecomposting and recycling biodegradable products can bechallenging and demanding, much of this packaging
    currentlyends up in landfills. Theextent to which a biodegradablecompostable plastic will break down in alandfill depends on
    theamount of air, water and microbial activity. Digestion occurs at highly variablerates and sometimes not at all. Whilelandfills are not designed to promote biodegradation, biodegradable or compostable plastics placed in alandfill may be
    broken down viaanaerobic digestion, in thesame way that other organic wasteis. However, it is unclear if this always happens
    or how long it may take. When biodegradable plastics break down in alandfill viaanaerobic digestion, they releasesome methaneand carbon dioxide, which are greenhouse gases. Water that comes in contact with waste, or leachate, is also an issuethat landfills need to deal with. Leachatecan bearisk to
    nearby surfaceand ground water if not managed carefully – forexample, by having alined and sealed landfill facility with
    leachate collection and treatment. If toxic compounds are present in plastics, they may contribute to leachate risks
  • So am I making a difference by putting biodegradable or compostable products in the right bin?
    The bin you choose matters. However, how much you help theenvironment depends on how good the disposal services that will deal with your rubbish are.
    In theory, certified biodegradable products could be processed in compost facilities. However, practicalities mean that
    composters cannot always accept these products – and unless the product has acorresponding recycling schemein placein
    New Zealand, it cannot berecycled.
    Thesechallenges for waste management facilities highlight the need for clearer guidance on disposal methods. The
    Commissioner has written to the Minister for theEnvironment urging clarity of guidance on disposal methods for compostable
    and biodegradable plastics.
  • Are biodegradable or compostable plastics better for the environment than conventional plastics?
    It depends.
    Biodegradation means that the plastic will not persist in theenvironment for as long. However, it should not beviewed as a way of dealing with litter. If littered, even certified biodegradable plastics may not break down in the wayexpected.
    Composting may bea way of diverting wastefrom landfill, but theability to deal with compostable plastics depends on the
    availability of facilities to process this waste.
    Compostable or biodegradable plastics may contain additives. Questions remain as to whether currentlyavailablestandards
    adequately address these additives. If additives are present, ultimate biodegradation into small molecules may not be possible within time frames that reduce or remove their environmental impact.
    There are also questions around the climate change implications of breakdown of biodegradable and compostable plastics.
  • Are bio-based plastics better for the environment than fossil-based plastics?
    Whiletheraw materials that are used to produceconventional plastics are generally sourced from fossil-fuel production, plastics can be madefrom many different raw materials, including plants and microbes. Thesource of the plastic does not
    determine whether it is biodegradable or not.
    Thereis no simpleanswer to the question of whether bio-based plastics are better than fossil-based plastics, as theentire‘life- cycle’ of anyalternative must beconsidered and contrasted. Thereareseveral key considerations.
    The properties of the plastic: How does the bio-based material perform when being used? Does it last longer? Is more
    material required to do the same job?
    Renewable resource: Is it a renewable resource? What are the advantages of using a renewable resource?
    Energy consumption: How much energy is used in theextraction, production and transport of the plastic?
    Pollution: What pollutants, including greenhouse gases, arereleased during thelife-cycle of the product?
    Land use: Are new crops required to producetheraw materials that may take up land that is needed for food production? Or aretheraw materials a by-product of some other industrial process, such as timber harvesting?
    Bio-based alternatives are being researched and developed herein New Zealand and internationallyand show great promise
    ( However, the
    impact of these alternatives remains to be seen.
  • Are there any solutions to the problem presented by single-use plastics?
    Use less of it!
    Sometypes of plastics servean important purpose or are hard to avoid. For instance, packaging plays arolein minimising food waste, and single-usesyringes used in the healthcaresector can guard against hygieneconcerns. But to minimise our pressure
    on theenvironment as individuals, it is best to look for opportunities to reduce our consumption of plastics, or reusethem
    wherever possible. Good examples includerefusing astraw at acafé or taking a durable, reusableshopping bag to the
  • What are the climate change implications of biodegradable and compostable plastics?
    Thereis afundamental difference between fossil-based and bio-based plastics in terms of the production of greenhouse gases.
    Even when a fossil-based plastic completely biodegrades, it will be adding new carbon dioxide to the atmosphere. By
    contrast, a bio-based plastic that completely biodegrades will effectively simply cyclethecarbon that was removed from the
    atmosphere when the plant grew – i.e. this is acarbon-neutral process that does not add any morecarbon dioxideto the
    Both types of biodegradable plastics could produce methane, a potent greenhouse gas, if they decompose under anaerobic
    Some have suggested that the burial of non-biodegradable plastics in a landfill is a good method of disposal. They
    point out that since most plastics originatefrom fossil-fuel sources, returning them underground in an inert and
    permanent form could be better than alternative fates.
  •  If this methane gas is captured, it may be flared or burned to generate heat or electricity.
  •  The ChCh City Council will not accept any compostable products or bags in their green bins. Click here to see CCC page
  • Click HERE to read about the CCC Kerbside Waste Scheme Guidelines on Compostable/Biodegradable Products