The role of biodegradation in reducing microplastics in the environmentKathleen McDonough, P&G

Microplastics composition, form, disposal route and ultimate end of life compartment effect biodegradation potential

Terrestrial

Freshwater

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Wastewater TreatmentMarine

Atmosphere

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Klein et al. 2018. Freshwater Microplastics,Hdb Env Chem 58, DOI 10.1007/978-3-319-61615-5_3

Cosmetic Microbeads: microplastics in personal care products

McDonough et al. 2017. Chemosphere, 175: 452-458.

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Exfoliants: replace with natural and synthetic biodegradable alternativesDominant route of disposal is down the drain to a wastewater treatment plant

Time in days

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

% E

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ed C

O2

0

10

20

30

40

50

60

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Jojoba beads Stearyl Stearate Beeswax

Blueberry seedsWalnut shells Rice bran wax

PHVB FP 500

Walnut shells

Blueberry seeds

Waxes and PHBV foamOECD 301B Test Method

Surface-Mediated BiodegradationMicroorganisms colonize the particle surface and biodegradation is an extracellular process that starts on the particle surface

Jojoba beads with no exposure to microorganisms

Jojoba beads after incubation with activated sludge

OECD 301B Test Conditions• Inocula: 17 mg/L MLSS • Dose: 20 mg/L Beeswax• 80% Carbon via SSM-TOC analyzer• Test Duration: 90 d• Test Temp: 22 ± 2 °C

Average particle diameter (μm)

Specific surface area (cm2/g)

Number beeswax particles per 1 L

test bottle

3000 21 1

1250 68 55

375 183 577

188 353 4935

94 740 43922

Impact of Particle Size on Biodegradation Rate and Extent

3000 μm Beeswax particle 94 μm Beeswax particles

Menzies et al. 2020. Manuscript in preparation.

Menzies et al. 2020. Manuscript in preparation.

Particle Diameter

(μm)28 days 60 days 90 days

94 74.3 ± 1.1 80.0 ± 2.7 81.4 ± 5.1188 69.2 ± 3.0 79.1 ± 6.3 80.3 ± 6.7375 57.6 ± 7.0 74.8 ± 6.6 77.3 ± 7.2

1250 50.8 ± 11.9 67.0 ± 5.1 75.5 ± 3.53000 7.8 ± 2.0 12.8 ± 3.2 19.1 ± 5.7

Impact of Particle Size on Biodegradation Rate and ExtentOECD 301B Beeswax Case Study

Key take-aways• Biodegradable exfoliant replacement materials would be beneficial and options do exist • Replacement materials need to be tested individually to understand their biodegradation potential• Materials need to be evaluated in the form that will enter the environment because the particle size will

impact the rate of biodegradation even in the microplastics size range

Evolved CO2 (%)

Textile Fibers

Zambrano et al. 2019. Marine Pollution Bulletin. 142: 394-407.

Typical environmental route of disposal is down the drain to wastewater treatment

Key Take-aways:• Textile fibers that biodegrade would be beneficial and

options do exist• Further work needed to understand rate of

biodegradation and impacts of dyes and additives

• ISO 14851 O2 Evolution Study• Microbial community from activated sludge• System limited in oxygen which slowed down

biodegradation• Cellulose, rayon and cotton biodegraded extensively• Polyester did not biodegrade• Question-influence of dyes and additives on

biodegradation

Controlled Release Fertilizer TechnologiesEnvironmental Benefit: Controlled release of fertilizers allows farmers to apply less resulting in less environmental impact

End of Life: ruptured capsule wall remains in soil compartment after use

Technology: active research is ongoing to find an capsule wall materials that are stable enough for application and use but also biodegrade after release of fertilizers

Key Take-away: there could be a real environmental benefit to finding biodegradable capsule wall technologies for fertilizer applications

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Plastic Bottles in the Aquatic EnvironmentIssue: pollution of the aquatic environment, eventually breakdown into microplastic pieces

Brandl & Puchner. 1992. Biodegradation. 2. 237-243.

• Field study in Switzerland Lake (6°C or lower)• PHBV 17 um films biodegraded completely in 254 d • PHBV shampoo bottles 10% mass loss in 254 d• Authors estimate 5-10 years bottle to completely

biodegrade

PHBV case study (biodegradable plastic alternative)

Key Take-aways• PHBV biodegradation is a surface-mediated process, size and shape of material effects rate of biodegradation• Time to biodegrade will vary based on actual field conditions, microbes present, temperature, starting material

size/surface area, etc., estimates for a fully formed bottle are in the timeframe of a few years • Need to carefully weigh end of life options collection systems, recycling infrastructure, time for complete

biodegradation to determine best alternative

• Extensive literature review biodegradation PHB/PHBV marine environment

• PHB/PHBV biodegradation surface mediated process• Mean rate of biodegradation in the marine environment

0.04–0.09 mg・day−1・cm−2 • PHB/PHBV water bottle estimated to take between 1.5

and 3.5 years to completely biodegrade.

Dilkes-Hoffman et al. 2019. Marine Pollution Bulletin. 142: 15-24.

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End of life compartments:• Air and WWTPs dominant• Surface water and ocean less dominant

Material: Stable product needed, natural and synthetic rubber and carbon black as filler

Biodegradation• Material needs to be very stable for use and

biodegradable after use- may be difficult to develop suitable alternatives

• If inhalation is the most important human exposure route then biodegradation during WWT and in aquatic environment is not a direct impact

Key Take-awaysThis is a difficult problem that will take a holistic view to solve. Biodegradation may not be the best way to handle this issue.

Cole et al. 2017. International Journal Environmental Research and Public Health. 14: 1265.

Conclusions• Biodegradation can be a valuable removal mechanism under the right use and disposal

conditions • Size of the plastic/microplastic will impact the time to reach complete mineralization• Need to carefully assess end of life scenario and the biodegradation potential of the

form of the material that will enter the environment in order to assess the value of biodegradation as a removal mechanism

• Need to carefully consider if other removal mechanisms are practical and available (waste collection, recycling, upcycling) and whether they would be a better alternative than biodegradation

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