Lecture 11: Microplastics and addressing water quality through economic mechanisms

Microplastics

Tiny plastic pieces < 5mm

Primary microplastics

Intentionally produced microplastics (e.g. toothpastes, shower gels)

Secondary microplastics

Degradation of larger plastics (e.g. plastic bags, packaging)

Primary sources of microplastic to the world oceans

• Synthetic textiles (35%)

• Tyres (28%)

• City dust (24%)

• Road markings (7%)

• Marine coatings (4%)

• Personal care products (2%)

• Plastic pellets (0.3%)

Entanglement and ingestion figures

• > 1 000 000 seabirds

• > 100 000 sea mammals

• Unknown number of turtles and whales

Environmental fate

• Fragmentation due to UV, mechanical and microbial degradation

• Adsorption/desorption of POPs

• Ingestion by zooplankton and fish

• Sedimentation with marine snow

• Sedimentation of HD polymers

• Sinking due to biofouling

• Defouling

• Trophic transfer

• Bioturbation

• Resuspension

Microplastics in food

• Honey (microfibres > 40μm, fragments 10-29μm)

• Beer (<109 fragments/L)

• Sea salt (<681 fragments/kg)

• Present in gastrointestinal tract of fish

• Present in bivalves for human consumption (11,000 microplastics/year)

Microplastics in drinking water across world

• USA (4.8 fibres per 500 ml)

• India (4.0 fibres per 500 ml)

• Ecuador (2.2 fibres per 500 ml)

• Europe (1.9 fibres per 500 ml)

Additives in plastic

• >10 000 known additives

• >900 chemicals associated with plastic packaging alone

• monomers, intermediates, solvents, surfactants, plasticizers, stabilizers, biocides, flame retardants, accelerators and colorants

Common analytical options for microplastics

• 50 μm

  • naked eye

  • optical microscopy

• 10-20 μm

  • FTIR

  • Raman spectroscopy

• Complex samples

  • Pyrolysis-GCMS

How much plastic do we release through sewage?

• Per-capita 8 and 877 g/person/year

• Mean of 200 g/person/year

• PMMA and PET release correlates with socio-economic factors

  • lower socio-economic shed more PET

Spatial distribution of plastics in Moreton Bay

• All seven plastics detected across region:

  • northern bay (524 μg/g/)

  • seagrass areas (373 μg/g)

  • mangroves (330 μg/g)

  • southern bay (55 μg/g)

• Polyethylene (PE) had the highest concentrations followed by Polyvinyl Chloride (PVC) and Polypropylene (PP)

• Total microplastic budget for Moreton Bay is estimated to be 7000 tonnes

Factors influencing plastic abundance

• Plastic production and population were among best predictors for plastic concentration in core sediments

• Flooding events are likely the biggest driver of plastic transport and deposition in Moreton Bay

Sources of MNPs to wastewater

• Dishwasher

  • release PP, PE, PS and nylon

  • 920 000 particles per cycle

  • 170 million particles/household/per

  • not considered a major source

• Tyres

  • 6PPD-quinone detected at 18 of 21 sites with concentration < 24 ng/L

  • TWPs detected at 18 pf 21 sites with concentration < 0.69-1.99 mg/L

  • concentrations of polymers ranged 00.2-1.8 mg/L

  • no correlation with population density, correlated with average daily traffic and concentration of tire additives

Environmental impacts within plastics cycle

• Bioaccumulation and biomagnification

  • ingested by aquatic organisms across all trophic levels

  • once ingested, plastics can accumulate in tissues and transfer up the food chain

• Physical and chemical hazards

  • cause internal injuries, blockages, or false satiation

  • act as vectors for harmful chemicals such as POPs and heavy metals (adsorb onto their surfaces and leach into organism upon ingestion)

• Habitat disruption

  • accumulation of microplastics in sediments may alter the physical and chemical properties of benthic habitat

Source controls

• Reducing plastic production and usage

  • ban certain microplastic-containing products (e.g. microbeads in personal care products)

• Domestic sources/ household wastewater

  • personal care products, washing machine wastewater (laundering synthetic clothing), dishwashers

• PVC pipes in sewer networks

• Industrial wastewater/trade waste sources

• Deposition (shower, sinks, toilets)

• Stormwater and surface water

• Household filters

Microplastic mitigation strategies

• Improved wastewater treatment technologies

  • deploy advanced filtration in wastewater treatment plants

  • microfibre filters in washing machines

• Improved waste management and plastic alternatives

  • enhance recycling systems and promote biodegradable plastic alternative (reduce introduction)

  • implement stricter regulation on single-use plastics and designing products that shed less (e.g. textiles and tires)

• Extended producer responsibility (EPR)

  • holding producers accountable for the entire lifecycle of their plastic products

  • policies encouraging development of eco-designs that minimise fragmentation

  • driving innovation toward sustainable materials and packaging

Lifestyle changes

• Use reusable water bottles and filter tap water

• Keep plastic from food (especially when heating it)

• Reduce plastic dependency

What does value mean in economics?

• Total Economic Value (TEV)

  • use values and non-use values

• All estimates of value need to be related to a baseline

• Markets are an imperfect capture of value to everyone across society