pollution 3 Flashcards
emerging contaminants in freshwater: microplastics (20 cards)
existing research on microplastics in ecosystem
- fist research about 50 years ago: looking at polystyrene beads
- term microplastics is new
- majority of research is on marine rather than freshwater ecosystem
- public interest e.g. due to blue planet documentary and news articles drives research
what are microplastics?
- operational definition
- non-degradable plastic less than 5mm
- primary microplastic: made to be that small
- secondary microplastic: made larger and break down to smaller fragments
- examples: fibres from washing clothes; fragments from break down of thicker plastics; pellets/beads and foams (primary plastics)
- diverse range of contaminants with range of properties
microplastic properties
- polymers: influence how fast they break down, could have toxic properties
- additives: (e.g. flame retardant) can be toxic to biota
- product source: influence properties
- size: nanoplastics or not – influence interaction with biota
- colour: help trace sources, can influence feeding
- exotoxins which can bind to plastics: plastics act as a vector e.g. PAHs, DDTs heavy metals
Fate of microplastic in freshwater
- most plastic enters as microplastic
- mechanical degradation
- biodegradation
- photodegradation
- photo-oxidation
then can become biofilms
then can be taken up by microorganisms and higher organisms e.g. small crustaceans and daphnia
can be broken into oligomers, dimers and monomers in river
transport of microplastics in freshwater
non-buoyant microplastics
- turbulent transport by river current
- aggregation with algae, dissolved organic matter and other things, settle but then potentially moved by storms (remobilisation) or buried in sediment
buoyant microplastics
- takes longer to fall of suspension
- more readily transported down stream so takes longer to be buried
Impact of particle shape and condition
- fibres have a smaller surface area for biofouling to occur so least prone to biofilm growth
- pellets and fragments more likely to form biofilm
- biofilm reduce transport distance and increases settlement in pellet and fragment
effect of sewage overflow on microplastics
Water companies allow sewage overflow to discharge during dry spells
this causes more movement of immobile microplastics
Microorganisms and freshwater biota
- size of plastic fragment uptake is linked to size of organism
- larger gape of organisms causes larger plastic particle size uptake
- feeding mode and selectivity determines uptake likelihood
example organisms found to contain microplastics
Baetidea: general deposit feeder (range of food)
Heptageniidae: obligate algal grazer (limited food)
hydropsychidae: generalist filter feeder (range of food)
all contained similar amounts of microplastics
shows microplastics enter organism through biofilms and other means besides diet
Microplastics taken up directly and indirectly though food web
too complex to track weather plastics is taken up directly or indirectly
Plastics and microbes
(Wang et al 2020)
- species richness and evenness of planktonic bacteria is lower with microplastic
- distinct community composition association with microplastics
- unique microhabitat for colonisation and migration/transport
- antibiotic resistant genes are higher in microplastic rather than planktonic bacteria
Microplastics and ARGs (antibiotic resistant genes)
- waste water treatment plants (WWTP) are main source for microplastics
- WWTP are bioreactors for production of ARGSs
- antibiotics sorb to microplastics
- MPs associated with pathogenic bacteria (higher prevalence of ARG)
Microplastics and primary producers
(Li et al. 2020)
- less photosynthesis when green algae contaminated with MPs
- less primary production, less energy in ecosystem
- to date it is only shown in experimental settings
- microplastics wrap around cells and damage cell membranes reducing ability to photosynthesise
Microplastics and primary consumers
(Weber et al. 2018)
- fluorescent polyethylene on G. Pulex (amphipod) over 24 hour exposure
- looked at microplastic body burned and survivorship
- no impact on survivorship but high body burden
- higher burden of MPs in juveniles
- implications on future generations and wider ecosystem is G.Pulex contain plastic?
- interactions with other stressors e.g. climate change
Microplastics and secondary consumers
meta-analysis to asses MPs in fish – 267 studies included (Wotton et al. 2021)
- MPs observed more frequently in freshwater fish (and higher load)
- feeding mode has implications on MP uptake likelihood
scale of impact in ecosystem
Cellular impacts: cell death, oxidative stress, DNA damage etc
organ/tissue impact: histopathology, altered metabolic activity, altered neuromuscular activity
induvial impacts: mortality, feeding, reduced and delayed hatching
(parker at all 2021): lit review identified known impacts
this concluded more research needed on impacts on population, community and ecosystem level
microplastics and human health
microplastics found in human blood
microplastics can cross the blood brain brain barrier
need more research on the effect of MPs on human health (ethical concerns)
interaction of MPs is governed by size of fragment and size of organism 9Winsor et al 2019)
issues with research into MPs
Cunningham and Stewart
- use of extreme dosages
- incompatible and incomparable units
- issues with experimental control
- short exposure time
public pressure and interest into MPs
- causes new legislation e.g. ban on wet wipes containing packaging
- needs more pressure on water companies
summary on microplastic lecture
- only just understanding toxicology of MPs complexities due to combination of particle size and type
- impacts of microplastics vary across trophic levels
- impacts of microplastics on ecosystem scale is unknown
- need focus on more realistic microplastic levels and longer-term studies
