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Plastic contamination of the food chain – a threat to human health?

Rosemary Waring from Tharos presented a fascinating webinar about plastic in the environment, it's impact and what can be done about it. The main points were:

Background and environmental fate of plastics

8.5 billion tonnes of plastic have been made since the 1950s and 75% of this is waste. Still 40% of plastics are single use packaging.

Four main groups of plastics:

  • Polyethylene (including LDPE, HDPE and PET)
  • Polypropylene (PPL)
  • Polyvinyl chloride (PVC)
  • Polystyrene (including rigid (PS) and expanded (EPS))

Size categories:

  • Macroplastics: 5 mm +
  • Microplastics: 100 nm-5 mm
  • Nanoplastics 1-100 nm
  • Photoxidation of macroplastics makes them brittle, after which they break down to micro and nanoplastic fragments.
  • In addition to the polymers, plastics also contain chemicals such as bisphenol A, phthalates, pigments, and brominated fire retardants. These have a range of health effects, including endocrine disruption and potentially effects on developing foetuses.
  • Plastics in the environment tend to end up in the oceans due to being moved by wind and rivers. Sources include manufacturing and industry, waste water and agriculture.
  • Microplastics frequently eaten by fish as they are similar in size to plankton. Bottom-feeding fish and those that feed in rivers tend to have the highest contamination levels.
  • Microplastics don’t seem to have significant health effects on fish generally, but filter feeders such as mussels and oysters are affected. Because these species are eaten whole by humans, they may be a significant source of microplastics to the human food chain. Behavioural changes are also observed in some species.
  • Plastics are hydrophobic and microparticles tend to clump together to form a “mat”. These can attract hydrophobic chemicals (e.g. persistent organic pollutants), and also colonies of pathogens can form (particularly near sewage outfalls).

Do microplastics have any effect on humans?

  • Microplastics can bioaccumulate up the food chain (e.g. soil -> worms -> chickens).
  • In addition to ingestion via food, can inhale microplastic fragments into the lungs (particularly in cities and in factories working with plastics).

Do microplastics enter the rest of the body from the gastrointestinal tract? Unclear, but it’s thought that there’s limited absorption from the gut into other organs. However, this assumes an intact intestinal wall, which may not be the case in some medical conditions such as irritable bowel syndrome (IBS).

  • Much less is known about nanoplastics. However, it’s known that nanoparticles are widely distributed within the body, and it’s likely that nanoplastics are the same. Nanoplastics are also known to affect the behaviour and fertility of aquatic life.
  • Potential (but unproven) links to mental health issues and oxidative stress (which could contribute to conditions such as Alzheimers or Parkinson’s)
  • Overall, nanoplastics are probably more of a problem than microplastics because they can be spread around the body more readily (although there is considerable uncertainty).
  • No evidence as yet that there is cause for significant concern.

However, possible precautions:

  • Avoid eating large amounts of shellfish (e.g. oysters and mussels), or the brain, lungs and “tripe” from animals.
  • Reduce air-borne plastic particles in populated areas where possible.
  • Collect all plastic waste, and incinerate for energy generation if recycling isn’t possible. 
  • Research new biodegradable plastics – and important to know what they biodegrade into. Obviously don’t want products that just biodegrade more readily into nanoparticles, and also can’t be too biodegradable or it will fall apart.
  • Land disposal of wastewater sludge is a source of microplastics to the environment and should be avoided.

Probably the difference in behavior/risk profile between microplastics and nanoplastics – although there’s still a lot of uncertainty around this.

There was a bit of discussion about “biodegradable” plastics – how biodegradable they really are, and what the breakdown products are. I.e., do they break down to monomers or other basic chemical products, or do they just break down more readily to form micro-/nano-plastics? Also, how to create genuinely biodegradable plastics that are still durable enough for the intended purpose.

Ongoing issues:

  • Rosemary talked a lot about the degree of uncertainty that still exists in relation to the health effects of micro- and nano-plastics.
  • Testing for micro- and nano-plastics in water and soil, particularly what tests are commercially available and how reliable they are, questions for our next webinar on this topic!

1st August webinar report submitted by Tim Muller, Landpro

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