Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
Happy New Year and welcome to the first library of 2022!
I went a little wild at the end of the year with the Cyberattack library and promised to get back to normal in 2022. Microplastics are the new normal. I take this as a sign that people are really desperate to have something to worry about. The first article is proof of this. Here the authors, from respected institutions (UCLA and Temple University) in a decent journal, are crying wolf about the potential hazard associated with wind-blown dust from biosolids applied soils. No- they aren’t worried about pathogens. Besides the critical work by Pepper and Gerber laid those fears to rest. They are worried about the combined hazard of PFAS and microplastics! You can either laugh or pull your hair out. I suggest the former. This paper is all conjecture. There is PFAS in household dust and PFAS is non- volatile so it must get in the dust by being attached to other particles and plastics are particles. If it can happen in your home then for sure it must be a hazard with biosolids. Take this sentence from the abstract:
Microplastics are more susceptible to suspension by wind than natural soil particles.
Wow- that sounds concerning. Then you realize that dust particles from soil are mineral. The average bulk density of a rock is 2.65 g cm3. If your Styrofoam cup had a similar bulk density you could count drinking coffee as part of your crossfit workout. Microplastics are more susceptible to being airborne because they are much lighter. Not nearly as scary. I have to admit. The article also bases this on the assumption that microplastics are large particles- ‘On the other hand, microplastics, owing to their large size,….’
Let’s move onto the next article. The next two articles in fact are from the same group in Australia. The first is based on how very small so many of those microplastic particles in biosolids actually are. They use a new technique that allows quantification of plastics without visually counting them. They separated the biosolids into different size fractions and then measured the plastic content in each size fraction.
One bone to pick right off the bat. The authors report the quantity of microplastics that are land applied with the biosolids (3, 700 tons). They do not place this in the context of how much biosolids are applied. So here is my approximation of context:
Australia has 26 million people. If each person makes 50 kg biosolids (0.05 tons) that means that 1.3 million tons of biosolids are produced each year. The article says that 80% are land applied, so about 1 million tons of biosolids are land applied in Australia each year. In other words, the microplastics make up 0.37% of the biosolids. I am not saying that this is good- just a little perspective.
Here are the plastics that they found by mass and what they are used for:
PE – polyethylene (54%) packaging film, trash and grocery bags, toys, housewares
PVC – polyvinyl chloride (21%) used for everything including piping, construction, electronics, cars etc
PET polyethylene terephthalate (15%) fabrics
Here is the size fraction distribution that they found for polyethylene as well as the concentration:
Conclusion is that the majority of the microplastics are in the previously undetected really small fraction of the material.
The next paper is more general. Describing the release of plastics into biosolids, amount per person and the fraction of total plastics used that actually end up in the biosolids. I had to really zoom in to be able to read the legend on the figure but per capita plastics use is 90,000 g per person per year. The quantity released in the biosolids tops out at under 300 g per person per year.
In other words, while these authors will likely continue to publish on microplastics in biosolids and call out potential hazards, biosolids are a ‘micro’ part of the problem.
Take article #4 for evidence of another source. Here the authors provide a general review of microplastics and where to find them. Landfills are discussed here as an overlooked source of plastic contamination which makes sense considering they store 21-42% of the plastics generated. Of course, biosolids are also a source, as is food waste. Foods themselves also contain microplastics. Here is the data point that got to me: There are 1.4-7 pieces of microplastics in an oyster.
Microplastics can have other things associated with them including metals and other organics so not only are the plastics themselves a contaminant, what is attached to them are also contaminants. This is a general review that is very helpful and very overwhelming.
The last article in the library is where the attention should be focused. It centers on green strategies for plastic reduction. Source control has worked for many contaminants over the years. A show of hands for anyone who remembers when cadmium was a concern (pardon the humor here but Cd was used as a yellow pigment among other things). This is a tough problem and the authors don’t have any silver bullet solutions. They talk about limiting single use plastics, improving the market for plastics recycling, combustion, and bioplastics as options. As this library has hopefully shown, while there are microplastics in biosolids, biosolids are a tiny drop in the bucket as far as the problems of plastic pollution are concerned. Don’t stop applying biosolids. Just get a few of these or ones like them for when you go to the supermarket. It’s a start.