Basically, I was looking for the laboratory method for microplastics observation from a seawater sample and beach sample. Most of the cases, they followed some criteria to get a precise amount of microplastics. According to the definition, we do consider size less than 5mm is as microplastic. But in many projects and research works, I saw that they only collect less than .3mm size sample particles to observe microplastics. My question is, during microplastics observation, why do they only consider the particles which are less than .3mm in size.
That's odd. My guess is that those studies aimed for that size for a specific reason. Do you mind mentioning those studies? But you are right, MPs are by definition
It would be good to have some of the references you looked at to try to find out out why they used 0.3mm as their criterion for microplastics. Can you post a couple below?
To the contrary, my impression that for most studies 0.3 is the lower cutoff at least for pelagic sampling as samples are often collected with 300µm nets (e.g. mounted on a manta trawl), thus looking at the 0.3mm to 5mm size range.
Thanks for clarifying Helena Hauss . That makes perfect sense in the absence of the references!
Helena Hauss, I apologize for my wrong words. After seeing your reply Again, I checked that paper. Then it became clear to me that my idea was wrong.
They run sieving with two sizes of mesh size stainless steel mesh sieves (one is 5mm and another is 0.3mm) and then collect only the 0.3mm sieve and discard the 5mm sieve.
That means they collect the particles which are sized in between 0.3mm to 5 mm. I did understand the matter in a wrong way that's why I raised that question. Thank you so much for clarifying me. Now, this is clear to me.
And I was exclusively following the protocol- Masura, J., et al. 2015. Laboratory methods for the analysis of microplastics in the marine environment: recommendations for quantifying synthetic particles in waters and sediments. NOAA Technical Memorandum NOS-OR&R-48.
Aleksandra Maljković Gabriel E De-la-Torre Thank you so much for answering my question.
Hi Md Bayzid, as the other replies mentioned, 0,3 mm is often a cut-off because the nets used for sampling have this mesh size. Everything smaller 0,3 mm unfortunately falls through and hence is not included in the analyses.
A reason for using the 0,3 mm mesh nets is that the net or manta is trawled along the water surface to collect the microplastics, and during this process the dynamic pressure is higher when the mesh size is smaller. in this case, the trawling needs to be slower, but with flowing water, this is difficult to maintain steady. another reason is, that small-sized mesh nets clogg faster with microplastic or other particles in the water.
however, there are many microplastics smaller 0,3 mm and studies should try to include those. sometimes they do that by taking some bulk samples of a few litres in parallel.
another reson why sizes are cut off sometimes is the (non-)availability of later sample analysis instruments (microscope, spectrometry, etc) and not all instrument work well with all particle sizes.
there are several good articles about this, e.g. Stock et al, 2020, or Scherer et al, 2020.
Cheers :)
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