From the start of sampling and the experimental procedure we tried to minimise the potential for contamination and loss of microplastic particles at the best of our capacity, considering the time frame and the materials available at our disposal. At the same time it has to be taken into consideration the main areas where our work could be improved to achieve the best results possible.
Sampling
Starting with the sampling, we made sure to always use purified water to rinse the tools used during the process, after observing literature that confirmed microplastic presence in tap water all over the world
https://orbmedia.org/. During this part of the project the potential for contamination and losses was kept under control. This was less true for the laboratory part of the experiment. The different tasks necessary for the drying, weighing, density separation/extraction, dissolving of organic matter, vacuum filtration and counting of the particles, required each sample to be moved in different containers most of the times, increasing the risk of contamination and losses. This problem was partly accounted before hand but, because of unforeseen problems during the experiment, some procedures couldn't be avoided.
Density separation/extraction
As explained in the methodology, during the density separation the SMI unit was rinsed thoroughly with distilled water after each use to prevent the mixing of the samples inside the device. After the content of the sample was separated and put through the nylon mesh, the latter was rinsed with ethanol to make sure that the whole content was transferred onto the petri dish. Then, Leaving the Petri dish open under the fume hood, ensured that the ethanol evaporated, leaving the sample dry and ready for count. During this process there was a high probability of contamination during the the transfer and drying of the samples.
Dissolving of organic matter and vacuum filtration procedure
During this process, which had not been accounted for at the start of our experiment, we had to transfer again the samples from the Petri dish to Erlenmeyer flasks to be mixed with the hydrogen peroxide, and next run them through the vacuum filtration system, increasing the possibility for losses during the relocation of the content and leading to possible contamination by air.
Counting of the particles
Afterwards, the meshes containing the material were transferred to the Petri dish, for the microplastic count under the low powered microscope. This task was performed by scraping the mesh with a metal ''Something'' onto the Petri dish. Also in this case the possibility of loss and contamination far fairly high. The same could be said for the counting of the particles where, during the procedure, the Petri dish were in fact open for different periods of time.
Considerations
It is important to note that some of the mistake during the experiment could have been avoided with better foresight, or at least the results could have been accompanied by data, collected to account for this complications. For example, during the density separation it could have been helpful to run blanks throughout the procedure to account for possible contamination. The same could be said by the other tasks. The continuous transfer of the samples to different containers could also be greatly reduced.
That being said, the whole process gave us the knowledge to improve in each step of the experiment to achieve the most representative results possible.