Follow up to question 2.2: When collecting biological tissues in an environment that may contain numerous sources of environmental plastic contamination (e.g., hospital surgery room where non-woven gauze, isolation curtains, IVs, tubing, packaging materials for housing sterile implements, etc. exist), what are best practices for collecting appropriate field blanks?

If at all possible, plastic should be avoided in sample collection/storage. Where this cannot be avoided - e.g. where standard kits for blood sample collection involve plastic, then the extent of sample contamination should be assessed. For example, pig blood should be drawn through the blood sample collection kit used for human sample collection, analysed for MNPs and the results compared to that obtained for the same sample without contact with the sample collection kit.

This aspect is not clearly presented in the revised manuscript.  In fact, this should be described in a paragraph under "Sample Collection" section.  In the analysis of biological samples, contamination from sample collection plays a critical role.  This aspect of contamination during sample collection is completely missed in that section although I commented earlier that this is the major source of contamination in all human biospecimen studies of MNPs.  The sample collection section discusses about the need for a minimum of 50 sample, mesh size, and storage, but there is no discussion about contamination while collecting samples.  Many studies involving MNPs in brain, blood, and placenta were collected using plastic syringes and medical devices and yet labs presented data without paying attention to contamination introduced during collection.  Hospital settings are a major source of contamination by MNP in human samples.  This discussion is important in the revised manuscript under sample collection section.  Otherwise, it is almost like missing an elephant in the room.

These field blanks should include procedural blanks (in triplicate, if possible), should match the exposure duration (i.e., keep blanks open for the same duration and under the same conditions as sample collection), and should also include lab blanks (not exposed to field conditions) to isolate contamination from lab procedures.

In my opinion, in the case of collecting biological tissues in environments that have an abundance of potential plastic contamination, such as surgical rooms, the best practice would be to use field blanks that replicate the conditions under which the samples were handled. More than that, all blanks should be processed identically to the tissue samples in order to be able to account for any background contamination that might have been introduced during the collection, storage, or laboratory analysis. To minimize the contamination, non-plastic consumables should be used wherever possible, tissues should remain covered when not being manipulated, and all sources of potential fiber shedding should be documented. Including several blanks per collection session, co-located near the tissue collection area and matched for exposure time, allows quantification of environmental and procedural contributions and provides the necessary context to interpret microplastic findings in biological tissues.

When collecting biological tissues in an environment of high plastic contamination, procedural blanks are better than air blanks as these blanks help identify contaminations introduced at any stage.
When collecting biological tissues in an environment of high plastic contamination, avoid plastic tools and containers. Instead, use glass and metals. Cover all equipment with aluminum foil. Use cotton lab coats and clothing.
When collecting biological tissues in an environment of high plastic contamination, filter all the solvents with glass fiber filters and be careful about the pore sizes of the filter.
When collecting biological tissues in an environment of high plastic contamination, document all the details, materials used, clothing, gloves, room conditions and steps. 

This depends on the purpose of the sample collection or (in other words) the underlying research question. When the purpose is to merely quantify the extent of environmental plastic contamination in a specific setting, then no references would be needed. When it is the intention to quantify the contribution of the sources present in the specific setting, then a similar environment without those specific sources should be sampled. When a comparison needs to be made with a 'clean' environment, then the outdoor environment should be sampled.

In the case of the example provided in the question of a hospital surgery room, one could firstl of all merely sample the surgery room and quantify the extent of plastic contamination - including focus on specific plastics in terms of composition or shape, or in terms of any other property of relevance. Secondly, one could sample the hospital surgery room and use a similar room without the equipment and without any activities as a reference to assess what is the contribution of the activities and equipment present/used in the hospital surgery room to the extent of plastic contamination in the hospital surgery room. Thirdly, one could sample outside of the building (upwind) to assess what is the joined contribution of the hospital facilities in general and the hospital surgery room to the level of plastic contamination detected in the hospital surgery room.
When combining the three approaches, the specific contributions of the environment (background contamination), the hospital in general and the hospital surgery room can be distinguished.

1st: awareness of ubiquity of polymers
2nd: identification of the ALL sources of polymers in the sampling environment
3rd: training (ubiquity, minimization is sampling environment, minimization of contamination during sampling/transport/storage, etc.)
4th: active and passive sampling of sampling environment such as surfaces, air, sampling apparatus, sample containers, etc.

One could use a dummy tissue like animal or synthetical tissue with similar composition and go through the sample process as the real biological tissue that is collected and intended to analyze.  In addition, numerous sources could be analyzed as well to understand their contribution to contamination. 

It's very challenging to collect an appropriate field blank in these environments. In other field environments, I have used and recommended pre-cleaned glass petri dishes that contain a water sample. The procedure performed on the animal is performed in the water in the petri dish.  Unused versions of all equipment and supplies are opened in the same room as the open petri dish and all supplies that enter the animal's tissues are submerged in the blank water.