At all stages, care must be taken to prevent the contamination or cross-contamination of samples. Airborne contamination of samples with synthetic fibers stemming from clothing [75,158] or atmospheric fallout [159] is a recurrent issue within the literature [52,53,58,61,63]. Sources of contamination should be eliminated where possible and otherwise quantified using environmental filters or procedural blanks. Here, we highlight sources of contamination during sampling and sample processing and consider protocols for contamination mitigation.

Contamination during Field Sampling

With marine species, animals are often sampled by way of polymer rope, nets or traps [123]. In these situations, animals should only be exposed for minimal periods and a reference sample of the gear should be retained to exclude contamination during the identification phase [77]. Avoiding airborne contamination of samples in the field is understandably more complex than in the laboratory, but remains an important consideration, nevertheless. Steps for mitigating contamination include thorough cleaning of all equipment prior to sampling, which will also mitigate cross-contamination; covering samples and equipment between use; wearing polymer-free clothing or cotton coveralls, and gloves and the use of procedural blanks.

Contamination during Sample Processing and Analysis

In the laboratory, forensic techniques, good laboratory practice and common sense should be applied to mitigate contamination [160]. Wherever feasible, researchers should process samples in a laminar flow hood (e.g., cell or algal culture unit) [12,54,55,82]; alternatively a fume hood [63] or “clean room” (i.e., nonventilated or negative flow) with low foot- traffic or embargoed to non-essential personnel can be used. Glassware is preferential to plastic consumables; Cole et al. [12] observed physical homogenization of specimens in polypropylene Falcon tubes resulted in the introduction of plastic shavings to the sample. Filtering media or liquids used in sample preparation has been recommended by some researchers [54,55]. Glassware, benches and equipment should be rinsed with deionized water [53-55,58,63,77,89], ethanol [12,82] or acetone [52] prior to use. Collard et al. [82] further suggests drying equipment with cellulose-lignin-based cloths from which reference samples can be taken. As with field sampling, all materials should be covered between use, and cotton coveralls or laboratory coats are widely recommended. Environmental filters (e.g., glass fiber filters) can be placed near equipment to quantify external contamination [77,89]. Lastly, procedural blanks (i.e., controls) are highly recommended for quantifying contamination and for identifying aspects of the experimental design where contamination can occur. Analysis of procedural blanks can reveal substantial contamination of synthetic fibers, ranging 5.8 ± 2.2 [61] to 33-39 fibers [137] per replicate. Where contaminating plastics are easily identifiable, for example, being brightly colored [137], >1.5 mm [38] or <36 mm [82], or resembling laboratory coat fibers [58], these microplastics can be removed from subsequent analysis.

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