Filtering Digestants

Following digestion, chemical agents can be filtered to retain any recalcitrant materials (e.g., undigested tissue, inorganic residue, microplastics). Viable filters include 0.2 and

0.7 mm glass fiber filters [38,74], 5 mm cellulose nitrate filters [75], 5 mm cellulose acetate membranes [101], 50 mm mesh [9] and 250 mm mesh [31]. Larger pore size facilitates rapid filtering but will result in the loss of smaller plastics [9]. Glass fiber filters can shed and might be considered a source of contamination; smoother filters (e.g., membrane filters) are typically easier to scrape and less prone to fragment. Microplastics on filters can be visualized directly, transferred to slides or extracted. Collard et al. [101] suggests placing filters in methanol solution, ultrasonicating (50 Hz), centrifuging (5000 rpm, 5 min, 20°C) and then removing pelleted plastic by pipette; while this method was suitable for a range of polymers, the methanol caused a 25% weight reduction in tested PVC particles.

Test

Number

Solution

Temp (°C)

Time (hrs)

Results

Notes

1

NaOH (20 g/L)

60

24

  • • Mussel tissue dissolved into yellow liquid
  • • Some 2-3 mm particles remain
  • • Nonsynthetic fibers start to leach color in an hour
  • • Hazardous
  • • Damages glassware
  • • Visible digestion effects in an hour; tissue surface is disintegrating
  • • Samples pass through glass microfiber filter effortlessly

2

NaOH (20 g/L)+SDS (5 gd.)

60

24

Dissolved tissues

  • • Foggy solution
  • • Nonsynthetic fibers start to leach color in an hour

• See #1

3

NaOH (20 g/L) + NaCIO (14%)

60

24

• See # 1

• See #1

4

NaCIO (14%) + SDS (5 g/L)

60

24

• Tissue digested nearly completely

• See #1

5

KOH (10%)

50

24

• Dissolved into liquid with several 2 mm pieces of tissue

  • • Hazardous
  • • Clogs glass fiber filters

6

KOH(10%) + SDS (5 g/L)

50

24

• See #5

  • • Sample turned into jelly when left in room temperature for 30 min after oven incubation
  • • SDS seems to aid the digestion process slightly
  • • See #5

7

Enzyme mix (1:1 Biozym F: Biozym SE)

37.5

48-72

  • • Deep yellow, dense solution with a few organic particles remaining
  • • Fibers not affected
  • • Works well with 20 pm plankton net filter, clogs glass fiber filter
  • • User friendly (not hazardous to use)
  • • Occasional remaining tissue particles break upon filtration

8

SDS (5 g/L) + Enzymes mix (1:1 Biozym F: Biozym SE) 24 h later

SDS: 70 Enzymes: lowered to 37.5

24 (SDS) + 48 (enzyrn.)

• See #7

  • • Contamination risk increased due to additional handling of samples
  • • Risk of enzyme denaturation if solution not cool enough upon adding the enzymes
  • • No clear difference in digestion speeds between protocol #8 and #9
  • • See #7

9

1:1 SDS (5 g/L): Enzymes mix (Ы Biozym F: Biozym SE)

37.5

48-72

• See #7

  • • Addition of SDS partially prevents particles from attaching to vial walls
  • • See #7

Source: Railo S et al. Mar Pollut Bullion, 130,206-214.

 
Source
< Prev   CONTENTS   Source   Next >