The Creation of Aerosols when Working with Liquids
Purpose
Aerosols are a common and under-appreciated laboratory hazard. This hands-on activity explores the production of aerosols and factors affecting aerosol production, particularly during pipetting and other operations involving liquids. As you go through the activities in this exercise, you will:
- Demonstrate how aerosols are created.
- See how aerosols can scatter over a flat surface.
- Design your own experiments to demonstrate how aerosols are produced.
Background
Aerosols or sprays are mechanically produced liquid droplets that are suspended in air. Aerosols are created by many routine laboratory activities and are therefore a significant cause of contamination when working with hazardous liquids containing infectious, toxic, corrosive, volatile or radioactive agents.
Pipettes are one of the basic tools of school and research laboratories. They are used for volumetric measurement of fluids and for transfer of these fluids from one container to another. If the fluids that are handled are hazardous then a pipette can spread this material if improperly used.
Aerosols, the most common hazard associated with pipettes, are created when liquid drops from a pipette to a work surface, when cultures are mixed by alternate suction and expulsion, when an inoculum is forcefully ejected onto a culture dish or when the last drop is blown out. It has been demonstrated by high-speed photography that an aerosol of approximately 15,000 droplets, most under ten micrometers in diameter, is produced when the last drop of fluid in the tip of a pipette is blown out with moderate force.
You can demonstrate the presence of contamination by using a florescent liquid. The florescent liquid shows up under UV light. It indicates that material contaminated the work space with routine lab techniques. Figure 1 shows some examples.
FIGURE 1
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Figure 1. AEROSOLS.
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Pipetting materials set up under normal light. A fluorescent compound was then pipetted repeatedly into and out of microfuge tubes placed in the blue rack.
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The microfuge tubes and the rack under UV light after pipetting. The large fluorescent spheres are from small drips and spills of liquid from the end of the pipette tip. The smaller bright spheres are aerosols that landed on the benchtop surface.
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Observe that some of the aerosols landed a distance from the rack. These smaller aerosols were not visible without UV light and in ordinary practice would not have been observable.
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PRE-LABORATORY PREPARATIONS
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| Read about aerosols on pages 638-639 in your textbook. Copyright: 2000. |
Laboratory Activities
In this exercise a safe fluorescent dye will be used to mimic hazardous liquids that might be spread as aerosols.
- Cover the lab benches with protective paper then put down a sheet of light-colored absorbent paper.
- Wearing gloves and eye protection, practice pipetting the saturated dyes from the stock bottle to a microcentrifuge tube, test tube or beaker. Record any spills or sprays your see on the paper.
- The dyes we are using will fluoresce under UV light, making very small spills or sprays visible. Dim the classroom lights then use the hand-held UV light to look for additional spills or sprays. Record the results. Do you see additional spills or sprays that you didn't see before? Do you see any dye on your gloves or lab coat?
- Put a clean sheet of absorbent paper down on the bench. Pipette some water in and out of a pipette tip, so that a tiny bit of water is left on the tip. Remove the tip from the micropipettor. Hold the tip about 12 inches above the lab bench then let it drop onto the absorbent paper. Circle the water droplets you can see on the paper.
- Pipette some dye in and out of a pipette tip, so that a tiny bit of dye is left on the tip. Remove the tip from the micropipettor and drop it onto the absorbent paper as before. Using a different colored pencil or pen, circle the dye droplets you can see on the paper.
- Were there more drops of dye or of water? Why?
- What size were the droplets of each liquid?
- Using the UV lamp, can you find more droplets?
- What common lab procedures may also create aerosols?
- What should you do when working with hazardous liquids to prevent aerosol contamination?
- Explore further; test other activities to see if aerosols are created. For example:
- Drop a used but empty ejected pipette tip onto the lab bench. Look for
aerosolized dye.
- Lightly line the inside of a microcentrifuge with white tape. Then centrifuge tubes containing the saturated dye stock. Look for aerosolized dye on the tape inside the microcentrifuge.
- Pop open a microcentrifuge tube containing dye. Check for contamination/aerosols on your gloves, pens and notebooks. Check for aerosols around the tube.
- Take apart one of the micropipettes you have been using to look for aerosols being sucked up into the barrel of the pipette.
- Check the inside of pipette bulbs for aerosols.
- Experiment
pipetting
with and without cotton plugs in the tops of serological pipettes or pipette tips.
- Put saturated dye solution into a small beaker with a stir bar and turn stir plate on high speed. Check for aerosol contamination near on or near the stir plate.
- Can you come up with more ideas?
Discussion Questions
- Here is a photo of gloves that were worn while pipetting the fluorescent compound back and forth from one tube to another. The bright spots are fluorescent compound that contaminated the gloves, though the wearer was not aware of this contamination. If the person wearing the gloves now opened a centrifuge and placed the tubes inside the device, what would be contaminated? How can the use of gloves be a cause of laboratory contamination?
- What happens to airborne aerosols? Do they remain in the air?
- Why are aerosols considered to be potentially a major source of laboratory contamination?
- How can aerosol production be minimized?
Materials and Preparations
- safety glasses or goggles
- lab coats
- 1-3 mg/mL of Dayglo fluorescent dyes in 50 ml bottles
We like this product, “Dayglo” from DayGlo Color Corp., 4515 St. Clair Avenue, Cleveland, Ohio, 44103, 216 391-7070, Part number D-282. This product is not on their website, so telephone to order.
- 150 ml beakers
- beakers containing water
- beakers for waste
- any form of light-colored absorbent paper, large sheets of filter paper work well, or butcher paper, craft paper, flip chart paper
- gloves
- stir bar & stir plate
- Pasteur pipettes
- test tubes
- serological pipettes
- test tube racks
- pipette bulbs
- cotton
- micropipettors and pipette tips
- lab bench paper/newspaper
- white tape
- hand-held UV lamps
- microcentrifuge tubes with snap caps
- microcentrifuge
- pencils or permanent markers (two different colors)
These technicians are using respirators to protect themselves from aerosols and airborne powders that might be harmful. They are also using a laminar flow hood that protects the product from contamination.
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