Ethidium bromide is the most commonly used dye for DNA and RNA detection in gels.
Why this substance is hazardous
- Ethidium bromide is a frameshift mutagen (causes changes to DNA) and intercalating agent (acts like insertion mutations). Although evidence shows that when applied in vitro it is a mutagen, contact with mammalian cells in other circumstance requires higher concentrations than that used in labs to cause an immediate risk to humans
- It is a risk to the environment
- It is toxic by inhalation
It is the most common and one of the cheaper nucleic acid stains but is also expensive to send into the waste stream.
Recommended control measures
Minimise the likelihood of exposure
- Use gels to lower the risk of spills and splashes from liquid
- Always use the minimum amount required
- Use of ready-made stock minimises the time spent handling the substance so lowers the risk of exposure from spills
- Only keep minimum stocks of higher concentrations of the substance as it is more difficult and therefore more expensive to send to waste
- Always carry out the work in a fume cupboard if making up stock, to ensure that airborne particles of ethidium bromide are separated from users and diluted before allowed into the environment
Minimise the risk of contamination
- Wash hands after use and immediately after a spill even if the gloves seem intact
- Eye protection is required and if working on an open bench a full-face mask is recommended
- Fasten the lab coat
- Double gloving, first set inside the cuff, second set outside the cuff
- Cover the workbench with containment trays or use similar coverings
- Ethidium Bromide is classified as hazardous chemical waste
- Solutions should be deactivated or filtered. Due to the hazardous nature of the chemicals required to deactivate the solutions, filtration is the preferred method. However, be aware that filtration will increase the concentration of the ethidium bromide
Should there be concerns that the chemical has penetrated the glove (glove breakthrough), monitoring for ethidium bromide contamination can be undertaken by placing the operators' hands beneath a standard UV light, where ethidium bromide will show as a reddish/brown colour on the skin. Benchtops can be similarly monitored.
Decontamination of Ethidium Bromide
The following solution must be prepared immediately prior to use and can be used to decontaminate equipment and work areas. The solution should be prepared in a fume cupboard as a small amount of nitrogen dioxide may be given off when the solution is initially mixed. The solution is also strongly acidic (pH 1.8).
- Mix 4.2 g of sodium nitrite (NaNO2, CAS # 7362-00-0) and 20 ml of hypophosphorous acid (50%) (H3PO2, CAS # 6303-21-5) in 300 ml of water
- Wash the area once with a paper towel soaked in decontamination solution
- Rinse the area five times with paper towels soaked in tap water, using a fresh towel each time
- Using a UV light, check the area to ensure that all the EB has been removed (no reddish-orange fluorescence). Repeat decontamination procedure as necessary. If the acid could damage the contaminated surface, use additional rinses with paper towels soaked in tap water
- Discard the decontamination solution, towels and gloves as hazardous waste
Cognisance must be taken of the specific hazards associated with using UV light sources; all persons in the area should wear appropriate Personal Protective Equipment (UV face shields, laboratory coat and long cuffed gloves fitted over the cuff of the lab coat).
Alternatives to Ethidium Bromide
There are alternatives available, however these are also hazardous chemicals so it will be substituting one risk for another rather than eliminating the risk.
A full risk assessment should be carried out to ensure that the best substance is used for your project.
Alternatives include but are not limited to MaestroSafe, SYBR Safe or GelRED and GelGreen.
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Last updated: Monday, June 7, 2021