Purpose and Applicability
Ethidium bromide is commonly used as a non-radioactive marker for identifying and visualizing nucleic acid bands in electrophoresis. It fluoresces readily with a reddish-brown color when exposed to ultraviolet
light, intensifying almost 20-fold after binding to DNA. This generic chemical safety guidance describes basic prudent safety practice for handling this chemical in research labs. The principal investigator (PI) or the lab manager is responsible for developing and implementing standard operating procedures (SOPs) for the purchase, storage, and safe handling of this chemical that are specific to the PI’s research.
Because ethidium bromide can bind with DNA, it is highly toxic as a mutagen. It may potentially cause carcinogenic or teratogenic effects, although no scientific evidence showing either health effect has been found. Exposure routes of ethidium bromide are inhalation, ingestion, and skin absorption. An acute exposure to ethidium bromide causes irritation of the mouth, upper respiratory tract, skin, and eyes.
When pure ethidium bromide is used, handling should be performed in a fume hood wearing full protection clothing including a lab coat, closed-toe shoes, chemical resistant gloves and chemical safety goggles.
For hand protection, gloves made of nitrile rubber are protective; surgical-style latex gloves are not recommended. When working with high concentrations or for a prolonged period of time, double gloving
can further reduce the risk of exposure, especially if the outer glove is replaced when contaminated. Users should wash their hands after removing their gloves, even if the gloves are not torn or punctured, to remove any residue that may have contacted the skin.
An emergency eyewash and shower should be accessible nearby. When using UV light to visualize ethidium bromide, the user must wear UV blocking eyewear or work in a UV cabinet with shielding glass in place.
In the event of exposure and/or spills, take the following steps:
- In case of accidental inhalation, remove to fresh air and get medical attention.
- If swallowed, get medical attention immediately.
- For skin exposure, remove contaminated clothing and wash skin with plenty of soap and water for at least 15 minutes; get medical attention.
- For eye exposure, wash eyes with plenty of water for at least 15 minutes, lifting upper and lower eyelids occasionally, then get medical attention.
Although ethidium bromide is not regulated as hazardous waste, wastes containing the chemical are assumed to pose mutagenic hazards. The wastes should be kept in sealed containers between use and disposal.
EHS recommends the specific disposal procedures for ethidium bromide as follows:
Filtering aqueous ethidium bromide waste solutions that are free of other contaminants through a bed of activated charcoal is a relatively simple and effective method for removal of ethidium bromide. The filtrate may be poured down the drain (the used filters are disposed of similar to gels; see below). There are two simple kits available for charcoal filtration:
Whatman supplies a commercial filter funnel kit that uses a packaged charcoal disk that is graduated for easily tracking the amount of aqueous solution calculated for a fixed quantity of ethidium bromide residue. This is particularly useful for labs that generate large amounts of solutions at a time. The kit is available in Biochemistry Stores (4-403 BSB, 335-7927, item # 108450) or through other suppliers. For the procedures, follow the manufacturer’s instruction.
Amresco Destaining Bags
The Amresco Destaining Bags. One bag has the capacity to remove 5 mg of ethidium bromide from solutions. Solutions are treated overnight; the special absorbant mixture retains ethidium bromide molecules and other biological stains in the bag. This product is also available in Biochemistry Stores (#108455).
Electrophoresis Gels and Used Solution Filters
Gels containing ethidium bromide and filters used to remove ethidium bromide from solutions are to be disposed of in a special waste box for ethidium bromide-containing materials. The box can be obtained upon request from EHS Waste/Environmental group (5-8501).
Ethidium Bromide Solutions
Aqueous solutions of ethidium bromide that do not contain other hazardous chemicals should be filtered or collected by EHS. Solutions of ethidium bromide that also contain alcohols or other solvents, heavy metals, cyanides, sulfides or other hazardous chemicals must be disposed as hazardous waste.
Gloves, Equipment and Debris
Gloves, test tubes, paper towels, etc., that are minimally contaminated with ethidium bromide should be placed in a biohazardous waste box.
Alternatively, ethidium bromide can be replaced with less toxic and mutagenic substances, such as SYBR Green I/II or Sybr®Safe. These products are widely used as alternatives to ethidium bromide and do not require special handling for disposal. Sybr®Safe is available in Biochemistry Stores (item #022495).
- The PI is responsible for SOPs specific to use of this chemical in their lab. The PI/Lab Manager is responsible for the site specific and hands-on training for the use of this chemical in their lab. Training should be directly documented in the researcher’s lab notebook. On each day of training, both trainer and trainee should sign the lab notebook.
- Initially, researchers should perform the reactions with the PI or senior researcher present to observe the safe handling of this chemical. Review the reagent-specific safety data sheets (SDSs). Evaluate the hazards associated with the chemical reaction and experimental setup.