How should ethidium bromide be neutralized?

Neutralizing ethidium bromide removes the mutagenic by-products from the solution and equipment used before they are discarded. The safest way to neutralize ethidium bromide is with sodium bicarbonate using the Lunn and Sansone method. Neutralization with bleach is not effective since mutagenic by-products may remain in the solution.

To neutralize solution containing ethidium bromide:

• Dilute the solution to less than 0.05% w/v (50 mg/100 ml dilution.
• Add 20 ml of fresh 5% hypophosphorous acid and 12 ml of fresh 0.5 M sodium nitrate solution for every 100 ml of EtBr.
• Ensure the pH of the solution is less than 3.0.
• Stir briefly and leave the solution for a minimum of 20 hours to give it sufficient time to react.
• After 20 hours, neutralize the solution with sodium bicarbonate.
• Pour the neutralized solution down the drain with copious amounts of water.

To decontaminate and neutralize equipment:

• First de-energize all electrical equipment and wear the appropriate protective equipment.
• Add 20 ml of 50% hypophosphorous acid to a solution of 2g of sodium nitrite in 300mL of water to prepare the decontamination solution.
• Soak a paper towel in the freshly prepared decontamination solution and use it to scrub the contaminated equipment or surface. Do this at least 5 more times, using a fresh towel soaked in the decontamination solution every time.
• Place all the used towels in a large container and soak them in fresh decontamination solution for a minimum of one hour.
• Use sodium bicarbonate to neutralize the used decontamination solution and towels.
• Discard towels in the trash, and rinse the solution down the sanitary sewer with plenty of water

Decontamination and neutralization must be carried out in a fume hood while wearing appropriate personal protective clothing and observing all recommended safety precautions for handling ethidium bromide