The precepts in molecular biology about Ethidium bromide and its hazards
Ethidium bromide (EtBr), a mutagen, moderately toxic, a probable carcinogen, is found in almost every molecular biology lab. Often EtBr has been a topic of debate for its genotoxicity in mammalian cells. However, there's no direct evidence of mutation upon exposure to EtBr. Additionally, a study by Youssef in 2010, suggests that EtBr dosages of 2.5 mg/kg and 1 mg/kg weekly for three consecutive weeks have successfully treated Trypanosoma vivax infection, and routinely used in treating cattle with African sleeping sickness. In 2015, Sayas et al. reported that EtBr induced mutation in eukaryotic cells (Saccharomyces cerevisiae) that caused a massive loss of mitochondrial DNA.
EtBr is a flat molecule, almost the perfect size to slide in between base-pairs, unwinding the helix slightly, and may cause DNA polymerase to slip and create short insertion or deletion. However, excessive concern about mutagenicity can lead to the negligence of its short-term toxic effects. The use of EtBr has escalated with the advances in molecular biology and modern techniques. Most of the molecular biologist is well aware of the concern associated with EtBr and a little skittery about sending a potentially mutagenic substance down the drain. A Common laboratory practice used to treat EtBr is by adding Sodium hypochlorite before its disposal. However, Lunn and Sansone (1987) discourage the bleach treatment because of its mutagenic by-products. Of all the alternatives, activated charcoal considered the safest way to remove EtBr from solutions, followed by incineration of the charcoal bag. Because of the generation of by-products, it is not advisable to use chemical neutralization. The best way to dispose of EtBr is unknown yet, and after considering all the alternatives, surprisingly, many researchers eventually end up pouring it down the sink. Such practice may result in large amounts of untreated ethidium bromide coming out of research laboratories every year. Though the use of EtBr is pretty much frequent in most molecular biology labs yet, many of them do not have any systematic arrangement for its disposal or lack the accountability of toxic waste. Therefore, it is of paramount importance for an institute to increase awareness of short-term toxicity and mutagenicity associated with EtBr.
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References:
B. Lunn, G. & Sansone, B. Ethidium Bromide: Destruction and Decontamination of Solutions. Analytical Biochemistry, 1987.
Youssif F.M., Mohamed O.S.A., Gameel A.A. & Hassan T., Efficacy and toxicity of homidium bromide (ethidium) in goats infected with T. vivax. Small Ruminant Research, 2010.
Enric Sayas, Federico García-López and Ramón Serrano, Toxicity, mutagenicity and transport in Saccharomyces cerevisiae of three popular DNA intercalating fluorescent dyes, Yeast, 2015.