Ethidium Bromide is a potent mutagen which has been commonly used as a nucleic acid stain for many years.
It fluoresces a red-orange colour under ultraviolet light and with increased fluorescence when bound to double-stranded DNA. Typically EB is purchased in powder or solution form and is soluble in water. The crystal or powder form is odourless and appears dark red in colour. Although EB is undoubtedly an effective tool it possesses high hazard properties that dictate that commensurate high level control measures must be implemented in order to mitigate health and safety risk, also special waste disposal measures are required.
The Control of Substances Hazardous to Health Regulations require that where ever possible exposure to hazardous substances be avoided. Where it is not possible to avoid exposure the Regulations require that exposure controls be implemented in a hierarchical order, the first of which is substitution with a substance that is non- hazardous, or less hazardous, before moving further down the hierarchy to mechanical controls and lastly Personal Protective Equipment. The requirement for substitution, where practicable, is absolute and has been tested in case law, therefore where there exists a practical (will achieve same or similar results) non, or less hazardous, alternative this must be adopted. Increased cost alone cannot be presented as a reason for non-implementation of a less hazardous alternative.
Several alternatives to EB exist which manufacturers claim are less toxic than EB and may not require UV light sources. Consequently the routine use of EB is to be discouraged and should only be used where product evaluation and risk assessment have concluded that there is no viable safer alternative. Should the latter be the case, consideration should be given, in the first instance, to purchasing only ready-made solutions so as to avoid the inhalation hazard.
MaestroSafe is a substance produced by Maestrogen and available to purchase from Oxford Biosystems & Cadama.
SYBR® Safe DNA Gel Stain is a highly sensitive stain for visualization of DNA in agarose or acrylamide gels.
GelRed and GelGreen are fluorescent nucleic acid stains from Biotium and sold by Cambridge BioScience.
In providing the above product information it is not implied that the Occupational Hygiene Unit of the Health and Safety Department endorses any of the above products. Their suitability as to specific use is beyond our level of expertise in this area, rather the information is presented here in order that it can be included in any evaluation process undertaken by a research group as to their suitability and practicality of use as an alternative to the high hazard material ethidium bromide.
EB is harmful if swallowed, it is very toxic by inhalation and in powder form is considered irritant to the upper respiratory tract, eyes, mucous membranes and skin. Although there is no conclusive evidence, at this time, for the carcinogenicity or teratogenicity of this substance in humans, EB is so strongly mutagenic, causing living cell mutations, that it should be regarded as a possible carcinogen and teratogen.
EB has been assigned the following EU Hazard and Precautionary statements:
Any risk and safety phrases directly replace by hazard and precautionary statements have been added in brackets above. Some risk and safety phrases may not have been replaced and therefore have no corresponding hazard or precautionary statements.
EB may cause extreme eye and skin irritation. It can be absorbed through the skin and contribute to chronic health effects. There is no data available to allow conclusive assessment as to whether or not this chemical would be likely to cause an allergic skin reaction. If ingested it may cause gastrointestinal irritation with nausea, vomiting and diarrhoea. Inhalation is a major hazard that may result in fatality, lesser causal effects are respiratory tract irritation and methemoglobinemia, which is characterised by dizziness, drowsiness, headache, shortness of breath, cyanosis (bluish discoloration of skin due to deficient oxygenation of the blood), rapid heart rate and chocolate-brown blood. Chronic health effects are methemoglobinemia and alteration of genetic material. Animal experiment evidence points to the possibility of carcinogenic and teratogenic effects.
As EB is so strongly mutagenic with the strong possibility of carcinogenic and teratogenic effect pregnant workers should not work with EB.
Before commencing any work practice that involves the use of EB a full and thorough risk assessment must be undertaken in compliance with the COSHH Regulations and safe systems of work/safe operating procedures developed. If practical you must use a safer, less hazardous alternative (examples given at top of page). In the unlikely case of a less hazardous alternative not being a practical approach you should take cognisance of the following good practice.
If your School has a dedicated spill response team you should call them out. Otherwise proceed as follows:
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.
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).
Guidance regarding the safe disposal methodology of ethidium bromide in this University is available in the form of Clinical Waste Management Briefing 1-07, on the Waste and Recycling Office website.
Generically, nitrile gloves should provide adequate protection against dermal contamination with ethidium bromide, however the only glove that we have found to have been specifically tested against ethidium bromide penetration, and for which test data is available from the company, is the N-DEX glove, manufactured by the "BEST" Glove Company of U.S.A.
The manufacturers claim that this nitrile glove allows the sensitivity to feel a pulse but is three times more puncture resistant than thicker natural rubber gloves, will not become sticky when exposed to chemicals and tape will not stick to them. It apparently tested no breakthrough after 8 hrs subject to a light concentration of ethidium bromide. It is available in two versions, medical or non-medical grades, and in three thicknesses - 4, 6, and 8ml. Agents in this country include:
Natural rubber latex gloves do not provide a suitable barrier to penetration by 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. Bench tops can be similarly monitored.
This article was published on Feb 1, 2012