Substitution of formaldehyde as a tissue fixative
Formaldehyde is an organic compound used as a tissue fixative for microscopy and histology. Formaldehyde was substituted by a product containing: ethyl alcohol, isopropyl alcohol and acetic acid under the commercial name Fixall-his.
Formaldehyde is a carcinogen cat. 1 according to IARC (R40). It is also a sensitizer: may cause sensitization by skin contact (R43). Because of these two important risks, formaldehyde is listed in the hazardous Substance Database according to SUBSPORT Screening Criteria (SDSC).
Formaldehyde is toxic by inhalation, in contact with skin and if swallowed (R23 /24/25)
Ethanol substance is 1 carcinogen (IARC), as listed in the Substance Database according to SUBSPORT Screening Criteria (SDSC).
Also is highly flammable liquid and vapour
Propan-2-ol Causes serious eye irritation ( R39 and H319) and ist vapours may cause drowsiness and dizziness (H336). Also is highly flammable liquid and vapour (H225).
Acetic acid Causes severe burns and eye damage (R35 and H314). Also it is flammable liquid and vapour (H226)
Though the alternatives have risks, these are much less important and the safety is improved.
A significant volume of highly toxic formaldehyde wastes was detected during the development of a plan for the reduction of healthcare wastes with the participation of the trade union (CC.OO.). Formaldehyde is classified as carcinogen by IARC. The heads of the regional trade union’s environmental and health and safety departments (Aragon) commissioned ISTAS to carry out a study on the viability of substituting formaldehyde by a less toxic chemical. Researchers sought alternatives to formaldehyde for the preservation and preparation of tissue samples in pathology labs of healthcare centers. Eventually the compound named Fixall-his was chosen for substitution. Fixall-his is the commercial name of a product containing: ethyl alcohol, isopropyl alcohol and acetic acid. The compound was chosen for its relatively low level of health risks and the successful experience of substitution in French hospitals. The fact that substitution had already occurred in other hospitals is a significant driver in convincing social players of its validity as a substitute of Formaldehyde as a fixative of tissue samples.
Less toxic for users
The alternative does not have an unpleasant smell.
Certain problems were found in immunohistochemical detections.
No bio-molecular tests have been conducted.
The mix is distributed in tanks of fluorinated polyethylene.
The mix is classified as highly flammable (R11).
The alternative contains isopropanol which vapours are neurotoxicants and may cause drowsiness and dizziness besides being irritating to eyes. However the original substance has much higher risks as formaldehyde is a sensitizer and according to IARC a carcinogenic for human beings.
The alternative is safer, but it should be handle with care, with proper ventilation and respiratory protection.
The conclusions of a ISTAS’s study on the alternatives are summarized below. There is no universal method of fixation. Fixatives adequate for certain types of tissues might not be suitable for others. Besides, not all fixative compounds preserve tissues indefinitely. Alternatives include:
Physical methods of tissue fixation
– Freeze drying (cryodesiccation) or lyophilization
During the transfer of samples to laboratories formaldehyde can be substituted by a vacuum packing equipment which can also be used for processing big samples.
Methods of chemical fixation
– Acetic Acid
– Sulfosalicylic acid
– Osmium tetraoxide
– Ionic liquids (ILs).
– 1-methyl-3 octyloximethylimidazolium tetrafluoroborate, which achieve the best results.
– Tissues fixed with alcohol-based non-crosslinking fixatives (RCL2)
The intrinsic risks of chemical alternatives compounds were assessed (see attachment).Further information Further languages available
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Publication or last update: 10.05.2012