Problems and Solutions in Histological Technique

Problems in Histopathological Technique

Prepared by

ROY ELLIS

IMVS Division of Pathology

The Queen Elizabeth Hospital

Woodville Road, Woodville, South Australia 5011

Did you know that zinc chloride can be substituted, quite successfully, for mercuric chloride in compound fixatives where the formula requires mercuric chloride?

You would only do this in order to avoid the deposits caused by mercury salts which appear in tissues after mercury fixation or for occupational health and safety reasons. Mercury deposits, of course also need removal before proceeding with most staining methods - unless the method uses iodine which is used to remove mercury pidment usually followed by sodium thiosulphate.

Both zinc chloride and mercuric chloride are highly toxic substances, although zinc chloride is not quite as toxic as mercury. But both do cause painful, uncomfortable death and you would be better off using neither. But if you must use either then zinc is a little safer and of course there are no deposits of salts to remove from tissue after its use.

So let us make a brief comparison of the hazards associated with these two chemicals - firstly MERCURIC CHLORIDE.

is toxic and corrosive and may be absorbed into the body by inhalation, ingestion or through the skin. It doesn't mind how it gets in!
It can cause blurred vision, sore throat, metallic taste, coughing, shortness of breath and laboured breathing in high concentrations but even low concentrations will eventually catch up with you because - .
Its toxic effects are cumulative, the body cannot excrete it. Large doses attack the kidneys and the central nervous system and can be fatal.

ZINC CHLORIDE on the other hand:

is a severe irritant and corrosive. Eye and skin contact will cause severe burns.
It is moderately toxic by inhalation and ingestion.
Symptoms include nausea, vomiting, dizziness and central nervous system depression.
Fatalities have occurred from severe damage to the respiratory system.

Like I said its not quite as bad as mercuric chloride although it is still quite toxic.

Anyway if you so desire zinc chloride can be substituted quite well for mercuric chloride. The one big advantage of zinc chloride over mercury is that it is soluble in processing agents and so is completely removed during the processing cycles which of course mercury is not.

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