Yesterday, and for the second time recently, I became aware of a research laboratory using ethidium bromide (EtBr) to stain electrophoresis gels.

Nothing unusual in that, except that each lab admitted discarding its EtBr waste comprising the gels, all consumables and towels used to wipe down equipment and workspace surfaces, and gloves, into a clinical waste sack for disposal. The expectation was that since “these wastes are incinerated”, all would be well.

One of the labs was about to changing from yellow to orange sacks as their previously large stock was running low and they had found that orange sacks could be ordered internally, saving money compared with a one-off external purchase.

EtBr fluoresces nicely but in neither case were checks made of the outgoing waste sacks to ensure that they were free from external contamination. That alone was a significant error, and sat uncomfortably against the diligent checks of all workplace surfaces to ensure that the lab was free from contamination. Perhaps others don’t matter quite so much, and their health and safety is optional?

Ethidium bromide is a nasty chemical. It is a potent mutagen intercalates double stranded DNA, that is it inserts itself between the double strands of DNA, deforming that DNA. It is assumed that it is the subsequent metabolites of ethidium bromide that actually cause the damage. It is readily absorded through skin and becomes fixed in the underlying tissues where it can induce tumour formation.

In most jurisdictions, EtBr can be poured down the sink for disposal, and low level solid wastes can be discarded without specific restriction. However, most reputable laboratories and many local policies dictate that even low level EtBr waste is managed as hazardous chemical waste. There is unlikely ever to be any risk of infection, so disposal as or with clinical wastes in entirely inappropriate, no matter how convenient this may be.

Chemical waste disposal may be expensive, but is necessary and appropriate for EtBr wastes. The Environment Agency would do well to issue a specific guidance note or reminder about this, to ensure correct classification and ensure proper packaging and handling of these wastes, and subsequent disposal in an appropriate facility. This will ensure that all those coming into contact with the wastes as they pass along the [presently and inappropriate] disposal chain are not exposed to EtBr residues.