Methylmercury poisoning
=======================

* Erica Weir

I thank John Ruedy for his careful reading of this public health column1 and for bringing forth Clarkson's excellent article2 on the physiology and toxicology of mercury. In writing the column, I relied on a clinical review article3 that distinguished diagnostic and management practices for mercury poisoning primarily on the basis of acute versus chronic exposure, rather than by type of mercury compound. It suggested that, in principle, blood samples provide the best modality for assessing acute poisoning, whereas urine and hair samples reliably measure chronic exposure. It also suggested that chelation therapy should be considered in cases of acute poisoning, with the caveat that chelation therapy is most effective for elemental mercury and least efficacious for methylmercury, although it cites a reference4 to substantiate the effectiveness of 3 chelating agents in ameliorating methylmercury-induced developmental toxicity. 

It is important that physicians be familiar with these principles because it may not be clear in most cases of suspected mercury exposure which mercury compound (elemental, inorganic or organic) is responsible for the poisoning. Having said that, it is evident both by Ruedy's letter and by Clarkson's article that these principles fail to translate into practice in the case of methylmercury poisoning, which, as Ruedy rightly points out, was the focus of the column. Methylmercury avidly accumulates in growing scalp hair and is mostly eliminated as inorganic, not organic, mercury through the fecal route.2 

Trust Mercury, the messenger of the gods, to shun principles, to assume a disguise and to slip surreptitiously through the back door.

## References

1.  1. Weir E. Methylmercury exposure: fishing for answers. CMAJ 2000;165(2):205-6.
    
    [FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiRlVMTCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiY21haiI7czo1OiJyZXNpZCI7czo5OiIxNjUvMi8yMDUiO3M6NDoiYXRvbSI7czoyMzoiL2NtYWovMTY1LzkvMTE5NC4xLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==) 

2.  2. Clarkson TW. The toxicology of mercury. Crit Rev Clin Lab Sci 1997;34:369-403.
    
    [CrossRef](http://www.cmaj.ca/lookup/external-ref?access_num=10.3109/10408369708998098&link_type=DOI) 
    
    [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=9288445&link_type=MED&atom=%2Fcmaj%2F165%2F9%2F1194.1.atom) 
    
    [Web of Science](http://www.cmaj.ca/lookup/external-ref?access_num=A1997XU64400003&link_type=ISI) 

3.  3. Ozuah P. Mercury poisoning. Curr Probl Pediatr 2000;30:91-9.
    
    [CrossRef](http://www.cmaj.ca/lookup/external-ref?access_num=10.1067/mps.2000.104054&link_type=DOI) 
    
    [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=10742922&link_type=MED&atom=%2Fcmaj%2F165%2F9%2F1194.1.atom) 

4.  4. Domingo JL. Prevention by chelating agents of metal-induced developmental toxicity. Reprod Toxicol 1999;9:105-13.