 |
| Module 3: Toxicology - Section 12: Heavy Metals |
| OHM12.X: Mercury - Part 3 |
|
| Module 3: Toxicology - Section 12: Heavy Metals |
| OHM12.X: Mercury - Part 3 |
 |
 |
 |
 |
Urine: Urine mercury excretion peaks approximately 2-3 weeks after an acute exposure to inorganic mercury and decreases with a half-life of 120-60 days for short-term exposure and 90 days for long-term exposure. Urine mercury can be used to indicate exposure to aryl and alkoxyalkyl mercury compounds, however it is of no value in estimating exposure to methylmercury. The urine mercury concentration is useful as a quantitative measurement of exposure provided that the worker has been exposed for a sufficiently long time to achieve a steady state and has not been off work for more than a few days; sampling is done at the same time each day; and the concentration is corrected for specific gravity and creatinine excretion. Under these circumstances the ratio between mercury vapor in air (in ug/m³) and mercury in urine in (ug/1) has been found to lie between 1:1 and 1:1.6.
In terms of toxicity, clinical signs of acute poisoning are unlikely to occur when the concentration of mercury in urine remains below 20-30 ug/1. However, increased prevalence of slight tremor and of renal dysfunction have been detected in workers excreting more than 50 ug/1 (corrected to a creatinine concentration of 1 g/1). This value of 50 ug/g creatinine is currently regarded as indicated the upper limit of acceptable exposure for elemental or inorganic mercury. In persons who have no occupational exposure to mercury, the urine mercury concentration is usually less than 5 ug/g creatinine. Dental restorations and the use of mercurial disinfectants on the skin will transiently increase urinary mercury excretion. Dietary habits do not appreciably influence the concentration of mercury in the urine since dietary mercury is mainly methylmercury (from fish).
Blood: Blood mercury is a useful indicator of recent exposure, (given the short half-life of 2-12 days), and correlates better with exposure than does the urine mercury. For organic mercury, whole blood is the preferred bioassay as it is concentrated in red blood cells and not excreted by the kidney but in the faeces. An average airborne inorganic mercury concentration of 50 ug/m³ corresponds to a blood mercury concentration of 3-3.5 ug/100 m1. An increased likelihood of proteinnuria has been found among workers whose blood mercury exceeds 3 ug/100 m1. In persons who have no occupational exposure to mercury, the blood mercury concentration rarely exceeds 2 ug/100 m1.
Among persons chronically exposed to alkylmercury, the earliest signs of intoxication may occur when the blood mercury exceeds 20 ug/100 m1. In light of this a level of 10 ug/100 m1 has been suggested as indicating the upper limit of acceptable exposure to alkylmercury. Whereas in the past speciation of metal compounds, (elemental, inorganic salt versus organic compounds), was problematic, newer analytical methods such as ICPM, Induction Coupled Plasma Mass Spectroscopy, allow for speciation from both environmental and biolobical assays.
Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za.
Last updated Jan 2007.
Disclaimer note: Some resources and descriptions may be out-dated. For suggested updates and feedback, please contact healthoer@uct.ac.za.