Mercury analysis by cold vapour atomic absorption spectrometry
The effects of mercury poisoning depend upon the route of exposure and its chemical form. Metallic mercury is slowly vaporised at room temperature and about 80% of vapour entering the lungs can be absorbed. It is lipid soluble and can enter the brain from which it is only slowly eliminated. The symptoms of low level mercury poisoning are subtle (e.g. headaches, fatigue, nausea, personality changes) and may be difficult to distinguish from other causes. Mercury exposure is particularly hazardous to pregnant women.
Various mercury compounds are used as fungicides, pigments and pharmaceuticals; elemental mercury is used in thermometers and scientific instruments and dental amalgam. Acute poisoning is rare but has been associated with irritation of the digestive tract, renal damage and acute pneumonitis. Chronic poisoning causes nausea, fatigue, headaches in the early stages. Muscular tremors and other central nervous system disorders develop together with renal damage after prolonged exposure to mercury vapour. Mercury poisoning is a notifiable industrial disease, although there is no statutory requirement to monitor workers at risk of exposure.
A direct service is offered to dental staff for monitoring mercury exposure. Initial screening is made by head hair analysis with follow up of abnormal levels with a more extensive screen based on hair, nail and urine analysis. This service is currently free to dentists working in the NHS in Scotland.
The mercury that is present in sea water from natural sources or environmental contamination can be metabolized by fish into methylmercury and tissue concentrations increase up the food chain with predatory fish such as swordfish, marlin, shark and tuna accumulating the highest concentrations. Methylmercury is more toxic to humans than inorganic mercury and the Food Standards Agency and the US Foods and Drug Administration advise that these fish should not be eaten by pregnant women, women considering becoming pregnant, infants and children under 16 and that pregnant women should limit their consumption of both tinned and fresh tuna.
Determination of mercury in blood is useful in cases of recent acute exposure. Hair mercury is used as a longer-term indicator of low level exposure.
Sample Requirements and Reference Ranges for Mercury
| Sample Type | Blood, urine, hair, nail | ||||
|---|---|---|---|---|---|
| Container | Blood: EDTA Hair: plastic bag Urine: universal container |
||||
| Precautions | Urine: Losses of mercury from urine start to occur soon after the sample is taken. If it has to be stored, store frozen but preferably try to ensure that it gets to our laboratory with minimal delay. | ||||
| Minimum volume* | Blood: 1.1 mL Hair: A bundle of hair about the length and thickness of a cocktail stick. Urine: 1.1 mL |
||||
| Reference ranges | |||||
| - blood | < 30 nmol/L | - urine | < 5 nmol/mmol creatinine > 20 nmol/mmol creatinine (associated with clinical symptoms – HSE Health Guidance) |
- hair, nail | < 2 µg/g |
| Turnaround time | Blood: 6 days (please telephone 0141 211 4494 if immediate turnaround required). Urine: 2 weeks |
||||
| Method | Cold vapour atomic absorption spectrometry |
* This is the absolute minimum volume; these volumes are insufficient to carry out a repeat analysis in the event of an analytical problem.