Scottish Trace Element & Micronutrient Reference Laboratory

Scotland's specialised laboratory for trace elements and vitamins in health and disease

Mercury (Hg)

Mercury is well-recognised to be potentially highly toxic. The effects of mercury poisoning depend upon the route of exposure and its chemical form. Metallic mercury slowly vaporises at room temperature and about 80% of vapour entering the lungs can be absorbed. When ingested, elemental mercury is not absorbed and so is relatively innocuous but when inhaled it can be highly toxic. On the other hand, ethyl and methyl mercury are highly toxic if absorbed via the skin or gut. Elemental mercury 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, 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 and 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.


The mercury that is present in sea water from natural sources or environmental contamination can be metabolized by fish into methyl mercury and tissue concentrations increase up the food chain with predatory fish such as swordfish, marlin, shark and tuna accumulating the highest concentrations. Methyl mercury is more toxic to humans than inorganic mercury and the Food Standards Agency and the US Food 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 or urine is useful in cases of recent acute exposure. However, mercury concentrations are less stable in urine compared to blood. Hair mercury is used as longer-term indicators of low-level exposure.

Sample Requirements and Reference Ranges for Mercury

Sample Type Blood, urine (random), hair.
Container Blood: EDTA.
Urine: universal container
Hair*/nail: plastic bag (nail samples should only be sent if hair unavailable)
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: 350 µL**
Urine: 1 mL
Hair: A bundle of hair about the length and thickness of a cocktail stick**
Reference ranges

Blood:                       < 30 nmol/L51

Urine:                        < 5 nmol/mmol creatinine (STEMDRL derived)

                                  > 20 nmol/mmol creatinine (associated with symptoms***)

Hair / nail:                  < 2 µg/g (STEMDRL derived)

Mean turnaround time Blood: 3.5 days (please telephone 0141 211 5178 if urgent result required).
Urine: 4.2 days
Method Inductively coupled plasma mass spectrometry
Traceability Blood and Urine: Traceable to reference material produced in accordance with EN ISO 17511:2003 “In vitro diagnostic medical devices. Measurement of quantities in biological samples. Metrological traceability of values assigned to calibrators and control materials” and reference materials with values determined by reference laboratories.
Hair: Traceable to certified reference material NCS ZC 81002b
Intermediate Precision (CV) Blood:    12.8% at 6.6 nmol/L, 4.3% at 362 nmol/L
Urine:    9.3% at 19 nmol/L, 6.0% at 163 nmol/L
Hair:      12.3% at 1.7 µg/g, 13.2% at 8.3 µg/g
Measurement Uncertainty, U Blood:    6.6 ± 1.7 nmol/L, 362 ± 30.9 nmol/L
Urine:    19 ± 3.5 nmol/L, 163 ± 19.5 nmol/L
Hair:      1.7± 0.4 µg/g, 8.3 ± 2.2 µg/g
Analytical Goals (CV) Urine:     Acceptable 11.7%, Desirable 7.8%****
Blood: 7%*****
Hair: 15%*****
EQA Scheme Blood and urine: UK NEQAS, Guildford
Hair: Quebec Multi-Element Quality Assessment Scheme

* A lock of hair, cut close to the scalp and about the thickness of a cocktail stick is required. Hair should be collected into a sealable plastic bag ideally with the lock tied to maintain its integrity. It is easiest to tie the lock at the root end before it is cut. To assess recent exposure, a section of hair close to the cut end is analysed. If the suspected date of exposure is in the past please indicate on the request form the approximate date; we will then analyse the appropriate section of hair based on the mean growth rate of hair of around 10.6 mm/month.
** Absolute minimum volume; this volume is insufficient to carry out repeat analysis if analysis fails.
*** Health & Safety Executive
**** Goal origin: biological variation52
***** Goal Origin: STEMDRL state-of-the-art

 

References

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