Scottish Trace Element and Micronutrient Reference Laboratory

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

Mercury (Hg)

Trace Elements

Vitamins

Specialised services

Mercury has been recognised as a toxic hazard for centuries. The effects depend upon the route of exposure and the nature of the mercury compounds involved. 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. Mercury metal is used in the manufacture of thermometers and scientific instruments, and in the electrical, electronic and chemical industries. Dentists and their assistants are exposed to mercury vapour when working with dental amalgams. 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 accumulating the highest concentrations. Methylmercury is more toxic to humans than inorganic mercury and recently the Food Standards Agency and the US Foods and Drug Administration have advised that shark, marlin, and swordfish 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. Nail and hair levels of mercury are used as longer-term indicators of low level exposure, such as is experienced in dental practice. These tests are useful in conjunction with monitoring of the local environment and measures to improve working practices.