Mercury may seem an innocuous metal but it is highly toxic in all its forms — even more so than arsenic. Indeed, mercury vapour is one of the most toxic substances known, so it is vital to monitor it in the workplace. Dave Howell reports.

Mercury occurs naturally in air, water, soil and therefore some food sources but at levels that do not usually pose a significant health risk. However, it is also present in many manufactured products, such as batteries, thermometers, electric switches and relays, lamps, light bulbs, cosmetics and pharmaceuticals. As such, all businesses that come into contact with mercury should have a monitoring system in place that tracks any elemental or inorganic mercury present in the working environment.

Elemental mercury is used to describe the pure form of the heavy metal. This type of pure form mercury is not often found in the natural environment, but usually within inorganic compounds (often referred to as salts) with the most common being mercuric oxide, mercuric sulphate and mercuric chloride. It is the volatile nature of these compounds, which can in some circumstances exist as a gas, that needs close attention in the workplace.

The legislation that impacts on workplace mercury exposure includes the Health and Safety at Work, etc Act 1974, and the Control of Substances Hazardous to Health (COSHH) Regulations 2002 (as amended). COSHH includes a workplace exposure limit that defines the level of the hazardous substance permitted in the air as a gas or vapour.

REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) covers hazardous chemicals in the workplace and REACH and COSHH work closely together to deliver a regulatory framework for the safe management of hazardous substances including mercury.

All businesses that use mercury in their production processes are required to monitor the levels of mercury vapour in the working environment. How mercury is monitored can be achieved with a number of techniques including the sorbent approach, online amalgamation approach and the offline amalgamation approach, each of which can be used in specific working environments.

Warren Corns, research and technical support manager, PS Analytical sums them up: “Three different techniques have been demonstrated for monitoring Hg in workroom air. All three techniques employ a CV-AFS (cold vapour atomic fluorescence spectroscopy) analyser to sample mercury captured on a substrate. Hydrar tubes (as the passive sampling device) follow a recognised method and can be used to monitor longer-term exposure. The offline amalgamation technique allows simple, rapid determination of the mercury levels for occasional/periodic monitoring in low risk locations. The online amalgamation technique provides a fully automated system for continuous analysis of a higher exposure risk workplace.”

It is important to be aware of how mercury can enter the body. Says the Health Protection Agency: “People working in factories making equipment containing mercury or in chemical processing plants that use mercury may be exposed to mercury vapour. If exposed to mercury, the harmful effects that may occur largely depend on the way people are exposed and the type of mercury they are exposed to. After swallowing small amounts of elemental mercury, very little enters the body, whereas after breathing elemental mercury vapour, about 80% enters the blood from the lungs. Inorganic mercury compounds do not vaporise hence are not generally breathed in and only small amounts may pass through the skin. If swallowed, up to 40% may enter the body.”

To gain an insight into how mercury is managed in the working environment, the author spoke with Tony Sweetland, Intertek Sunbury laboratory manager, with over 20 years’ experience analysing mercury in various matrices from soil, gas, oil and water serving the environmental, agriculture and petrochemical industries.


Do the levels of mercury within working environments continue to be an issue for businesses and legislators alike?

In my opinion yes, there are a number of working environments, oil industry, waste disposal (bulbs), and these need accurate monitoring to ensure that harmful levels are not met — harmful levels also need to be kept up to date as new evidence comes to light.

For business owners, what’s your key advice for mercury monitoring at their premises?

My key advice would be to carry out regular monitoring with a known and proven methodology. Unless continuous monitoring systems are used, then any sample taken is purely a snapshot in time and may not take into account all the factors that may produce mercury vapour in any particular area (wind direction, conditions of the plant, production at the time, type of raw material being used, etc).

In some industries — farming and petrochemical for instance — low levels of mercury can exist yet are difficult to detect because of other contaminants. How should a business in this situation approach its mercury monitoring?

I disagree slightly with this statement. Mercury analysis is not too difficult if carried out using the correct methodology. Unfortunately there are a lot of methods available which are not robust enough for the type of analysis/ sample matrix required, but there are also methods, which will only detect mercury and no other interfering species. My best advice would be to consult with a reputable business or consultancy with a good track record of providing good quality mercury data in the areas concerned and who would be happy to share their quality control data with you.

Do you think the awareness levels of business owners to the dangers — particularly of cumulative effects of low-level exposure — to mercury are high enough?

This in my opinion varies between industries and even companies within those industries. There are some that have a very high level of awareness and will regularly monitor all staff who could potentially come into contact with mercury and there are others that may not even be aware that mercury exists!


Mercury is in the natural environment, where low-level exposure takes place. It is also an essential component of some manufacturing processes. Businesses that come into contact with mercury must ensure they have adequate detection on site to ensure mercury levels are within legal limits.

Going forward, an awareness of how mercury could enter the working environment, as part of normal health and safety assessments is a sensible step to ensure mercury exposure remains at a minimum.

Last reviewed 4 May 2015