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Environment

Preventing mercury poisoning

   
 
Picture
Factories discharge methyl mercury waste.

Methyl mercury is known to be especially dangerous to human life. This is often due to the consumption of poisoned fish. To accurately measure the levels of this compound in the environment, an improvement in laboratory analysis was necessary.
A European research initiative provided laboratories with the opportunity to improve their techniques and produce reference materials to be available to all institutes monitoring the concentration of methyl mercury in the environment.

 

Many people associate mercury, the slippery liquid metal, with thermometers. In fact, mercury and mercury compounds are toxic. Amongst the most dangerous is methyl mercury which causes particular concern because it accumulates in the tissues of animals, such as fish. When people eat the contaminated fish, the heavy metal poisons are passed into the food chain.

These effects were noticed in 1955 in Minimata, Japan. The story began with a local PVC plant which was using mercuric sulphate, a chemical used to catalyse the production of plastics. In this process, effluent of mercury compounds was discharged into the ocean. The contaminants found their way into the food chain and consequently, the inhabitants of Minimata, whose staple diet was fish, were affected by heavy metal poisoning. The entire body can be affected by this illness. Symptoms include numbness, inability to control limbs and eventually seizures. In this tragedy, there were 43 fatalities and 22 babies were born with brain damage, to mothers who had consumed tainted fish.

A second large-scale poisoning by methyl mercury occurred in Iraq in the seventies. In this case, people consumed wheat flour made from seeds treated with methyl mercury.

Because there are such devastating health risks associated with mercury and organic mercury compounds, widely used in industry as catalysts and in agriculture, the World Health Organisation has placed limits on the allowed mercury content in food. At 0.05 mg kg-1, it doesn't take much contamination to make food a real risk to the consumer. The levels must be closely monitored to prevent any of these poisons from getting into the food chain. Due to the extreme risks involved, many organisations have followed the WHO's lead and now specifically monitor the levels of methyl mercury in fish before they go to market.

Awareness of the problems intensifies

As environmental awareness increases, the need for accurate and reliable measurements increases in parallel. This is because stricter limits are imposed to protect people and regular checks for safety are needed. Of course, it is a waste of time and money to monitor if the results are not reliable and cannot be compared between laboratories.

Checking the levels of contamination sounds simple in theory - just sample fish and see how much methyl mercury is present, right? Wrong! Measuring methyl mercury content presents the analytical chemist with a real challenge. For a start, it is often difficult to analyse biological materials and it is even harder to achieve consistent results. This is because anything that is living, or was living, is in fact a complicated mixture of countless chemicals, some of which are very similar. It is difficult to separate them and measure the amounts of each one.

The method originally developed to determine mercury levels in living materials was outdated as it had a number of shortcomings. It had high detection limits and was not much use for measuring very low levels of contamination.

Another problem was that it only measured the total amount of mercury present rather than showing levels of methyl mercury in the sample. It is important to distinguish between each methyl mercury and other sources because methyl mercury is extremely toxic.

Due to these issues, laboratories' results were not always meaningful. To adequately protect the public from these risks, improvements were necessary.

A group of European laboratories tackle the problem

In 1987, a consortium of European experts in the field of mercury analysis came together to discuss improving methyl mercury measurements. Many of the laboratories were using different methods. They decided to critically examine each step of their current measurement procedures to find and remove possible errors.

A series of measurement exercises were performed by each laboratory. About 20 partners, from 8 different European countries, worked through each part of the measurement method and verified the accuracy of each step. As time went on, the exercises became more technically difficult. Each laboratory had the opportunity to see how other analysts were solving problems. Much collaboration was needed and the group held many meetings to discuss their results and conclusions.

As well as improving measurement techniques, the group also produced Certified Reference Materials. These provide a tool for laboratories around Europe, and further afield, to check that their procedures are valid and are producing accurate results that can be compared to any other laboratory also using the reference materials. These materials are specially prepared tuna fish and sediment samples with very similar properties to those measured routinely in laboratories. The difference is that they have specified levels of methyl mercury and total mercury content.

Special treatment for reference materials

These samples were challenging for the project team to prepare. Hundreds of kilograms of fish and sediment contaminated with methyl mercury had to be specially treated and prepared so that there would be enough samples to be distributed all over Europe over several years.

Collaboration was necessary to produce these materials. As well as providing environmental monitoring laboratories with CRMs, the project group themselves also benefited from the studies as they improved and optimised their own skills and made contacts with colleagues from around the Community.

The value of CRMs cannot be overstated. They ensure accurate and comparable measurements of the levels of toxic chemicals. Without this accuracy, checking the environment for contamination would be useless and the risk associated with methyl mercury would be much greater.

For reference, the CRMs described are CRM 463, 464 (tuna fish) and CRM 580 (sediment).

 

 

Project Title:  Methyl Mercury Speciation

Programmes: Standards, Measurements and Testing
Contract Reference:  

Cordis DatabaseFor more information on this project,
go to the Cordis Database Record

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