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image European Research News Centre > Medecine and Health > Monitoring and controlling lead
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image image image Date published : 11/04/2001
  image Monitoring and controlling lead
 
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  The lead content of drinking water is now subject to a strict European directive. But its application is not without problems. So what is the best way of measuring this capricious poison?
   
     
   

Tap water must be fit to drink. That goes without saying. At the collection stage, distribution companies carefully analyse the water and carry out the necessary treatments to eliminate any pathogens. But after that another parameter comes into play, one which is singularly difficult to monitor and control: its lead content. Although there may not be a problem between the collection stage and transit through the principal distribution pipes, the risk comes through contact with the secondary pipes which carry it to the consumer's tap. Lead may contaminate the water as it passes through the branch pipes linking the public system for a particular street to the water meters in individual buildings, or as it passes through their old piping networks.

Because of its toxicity, lead is one of the most closely monitored chemicals under the new Community drinking water directive, which was adopted two years ago and was supposed to have been transposed into national legislation by 25 December 2000. The directive is based on WHO recommendations which set a maximum lead concentration of 10 micrograms/litre (compared to 50 µg/l at present). Member States have another three years to achieve an intermediate objective of 25 µg/l, and 13 years to meet the final target.

The new regulations will require a considerable effort on the part of certain countries - France, Great Britain, Italy and Spain in particular - where a number of branch and internal piping systems are still made of lead. 'In Paris, the proportion is around 70%,' states Ierotheos Papadopoulos of the Environment Directorate-General. 'A socio-economic study financed by the European Commission puts the cost of making the necessary changes across the European Union at 35 billion euros.'

But there remains the matter of reaching agreement on how to assess the lead content of drinking water. When measured at the tap (as stipulated in the directive), the lead content varies considerably depending on the distribution zone, the individual building and even, within the same building, on the time of day or consumption habits. 'The stagnation time in lead piping is a crucial factor,' explains Alain Boireau, who is responsible for lead contamination at Vivendi Water. 'The longer the period of stagnation, the greater the amount of lead which is dissolved. Any measurement is therefore going to give very different results depending on the time of day it is taken.'

Measure for measure

Before the directive can be implemented coherently, the Member States must agree on a sampling method. A recent study, supported by the Commission (Developing a new protocol for the monitoring of lead in drinking water), evaluated the various existing methods. None seems to be perfect. One of them, considered to be the reference method, was found to be very reliable in terms of obtaining a representative sample of the lead content of drinking water in a given building. It involves fitting a unit which draws off a small proportion of the water used to a flask. At the end of a week the flask contains a sample of water whose lead content represents the average for the building. However, apart from being difficult to implement, this method is also very costly.

Three other methods were evaluated on the basis of 300 samples taken in five countries. The first, known as random daytime, involves taking a sample at a random moment during the day in a randomly selected building. 'This method has no value as far as the individual building is concerned, but it can be a good indicator for a complete distribution zone, provided at least 30 samples are taken,' says Mr Boireau. 'The study showed that this was the most suitable method for compiling global statistics on a given country, region, town or neighbourhood. It is also the most economical of all the methods currently available.'

The second method, known as fully flush, involves taking a sample just after the pipes have been cleared of any stagnant water. 'There is a need for campaigns to promote good practice,' points out Mr Boireau. 'It is advisable, for example, to use water for washing up before filling bottles with drinking water and to take your morning shower before drinking the first glass of water. On condition that people take these precautions, this method then makes it possible to check whether the lead concentrations present - after running off stagnant water from the system - are acceptable in terms of public health.'

The third method, known as 30 MS, involves sampling the water after 30 minutes of stagnation. This is then considered to represent an average lead content for the user. The European study showed that this method gave results which were closest to the reference method, but also incurred a cost (an average of one hour on the spot to take the sample) which is unacceptable for routine health checks.

Pointers to a better choice

'The results of this study can serve as a basis for an interesting and concrete discussion,' believes Mr Papadopoulos. 'They have also highlighted the complexity of the problem and the importance of the precise moment when the sample is taken.'

Exposure to lead also depends on social, economic and cultural data which are very difficult to determine. In southern countries, for example, old people more often live with their children than in the north, consuming water during the day and thereby limiting the stagnation. Similarly, houses which are permanently occupied differ from those which are empty part of the time.

The study results are now in the hands of the Commission, which plans to submit proposals to the Member States before the end of this year.

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