Our groundwater can be contaminated by
Two project teams have developed quality control tools that will help testing laboratories across Europe to monitor our groundwater supplies. These laboratories test water for a range of elements and compounds that are detailed in two European Directives. Preparing these reference materials provided technical challenges for the scientists and also gave them the opportunity to compare the best practice and share ideas. Now, water-monitoring laboratories can better control the quality of their groundwater measurements.
Water is essential to life. Agriculture and industry depend upon constant water supplies but perhaps the most important use is public health and sanitation. Although the water we drink and wash with may look clean and pure, this may not be the reality. Pollutants that we put into the ground, atmosphere and river systems seep into groundwater supplies.
These supplies must be regularly monitored in European laboratories to control the level of contamination by major and trace elements and so reduce the threat of health risks. Two European Directives prescribe the determination of a number of elements and compounds. Some elements that may be found in groundwater, such as heavy metals, are toxic. Other naturally occurring chemical species can be turned into more dangerous ones during water purification processes. When groundwater is cleaned by ozonation, bromide is transformed into bromate, which medical evidence suggests is mutagenic.
Measuring water for contamination can be a real challenge for laboratories. Establishing true comparability between laboratories is notoriously difficult as different methods of analysis are used by different testing bodies. Even if the laboratories use the same measurement technique, they may prepare their samples using contrasting procedures. Testing becomes a minefield and the results cannot be trusted, leading to potential, economic and social problems, especially when contaminated water from one country flows into another.
For monitoring purposes, results must be comparable between laboratories and also within the same laboratory. Trends can only become established over several years if the analysts know that the results that went before were accurate and reliable.
We, the public, put our trust in testing regimes but we often do not realise that many technical hurdles have to be crossed to achieve useful measurements. We can easily take it all for granted. This may not be a glamorous area of scientific research but it may be more valuable to us in our day-to-day lives than incredible new materials or computer systems.
Two recent projects under the Measurements and Testing programme have been working towards better water measurement quality control. Each of the project teams produced tools that laboratories across Europe can use to help them validate their own measurement methods. These tools are Certified Reference Materials, known in the measurement and testing world as CRMs.
At first glance, a CRM may just look like another sample ready for testing, in this case, an ampoule of water. But there is a lot more to it than meets the eye. This sample is special. There are thousands of other samples just like it in laboratories around Europe and they all have exactly the same composition. What's more, the parameters of concern will have been certified in a study between expert laboratories. Testing laboratories can then use the material to check that they can achieve the same results with their own methods, which may be different to the ones used during certification.
Understandably, years of work go into producing and certifying reference materials. It all begins with a group of laboratories coming together to prepare a feasibility study on preparing and testing the material. It is vital that as many laboratories with proven quality as possible participate in the study. In each of the groundwater projects more than 14 laboratories from ten countries participated. In the study, each laboratory uses its own measurement technique to determine levels of chemicals in a common water sample. This gives the analysts a chance to see how well their method performs against others. It also provides a forum for discussing the results and, more importantly, the reasons for varying results. The participants pick up new skills and ideas from this technical meeting.
Specialised laboratories prepare reference materials. They start with an enormous sample of water that has been contaminated, up to 200 litres. For instance, the Danish Geological Survey knew where to find natural groundwater supplies with quite high levels of bromide. Sometimes, natural supplies cannot be used because of dissolved organic material that changes the water's composition over time or disrupts measurement of certain substances. In these instances, artificially prepared groundwater is used.
Certifying the samples
The groundwater is divided up into about 1,000 samples. These are tested thoroughly to make sure that the content of certified elements are constant throughout the sample and that these levels remain constant over time in typical storage conditions. The water can be irradiated to remove micro-organisms that may affect the stability. Once these tests are complete, certification can begin. Each laboratory analyses the water carefully six times and logs the results. As in the initial study, experts meet to discuss and solve any problems. The results are pooled and undergo statistical number crunching to assess the degree of variation. If, and only if, the laboratory agreement is acceptable and corresponds to the state of the art, can the material achieve certified status. On certification, the remaining samples are made available to laboratories around Europe and further afield.