Innovation: Genetic trace is on to catch the river rats: Engineered virus will help net the water polluters

SCIENTISTS at Lancaster University are working on a genetically engineered virus for tracing the source of pollution in rivers. The evidence supplied by the modified virus will be used by the National Rivers Authority to bring prosecutions against polluters.

The NRA received approval from the Department of the Environment last month to go ahead with controlled tests to assess the technique. The experiments will take place next summer, but it is yet to be decided where.

Dr John Smith of Lancaster University is about to begin development of a bacteriophage - a virus that grows on specific bacteria - which will have a piece of artificial DNA inserted into it. The aim is to produce a library of viruses, each with a slightly different modification. The genetic modification will in effect give a different 'bar code' to each variant. This will make it possible to demonstrate a route between a pollution source and a pollution incident.

Dr Smith says the technique could be applied to any form of industrial or agricultural pollution. In 1992 the NRA detected 23,331 pollution incidents, and in the financial year 1992-93 the authority brought 435 successful prosecutions resulting in fines of pounds 1.09m. An NRA spokesman said that thousands of pollution incidents are currently impossible to trace. 'In a lot of cases we can't prosecute because we can't find anyone to blame.'

The authority has right of access to premises to inspect drains and holding tanks, but in most cases, by the time inspectors have set out to trace the source, the offending drains are free of the pollution. 'This technology will give us greater teeth because it will provide a very accurate pollution trace,' said the spokesman.

For example, in the case of slurry pollution, there are usually several farms in the area. A different version of the modified virus could be inserted into the outlet pipe from each slurry tank. Samples of the water would then be taken at the site of the pollution to see which, if any, version of the virus showed up. The NRA already uses an unmodified or wild virus to trace pollution sources, but the problem with this approach is that only one potential source can be tested at once. Inspectors also use dyes, but this is not very effective in marking some kinds of pollution such as slurry or oil.

Dr Smith says there is no danger of the modified virus, known as M13, harming the environment. M13 is a standard tool in genetic research, and for the past 20 years has been widely used as a vector to carry DNA into cells.

In this application, the virus will be tagged with an extremely small piece of DNA with markers on either side. These markers will highlight the presence of the barcoded DNA when water samples are analysed. The fragment of DNA is so small that it does not provide enough genetic code to alter the virus when it replicates. As an extra safeguard there are 'stop signals' that prevent the artificial DNA linking up with natural DNA.

The pollution incident may be a long way from the pollution source, meaning that the concentration of virus in a water sample is extremely low. The polymerase chain reaction - the standard technique for amplifying DNA to produce a large enough sample for analysis - will be used to detect the virus at low concentrations.

The 1993 figures for pollution incidents, due to be published at the end of September, will show an 8 per cent increase over 1992. The spokesman said this shows the NRA is getting better at detecting and dealing with spills, and also reflects an increase in reports from the general public to the authority's pollution hotline.

The NRA believes the viral tracing technique will reduce incidents tion because polluters will realise there is a much greater chance of being found out and then convicted because of the strength of the evidence.

(Photograph omitted)