WILTSHIRE'S public health director has asked doctors to inform her if their patients are being affected by pollution emanating from the chimney at Lafarge cement works.

Maggie Rae, Wiltshire public health director, is concerned with a phenomenon called plume grounding, which is when smoke from the chimney comes into contact with the ground.

This can occur under certain meteorological conditions and because Lafarge uses a wet process much of the plume is water vapor and is therefore visible.

Mrs Rae said: "The Environment Agency have received direct contact from six members of the public who say the occurrence of the plume coming into contact with the ground may have increased in frequency and some of those standing near or within the grounded plume have experienced symptoms including sore throat and tightness in the chest.

"We want to document accurately these reports, including any symptoms experienced, as well as any treatment necessary, and the Environment Agency will be recording incidents of plume grounding whether it results in a visit to the GP or not."

Ian Bartlett, from The Butts, Westbury, is concerned with smoke dropping from the Lafarge chimney, and said: "If the cement works' directors are absolutely clear that there is no risk to people's health, would they be prepared to stand in a room full of what comes out of their chimney and how long would they stay in there for?

"On a number of occasions when I came back from work in Trowbridge I've noticed the smoke leaves the chimney and drops down and appears to be grounding. I have taken pictures of this. The worst occasion was when I arrived home and my garden was full of what looked like fog. It was smoke from the chimney and it had an awful sulphur smell."

David Levy from The Air That We Breathe environmental campaign group is worried that the Environmental Agency are not monitoring the discharge from the cement works' chimney correctly.

He said: "The Environmental Agency and Lafarge do not give accurate readings on the monitoring of dioxins and I can say that with absolute confidence. Lafarge has to adhere to the BSEN 1948 standard, which is the Environment Agency standard for measuring dioxins in a one-metre duct pipe, but that standard does not operate during start-up and close-down conditions and there really should be monitoring during these times."

Lafarge cement works manager Jim Cross said: "We continue to examine the effect of different processes and conditions on the behaviour of our plume, for example whether recently introduced techniques to reduce emissions have increased the plume's visibility.

"However, it is important to remember that although a number of factors can influence plume visibility, the emissions inside the plume remain within regulatory limits.

"In fact, we have recently achieved significant improvements in emission levels, investing over £5 million in new filtering and abatement technology to halve the emission of oxides of nitrogen, cut dust levels by a third and reduce our sulphur dioxide emissions by 10 per cent in 2007."