AT the recent incinerator inquiry the medical evidence of local consultant anaesthetist Dr Reg Johnstone and that of Wyre Forest MP Dr Richard Taylor was supported by very relevant research evidence by toxicological pathologist Dr CV Howard.

He stated that except for newly born children (which are his speciality), "the human body has a well-developed defence system to deal with many toxic chemicals it encounters in the course of living".

However, one of his main health concerns was the emission and accumulative effect in the body of the newer type of toxic material, namely "dioxin compounds".

These are produced from the combustion of the many old and new plastic materials based on chlorine and bromine.

In order to abate the emission of these dioxins (and also mercury) the proposed incinerator is designed to inject fine activated carbon powder into the waste gases in order to absorb them.

Thus, in addition to lower porosity carbon soot particles, there will be these purposefully added, highly porous activated carbon particles that will also act as "carriers" of absorbed toxic materials including dioxins, mercury and the so-called volatile organic compounds.

The carbon injection is made just before the final cleaning of the waste gases by a fabric material bag filter system.

Unfortunately, the capture efficiency of these filters is not very good for the sizes of particle that on inhalation are retained deep in the lung.

Such particles will include the dangerous insoluble "toxic-loaded" carbon particles described above and will, therefore, be of great public health concern.

As a retired physicist turned furnace technologist, I was concerned about this and wrote to the Environmental Agency (EA) well before they granted their permit for the proposed incinerator.

I also submitted a detailed document as evidence at the inquiry.

This evidence included a rough calculation of the number of "loaded" activated carbon particles that would be inhaled and retained in the lung of a healthy adult.

A value of 80 per day was obtained and this figure would be greatly increased if the much larger number of less porous soot particles were included.

Whatever the calculated number might be, this evidence demonstrates the importance of assessing the nature and the size of particles at ground level and not solely the total mass concentration of these particles.

This is the crude index used by the EA to assess the effect of particulate material on public health, and was first recognised to be of limited value by the US National Research Council in 1979.

This leads to a dilemma for the inspector who conducted the inquiry.

After hearing all the medical evidence he has to decide if West Mercia Waste Ltd and the EA are right in their common claim that the proposed incinerator "does not give grounds for concern" for the health of Kidderminster residents living 500 metres upstream from it.

Dr GR MATTOCKS

Blakebrook

Kidderminster