Thanks MikeC.
Unfortunately, as you may already be aware, the National Academy of Sciences were not given vital details of many of the tests which is a major concern.
For instance, the NAS report states:
"THE CONCENTRATIONS OF airborne fluorescent particles of ZnCdS in the Army atmospheric-dispersion studies were measured with impingement and filtration methods. Two of those methods are thoroughly described by Leighton and others (1965), but the methods used at specific locations are not described in detail in Army risk-assessment documents."
This is an important admission because, according to Porton Technical Paper No 811 - Loss of Fluorescence by Airborne Tracer Particles (FP), ZnCds particles collected by Impactor (impinger) sampling devices run a great risk of being obscured by local pollution and are not suitable for use in making estimates of particle concentration (and therefore dosage estimates).
The US Army used two types of sampling devices for particle collection in its ZnCds field trials: the Roto-Rod and the Millipore filter. While the filter device was thought by Porton Down to be able to provide particle counts accurate enough to estimate received dosage, the Roto-Rod was not. It is acknowledged to have low efficiency when sampling particles lower than 10 microns, which is unfortunate as the particle size used in the ZnCds field trials was between 0.5-6 microns. While impactor/impinger samplers were considered suitable for use in tracer trajectory studies, they were not thought to be suitable for providing particle counts suitable for concentration or dosage estimation.
The Roto-Rod was not used in Porton Down’s numerous ZnCds field trials.
If the US Army were unable to inform the NAS which sampling device (Filter or Roto-Rod) was used in which trial, then this raises concern about the accuracy of the particle count data provided for the NAS dosage estimates.
Another concern raised by the report was the lack of available toxicity data concerning the inhalation of ZnCds particles of the size used in these field trials.
“"No toxicity experiments of inhaled ZnCds are available in literature. Because the ZnCds particles used in the Army's dispersion test were so small, the particles could probably be inhaled and deposited in the deep lung. The lack of solubility of the particles suggests that they are not likely to be absorbed from the lung into the blood for systemic distribution. No information is available on the potential toxicity of the particles in the lung.
It is not known whether ZnCds can be broken down by pulmonary macrophages into more soluble forms of cadmium."
All in all, the NAS can be said to have done their best, but without access to all relevant data all they could do was to make a guess as to the real dosage received by those exposed in the ZnCds field trials programme.