Human Estimates of Nerve Agent Toxicity

It is difficult to determine the toxicides of OPs from cases of human poisoning, since the dose of the OP and often its identity are not known. Additionally, many cases receive medical antidotal treatment, which is likely to affect the toxicity. Estimates of the human toxicity of OP anti-ChEs are, therefore, largely derived by extrapolation from data obtained using animals, usually rodents such as rats and mice. 

The current military toxicity estimates for the agents GA, GB, GD, GF, VX and HD were established in a 1994 US Army report published in 2004, from which some data have been collated into Table 3.4. 

Previously, attempts were made to estimate chemical warfare agent toxicity for occupational exposure standards relating to demilitarisation oper-ations. ° Studies that have included repeated dosing to animals, ie. subchronic dose studies, have generally focussed on doses that produced measureable inhibition of red cell ChE arguably, this is a biomarker of exposure rather than an indicator of toxicity, and therefore its selection as an indicator of lowest or no observed adverse effect may increase the uncertainly in subsequent extrapolations to the human.  

The climate in the world today in respect of chemical weapons is very different to that of post-war Britain (1945) when some of the research reported in this chapter was taking place. At that time, the pressing requirement for accurate assessment of the hazards facing military personnel attacked 

Year GB lethality (LD50 or LCtjo) GB severe effects (ED 50  

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