LD50 is an incredibly crude approximation. I once conducted a series of experiments in which we measured the LD50 to be approximately 10 times higher than the previously published data. Admittedly the previous data was
40 years old by that point and a lot of experimental techniques (and for that matter animal strains) had changed in that time. That is not to say that LD50 is useless - it works well as a 'quick & dirty' approach when setting up pilot studies but otherwise it is only really useful as a comparative measure of toxicity.Cheers
Mark