Hi Munish,

Can you provide some detailed background of your query?

Dose response curve will have toxicity and dose on X & Y axis, in all cases. So, normally threshold model could be useful.

Please inform if you have any specific case in mind, or any specific manuscript you can share regarding your query? Only, then I will be able to reply.

Thanks@Prof Ahuja. Let us take example of Hg or Arsenic, which model we should apply, when:

Toxic metal causes cancer.

I would say threshold models would apply mostly to metal toxicology including carcinogenesis also due to the fact that metals and metalloids are omnipresent in the environment (unlike most organic chemicals) so any subject has certain (sometimes undetectable by most methods) baseline exposure. This should be true for Hg and As too.

Since everybody has this baseline exposure, we are evolutionarily protected to a certain extent against metal toxicities. This works differently for different elements depending on this baseline exposure. For copper (which is geochemically relatively labile), neurotoxicity is really a problem only for the patients with genetic disruption of Cu metabolism (e.g. Wilson's disease), due to the regulated uptake and controlled excretion. At the same time, we have much less innate protection against Hg. Hg was poorly bioavailable in the pre-industrial periods since it was mainly present in a highly stable and insoluble sulfide form.

Thanks@ Nikolay D Solovyev . But What about chemical toxicity of U, Th, Pu and Be and their models

Thanks MUNISH KUMAR , I am afraid it's a bit separate story for radiotoxicity (U, Th, and Pu) so here I am not so sure - I'm too far away from radiobiology. What I may say, it's often hard to separate the toxic effects related to chemical toxicity and radioactivity under non-laboratory exposure. Non-laboratory U, Th or Pu will have the impurities of decay products some of which may be e.g. strong gamma-emitters (dangerous from the outside) or strong alpha-emitters (bad when ingested/inhaled). Uranium (as depleted uranium) is a rather popular laboratory model of nephrotoxicity in rats or mice, in which the radioactivity factor can be neglected. As for Be, there are studies showing that specific inflammatory response can be observed at extremely low exposures. For instance, family members of Be workers show some immune cell activation due to the contact with residual Be dust from the clothing of the workers. Be though is very rare in the environment (due to specific nucleosynthesis of Li, Be, B, and its geochemistry). To conclude, I would say U, Th, Pu, and Be are a more complicated matter than Hg or As.